The Problem: Treatment of Chimney Damp

Damp patches and salt staining were occurring on the chimney breasts in the upstairs rooms of this late Victorian house. The owners wanted the problem to be dealt with before refurbishing the rooms.

The source of water ingress was traced to defective flashings and pointing on the chimney stack. These were rectified by a specialist roofing contractor. Monitoring of the chimney breasts over several months demonstrated that the chimney breasts were starting to dry out – even after periods of extremely heavy rain during the winter of 2013/2014. It was therefore decided that the source of moisture had been successfully identified and dealt with.

The Need to Replaster

Unfortunately damp patches on chimney breasts can be very persistent, even when the source of dampness has been dealt with. This is because chimney breasts are usually contaminated with moisture-attracting hygroscopic salts that have built up in the chimney structure as a result of the burning of coal over many decades. If the wall is simply repainted or replastered using a standard gypsum plaster, these salts will usually migrate to the wall surface resulting in decorative spoiling.

For this reason it is normal practice to hack off the contaminated plaster and apply a cementitious waterproofing slurry or render to the wall before a finishing plaster is applied. Alternatively a studded, meshed plastic membrane (known as plaster membranes) can be applied to the wall before replastering takes place.

Both these methods are very time consuming, resulting in added cost to the property owner. Waterproofing slurries and renders are typically applied in several coats, meaning that the contractor has to visit the property for several days in a row. Plaster membranes can be applied more quickly, but inhibit drying of the plaster that is applied on top of them – meaning that it can often take over a week before paint or wallpaper can be applied to the plaster.

The Solution: Dryzone Express Replastering System

The Dryzone Express Replastering System was originally developed as a method of replastering salt-contaminated walls as part of a rising damp treatment strategy. However it is just as applicable to replastering over salt contaminated chimney breasts provided that any water ingress has been identified and dealt with. It’s key advantages are:

• Applied more quickly than traditional methods
• Can be redecorated over more quickly than traditional methods
• Breathable

In this example the The Dryzone Express Replastering System was used in conjunction with a skim coat of plaster which was dry after just three days. A faster option would have been to use dry jointing instead of a skim coat – allowing redecoration to take place the same day.

The Result

A dry wall surface to a high decorative standard was achieved much more quickly than would have been possible using traditional methods. Hacking off of the plaster, installation of the Dryzone Express Replastering System, and application of the skim coat were carried out in a single day. Painting took place three days later.