A dash of lime
Updated: Jan 2, 2020
..of the natural hydraulic variety I’m afraid. I’m going to get disappointed googlers looking for hockey if I use the term NHL.
So last post we were down to the stone wall, but at last we can start putting that wall back together. Old houses like this work quite differently from a modern building. There is no damp course and no cavity in the walls. Solid walls get damp and moisture gets inside them, from the ground and the elements. But that’s fine, if they are allowed to breathe. Many old houses have damp and mould problems because modern paint and cement repairs seal the walls, trapping the moisture inside. It will wick from the ground upwards, until it gets trapped. For this kind of house we need to use breathable materials, hence the lime render rather than modern cement, and special breathable paint, inside and out. Lime is like Gore-tex while cement is a plastic mac. Lime render acts a bit like a sponge, soaking up moisture and allowing it to evaporate.
Lime render is tricky stuff. And expensive. It only lasts a short time, and once mixed it starts drying while undergoing a chemical reaction, so you can’t just wet it again. And you have to worry about the weather.
Lime does not like the cold, nor does it like the rain. But this is Devon, in spring. Would you believe we had a frost. This is about the worst thing lime can experience. I have heard reports of the moisture of drying lime freezing and whole sheets of render dropping off. Thankfully we didn’t have anything that dramatic happen. Our builders made it look easy.
First they used lime mortar to point the deepest holes. Then when they were ready for the first layer of render, they sprayed the whole wall down with water. The first layer is thrown on, with as much pressure as possible, and is quite lumpy. It’s sometimes called a scratch coat, a bit like a crumb coat when icing a cake.
A bit of drying and then a second layer, which is much smoother. But then it gets scored to allow the third top layer something to grip to.
The walls were left waiting for the final skim coat, while the whole process was repeated to either side of the first repair. The skim coat is a runnier mixture and would be used to blend in the different parts of the repair so you can’t see the join.
So this is the north end, which we started with shot blasting the plastic paint coating off, hoping that would be enough, then ended up going all in and chipping the whole lot off again.
The woodwork was a bit dodgy behind those barge boards…
but they soon had that sorted. And the walls, similar cracks needed some reinforcement. Then off they went again with the lime. Luckily for us, that ugly vent pipe in the centre of the wall was no longer connecting to anything useful, so that could be tidied away.
Same process along the other side of the first repair…
…then woodwork starts to go back on. It’s already starting to look quite different as the drying lime lightens. Now wait 28 days before painting can begin. While taking all the windows out. As you can see, the rain clouds are moving in!