Posted On By Danny Neill

How To Install a Damp Proof Membrane

How To Install a Damp Proof Membrane

Author: Danny Neill - Operations Manager at Platinum Chemicals Ltd

How To Install a Damp Proof Membrane

Damp Proof Membranes are an excellent solution for damp problems on walls inside the home.

Damp causes many problems in properties and it's important to properly identify the the type of dampness in question and the cause.

Generally speaking, there are THREE types of damp problems that can occur in a building:

  • Rising Damp

  • Penetrating Damp

  • Condensation Damp

Identification of the type of damp is important. Once the type of dampness has be identified, there are often measures that can be taken to help treat the problem.

Damp Proof Membranes are ideal for use on walls affected by Rising Damp or Penetrating Damp. For information on how to deal with Condensation Damp, please refer to our blog on How To Stop Condensation With PIV.

Spending the time looking over your property thoroughly to try and identify the cause is certainly useful as it may be something you can fix quickly.

Depending on the cause of the dampness, remedial measures may be required to remove the damp and prevent further occurrence, ensuring that your property is kept warm and dry.

What is a Damp Proof Membrane?

Damp Proof Membranes are manufactured in the form of a studded plastic sheet made from either High Density Polyethylene (HDPE) or Polypropylene (PP). HDPE and PP are impervious to moisture and salts and can be fixed to internal walls.

The surface of the membrane has a studded profile (either 2mm, 3mm or 5mm, depending on which type membrane), and the studs face the wall to create an air gap that allows for vapor equalization to take place between the membrane and walls.

Most Damp Proof Membranes have a MESHED Surface on one side which acts as a 'key' for Plaster, Render or Plasterboard bonded using Adhesive Dabs.

If the membrane is NOT to be used as a render base, where a block wall or dry-lining frame is used as the wall finish, a NON-MESHED Membrane should be used instead.

At Platinum Chemicals, we supply a huge range of Premium Quality Damp Proof Membranes. Our Damp Proof Membranes can easily be ordered online and installed at your home as part of a home improvement project.

Our Range of Damp Proof Membranes are effective and long lasting. They will protect your property from damp problems and are suitable for a wide range of applications. Our Wide Range of Damp Proof Membranes Include:

  Platinum Damp Proof Membranes

  Newton Damp Proof Membranes

  Platon Damp Proof Membranes

  Wykamol Damp Proof Membranes


We also supply a wide range of Damp Proof Membrane Kits, which includes the Damp Proof Membrane supplied with Fixing Plugs, a Plug Sealing Product in the form of Mastic or Sealing Washers (Optional) and an SDS Drill Bit.

Our FULL RANGE of Damp Proof Membrane Products can be found here.

All our products are of the highest possible quality and can be used in conjunction with each other to create a comprehensive damp proof course for any property.

What are the Benefits Of Using Damp Proof Membrane?

Damp Proof Membranes are an extremely effective way to protect a building’s interior from water penetration whilst remaining sympathetic to the structure.

Benefits of Using Damp Proof Membrane include the protection against:

  • Mould Growth

  • Damp Patches

  • Salt Contamination

  • Fragmenting Plaster

  • Discolouration

  • Blistering Paint

  • Peeling Wallpaper

  • Fungal Decay

  • Deterioration of Internal Décor

  • Heat Loss due to Poor Thermal Performance

Damp Proof Membranes will also protect the rest of your home from developing damp related problems. They will be shown on property surveys and will make up part of a surveyor’s report which will be useful when selling a property.

How do you Install a Damp Proof Membrane?

Here we will focus on installation of MESHED Damp Proof Membranes.

When fitting Damp Proof Membranes on walls you should follow these steps:

1. Surface Preparation
2. Cutting the Membrane To Size
3. Membrane Jointing
4. Sealing around Protrusions
5. Fitting and Fixing The Membrane To The Wall
6. Apply a finish

Damp Proof Membranes are easy and quick to install, and the wall does not require extensive and damaging substrate preparation.

1. Surface Preparation:

Clean the substrate to remove all loose debris and organic matter. Plaster should be removed as it can soften over time, which will weaken the fix of the membrane to the wall. If the wall render is in good condition, it does not have to be removed and the Damp Proof Membrane can be fitted directly. If the render is damaged, loose or crumbling, local repairs may be required. The render may need to be fully removed if it is in especially poor condition.

Obtain as flat a surface as possible. If the wall is undulating, better results are produced if the wall surface is dubbed-out flat with sand & cement prior to installation of the membrane, rather than dubbing out over the top of the membrane. A flat, uniform surface to the substrate means that the plaster or render above the Damp Proof Membrane will also be uniform and less likely to have cracking caused by differential thicknesses.

If any evidence of wet rot or dry rot is seen, have it dealt with by a qualified remedial specialist.

2. Cutting the Membrane to Size:

Decide whether the membrane is to be fitted horizontally or vertically. Then, cut the Damp Proof Membrane with a sharp utility knife, scissors or shears. 

3. Membrane Jointing:

Joints may be made horizontally or vertically by butt jointing the two edges together and then over-sealing the joints with a MESH TAPE. Mesh Tapes have a fleece surface on one side to also accept plaster, render etc.

Damp Proof Membranes can be installed round corners. On particularly difficult shaped corners, cut the Membrane and butt joint and seal with the Mesh Tape. The Mesh Tape should be firmly pressed into the mesh of the Membrane to facilitate the joint.

In cold and damp conditions, use a heat gun to gently evaporate surface moisture and to assist in pressing the Mesh Tape into the mesh of the membrane.

4. Sealing Around Protrusions:

Carefully cut the membrane around the protrusion (such as a pipe) and then seal around the protrusion with Newton 801-M Sealing Mastic to ensure there is no bridging between the damp substrate and the new finish.

5. Fitting and Fixing the Membrane to the Wall:

Cut the membrane to size. Ideally, Damp Proof Membranes should continue up into ceiling voids and down past the slab to the oversite. If this is not possible, cut the membrane so that it finishes tightly to the soffit and floor finish. A gap is not required at the soffit or floor, indeed the system works more efficiently when the system is not ventilated as this impedes the natural vapour drive from inside the property to the outside that still continues through the Damp Proof Membrane.

Fit the Damp Proof Membrane to the wall as level as possible, either horizontally or vertically, with the studs facing the wall and the flat meshed surface facing inwards towards the applicator. When fitting the membrane to the wall, the best results are achieved when a long builders level or a rotating laser level is used. Care must be taken to ensure that the membrane is pulled tight and square while fixing as this will avoid sagging or bulging which can cause problems when plastering or rendering.

Using a 7mm or 8mm Drill Bit (depending on substrate), drill through the membrane into the wall to a depth of at least the length of the fixing plug.

If there is a greater risk of dampness, apply a bead of Newton 801-M Sealing Mastic around the hole to the membrane so that when the plug is hammered in, the Mastic will seal between the plug and the membrane, which will prevent dampness from migrating and salting from the substrate to the wall finish. Plug Sealing Washers may also be used as an alternative method.

Fix the membrane to the wall with the Plaster Membrane Plugs (i.e Platinum Mesh Fix, Platon Plaster Plugs, Wykamol CM Plaster Plugs, Newton 800 Mesh Plugs). Use a small number of fixings to initially fit the membrane to the wall while it is level. Once the section of membrane is on the wall, add the further fixings. Hammer the plugs home using a wide headed hammer such as a lump hammer or mallet. Plugs can be used to fix membranes to all substrates except plywood or timber, when a galvanised clout nail should be used, or to slightly friable mortar substrate, when a Cob Plug should be used.

A smaller-diameter bit can be used on softer substrate to ensure a tight fit for the plug. Fixing centres internally must not be greater than 250mm. On curved or uneven surfaces, closer fixings should be used. On exposed areas closer fixings are recommended, to restrain possible thermal movement.

Fit the Damp Proof Membrane 300mm to return walls to isolate wall finishes from dampness transmitting from the main wall being treated. Damp Proof Membranes can be taken into reveals. Fixing should not take place above 30°C and below -5°C.

What Finishes can be used on a Damp Proof Membrane once it's been Installed?

Damp Proof MESHED Membranes are suitable for wall finishes including:

  • Plaster

  • Render

  • Hydraulic Lime

  • Plasterboard (bonded to the membrane with a proprietary adhesive compound)

Whilst cement based renders are prone to cracking, careful application can reduce or avoid this. Problems occur when the scratch coat has not been allowed to fully cure prior to the float coat being applied, but the most common problem we see is where the render has not been allowed to fully cure due to accelerated drying. It is extremely important that the render is slowly cured for a period of 7-10 days, longer if possible. The render gets its strength from the chemical processes that take place between the cement content and the added water. The cement needs the correct amount of water to be available to it during the whole of the curing period. If the render dries too quickly due to exposure to sunlight, wind or even dehumidification, the cement will not be able to react with water, producing a weak render that will be prone to cracking.

The render should be dampened regularly during the curing process and protected from accelerated drying with hessian and plastic sheeting.

Hairline cracking can be made good with fine fillers or alternatively a high-build masonry paint can be applied.

DO NOT APPLY DECORATIONS UNTIL PLASTERS OR RENDERS ARE THOROUGHLY DRY.

Finishing Profile:

It is recommended that plasters and renders are raised from the floor by 20-25mm to prevent bridging from the floor. Newton 800 Finishing Profile, available in 2 metre lengths, should be fitted to the bottom of the Damp Proof Membrane as a plaster stop, guaranteeing that the plaster/render will stop short of the floor.

Newton 800 Finishing Profile must be fixed at the same time as the Damp Proof Membrane and therefore before the plaster or render is applied.

Newton 800 Finishing Profile is not recommended where the run of wall is uneven or when the membrane is extended down past the slab. Once the finish has been applied and has dried, the 20-25mm gap to the bottom of the plaster / render should be covered by a timber skirting.

Plastering:

Tarmac Whitewall Once Coat is the recommended plaster for Damp Proof Membranes. Please note that we do not recommend that this product is used in one single coat with our Mesh membranes.

The plaster should be applied in Two Coats: 6mm scratch coat and a 6mm second or float coat. If a finish coat is required this should be 3mm.

Tarmac Whitewall should be applied in accordance with good plastering practice as described in BS 8481:2006, BS EN 13914-2:2005.

Always allow 24 hours drying time between coats of plaster. For a high impact resistant finish, use Whitewall High Impact Backing Plaster.

NOTE: Tarmac Whitewall and Tarmac Whitewall High Impact Backing Plaster are not suitable for high humidity or wet areas such as swimming pool surrounds.

Rendering:

Render, with a mix of sand, cement and lime, should be applied in two coats using the procedures defined within BS EN 13914-1:2005 to a total thickness of 14mm. A 3mm skim coat of finishing plaster can be added once the render is fully cured

The scratch coat should be a mix of: 1 part lime, 1 part cement and 5 parts clean well-graded sharp sand. The second or float coat should be a mix of: 1 part lime, 1 part cement, and 6 parts clean well graded sharp sand. The scratch coat should be 7mm and the second or float coat should be 7mm.

To lessen incidents of cracking, it is best to mix the lime and sand a day or more before use. Cement can then be added at the time of rendering.

The work should be of two coats of render and if required, a third coat of finishing plaster. The purpose of the 7mm scratch coat is to stiffen up the lath and to provide rough and absorbent, backing for subsequent coats. Work this scratch coat well into the mesh. Each 7mm coat of render should be allowed to dry for a period of not less than seven, preferably ten days, longer if possible. Cracking may occur if shorter time is allowed between coats.

It is important that the render coats are allowed to cure correctly over the 7 to 10 day period with the render dampened as required. If the scratch coat has not fully cured, slumping of the render can result.

Before applying the second or float coat, carefully drill or scratch out a small section into an area behind the mesh, within the membrane stud, to confirm that it is fully cured. The surface will cure quite quickly but the area behind the mesh must be fully cured also.

In warm periods the render should be protected from excessive drying out by covering with damp hessian sheets and plastic sheeting over it.

Dampen down the scratch coat before application of the float coat. A smooth finish is not recommended. Expansion joints should be trowelled in through the render to the membrane. These joints must be filled with a suitable flexible polymer-based sealant. Expanded metal angle beads and stop beads can be fixed where appropriate using dabs of the same material mixed for the scratch coat.

Hydraulic Lime:

NHL (Natural Hydraulic Lime) 3.5 should be used to a combined depth of 20mm with a 10mm scratch coat and a 10mm second or float coat. The mix ratio is 2.5 parts sand to 1 part NHL, 3.5 mixed as per manufacturers instructions. The 10mm scratch coat is pushed firmly into the membrane mesh.

Check the application the day after and rub out any cracks. The surface should be thoroughly scratched without breaking the surface of the mesh. The scratch coat has to be left for a minimum of 7 days to set. It should be protected from draughts and extremes of temperature

Before applying the second or float coat, carefully drill or scratch out a small section into an area behind the mesh, within the membrane stud, to confirm that it is set and reasonably hard. The surface will cure quite quickly but the area behind the mesh that has to be set.

The second coat is the float coat and is applied then ruled off to flatten the wall surface. The mix ratio is 2.5 parts sand to 1 part NHL 3.5 mixed as per manufacturers instructions.

The scratch coat has to be dampened down before application of the float coat.

The work has to be protected and tended as per the scratch coat. The second coat is floated or trowelled so a finish coat or a further coat can be applied

Plasterboard on Dabs:

Plaster board panels can be fixed to Damp Proof Meshed Membranes by the dot and dab method, giving a dry surface ready for immediate decoration. ‘Dabs’ should be applied to the heads of the Plaster Plugs, board edges and membrane to cover 50% of the Damp Proof Membrane. Alternatively, a Low Expansion Adhesive Foam, such as Soudabond Easy, may be used for this method.

NOTE: We do not recommend that laminated or insulated plasterboard is dot & dabbed to meshed membranes. Laminated boards have to be fixed to the wall with a mechanical fixing at each side of the board, just above half way up, so that the board does not come apart and block exits during a fire. This is a requirement of UK building code. It is not possible to mechanically fix through the laminated board without puncturing the membrane.

If insulation is required to the wall build, use a Non-Meshed Membrane Damp Proofing Membrane, with an independently supported wall frame.

​Platinum Chemicals - Providing High Quality Products and Inspiring Confidence.

At Platinum Chemicals, we pride ourselves on providing an excellent service every time, with bulk discounts and speedy delivery available.

You can buy from Platinum Chemicals with confidence you’re getting the best products at excellent prices every time. If you require advice on these products please contact us on 01355 222777 or by emailing info@platinumchemicals.co.uk

Main Image Credit: Newton Waterproofing

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