Plastering or rendering a basement wall built from rough rubble stone but not hiding the outlines of the stones

[silvosa]

I dont want to make the wall flat but I do want to have a more or less uniform finish to which I can apply Snowcem or similar cement based paint. The wall is below ground and as a novice in this type of work I applied a waterproofing cementitious slurry called KA Tanking slurry. The wall doesnt and didnt let water through but I thought belt and braces the best approach as where I live the rain is intense during winter. All ideas or experience welcome.

 

[88v8]

Hello and welcome.

On the whole this forum has not found that it is a good idea, trying to shut out damp by using cement.... but as you already have, it may be useful to know how you can avoid making the wall flat. I agree that hiding the underlying stone can be a visual crime, all too often perpetrated by those obsessed with making things flat, level and smooth.

This wall pictured below, of coursed rubble, was plastered in one coat (with lime) by applying the plaster with a float and/or trowel but then knocking it back with a churn brush.
The lime had hemp reinforcement mixed in.

It is hard to see the texture in these pictures, but you can get an idea by looking at the window reveals.

After applying the plaster I had to damp it for three days or more, and repeat the churn brushing to prevent cracking and stop the plaster from pulling out of concavities as it dried.

If you are not familiar with churn brushing, the technique is to hit the plaster with the brush, not to stroke it. The result happily reveals the underlying texture of the wall. I would recommend not to apply a second coat as this would tend towards more flatness.







My wife calls this the Hobbit window.

Ivor

 

[silvosa]

Hi Ivor, Thats exactly what I had in mind. Thanks for the pictures. I've never used lime before but have seen it in local builder merchants.

 

[88v8]

I used lime because the cottage is damp and needs lime for 'breathing'.
The coat was quite thick and the hemp prevented it from slumping. It also helped to avoid bald spots over high points in the stone.

Where the dips in the wall were deep so that the churn brush did not reach to the bottom, I used a pounce bag to press the mortar into the dips. A pounce bag is a small bag of leather, fitted with soft sand.
It was all quite slow and labour-intensive.

This was a typical piece of wall elsewhere in the cottage before I started. That was in the cellar where there was an anti-damp plaster applied some years before, it was making the wood above damp.... so we hacked it off.



You may be able to use a cement render, given that you've already cemented it If you use lime, protect your hands or it will burn your skin.

Try a small area and see how you get on.

 

[silvosa]

I've lived in this hillside cabin Galicia in Northern Spain for the last four years. It cost me less than a secondhand car in UK. Our village is in danger of becoming abandoned but its surrounded by forested hills and is pretty tranquil. It rains a lot in winter sometimes for weeks on end but the basement has not admitted any water as far as I can tell although because of humidity the cold walls form condensation easily. I wonder would a lime plaster absorb the humidity though perhaps I ought not mix the two methods, lime and cement. I'll give it a go. Luckily close by in Portugal is the Secil company which makes a wide variety of eco building materials such as this lime based plaster which also contains cork. https://www.secil.pt/en/products/mortars/argamassas-com-cortica/ecocork-lime