Replastering After a DPC installation

The installation of either a chemical or electrosmotic damp-proof course (dpc) is only one part of the treatment.

Even when a new damp proof course has been installed and the rising damp problem is under control, the affected wall is still going to contain residual dampness within it, as well as hygroscopic salts carried up from the ground. These will continue to attack plaster and decorations.

Plaster contaminated by visible dampness and / or Hygroscopic salt contamination must be removed (usually at least 1m high) and be replaced as well. This is well documented in British Standard 6576:2005.

Both the installation of the dpc and the associated replastering when carried out by ourselves form part of the damproofing solution and accordingly both are usually included in any guarantees offered by Cook Group Ltd.

For instance if you were to carry out replastering only to a wall that continues to suffer from ingress of water (such as a wall without a damp proof course), the treatment is unlikely to prove successful in the long term. This is because renovating plasters are usually only capable of holding back moisture for a short period. Such a period would normally be during drying out of the wall after damp proof course has been installed.

On the other hand of you were to install a dpc only in a wall that has damp and salt contaminated plaster on, it will not allow the wall plaster to dry out or for the salts in the plaster to diminish. Salts can absorb moisture and whilst your new damp-proof course is working well, these salts can readily absorb condensation from the air and your ‘damp’ stays and can probably look worse than before your ‘part treatment’.

Therefore plaster removal and replacement must take place. All too often we visit properties where a dpc only has been installed and the wall plaster still tests and looks visibly damp.

Replacement plasters must either be of the renovating cement-based type, i.e. Wykamol Renovation Plaster or our Chemical rendering system.

No replastering to walls treated by ourselves should ever have any gypsum content in the backing or first coat and most certainly under NO circumstances should you even consider using the ‘dot and dab’ method of dry lining directly onto a treated wall.

Gypsum is very sensitive to moisture and salts and degrades easily in the presence of both. The design of a renovating plaster is to provide two distinct layers. The render or backing coat is that applied directly to the exposed masonry, when the old plaster has been hacked off. One of its purposes is to provide a rough surface onto which a finishing coat can be applied. However, its main purpose is to protect the finishing plaster coat from residual moisture and salts left in the masonry of the wall after the old plaster has been removed. Therefore the backing plaster contains both water and salt resistant additives to allow it to work.

Finishing plasters are gypsum based. Their function is cosmetic only; to provide a flat, smooth surface on to which wall decorations can be applied. Finishing plasters are sometimes also called “skim” plasters.

If you have any queries simply contact us and we’ll be happy to help

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Replastering 9th January 2019