Bedroom insulation is all up and the room sounds quieter and feels softer. The next stage is for lime plaster to be applied.

We needed to use lime plaster because it’s breathable ie: it allows water vapour to pass through the wall from the inside out and vice versa. I know – the very word implies it’s about movement of air – but trust me, this is about vapour. (Find an explanation in my book) And without breathable, there’s a risk that vapour sits in the wall, unable to move through a non-breathable barrier, causing damage to the structure.

Every house built before 1920 will be breathable. If your house was built between 1920 and 1950, it’s worth checking. Some of them will also have been built with breathable materials.

Once a breathable system, always a breathable system

If you start with breathable materials, you have to continue right through to the plaster and paint or you could end up with problems. . 

Plaster is made up of either lime or gypsum, plus water and sand. The most commonly used plaster is made with gypsum. It’s quick drying and easy to work with – as long as the plasterer is skilled and able to get a smooth surface in quick time.

However gypsum isn’t breathable, so when talking retrofit and older buildings, lime plaster is high on the agenda. We used lime plaster throughout, since our house was built in 1901. For us, the lime process was one of the most frustrating!

We faced a couple of challenges:

First, finding a lime plasterer. The building profession generally doesn’t take in how important breathability is, so not many people work with lime. And when they do, they are most likely to be specialists in very old properties.

Second, the time taken to complete the job. Original lime plaster goes on in three coats, each coat needing to dry fully before the next layer can be applied. For us, doing this in late December, with the kitchen due to be fitting in early January, was a bit nail biting.

Don’t lose heart – two years on, it’s already easier

It was such a relief to discover that an easier form of lime plaster has come onto the market in the time since we finished our main work and started the bedroom. Now there is a product, Lime Green Solo, that’s easy to apply and can all be done in one day. Brilliant!

Harry and Jack put on a skim of plaster that needed one hour to ‘go off’ (a phrase often used by builders – no idea what it means. But I assume it means it sets a bit!) Then a mesh is put on the skim and a thicker coat of plaster applied. That takes a little longer to dry than the skim, but by the next day it was done. So no waiting, plus a smoother finish that traditional lime. All the stress gone!

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