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Writer's pictureSimon Hollis
Mar 21, 20223 min read

Ilkley

Next in the review of the last year, of up to Ilkley (which I always thought was part of Leeds, but is actually part of Bradford).


What a superb home this is. Thankfully, in comparison to a lot of houses I see, this one had minimal problems. The client was concerned about the several areas of penetrating dampness in two of their bedrooms. A couple of things were contributing to this.


One of the chimney flues had been crudely capped off and there were gaps around where the flashing was dressed into the stack and over the verge of the roof. Moisture was getting into the redundant flue and as this was not vented in either the room or at the top of the stack, it could not escape. Chimney flues are full of impurities and salts from years of burning fossil fuels. When there is moisture in the flue, these impurities dissolve and move around in the masonry until the moisture finds somewhere to evapourate and the impurities are left on the surface. The pressure of these impurities will often blow gypsum-based plasters and plastic-based paints.



To compound this problem, the rear elevation had been painted in many layers of plastic-based masonry paint. This was hairline cracking in in many places and causing rainwater to get trapped in the wall from where it could not escape. The wall had been painted so many times, the paint had almost entirely blocked up the passive ventilation brick.


Further, there was no projection on the stone windowsills. This is a common, but poor detail. Newer sills project clear of the elevation and have throating on their underside so that rainwater is shed to the ground below and it does not saturate the wall below the window. This property had been partially re-pointed in a very hard sand and cement-based mortar which is totally inappropriate for a traditionally constructed building. This mortar mix completely inhibits the pointings' ability to manage this moisture and forces moisture management to take place via the stone, which is not only drastically less efficient but will accelerate decay to the stone. You can see in the thermal imaging that the areas under the windows are cooler, likely as a result of the wall holding this moisture. Once a wall is wet, it loses most of its thermal mass and becomes very difficult to heat and this starts a cycle of decline.



The proposed solutions in this case are:


  • Open up the redundant chimney flue – a vented cap on top of a new chimney pot on top of the stack and either a fireplace or suitably sized vent in the room. Replace the existing flashing with a more appropriate detail.


  • Remove the layers of plastic-based masonry paint. This needs to be done at a low PSI with something like a DOFF or TORC machine. Using something like a sandblaster will damage the stone further. Assess the condition of the stone underneath and undertake repairs and re-pointing as required. Apply 3+ coats of limewash, burnishing in between coats.


  • Remove the cementitious areas of re-pointing by hand with a plugin chisel or with an Arbourtech. Re-point with a non-hydraulic hot mixed lime-based mortar to a beaten back finish.


  • Allow the wall to dry out naturally. Forced drying will likely trap moisture in the centre of the wall and so is not a good idea.


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