Wykamol Group | Damp Proofing
RenderProof is an additive based on an alkaline soap mixed with fatty acids, designed for use in sand / cement, external render coats following the insertion of a chemical DPC.
Efflorescent salts are often left behind in the wall after a chemical DPC, which are harmful to the plaster finish, leaving the appearance of damp patches.
A suitable re-plastering specification must therefore be used, including a salt inhibiting and waterproofing product such as RenderProof.
Renderproof is part of the Wykamol Re-Plastering Specification which is supported by BBA Certification Certificate No: 02/3961.
Available in 5 Litre and 25 Litre Containers.
Reduces pore size in Render to prevent passage of water
Covers large areas in a single application
Highly Concentrated: 1 part RenderProof to 24 parts water
Prevents passage of residual ground salts which are harmful to plaster finishes
Vapour permeable, allowing the walls to breathe
Masonry joints should be raked out and all surface thoroughly cleaned to remove dust or other friable material. All traces of previous plaster must be removed. Any organic matter (including timber fixings) must be removed
Where appropriate, fixing points which necessitate cutting into the background must be prepared.
High suction surfaces should be thoroughly wetted or primed using an SBR Bonding Agent. SBR can also be used to provide a mechanical key on smooth, dense surfaces.
Where very high levels of salt contamination are present, or suspected, further preparation with Salt Neutraliser may be necessary before application commences. Consult our Technical Department if the extent or nature of the salt contamination is unclear
A mix of 3 parts by volume of washed, sharp sand to 1 part of cement, gauged with potable water containing 1 part of RenderProof with 24 parts of water. The constituents of mixes should conform to the following descriptions:
Ordinary portland Cement (OPC) to BS EN 197-1:2011
Aggregate-clean, sharp, washed sand. The coarsest, sharpest sand, suitably graded for plastering, should conform to BS EN 13139:2002
Water - Fit for drinking and free from organic matter.
N.B. The amount of gauging water in the undercoats should bethe minimum consistent with reasonable application.
A mix of 4 parts volume of washed, sharp sand to 1 part by volume of Ordinary Portland Cement.
The plaster should be applied to a thickness of 10-12mm. The backing coat should finish at least 50mm above the solid floor and must not bridge the Damp-Proof Course.
Care should be taken to avoid dropping plaster or other debris through the gap between the wall and the edge of any suspended floor.
The surface should be scratched as it begins to set, to give a good key for subsequent coats.
The plaster should be applied to a thickness of 8-10mm in the same areas as the backing coat.
No more than two plaster coats should be applied in one continuous working process. If a greater thickness is required:
The first coats should be scratched and left to cure for 7-14 days
Apply SBR Bonding Agent as a primer before proceeding
The sand/ cement undercoats should be scrape finished and mist sprayed for the first 48 hours to reduce the risk of shrinkage and cracking.
Under no circumstances should Gypsum based plaster be used for the backing or float coat, nor should it be added to the mix of either coat.
RenderProof is not suitable for use in lime-based mixes or mixes with a lower cement content than recommended.
The recommended sand and cement mix can be used to to ‘dab’ any angle beads etc. to avoid salting.
A minimum of 24 hours curing time must be allowed after application of the float coat, even under ideal curing conditions.
The finishing plaster should be applied at a thickness of 1.5mm - 3mm. Since polished surfaces are undesirable, excessive use of the trowel or brush should be avoided.
Initial decoration should be delayed as long as possible and should not be applied within 14 days of the finish plaster coat.
Temporary decoration should be limited to a vapour permeable finish such as a breathable paint. Final decorations which reduce permeability, such as papers and oil paints, should not be applied until the walls have dried out, with at least 12 months being allowed following temporary decoration (for typical 225mm brickwork walls).
Drying times for thicker walls may extend to several years and will depend, in part, on the level of winter time heating etc. If impermeable decorative finishes are to be applied, in such situations an alternative approach to reinstatement may be considered, involving the use of vapour impermeable ‘air-gap’ membranes
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