Wykamol CM3 - Waterproof Membrane (3mm Stud)

Health & Safety And Installer Competency

Wykamol CM3 forms part of a specialist structural waterproofing system and should be designed and installed by competent people experienced in cavity drain membrane work. The installation must follow the current Wykamol technical data, BBA Certificate 18/5595, product instructions for every ancillary and the project-specific waterproofing design.

Before work begins, confirm the structure, expected water conditions, internal environmental grade, drainage layout, outlet or sump position, pump duty, discharge route, ventilation strategy, final finishes and future maintenance access. A specialist survey is necessary for below-ground or persistently damp areas so the moisture mechanism, structural defects, contamination and any separate remedial work are identified.

Wear appropriate PPE, including gloves, eye protection and safety footwear. Use suitable dust extraction and respiratory protection during drilling or substrate preparation. Provide correctly erected access equipment for high walls, arches and vaults, and keep the work area well lit and clear of loose rolls, open channels and trip hazards.

Scan for concealed electrical cables, gas pipes, water services and structural hazards before drilling. Control cutting tools, hammers, SDS drills and heat guns carefully. A heat gun may help dry the membrane surface or improve tape adhesion in cold or damp conditions, but the HDPE and butyl products must not be overheated or exposed to flame.

System Design Principles

CM3 is not resistant to hydrostatic pressure as installed. Its studded sheet, sealed fixings, joints and drainage components form a depressurised cavity that accepts and controls water entering through the structure. The building should still limit ingress so the quantity never exceeds the designed cavity, channel, sump, pump or outlet capacity.

The waterproofing designer must assess retaining conditions, groundwater risk, construction type, permeability, wall and slab junctions, movement joints, cracks, service penetrations, slab levels, internal use and acceptable consequence of failure. Where Grade 3 protection is required and retained ground exceeds 600mm, the BBA certificate requires CM3 to be combined with Type A or Type B protection.

Every part of the cavity must connect continuously to drainage. The wall membrane, floor membrane, Waterguard, Floor Drain, outlets, sumps and discharge pipework should form a coordinated route without sealed pockets, backfalls, trapped sections or details that direct water onto a joint. The shallow 3mm cavity makes cleanliness and continuity particularly important.

Where pumping is essential, the design should consider duty and standby pumps, separate electrical supplies where appropriate, high-water alarms, battery back-up, telemetry and safe discharge. Receiving drainage must accept the design flow without surcharging, freezing or returning water towards the protected structure.

Suitable Substrates And Finishes

CM3 must be installed against a background stable enough to accept the specified fixing and support the final construction. Active structural movement, hazardous contamination, collapsing masonry and defects requiring engineered repair must be resolved before the membrane is concealed.

Preparation Of Walls, Floors And Soffits

Complete a specialist survey and remedy major causes of damp or water ingress that can reasonably be corrected. Repair structural defects, address leaking services, external drainage faults and defective rainwater goods, and specify any separate rising-damp or timber treatment only after the moisture mechanism has been diagnosed.

Remove unsound plaster, render and screed. Stiff-brush the exposed substrate to remove loose material, laitance, salts, dust, mould, adhesive and organic debris. Sound existing render may remain where the surveyor and fixing specification accept it, but soft, friable or poorly bonded layers must not be relied upon to retain plugs or support finishes.

Treat appropriate biological contamination with Wykamol Microtech Masonry Biocide in accordance with its separate label and instructions. Active dry rot, wet rot, timber decay or insect attack requires specialist assessment and a complete remedial specification; simply covering affected materials with CM3 is not acceptable.

Make good severe depressions, open joints and unstable areas with Wykamol HydraDry Universal Mortar or another approved compatible material. A concrete base receiving board directly over the membrane should have a maximum departure of 5mm beneath a 2m straightedge. Allow repair and levelling materials to set before covering.

Apply Wykamol Anti-Lime Sealer to suitable concrete where free lime or dust could migrate into the cavity and drainage system. Keep the prepared surface and channel route free from mortar, drilling debris and sharp projections, because blockage or puncture can compromise the shallow cavity.

Anti-lime sealer being applied to prepared concrete before installation of Wykamol CM3 Waterproof Membrane.

Tools And Ancillary Products Required

Typical installation equipment includes a tape measure, straightedge, spirit or laser level, marker, sharp utility knife, scissors or shears, 110V SDS hammer drill, suitable 10mm masonry bits, club hammer or mallet, hand roller, clean cloths, stiff brush, vacuum or dust extraction, and a controlled hot-air gun for drying and assisting butyl adhesion where necessary. Vaults and high walls also require appropriate scaffold or access equipment.

Set out all Wykamol CM Brick Plugs, Membrane Sealing Tape, Sealing Rope, Corner Strip Tape, Waterguard components, repair products and protection materials before work starts. Confirm that roll sizes, fixing quantities, tape lengths, channel fittings, outlets, pumps and alarms match the drawings and calculated wastage. Do not improvise critical joints with generic tapes, mastics or sealants that have not been accepted for the detail.

Tools must be clean and serviceable. Dull blades can tear the membrane, worn drill bits can oversize holes, and contaminated rollers or cloths can reduce tape adhesion. Keep butyl surfaces clean and use firm, even pressure throughout each seal. Heat should assist drying and tack only; it must not distort the studs or soften the membrane.

Drainage Requirements

Below-ground CM3 installations must include a dependable method of disposing of water that may collect behind or beneath the membrane. Floors require a drainage outlet and a suitable fall towards it, or a perimeter drainage channel connected to a safe gravity outlet or correctly sized sump-and-pump arrangement.

Wykamol Waterguard is normally positioned at the vulnerable wall-to-floor junction, while Floor Drain can provide cross-floor routes, threshold details or a connection to a central sump. The channel layout must collect water from every membrane cavity and structural junction without relying on water to cross unplanned obstructions or sealed pockets.

Provide inspection and jetting access at suitable locations, including changes of direction and channel runs that require future cleaning. Covers and access eyes must remain reachable after screed, flooring, dry lining and joinery are completed. Record their locations before concealment and include them in the owner’s maintenance information.

If pumps are required, calculate inflow, duty point, static head, friction losses, discharge distance and chamber volume. Consider pump redundancy, high-water alarms, power-loss resilience and telemetry according to risk. The final discharge point must be lawful, dependable and arranged so water cannot flow back towards the building.

Wykamol Waterguard Channel positioned at the wall-to-floor junction to collect water from behind Wykamol CM3 Waterproof Membrane, with the specified compatible sealing and insulated floor build-up maintaining continuity to the drainage system.

Wykamol Waterguard And Floor Drain Preparation And Installation

Form the Waterguard route at the wall-to-floor junction in accordance with the current Wykamol channel instructions and project drawings. The supporting bed must be stable and level, and the channel must not be distorted or obstructed by mortar, debris or uneven infill. Position the upstand against the wall membrane detail so collected water can enter the channel freely.

Join channel lengths with the correct Wykamol components. Use Swept Corners at 90° direction changes, T-Pieces where perimeter and cross-floor runs meet, and Floor Drain where a channel without a wall upstand is required. Connect the selected 50mm End Outlet or Universal Channel Outlet to approved pipework leading towards the sump, gully or gravity discharge.

Install Flexible or Extended Jetting Eyes where the maintenance design requires them, ensuring each remains reachable after the final floor build-up. Keep internal channel surfaces clean and check that each connection presents an uninterrupted flow path. Do not rely on adhesive, foam or improvised fittings that could create an internal lip or detach later.

Before concealing the drainage system, flush it with clean water and confirm flow to the outlet or sump. Inspect joints, corners, access points and discharge pipework, then photograph and record the installed layout. Where a pump is fitted, test normal operation, alarm function, back-up provision and discharge under controlled conditions.

Wall Installation

CM3 may be installed vertically or horizontally. Measure the wall carefully and cut the roll on a clean, protected surface with a sharp knife, scissors or shears. Position the sheet with the studs towards the wall and the flat face towards the room, keeping it level and tight into corners without excessive stretching, bridging or distortion.

Begin at the top of the wall and make sufficient initial fixings to support the sheet before completing the chosen fixing pattern. Drill a 10mm hole centrally through a membrane stud and into sound masonry to the depth required by the CM Brick Plug. Minimise drilling dust behind the sheet and avoid striking edges between studs.

Insert a CM Brick Plug With Seal and drive it fully home so the elastomer washer is visibly compressed against the membrane. Where an unsealed plug and Wykamol Sealing Rope detail is specified, form a continuous ring around the plug so the butyl compresses into a watertight gasket. Reject loose or poorly sealed fixings and repair the location correctly.

Continue the membrane into ceiling voids and down to the floor or drainage detail where possible. Return it onto adjacent walls sufficiently to isolate the final lining, and plan openings before fixing. Electrical points, cables, pipework and switches should remain on the dry side wherever practicable.

Wall Fixing Centres And Internal Finishes

Fixing density depends on the selected dry-lining system and substrate. The BBA detail gives maximum centres of 400mm vertically and 600mm horizontally for preservative-treated timber battens. Proprietary metal or independent frames may require fewer membrane fixings, but enough must be installed to hold CM3 reasonably tight, particularly around corners, openings and junctions.

Use preservative-treated timber battens at least 25mm x 38mm where the lining design relies on battens. Fix suitable screws into the central core of CM Brick Plugs so no separate hole is made through the membrane. Maximum screw penetration into the plug is 30mm plus the batten depth, and every screw must stop short of the HDPE behind the batten.

An independent floor-supported frame avoids routine secondary fixing through CM3 and can suit irregular substrates or service zones. Compatible proprietary metal lining systems and correctly restrained internal masonry linings may also be used where their loads and ties have been designed without uncontrolled penetrations.

Fix plasterboard or other approved lining boards so nails and screws penetrate less than the batten depth. Keep services in front of CM3 and support heavy fittings from predetermined battens or structural fixings. Only exceptional through-fixings should penetrate the membrane, and each requires a designed sealed detail.

Wykamol CM Brick Plugs & Seals fixing Wykamol CM3 to the wall, with fixing centres set to suit the internal finish, typically 600mm vertically and 400mm horizontally for timber battens.

Jointing And Sealing

Wykamol CM3 has no flange. Position adjacent sheets edge to edge as a close, accurately aligned butt joint, keeping the cut edges straight and free from gaps, overlaps or distorted studs. Clean and dry the membrane face on both sides of the joint before sealing.

Apply 150mm Wykamol Corner Strip Tape centrally over the joint so approximately equal tape width bonds to each sheet. Press it firmly with a hand roller or palm, working progressively along the joint to remove wrinkles, bridging and trapped air while maintaining full contact across both membrane faces.

In cold or damp conditions, dry the HDPE gently with a controlled hot-air gun and warm the butyl only enough to improve tack. Never seal over visible water, dust, mortar, grease or loose contamination. Use continuous tape lengths where practicable, and carefully lap any unavoidable tape ends in accordance with current Wykamol guidance.

Straight joints may run vertically or horizontally, but unnecessary joints should be avoided and the membrane must remain flat on both sides of every connection. Inspect the complete seal before concealment and repair damaged areas with compatible CM3 and the specified Wykamol tape or rope arrangement.

Wall-To-Floor Junction And Waterguard Integration

The wall-to-floor junction must transfer water from behind CM3 into Wykamol Waterguard without leaving a sealed pocket or unprotected gap. Position the wall membrane and channel upstand to the approved project detail, then clean and dry the surfaces before applying Wykamol Corner Strip Tape.

Where CM3 continues across the floor, turn the floor membrane up at the wall and seal it to the wall membrane or Waterguard upstand with Corner Strip Tape as specified. Form corners neatly and avoid bunching the membrane, blocking drainage holes or pulling the tape across unsupported voids.

If the finished floor build-up extends above the effective Waterguard upstand, the waterproofing designer must provide a compatible detail that allows condensation from the room-facing surface of CM3 to enter the drainage system without obstructing water from the structural side. Use only components confirmed as compatible with the specified Wykamol system, keep the collection route open and coordinate the detail with the project’s ventilation and humidity-control strategy.

Before floor finishes are installed, pour controlled clean water behind the wall membrane and confirm that it enters Waterguard and reaches the outlet or sump. Rectify slow flow, leakage, trapped sections and unsealed junctions before the system is concealed.

Floor Installation

Provide a suitable outlet and fall or install the designed Waterguard and Floor Drain layout before laying CM3. The concrete base must be clean, stable and free from sharp projections. Where board will lie directly over the membrane, the BBA requires a maximum surface departure of 5mm beneath a 2m straightedge.

Roll CM3 across the floor with the studs facing down. Cut sheets neatly around the perimeter, channels, columns and unavoidable services without stretching or distorting the studs. The floor membrane must remain loose laid and must never be fixed through to the slab.

Bring adjacent floor sheets together as clean, close butt joints without overlapping the membrane. Centre 150mm Wykamol Corner Strip Tape over each joint, press firmly across its full width and check that both edges remain aligned while the seal is formed. The finished floor membrane must remain continuous and free from open edges, wrinkles or trapped debris.

Protect CM3 promptly. Suitable tongue-and-groove board should be loose laid with a 10mm perimeter expansion gap and staggered, bonded joints. Closed-cell XPS of at least 30kg/m³ density may be placed above CM3 where specified. Wykamol High Load can be incorporated within a compatible drained and load-checked floor design. Alternatively, use at least 50mm reinforced concrete or screed directly over CM3, or at least 65mm where laid over insulation, in accordance with BS 8204-1 and the project specification.

Vaulted Soffit Installation

CM3 may be installed to suitable arched or vaulted ceilings where the construction provides a continuous fall to drainage. Survey the curve, end walls, joints and outlet route before cutting so the membrane can follow the substrate without excessive tension, open folds or areas of sagging that could retain water.

Position the membrane studs towards the soffit and support it with sealed Wykamol CM Brick Plugs. Where a standard elastomer washer does not seat evenly on the curve, use CM Brick Plugs Without Seals with a continuous ring of Wykamol Sealing Rope, driven firmly enough to compress the butyl into a watertight gasket.

Where separate sections meet across the vault, form a close butt joint and seal it centrally with 150mm Wykamol Corner Strip Tape. Plan shaped cuts carefully and keep the number of joints to a practical minimum. Prevent sagging between fixings so no pocket can hold water or debris.

At each end wall, turn the vault membrane down by at least 200mm. Mitre only as necessary to follow the curve, seal every cut with approved tape or rope, and fit the wall membrane in front of the turned-down ceiling sheet so water continues towards the designed drainage route.

Flat Soffit Restrictions

Flat below-ground soffits should not be lined with CM3. The Wykamol technical data requires a minimum slope of 10% so any water behind the membrane can move towards the designed drainage point instead of ponding against the sheet or a sealed joint.

Where the soffit does not provide this dependable fall, select another waterproofing approach through the project designer. Do not attempt to create drainage by allowing the membrane to hang or by relying on a loose sheet to form channels, because sagging creates uncontrolled pockets and places stress on fixings and joints.

Arched, vaulted or suitably sloping soffits must still be checked across their complete width and length. Local depressions, ribs, beams, abutments and changes of direction can interrupt the fall even when the general geometry appears adequate. Resolve those details before installation and ensure every cavity terminates at a safe collection route.

Door Reveals, Corners And Junction Details

Run CM3 continuously around internal and external corners where the sheet can be folded neatly without excessive distortion. Form a square crease and fix the membrane tightly into the angle so the final lining remains straight and the cavity does not bridge across the corner.

If the sheet becomes misshapen around a return, stop at the corner and begin a new piece rather than forcing a distorted fold. Seal the adjoining edges with Wykamol Corner Strip Tape or the approved rope and over-seal arrangement. Keep all faces clean, dry and fully supported while pressure is applied.

Where possible, install CM3 across window openings and cut it away afterwards so the main sheet remains continuous. Seal the exposed perimeter using the correct combination of Membrane Sealing Tape, Sealing Rope and Corner Strip Tape. At doors or fixed obstacles where this method is impossible, bring the membrane accurately to the perimeter and seal the gap with the same care.

Coordinate thresholds with Wykamol Floor Drain, Waterguard or a suitable DPC before fixing. Avoid isolated cavities beside frames, and never leave an unsealed reveal or return where water can bypass the membrane and reach the dry lining.

Protrusions Through Wykamol CM3

Avoid services through the membrane wherever practical and route pipes, cables, conduits, sockets and controls on the dry side. Where a penetration is unavoidable, establish its position before cutting and keep the opening as small and regular as possible.

For floor services, trim CM3 to within approximately 5mm to 10mm of the pipe or conduit and fill the gap completely with Wykamol Sealing Rope. Where necessary, add a compatible membrane or DPC patch, seal it to the service with rope and seal its outer edge with Membrane Sealing Tape or Corner Strip Tape.

Use suitable proprietary collars or sleeves for larger, grouped, moving, hot or irregular services where a simple rope-and-patch detail cannot provide durable continuity. The service material, temperature, expected movement and future replacement method must be compatible with the selected seal.

Exceptional structural fixings through a lined wall require a predetermined load-bearing and waterproofing detail. Fix heavy objects into designed battens or structural supports wherever possible. Any hole through CM3 must be packed and sealed with compatible flexible butyl products before it is concealed.

Protection Of Wykamol CM3 After Installation

Protect CM3 from sharp tools, dropped fixings, masonry fragments, wheelbarrows, ladders and concentrated foot traffic as soon as each area is complete. Although the BBA records good puncture resistance under normal installation traffic, a concealed tear or crushed drainage path can compromise the finished system.

Keep ultraviolet light, high temperatures, open flame and incompatible chemicals away from exposed rolls and installed sheets. Do not leave CM3 uncovered longer than necessary, and prevent wet trades from dropping mortar, screed or plaster into the cavity, Waterguard or inspection points.

Coordinate all subsequent work through one responsible person. Electricians, plumbers, joiners, dry liners and floor installers must understand that they cannot drill, nail or screw through the membrane without an approved sealed detail. Mark restricted fixing zones and provide predetermined battens or service routes before finishes are closed.

Where temporary protection board is used, ensure it does not crush the studs or block drainage. Remove protective materials carefully, inspect the complete membrane and clean the channels immediately before applying permanent floor or wall protection.

Ventilation And Humidity Control

CM3 has very high resistance to vapour diffusion. When positioned on the cold side of insulation, it can increase interstitial-condensation risk unless the wall or floor build-up and internal environment are designed properly. Carry out the appropriate BS 5250:2021 assessment and consider a vapour-control layer on the warm side where required.

Habitable basements and Grade 3 spaces normally need planned mechanical ventilation, background heating or another specialist environmental-control strategy. The required air-change rate, extract location, make-up air, noise, energy use and control method must be designed for the room’s occupancy and moisture generation.

Do not assume that opening the cavity to the room will solve condensation. A below-ground system may need to remain sealed because of odours, vermin, moisture movement or waterproofing continuity. Any high- and low-level aeration slots used in an above-ground damp-proof dry-lining application must follow the specific design rather than being added routinely.

Monitor relative humidity after completion and address persistent sources such as wet construction materials, clothes drying, unvented appliances or inadequate extraction. Waterproofing controls ground water; it does not replace normal management of indoor moisture and air quality.

Inspection Before Finishes

Inspect the full CM3 installation before dry lining, flooring, concrete or screed conceals it. Confirm that the membrane is correctly orientated, tight to walls and vaults, studs are not crushed, every fixing is sealed and no tears, open edges, wrinkles or unsupported joints remain.

Check every butt joint, corner, window and door detail, service penetration, wall-to-floor transition and Waterguard connection. Confirm that 150mm Corner Strip Tape remains centred over each sheet joint, then roll it firmly and replace any section contaminated by dust, water, oil or loose debris rather than attempting to press it back into service.

Vacuum the cavity edges and drainage channel. Flush Waterguard and Floor Drain with clean water and verify free movement to the outlet or sump. Operate pumps, high-water alarms and any back-up system, and check that discharge cannot return towards the structure.

Photograph the finished membrane, channels, outlets, sump, pipework and all concealed details. Record dimensions from permanent reference points and complete the installer’s inspection documentation. Do not approve concealment until defects are repaired and the system performs as intended.

Repairs To Wykamol CM3

Repair damage before it is concealed. Clean and dry the affected CM3 thoroughly, trim ragged material where necessary and assess whether the studs and cavity remain serviceable. A small clean puncture may be repaired with the approved Wykamol tape detail, while a larger tear requires a compatible patch extending well beyond sound membrane on every side.

Use Wykamol Sealing Rope around irregular holes, plug penetrations or three-dimensional details, then secure the repair with Membrane Sealing Tape or Corner Strip Tape as appropriate. Apply firm pressure across the complete seal and use controlled warmth only if needed to remove surface moisture or improve butyl tack.

Where damage has crushed a significant area of studs, affected a critical joint, or occurred beside a channel, penetration or wall-to-floor junction, replace the membrane section or obtain a project-specific repair detail. A flat patch that seals the face but blocks the drainage cavity is not acceptable.

After repair, repeat the relevant inspection and controlled water test. Photograph the completed work and add it to the waterproofing record so later owners and contractors understand the location and method of the concealed repair.

Maintenance And Future Alterations

The protected CM3 sheet itself does not require routine maintenance under normal service conditions. The drainage system that makes Type C waterproofing function does. Waterguard, Floor Drain, jetting eyes, outlets, sumps, pumps, alarms, back-up power and discharge pipework must remain accessible and be inspected and serviced at the intervals set by the system designer and equipment manufacturers.

Flush drainage channels through the provided access points and remove lime, silt or debris before it restricts flow. Test pumps and float switches, clean sump chambers, operate alarms and confirm back-up systems under controlled conditions. Keep written service records and investigate changes in pump frequency, unusual noise, odour, dampness or water level promptly.

Future shelving, cupboards, skirtings, flooring, services and wall-mounted equipment must not be fixed through CM3 casually. Use recorded battens and designed support points, or obtain a waterproofing detail for each new penetration. Even a small unsealed fixing can provide a route for water to bypass the system.

Provide the owner with drawings, photographs, product information, test records, access-point locations, pump manuals and maintenance contacts. Any contractor altering the space should review this information before drilling, lifting floors or opening linings.

Key Limitations

• CM3 is a cavity drain membrane and is not resistant to hydrostatic pressure as a standalone barrier; it requires a complete designed drainage and discharge system.
  
  

• The shallow 3mm cavity must remain clean and unobstructed, making control of drilling dust, mortar, lime deposits, silt and crushed studs particularly important.
  
  

• Where Grade 3 protection is required and retained ground exceeds 600mm, BBA Certificate 18/5595 requires CM3 to be combined with Type A or Type B protection.
  
  

• CM3 has not been BBA assessed for chemically contaminated brownfield sites; hazardous or unknown contamination requires specialist investigation and project-specific materials assessment.
  
  

• Flat below-ground soffits are unsuitable. Vaulted, arched or sloping soffits require a dependable minimum 10% fall and fixing sufficient to prevent sagging and ponding.
  
  

• Floor membrane must never be punctured by fixings. Screed, board, insulation and Wykamol High Load build-ups require appropriate support, drainage and load checking.
  
  

• Very high vapour resistance can increase condensation risk when CM3 lies on the cold side of insulation; ventilation, heating and BS 5250 assessment remain essential.
  
  

• CM3 must be protected from fire, impact, ultraviolet exposure, high temperatures and uncontrolled penetrations by later trades throughout installation and service.
  
  

• CM3 sheet-to-sheet joints must be formed as close butt joints and sealed centrally with 150mm Wykamol Corner Strip Tape; do not overlap the sheets or attempt to create a flange.
  
  

• Pumps, alarms, battery back-up and telemetry do not eliminate risk. Their capacity, power provision, discharge and service regime must match the consequences of failure.

Storage And Shelf Life

Store CM3 rolls upright, in their original protective wrapping, under cover and away from sharp objects, direct sunlight, high temperatures and open flame. Do not stack or position the rolls where they may be crushed, distorted or punctured by other materials.

Keep tapes, rope, plug seals and other butyl products clean, dry and within the temperature conditions stated on their own packaging. Protect Waterguard components from impact and deformation, and store cementitious products, biocides and Anti-Lime Sealer according to their separate labels and safety information.

Wykamol states a service life equal to that of the structure for correctly installed and protected CM3, rather than a finite shelf life for the wrapped roll. Inspect all stored materials before use and reject membrane with brittle areas, damaged studs, contamination or prolonged uncontrolled exposure.

Other Technical Information

CM3 is recyclable polyethylene, subject to clean recovery and the recycling facilities available at the time of removal. Offcuts contaminated with butyl tape, mortar, hazardous substrate material or other site waste must be handled through the appropriate waste stream.

Technical values describe laboratory or declared product performance and do not determine the suitability of a complete wall or floor. Structural loading, insulation, screed reinforcement, fire performance, condensation, drainage capacity, groundwater, penetrations and final occupancy require separate project-specific assessment.

Use the latest applicable Wykamol technical data sheet, BBA Agrément Certificate 18/5595, Declaration of Performance and instructions for every system component. Installation must also follow the project-specific waterproofing design and any applicable Building Control or structural-warranty requirements. Where site conditions fall outside the published scope, obtain project-specific advice from Wykamol and the waterproofing designer before work begins.

Q) What is Wykamol CM3 Waterproof Membrane?

A) Wykamol CM3 Waterproof Membrane is a high-density polyethylene cavity-drain sheet with a compact 3mm studded profile. It is designed for internal waterproofing and damp-proofing on suitable walls, floors, vaults and tunnels. The studs hold the flat face away from the substrate, creating a shallow air or depressurisation gap that separates the new internal finish from damp, salts and contaminated masonry. Below ground, CM3 forms part of a Type C drained-protection system connected to appropriate drainage and discharge. Above ground, it can isolate dry lining, battens or an internal block wall from a damp background. The product is non-meshed, so it requires a compatible protected finish rather than direct plaster or render.

Q) How does Wykamol CM3 work as Type C waterproofing?

A) Wykamol CM3 manages water after it enters the structure instead of trying to resist all hydrostatic pressure at the internal surface. Its 3mm studs create a controlled cavity behind or beneath the membrane. Water can move through this space towards Wykamol Waterguard, another compatible floor-drainage route, a safe gravity outlet or a correctly sized sump-and-pump system. The room-facing side remains separated from the damp, salt-contaminated substrate, helping protect plasterboard, flooring and decorative finishes. This approach is called Type C drained protection. CM3 cannot perform reliably as an isolated sheet: joints, fixing points, wall-to-floor transitions, penetrations, drainage capacity, discharge arrangements, inspection access and long-term maintenance must all operate together as one coordinated system.

Q) Can Wykamol CM3 be used for above-ground damp proofing?

A) Wykamol CM3 can be used above ground as a damp-proofing membrane where a meshed surface is not required. Typical finishes include timber battens and plasterboard, a dry-lining frame or an internal brick or block lining. The membrane separates the finish from damp, salts or a defective background and helps control water vapour. It should not be used merely to hide avoidable moisture. Defective rainwater goods, leaking plumbing, poor pointing, high external ground levels and other sources should be corrected wherever practical. Where rising damp is correctly diagnosed, an appropriate damp-proof course may be installed before CM3. Any mould, rot, structural weakness or hazardous contamination also requires proper assessment and treatment before the wall is enclosed.

Q) Why does Wykamol CM3 have a 3mm studded profile?

A) The 3mm profile provides a shallow cavity while using very little internal space. This makes Wykamol CM3 particularly useful near stairs, low ceilings, door details, narrow passages and floor build-ups where a deeper membrane would reduce headroom or usable room dimensions. It can also make refurbishment easier when finished levels must align with existing thresholds. The trade-off is that a shallow cavity is more sensitive to obstruction. Mortar, drilling dust, loose debris, silt, limescale or standing water can reduce the available drainage path. The substrate, floor levels and Waterguard connections therefore need careful preparation and testing. A 3mm membrane should be selected because it suits the project’s water flow, loading and space constraints, not simply because it is thinner.

Q) Which roll sizes are available for Wykamol CM3 Waterproof Membrane?

A) Wykamol CM3 is available in 2m-wide rolls measuring either 10m or 20m long. These provide nominal gross areas of 20m² and 40m² respectively. The quoted area is the uncut sheet size rather than guaranteed completed coverage. Measure every wall, floor, return, reveal, column, opening, vault and junction before ordering, then allow for trimming, shaped details, repairs and reasonable waste. CM3 does not have a normal flat flange, so standard wall and floor sheet connections are close butt joints sealed with 150mm Wykamol Corner Strip Tape. Calculate tape, CM Brick Plugs, Wykamol Rope, Waterguard and other ancillaries separately because their quantities depend on the sheet orientation, fixing pattern, room geometry and drainage design.

Q) What are the main advantages of Wykamol CM3 Waterproof Membrane?

A) Wykamol CM3 combines low build-up depth with the flexibility to waterproof below-ground structures or damp-proof suitable walls above ground. Its 3mm profile preserves headroom and floor area, while the HDPE sheet is quick to cut, position and mechanically fix. It can isolate damp or salt-contaminated surfaces without the extensive preparation sometimes required for a fully bonded coating, provided loose and unsafe material is removed. The membrane supplies vapour control, resists water, salts, roots and contaminants, and has no curing period of its own. BBA certification and published performance data support specification within the approved system scope. These benefits still depend on competent design, correct butt-joint sealing, protected finishes, effective drainage where required and maintenance of channels, sumps and pumps.

Q) Where can Wykamol CM3 Waterproof Membrane be used?

A) Wykamol CM3 can be used on appropriate walls, floors, vaults and tunnels in domestic or commercial projects. Below-ground applications include basements, cellar conversions, earth-retained walls, underground stores, corridors and plant areas connected to designed drainage. Above ground, the membrane can isolate dry lining or an internal wall from residual damp, salts or a defective background where the moisture cause has been properly assessed. Its shallow profile is valuable around stairs, low headroom, narrow spaces and constrained floor levels. CM3 is not automatically suitable for every wet surface. The structure, water risk, substrate strength, intended room use, finish, drainage capacity and access for maintenance must all be checked before installation, especially on habitable or high-risk schemes.

Q) Can Wykamol CM3 help create a habitable Grade 3 basement?

A) Wykamol CM3 can contribute to a waterproofing system designed to provide Grade 3 internal conditions, where water penetration and dampness are unacceptable, as commonly required for habitable basements. The membrane isolates internal finishes from the retaining structure and directs incoming water towards controlled drainage. CM3 does not achieve Grade 3 performance on its own. The structure, anticipated water ingress, sealed details, drainage capacity, gravity or pumped discharge, pump resilience, alarms, ventilation, humidity control, heating and maintenance must work together as part of a project-specific waterproofing design. Current projects should be designed in accordance with BS 8102:2022 and any applicable Building Control, warranty and project requirements by a competent waterproofing design specialist.

Q) Can Wykamol CM3 be installed on both walls and floors?

A) Wykamol CM3 is suitable for wall and floor use, although its orientation, restraint and finishing details differ. On walls, the studs face the substrate and the flat face points towards the installer. The membrane is mechanically secured using appropriate sealed CM Brick Plugs or Cob Plugs where the mortar is slightly friable. On floors, CM3 is normally loose-laid with the studs facing down, cut to the room perimeter and connected to the wall membrane and Waterguard upstand. Adjacent sheets form butt joints sealed with 150mm Corner Strip Tape. The floor membrane must not be punctured by fixings and requires a compatible load-spreading finish. In both applications, water must have an unobstructed route to the designed discharge point.

Q) Which substrates are suitable for Wykamol CM3?

A) Wykamol CM3 can be fixed to suitable brick, blockwork, concrete, stone, stable render and comparable masonry backgrounds capable of holding the specified plugs. Slightly friable mortar may require Wykamol Cob Plugs rather than standard CM Brick Plugs. On floors, the supporting slab or screed must be sound, level and free from sharp projections or debris. Sound render may remain, but loose or crumbling render, unsound plaster and defective screed should be removed. The membrane should not conceal structural movement, unstable masonry, collapsing finishes, running water beyond the system’s capacity or hazardous materials. Deep voids and severe irregularities require suitable repair. The substrate does not need to be cosmetically perfect, but it must support secure fixing, unimpeded drainage and the proposed internal lining.

Q) How should a wall or floor be prepared before installing CM3?

A) Remove loose debris, organic matter, unsound plaster, weak render and defective screed. Sound render may remain if it is firmly bonded and will not undermine fixing security. Level severe depressions and repair unstable areas with a compatible mortar, allowing all new work to dry thoroughly before fixing the membrane. Brush visible mould or masonry fungal growth from the surface and apply a suitable masonry biocide in accordance with its instructions. Dry rot requires detailed specialist assessment, while wet rot and affected timber should be treated by a qualified remedial contractor. Floors must be clean, stable and sufficiently even. Above ground, reduce avoidable moisture at source wherever practical, including defective plumbing, rainwater goods or an absent damp-proof course where rising damp has been correctly diagnosed.

Q) How is Wykamol CM3 installed on a wall?

A) Cut the membrane to size with a sharp knife, scissors or shears and position it with the studs against the wall. Where practical, continue it into the ceiling void and down beyond the slab; otherwise, finish it tightly at the soffit and floor detail. Set the sheet level using a long builder’s level or rotating laser. Drill through the centre of selected studs with a 10mm SDS bit to a minimum depth of 60mm, then insert the appropriate plug and drive it home with a wide-headed hammer or mallet. Add sufficient fixings to hold the membrane neatly and to support the intended lining. Butt adjoining sheets together, seal them with Corner Strip Tape and inspect all joints, corners and penetrations before covering.

Q) Which plugs and fixing centres are used with Wykamol CM3?

A) Standard wall areas normally use Wykamol CM Brick Plugs, while slightly friable mortar may require Cob Plugs. Fix through the centre of a stud into a clean 10mm hole at least 60mm deep. Centres depend on the final lining: typical guidance is 600mm vertically by 400mm horizontally for timber battens and 800mm vertically by 600mm horizontally for fixed metal-track systems. Barrel vault guidance uses approximately 300mm around the curve and 600mm along its length. Free-standing frames or walls do not need a support grid tied to the membrane, but enough plugs must hold it neat and tight. Align every fixing row and increase restraint at corners, reveals, edges or overhead areas where sagging could occur.

Q) How are Wykamol CM3 sheet joints sealed?

A) Standard CM3 has no flat jointing flange, so adjoining sheets are brought together edge to edge as a close butt joint. Clean and dry both membrane faces, then centre 150mm-wide Wykamol Corner Strip Tape over the joint. Press the entire tape surface firmly with the palm or a suitable roller so it bonds continuously without wrinkles, fish-mouths or trapped debris. In cold or damp conditions, carefully use a hot-air gun to evaporate light surface moisture and assist bonding, but never overheat or distort the HDPE. Wykamol Membrane Tape is used for compatible DPC interfaces and particular lapped details rather than as the standard face seal over a CM3 butt joint. Inspect every junction before it becomes inaccessible.

Q) How should corners, returns and door reveals be detailed?

A) Take Wykamol CM3 neatly around internal and external corners where possible, forming square creases without stretching the sheet or crushing its studs. If wall contours cause the membrane to distort, stop, make a controlled cut and begin again with a new butt joint sealed by Corner Strip Tape. Extend the membrane onto return walls so dampness cannot bypass the treated face and contaminate adjacent finishes. At door openings in vaulted work, a separate head section may lap approximately 100mm down the sides before the wall sheet wraps into the reveal. Seal small angled gaps with Corner Strip Tape. Keep cuts to a minimum, use compatible patches or Wykamol Rope where required and leave each complex detail visible for inspection.

Q) Does Wykamol CM3 require Waterguard drainage or a sump?

A) In a full or partly earth-retaining application, Wykamol CM3 must connect to effective drainage. Wykamol Waterguard is commonly installed at the wall-to-floor junction to collect water from behind the wall membrane and the structural junction. It can connect to Floor Drain routes, a safe gravity outlet, gully, waste pipe or suitable sump-and-pump arrangement. The discharge must handle anticipated water flow without backing up towards the waterproofed space. Standing water can carry silt or limescale into the shallow cavity and obstruct it, so drainage should be continuous and maintainable. Flexible jetting eyes provide access for checking and flushing Waterguard. Pumps, alarms, backup provision, pipework and inspection access should be specified from the project’s water-risk assessment and consequences of failure.

Q) How is Wykamol CM3 installed on a floor?

A) Begin at one side of the room and unroll Wykamol CM3 with its studs facing down, cutting it accurately to the perimeter in a similar manner to fitting a carpet. Lay the next width so the edges meet as a close butt joint. Clean and dry both faces, centre 150mm Corner Strip Tape over the joint and apply firm pressure across its complete width. Seal the floor membrane to the Waterguard upstand with the specified tape detail, maintaining a route for water to enter the channel. Compatible horizontal DPC connections use Wykamol Membrane Tape. Avoid all fixings through the floor membrane, protect it from tools and debris, and confirm drainage flow before installing the specified load-spreading floor finish.

Q) Can Wykamol CM3 be laid over green concrete to speed up finishing?

A) The product guidance states that a suitable floor membrane can be laid over green concrete once the surface is sufficiently firm to walk on, allowing the dry-side floor build-up to proceed without waiting for conventional concrete relative-humidity targets. Construction moisture continues to cure beneath the membrane and is controlled within the air gap. This fast-track approach can shorten programmes, but it is not permission to ignore structural strength, surface regularity, drainage, slab design or the requirements of the chosen floor finish. The membrane must be specified for the complete build-up, protected from punctures and connected correctly to drainage where required. Levelling compounds, adhesives, screeds and other associated products remain subject to their individual curing and compatibility instructions.

Q) How should pipes and services passing through Wykamol CM3 be sealed?

A) Services should be routed on the dry side of the membrane wherever possible, particularly in floors and overhead areas where penetrations create significant weaknesses. If a pipe, cable, conduit or duct must pass through CM3, cut the sheet neatly and keep the opening as small as practical. Floor guidance permits the gap to be filled and sealed with a suitable high-quality MS or SMX polymer adhesive. Where greater detailing is needed, apply a CM3 or compatible DPC patch, seal it to the service with compressed Wykamol Rope and seal its perimeter with Wykamol Membrane Tape or the specified compatible tape. Check movement, temperature and future access, inspect the entire circumference and photograph the detail before concealment.

Q) Which wall and floor finishes are compatible with Wykamol CM3?

A) Suitable wall finishes include treated timber battens with plasterboard, a free-standing timber or metal dry-lining frame, compatible proprietary metal-track systems and a properly restrained internal brick or block wall. Battens should be at least 25mm x 38mm, although 25mm x 50mm can support board edges more effectively. They may be attached to the hollow plug cores using controlled-length 5mm self-tapping screws. Floor finishes must protect and spread loads over the membrane and may include compatible boards, timber systems or other project-specified constructions. No fixing may penetrate the floor sheet. Every finish must meet structural, fire, thermal, acoustic and moisture requirements while leaving Waterguard jetting points, sump covers and other maintainable components accessible after completion.

Q) Can plaster or render be applied directly to Wykamol CM3?

A) Direct plaster or render should not be applied to standard Wykamol CM3 because it is a non-meshed HDPE membrane and does not provide the required mechanical key. The usual solution is a protected dry-lining arrangement, treated battens and boards, a free-standing frame, proprietary metal lining or an internal masonry wall. Fixings for battens or brackets should use the hollow centres of correctly installed CM Brick Plugs so no uncontrolled penetration is drilled through the waterproofing. Screw length must be calculated carefully because the plugs accept approximately 30mm of screw, and overlong fasteners can loosen the plug or puncture the sheet. If a direct wet-applied finish is required, specify a suitable meshed cavity-drain membrane rather than modifying CM3 on site.

Q) Can Wykamol CM3 be used on vaulted ceilings or soffits?

A) Wykamol CM3 can be used on suitable arched or vaulted ceilings where the membrane follows a dependable fall to drainage and cannot sag or allow water to pond. Fixings and mitred joints must be sealed using the compatible Wykamol components specified for the detail, and the ceiling membrane must remain continuously connected to the drainage route. Flat below-ground soffits should not be lined with CM3; the Wykamol technical data sheet requires a minimum slope of 10%. Because overhead waterproofing is detail-sensitive, the fixing layout, junctions, end-wall returns and finishes should follow the project-specific design and current Wykamol guidance.

Q) What tools and accessories are needed to install Wykamol CM3?

A) Typical tools include an SDS hammer drill, suitable 10mm masonry bit, wide-headed hammer or mallet, sharp utility knife, scissors or shears, tape measure, long builder’s level, rotating laser, clean cloths and a roller or firm pressure tool for tapes. A controlled hot-air gun can assist surface drying and tape bonding in cold conditions, but open flames must never be used. System accessories may include CM Brick Plugs, Cob Plugs, 150mm Corner Strip Tape, Membrane Tape, Wykamol Rope, DPC patches, Waterguard, Floor Drain components, jetting eyes, outlets, a sump and pumps. Suitable PPE, lighting, access equipment and dust control are also needed. Confirm all critical components and the installation sequence before cutting or fixing the membrane.

Q) Does Wykamol CM3 require a curing or drying period?

A) Wykamol CM3 itself has no curing period because it is a prefabricated HDPE sheet rather than a wet-applied coating. Once its fixings, butt joints, corners, penetrations and drainage connections have been completed, inspected and tested, the specified protective finish can normally proceed. However, preparation materials and other parts of the construction still need proper drying or curing. The product guidance instructs installers to allow new repair work to dry thoroughly before fixing wall membrane. Mortars, renders, screeds, biocides, adhesives and sealants must follow their own instructions. A separate fast-track floor arrangement may permit suitable membrane over walkable green concrete, but this must be distinguished from ordinary wall repairs and coordinated with slab strength, drainage, loading and the selected floor build-up.

Q) What are the main technical specifications of Wykamol CM3?

A) Wykamol CM3 is manufactured from high-density polyethylene and has a stated sheet thickness of 0.6mm, unit weight of 0.5kg/m² and stud height of 3mm. Its stated softening temperature is 126°C, with a working temperature range of -50°C to +80°C. Published tensile strengths are 416N in the machine direction and 488N across the sheet to BS EN 12311-2. Water-vapour resistance is stated as greater than 3020MNs/g, resistance to static loading exceeds 20kg and compressive strength is 250kN/m² to BS EN ISO 25619-2. The Declaration of Performance records reaction to fire as Class E to EN 13501-1:2007+A1:2009.

Q) Is Wykamol CM3 BBA approved and compliant with current standards?

A) Wykamol CM3 is covered by BBA Agrément Certificate 18/5595 for the applications and conditions defined within the certified scope. It is suitable for inclusion in Type C drained-protection systems designed in accordance with BS 8102:2022. Where Grade 3 protection is required and the below-ground wall retains more than 600mm of ground, CM3 should be combined with Type A or Type B waterproofing protection in accordance with the BBA certificate. Certification applies to the specified use of the product and does not make CM3 a standalone waterproofing system; drainage, discharge, detailing, ventilation, installation quality and maintenance remain essential.

Q) How long should Wykamol CM3 Waterproof Membrane last?

A) Under normal service conditions, BBA Agrément Certificate 18/5595 states that Wykamol CM3 can provide an effective barrier to salts, liquid water and water vapour for the life of the structure in which it is incorporated. This depends on the membrane being correctly specified, stored, installed and protected, and connected to a functioning waterproofing and drainage system. Joints, penetrations, drainage channels, sumps, pumps, alarms and finishes must be inspected and maintained in accordance with the system design.

Q) What maintenance does a Wykamol CM3 waterproofing system need?

A) The protected CM3 sheet normally requires little direct routine attention, but its drainage and discharge system must remain accessible and serviceable. Waterguard jetting eyes should be retained so channels can be inspected and flushed if silt, limescale or debris begins to restrict flow. Sumps should be cleaned, pumps and floats operated, non-return valves checked and discharge pipework examined in accordance with the system specification and component instructions. High-water alarms, standby pumps and backup power also need testing where fitted. Maintenance frequency should reflect the site’s groundwater risk, water flow, lime exposure, pump activity, occupancy and warranty conditions. Keep as-built drawings, photographs and no-fix zones so future contractors do not puncture CM3, block drainage or conceal access covers permanently.

Q) What are the main limitations of Wykamol CM3 Waterproof Membrane?

A) Wykamol CM3 is not a stand-alone barrier against hydrostatic pressure and requires continuous drainage in earth-retaining applications. Its shallow 3mm cavity can be obstructed by debris, silt, limescale or standing water if preparation and drainage are inadequate. Standard CM3 is non-meshed, so direct plaster or render is unsuitable. Butyl-taped joints need clean, dry surfaces, and all floor penetrations should be avoided wherever possible. Flat soffits require dependable falls, close support and specialist detailing to prevent ponding. The membrane cannot correct structural instability, uncontrolled water entry, dry rot, hazardous contamination or avoidable building defects. It also needs protection from punctures, ultraviolet light, heat and flames and does not remove the need for ventilation and condensation control in occupied rooms.

Q) What practical tips help ensure a reliable Wykamol CM3 installation?

A) Plan the sheet orientation, plug rows, wall-to-floor connection, Waterguard route, sump, services and final finishes before cutting. Measure gross areas separately from waste and calculate 150mm Corner Strip Tape, plugs and other accessories from the actual layout. Keep the 3mm cavity free of drilling dust, mortar and debris, and use a level frequently so long sheets do not drift or kink around corners. Clean and dry every taped surface, press joints firmly across their full width and use controlled warm air only when necessary. Fix through stud centres, control later screw lengths and mark no-fix zones. Before concealment, inspect all membrane, joints and penetrations, flush drainage, test pumps and alarms, photograph critical details and provide a maintenance schedule.

Technical Data Sheet

Declaration of Performance (DoP)

BBA Certificate