Replacing roughcoat render - silicone?

[coldwater56]

Our house is currently rendered in roughcast cement render which is cracked and blown in various places. We would like replace the render if possible.

The main part of the house dates to the 1700s, with extensions from the late 80s and early 00s.

We're looking at lime render as an option, due to its breathability, but appreciate this will be expensive.

I've read silicone render is breathable. Could this be a cheaper option which we could go with and will be ok on the type of walls we have?

Do we need to remove the cement render before putting on new render? We had also considered patching up the cracks - would this be a sensible move to save cost or would this cause problems with the property? Or even restoring the bricks and having these exposed but no idea what the bricks would be like underneath or how this would work along side the extentions.

Worth pointing out that we are experiencing condensation damp on some of the old walls.

Lots of questions there, but hoping someone can provide some guidance. Thank you.

 

[Abi Cott]

Welcome to the forum.

I've no real expertise on render, but from comprehensive reading of the posts I'm going to say the cement render definitely needs to come off.

Now that your post is bumped you should get a few more informative answers from people with more knowledge than me

 

[TheForge]

A few points to consider:

- Are you certain that the current render is cement based?
- if so the surface of the 1700s bricks underneath will likely be in a state when the render is removed and restoring them to a presentable state will likely be the most expensive option.
- Lime render is the traditional, tried and tested material for this sort of construction, why mess around with un tested modern alternatives like silicone in this situation? Lime rendering may be more expensive due to the time required to tend the work and provide after care but the application and material costs shouldn’t be hugely different. If the building is listed I doubt the CO will be keen on silicone either.

For the long term good if the building the cement will likely need removing if it is cracked. Each crack will be allowing water into the fabric and trapping it behind the render. Patching the cracks is unlikely to be successful as more will likely replace them. Photos would be helpful, especially if any render that has come off in close up cross section.

Are you certain the damp is condensation and not penetrating through the wall? If the wall is wet because of the failed render this will also make the wall cold and potentially promote condensation.

 

[MikeG]

I wouldn't put this product on an old building, particularly as there is a perfectly good and historically accurate material readily available and well understood. I would also reiterate that if your house is listed then you must apply for permission to re-render, and I would bet my bottom dollar that you wouldn't be permitted to use silicon.

You haven't said what construction your house is. The previous responses have assumed brick, but if it is timber framed then removing the render is going to result in a requirement for a replacement substrate. Again, if you are listed, this is likely to be timber laths, which won't be suitable for silicon. If you aren't listed you could use EML or a render carrier board. A silicon based system will have its own specific type of board, and this may affect the visual appearance of the building.

 

[coldwater56]

Deleting this one as it's a duplicate!

 

[coldwater56]

Thank you for your comments and for bumping my post!

The house isn't listed nor in a conservation area, so that isn't an issue. It's made of brick mainly, but has been extended which will be blocks.

We want to do the right thing by the house but concerned by the cost. I guess with silicone we'd hoped this may be a cheaper and suitable solution! It does need doing though as don't want water getting behind the render.

We've not got any exposed bricks to determine what it's like underneath. Would love to restore it back to its original brick but I think the extention would cause an issue with it being so different.