Inappropriate cement pointing causing damp issues in my property by reducing the ability of the walls to breathe?
The breathability of a building is a contentious statement, often argued about by builders and surveyors alike over a scaffolding tower or healthy full English breakfast! It is often a term that is misunderstood or generally not considered when dealing with older buildings. But making the wrong decision, not understanding the materials that are or have been used can cause many many problems.
So what is all about? Are we at Smith Heritage just a bunch of tree huggers who love lime and thatch or is there an element of sense between Dave’s many daily cappuccinos?
Well we think so. We have helped many hundreds of people deal with issues in their properties by identifying non porous alterations and improving breathability.
What is breathability you ask? To put it simply, it is the ability for a porous material such as timber, old bricks, lime etc. to absorb moisture such as during heavy rain, high occupancy and then release that moisture naturally. So in and out or through the building fabric. Simple.
So, what’s the problem? Well, not all building materials are breathable. Historically and flor many thousands of years we used local materials to build our buildings. They were built, set and bed in lime mortars. These materials were open cell and allowed moisture to freely move between them. Modern materials such as Portland cement, gypsum plaster, plasterboard and vinyl/ plastic are not.
One question we get asked a lot is, why is hard cement pointing inappropriate for an old building? The use of cement for repointing the joints of traditional buildings can lead to decay (which often looks like frost damage) of the bricks or stone as they become the most permeable part of the wall and suffer the greatest frost and salt action.as well as reducing the breathability, and leading to damp by trapping moisture in the wall.
We often find that lime mortars are raked out and replaced/ repointed with hard cement based mortars when they were not needed. Think jolly builder looking for an easy job in the 80s knocks on Mrs Jones door. A study Herriott Watt University found that lime pointing could be left even when eroded/ set back up-to 20mm from the face of the masonry, and then isolated lime repointing will suffice. The full repointing of a building is rarely necessary.
What about heating your home? Does that become more difficult when the walls become less breathable because of cement materials applied over them? Yes. A study by the society for the protection of ancient buildings found that a damp or wet wall reduces the ability of masonry to retain heat by up to 30%. That means that those nice thick solid walls cannot perform as they were designed. Again, another common statement we hear is, old buildings are damp or that you should expect an element of damp in an older building!!! Absolutely not. They were not designed damp. The builders were far superior to modern workmen. The materials better. Greater access to land. More labour available. The list continues. They were designed and built very well and certainly were not built to be damp. Something has changed to make it that way and in most cases those changes have occurred in the last 30 years or so. What we need to understand is what changes have occurred, how much damage or impact are they having and then look to undertake a minimal approach to allow the building to perform as it was designed.
If my buildings been pointed or rendered in cement, can anything be done? Hard pointing can possibly be cut out with hand tools or a tool called an All-saw. The use of mechanical tools or hammer and bolster is not recommended.
When repointing, you may be able to take a sample of the original lime mortar away for analysis and then reproduced to ensure the mortar matches the building fabric. The main factor is to ensure that the new lime is weaker than the masonry so that is superficial and that the moisture will choose to evaporate through the mortar as the least path of resistance. If you contact Ty-Mawr or Mike Wye they have the expertise and facilities to assist with this. We recommend using a hot lime mortar on traditional buildings, as this is generally easier to apply and is more flexible and porous compared to certain NHL’s.
If you should understand one thing when looking at buildings it is this. Traditional, solid wall buildings are different to modern, post 1930 buildings. They use different materials and are designed to operate differently.
Traditional buildings relied on open fires, open/ poorly fitted windows, breathable materials and constant low level heating through open fires, cooking appliances etc. Modern buildings have a cavity, use mechanical ventilation to extract moisture, the materials are not porous and rely on expelling moisture. So, think, one absorbs and releases through soft open cell materials, the other repels through hard closed cell materials. So, when we apply a modern material to an old building, we will have problems because you are changing the way that building was designed to perform. Breathable materials can be used on modern buildings, but not the other way round. Traditional building materials are far more environmentally hence why we are seeing a resurgence in timber and earth-based products. A little bit confusing for those of us who deal with older buildings is why there is such difficulty creating a sustainable building practice when we have done so for thousands of years. Timber frame or cob walls with a nice thatched roof. Simple. Where’s Rishi? Or whose PM this week?
If you have a bit more time and would like to read more about our damp surveys, visit the damp and timber survey page on this website or read this blog highlighting some of the issues we picked up on a recent damp survey in London.
Damp survey London is one of our largest areas of work. If you are a qualified building surveyor who loves old buildings, please get in touch to enquire about helping building owners make informed decisions.