Render or Not?

[rob82]

Hi Everyone,

I'm unsure whether i need to render our internal walls or not.

We are doing up a mid terreace property in Sheffield and it has emerged that when they were built (1900), they used slag from the steel works, instead of sand in the cement. This has made the mortar quite crumbly and although the walls still feel quite sound, we don't know whether it is advisable to render the walls before we "dot and dab" them.

We are going to get a damp proof menbrance fitted to all the downstairs walls and when we spoke to the surveyor, he said that it wouldn't matter either way if the walls were rendered or not.

My question is, is it advisable to render the walls for support given that the mortar is of poor quality? If so, how far would you suggest taking the mortar back, because you could keep going until there's none there?

Or, is mortaring pointless as it's going to be plaster boarded? My concern is, that adding another layer onto a damp wall, with a DPM over the top and then plasterboard; may mean that there's more to go wrong. The last thing i want is to do everything and have render falling off behind the plasterboard and taking the DPM with it.

Any advice would be greatly appreciated and many thanks in advance.

Kind regards

Rob

 

[^woody^]

The crumbliness of the mortar is most likely due to sulphates from the ash attacking the cement. Any cement mortar or render must use sulphate resistant cement, or that too will crumble.

But there is no need to render if you are dry lining and installing a vertical DPM

You wont be able to dot and dab though, you will need to fit timber battens and fix the boards to these.

Also consider a water repellent coating (eg Thompsons) to the external walls to reduce the moisture getting to the mortar, and so reduce the production of the sulphate solution/reaction in the first place

 

[rob82]

Thanks woody, i will do everything you mentioned and it's good to know about the cement.

Next summer, I'm hoping to remove the Wether Tex from the rear and repoint front and back, so will probably use Thompsons then.

Thanks again