Waterproofing Solid Brick Walls

As a result of the extreme weather over recent weeks I’ve taken a couple of calls from owners who have experienced dampness penetrating through solid walls as a result of driving rain. You’d think that a 215mm thick solid brick wall would provide a sufficient barrier to rain but often defects will arise which means that’s not the case.

When investigating such a scenario the first step is to rule out other possible causes; the most obvious one being leaking gutters. In my experience leaking gutters, hopper heads or downpipes are by far the most common cause of dampness in period properties. As the homeowner only tends to notice the internal symptoms (damp patches, mould growth etc.) it’s also possible that the problem has originated internally in the form of condensation.

Once it has been established that rainwater must be penetrating directly through the wall the condition of that wall should be examined closely. Start with the mortar joints, most solid brick walls were built using lime mortar which has some excellent qualities (such as the ability to self-heal) but over a long period it will become crumbly (often described as ‘friable’ by surveyors).

If the mortar joints have eroded a program of re-pointing should make the wall water-tight again. It’s always best to replicate the original materials when undertaking repairs such as this so with solid brick walls that’s likely to be lime mortar.

If the mortar joints are not defective the problem may lie with the bricks themselves. Most bricks are porous so water is absorbed during wet weather and evaporates later. The risk is that during a prolonged wet period the temperature drops below zero and the water freezes while still in the brick. The expansion of the frozen water particles can damage the surface of the brick and in extreme cases cause it to delaminate (described as ‘spalling’ by surveyors).

So what are the options if the surface of the bricks becomes damaged?

If you’re not bothered about retaining the brick finish (say if the affected wall is in a less prominent location) render could be applied as a permanent water-proof finish. That would be a cost effective solution and will not require any further maintenance if it is left unpainted.  It’s essential that the drying process is controlled to avoid shrinkage cracking and de-bonding later.

If the appearance of the wall must be retained it will be necessary to cut out any affected bricks and replace them with similar second hand stocks. It’s a time consuming, and therefore costly, process but if done properly will reinstate the wall to its original condition. The Brick Development Association maintains a database of bricks and their manufacturers and may be able to help you source a match.

If only light spalling has occurred one possibility would be to apply a sealant. The Brick Development Association and others recommend against such action on the grounds that it may seal in whatever moisture is already present and speed up the deterioration. There are now breathable sealants available to buy but as I’ve not had personal experience of them I’d advise caution.