Dealing with Damp
Moisture reading of 99.9 taken in the Cottage lounge at the time of Survey.
Mouldy corners, blown plaster, musty smells, and rotting beams. I’m willing to bet that damp is an issue that almost everyone who owns a pre-war property has faced. But damp is often misunderstood, and can also be one of the most expensive issues to resolve. Before we get stuck into this post, a little disclaimer to get us started. As anyone who has followed our journey for a while will know, my day job is as a Textile Designer. Whilst I moonlight as a renovator and fairly avid DIYer, I am by no means an expert on damp (or renovation as a whole!). All of my knowledge is just from my own research and experience, and whilst I hope it is helpful to you, it’s important to remember that every property is different, and so solutions in our home may not be exactly what you need. It’s always worthwhile doing your own research and consulting professionals (such as heritage lime specialists) if you need an extra opinion.
Anyway, on to the fun stuff! Prior to moving in to the Farm, we had a full Level 3 Buildings Survey carried out on the Farm, which highlighted extremely high damp readings in the property. In the Cottage, each wall measured a humidity level of 99.9, which is obviously not ideal! We weren’t remotely surprised by the high levels of damp identified, having already spotted some suspicious looking damp patches, peeling paint and black mould when we viewed the houses. However, receiving the survey which so clearly highlighted these issues pushed us to research what could be causing the damp, and how we could help to remedy it. We knew the Farm had had an injection damp proof course (DPC) applied by the tell tale holes drilled just above ground level, and had also had a tanking system put in place, but clearly from the high moisture readings picked up in the survey, the costly DPC hadn’t remedied the situation. Why? Because these methods are not suited to older, solid walled properties, and actually cause more harm than good.
The tanking system we found hidden behind a false wall in the Cottage Lounge.
Damp is not a mythical, inexplicable phenomenon that shows up in your home without rhyme or reason.
It’s important to remember that damp is a physical reaction where moisture cannot track away from a building, and instead comes out in rather unsightly ways. Period properties (which for the purposes of this blog refers to anything built prior to WW1) were built long before the days of long hot showers, kettles, and the humidity that our contemporary lifestyles introduce. As such, the were never designed to manage these moisture levels. However, solid built stone and brick properties can manage moisture levels through the inherently breathable nature of the materials they were traditionally built with.
Historically, solid walled houses such as the Farm were built using readily available materials from the local area. For example, the Farm is built in Yorkshire stone quarried locally, set with a lime mortar from a lime kiln a few villages away. Dependent on your location, your period property may be built of different materials, which were selected by how affordable or available materials were at the time of building. If you are outside of Yorkshire for example, it’s unlikely your house is built from Yorkshire stone, and instead it’s more likely to be built from your local stone or from brick (we’ll call the material your house is built on the ‘host masonry’ from now on). Additionally, if you live in an area that didn’t have a lime mine and kiln, your mortar would likely have been earth based instead.
Lime and earth mortars were used as not only were they readily available materials, but as they are softer than the host masonry used to build a property. Using a mortar softer than the masonry allows some movement in the structure as the host masonry expands with heat and contracts with cold, and also allows moisture to move through the structure, thus creating what we define as a breathable building.
“A breathable structure is one that allows the passage of moisture in order to prevent the accumulation of harmful water within the building fabric or its surroundings.”
Under the tanking- mould, mushrooms and blown plaster.
Breathability in period properties, defined above by the Alliance for Sustainable Building Products (ASBP), is incredibly important, as it naturally manages the moisture levels in a structure in order to prevent damage. When this breathability is impaired through the introduction of non-breathable materials, damage to the fabric of a building is almost always inevitable. Modern alterations or repairs made to property can stop this process of breathing from working correctly, leading to many of the problems heritage property owners now face - such as our 99.9 humidity reading in the Cottage, blown stone, damp spots and lots of mould. Through lots of research and investigation, we found three key areas at the Farm that were exacerbating the damp issues. We’re currently part way through remedying them, so be sure to follow us on Instagram to keep track of our progress, and hopefully some of the problems we found might provide a solution for your damp problem too.
1. Blocked gutters and drains
Correct drainage is incredibly important to ensure properties stay dry. When we moved into the Farm, we quickly found that every drain and gutter at the property was blocked with years of muck and leaves. Every time it rained, they overflowed, causing water to run down the stone walls of the building rather than draining away. Additionally, the drains at the back of the property were blocked, which meant that surface water couldn’t run off as intended, and instead was taken up into the walls of the house.
This was worsened in the case of the Cottage. As the Farm is built on a hill, the Cottage is built at a lower level to the Farmhouse and the Mistal, dug out into the hill. At the rear of the house, on the north elevation, the foundations are exposed above ground level, and were unpointed. This meant that the rain that could not drain away through the blocked drains had an easy route into the structure of the Cottage through the foundations.
This was a simple, if unpleasant, fix - involving some very long rubber gloves, a peg for our noses and a few buckets to clear the drains.
2. Missing and unsuitable pointing
The North elevation of the Cottage, with the lower half repointed in Lime.
In our case, over the years the original lime mortar pointing at the Farm had failed (no material will last forever, and lime requires upkeep in the same way modern alternatives do) and the lime mortar was replaced with cement mortar. Cement sets much harder than lime, and often much harder than the host masonry. This means that when the water penetrates the fabric of a structure, its route out is not so easy. Some of the pointing at the Farm was cracked or missing, like around the foundations of the Cottage, allowing a point of entry for water that needed repair
Water is, in my opinion, a particularly lazy element. It always takes the easiest route through a property. For example, if water enters a building through a crack in pointing, the water will take the easiest route it can to get back out. In properties constructed from breathable materials, such as stone and lime, this isn’t so much of an issue, as water can move around the stone through the softer lime, and egress from the building.
In the Cottage, instead of being able to ingress and egress through the lime pointing, the water had to work much harder to escape through the cement pointing. It lead to the plasterwork becoming very damp and mouldy, but in extreme situations where the problem is left to develop the stone can ‘blow’. Effectively, since the water can’t work through the hard cement, it instead works its way through the host masonry, causing extreme damage in the process.
Our solution to this was to repair any cracks and missing pointing, and to repoint the north elevation of the Cottage in Lime mortar. We are using Cornerstone Drymix from Cornish Lime, and long term plan to repoint the entire property in Lime, tackling a small area each year.
3. Use of non-breathable materials
As we’ve already discussed, the use of breathable materials in period properties is really important, but this doesn’t stop at the type of mortar used. Using Lime mortar allows the moisture to move through the walls externally, but this is impeded if internally non-breathable materials are used.
In the Cottage, the original Lime plaster walls were covered in gypsum plaster and cement render, and we even found that the lounge walls had been tanked, despite being above ground. None of these materials or methods are breathable, adding to the damp problem by trapping water between them and the host masonry. Gradually, room by room we are stripping back the cement renders, the gypsum and the plaster, and taking the house back to stone. We are allowing the masonry to dry out, and then replacing what we remove with a range of breathable lime plasters.
Scratch coat of insulating lime plaster applied in the Cottage lounge.
Whilst we had always planned to replaster the Farm in Lime, I’m very aware that the ability or option to replaster is not something that is accessible to everyone. Perhaps your house renovation is almost or completely finished, and you don’t want to go through the turmoil of ripping back the walls and starting again, or perhaps the expense is just too much and not viable in your situation. That, of course, is absolutely fine and in your home it is up to you to decide what is and what isn’t achievable, or worthwhile. The purpose of this post isn’t to guilt trip or shame anyone that has tried to deal with damp issues in their home by what they felt was the easiest or best solution at that time. Rather, it’s an attempt to open up discussion around the issues of damp, and a call to find the problem rather than spending your pennies on solutions like a DPC which will likely do your home more harm than good in the long run.
There are no hard and fast rules of do’s and don’ts when it comes to renovation.
However, if you find yourself in a position where every other avenue of remedying a damp issue has been exhausted, or perhaps if you are in the early stages of renovating or are planning a new project, I’d encourage you to look into lime plaster a little more. I’ll be writing another blog post over the next few weeks, specifically focussing on lime plaster, how we are using it and our journey with it so far. So, if you do have any questions on that, or indeed on Damp, feel free to ask them below and I’ll do my best to answer them if I can!
Watch my Q&A on Damp on my Instagram highlights here
