Vapour permeability – what does it actually mean?
Following damp proofing and specialist plastering works, it is always advisable to allow the walls to dry out for as long as possible before redecoration is carried out. We normally advise delaying for a period of 4-6 weeks after rendering / plastering and using vapour permeable water based micro porous emulsion. It is important that permanent decoration – especially wall papering – should not be applied for at least 12 months or until such times as all residual moisture has dried out of the walls. This includes the use of lining papers, which should also be avoided during the first year.
It is imperative that the walls are not force dried following our works, using dehumidifiers, space heaters or turning up the radiators etc., as this may cause shrinkage, cracking and de-bonding of the specialist renders.
There are many branded water-based emulsions on the market, however we do not specify a specific brand. The important thing to remember is that this should not be carried out too soon, and impervious materials should not be used in an attempt to permanently seal trapped moisture into the structure i.e. vinyl silks/glosses. Some of the new, more expensive emulsion paints, such as egg-shell texture, state that they are vapour permeable. However, we have found that they are not as vapour permeable as a typical water-based matt emulsion. The use of such materials can lead to future problems i.e. blistering of the paintwork decoration.
Sometimes small shrinkage cracks may appear in the new finish plaster, this is normally due to the dense nature of the render mixes that have been used beneath the finish plaster and the differential in drying times. It does not mean the render is failing, or has been applied incorrectly. Where this occurs, the hairline cracks should be filled with a fine filler as part of the redecoration works.
The rule is that a wall will dry out at the rate of approximately 25mm (1”) per month, so a standard 225mm (9”) solid wall can take up to 9 months to dry out, according to British Standard BS6576
It is important that the finish plaster skim (set) coat is short of the floor to avoid any residual dampness at floor level, which could be condensation, being absorbed by the finish plaster.
For any basement waterproofing works below ground level, it is important to discuss the timing and suitability of redecoration works with the Surveyor concerned, as this can vary upon site conditions and the systems which have been used.
Occasionally during the drying out process efflorescence may occur on the surface of newly plastered, undecorated walls. This usually forms as a soft, white fluffy deposit on the surface and should be lightly brushed off. Where this does occur, subsequent re-decoration should be delayed until such time that the efflorescence stops. Efflorescence on a wall surface is usually caused by sulphate salts which are soluble, but not hygroscopic. Where it does appear, it means the water has evaporated, leaving the salt deposits on the surface.
If you would like to discuss any damp problems you may have, or redecoration following our works, in more detail we would be be delighted to be of assistance. Our contact details are:
Tel: 01276 66466
Email: ptl@preservationtreatments.co.uk
Website: www.preservationtreatments,co.uk
Preservation Treatments provide Damp Proofing, Structural Waterproofing, Timber Treatments, Condensation Solutions and Structural Repairs throughout London, Hampshire, Middlesex, Surrey, Berkshire and Sussex.
Contact us now to discuss our services further or to arrange a survey.
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