It is always advisable to allow the walls to dry out for as long as possible before redecoration is carried out, following damp proofing and specialist plastering works. We normally advise delaying re-decoration for a period of 4-6 weeks after rendering / plastering. We advise that you use a 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.
There are many branded water-based emulsions on the market. We do not specify a particular brand. The important thing to remember, is that this should not be carried out too soon. Impervious materials i.e. vinyl silks/gloss paints etc. should not be used when decorating after damp proofing work, as this could permanently seal trapped moisture into the structure. 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 such as blistering of the newly applied decorative finishes.
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 happens, the hairline cracks should be filled with a fine surface filler and sanded back, as part of the redecoration works.
The general 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 9-12 months to dry out, according to British Standard BS6576
It is important that the finish plaster skim (set) coat is left short of the floor, to avoid any residual dampness at floor level, as this could be condensation, being absorbed by the finish plaster.
For any basement waterproofing works which are below ground level, it is important to discuss the timing and suitability of redecoration works with the Surveyor. This can vary upon site conditions and the systems which have been used.
Occasionally during the drying out process salt 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 efflorescence does appear, it means the water held by those salts has evaporated, leaving the salt deposits on the surface. Where this happens, subsequent re-decoration should be delayed until such time that the efflorescence stops. Efflorescence on a wall surface is usually the result of sulphates, which are soluble, but not hygroscopic. This means they will not absorb residual, or air-borne dampness.
If you would like more information, or would like to speak to somebody concerning re-decoration of walls following damp proofing work, please do contact us on:
Tel: 01276 66466