Green Building Forum - Cracked sandstone repairs.

Cracked sandstone repairs.

Davycrocket — Sun, 21 Aug 2022 08:56:37 +0100

Having chipped off the bottom 2 meter of cement render I've discovered some quite alarming cracks / voids in the stone work.

I'd like to think I can repair these areas with your help.

What is the method for these repairs please ??

Thanks in advance

Cracked sandstone repairs.

Davycrocket — Sun, 21 Aug 2022 09:01:18 +0100

This void / crack was created when the chimney breast was removed and probably runs all the way up the wall.

Cracked sandstone repairs.

Davycrocket — Sun, 21 Aug 2022 09:02:44 +0100

More cracks from floor to soil pipe and beyond.

Cracked sandstone repairs.

Peter_in_Hungary — Sun, 21 Aug 2022 11:24:16 +0100

It looks like a stone/rubble wall with sand/lime mortar - correct ??

How old is the building ?

Any foundations ? If so what and how deep ?

You say you removed the bottom 2M of render and discovered cracks. This implies that the cracks were not apparent before the render was removed - correct ?

Why did you remove the render ?

Cracked sandstone repairs.

Davycrocket — Sun, 21 Aug 2022 12:33:27 +0100

Stone rubble is correct Peter.

1850s
â·7
Not sure re foundation but when the extension was added there was a large river type boulder at the outer elevation

The render was cracked before removal.

Probably caused by removing the chimney breast.

Thank you for your reply.

Cracked sandstone repairs.

tony — Sun, 21 Aug 2022 12:51:11 +0100

EWI would work and bring huge benefits

Cracked sandstone repairs.

Davycrocket — Sun, 21 Aug 2022 13:52:00 +0100

Posted By: tonyEWI would work and bring huge benefits

I've thought about it in the past.

Wouldn't it still need the old render repaired and plastered anyways ?

Genuine question as I never fully understood it ?

Cracked sandstone repairs.

Peter_in_Hungary — Sun, 21 Aug 2022 14:49:33 +0100

Posted By: DavycrocketStone rubble is correct Peter.

1850s
â·7
Not sure re foundation but when the extension was added there was a large river type boulder at the outer elevation

The render was cracked before removal.

Probably caused by removing the chimney breast.

stone rubble walls of similar vintage that I have are built with foundations that are the same construction as the wall and no wider, essentially no foundations as such, just the wall continues into the ground for a bit.

The render on such walls is necessary as weather proofing, without rendering the rain can wash out the wall which in time will cause structural failure of the wall. But the render should be lime based.

If the cracks are not displaced then IMO you will do more damage by trying to 'repair' them than by leaving them alone.

If displacement has occurred then the reasons should be found and underpinning considered.

Walls of this type are held together by gravity. The mortar provides no strength, it just holds the stones in place with very little if any adhesion to the stones. You generally can't make a small hole in such walls or easily drill through (e.g. to pass a pipe through) because the internal loose fill will generally fall into the hole as the drill is withdrawn.

If the render is not loose or hollow sounding when tapped then there is no need to replace it but cracks should be made weather tight.

I agree with Tony EWI is a good solution. I have put EWI on a couple of buildings of this type with great benefit. If you use EPS as the EWI this is breathable and weather proof and where I did it there was a tremendous improvement in the 'liveability' of the house in that there was reduced energy use, the houses were much more comfortable both winter and summer and the black mould that was a 'corner feature' disappeared. (I used 10cm EPS EWI)

Foot note - If you click the Html button below the comments box the quotes come out in blue

Cracked sandstone repairs.

fostertom — Sun, 21 Aug 2022 22:57:41 +0100

Posted By: Peter_in_HungaryThe render on such walls is necessary as weather proofing, without rendering the rain can wash out the wall

Not necessarily - some common renders e.g. normal (i.e. strong) sand/cement render usually exacerbate weather-resistance problems they were meant to cure.

This wall looks well put together and removing what looks like modern cement render and quality repointing it with lime mortar, will leave the wall much healthier and able to deal with weather elegantly i.e. absorb driving rain but allow it to dry out again soonest.

Breatheable EWI (not with closed-cell types of plastic insulation) will serve same function but even better - the wall wd need just minimal rough lime pointing first, where it's missing or failing..

Cracked sandstone repairs.

Peter_in_Hungary — Mon, 22 Aug 2022 08:29:36 +0100

Posted By: fostertomBreatheable EWI (not with closed-cell types of plastic insulation) will serve same function but even better - the wall wd need just minimal rough lime pointing first, where it's missing or failing..

Agreed - But I would suggest a thick parge coat put on with a float would do as well and be much cheaper than pointing due to the significantly less time needed.

Cracked sandstone repairs.

fostertom — Mon, 22 Aug 2022 08:34:09 +0100

Yes, and an aside - I'm always amazed at how people (aka builders) don't carefully clean, de-dust, slightly damp-down, such surfaces before trying to 'stick' cementitious (incl lime) stuff to it. Seems to me, half the 'stickiness' gets squandered in soaking through or encapsulating the muck on the surface, before it can get to the solid. You see slabs of trowelled-on material sort of peeling off, its back coated with dry dust - which gets patted back with another pass of the trowel so it looks perfect.

Cracked sandstone repairs.

Davycrocket — Mon, 22 Aug 2022 11:38:19 +0100

Just to reiterate,

There is a void behind the visible stonework from top to bottom of the wall where the internal chimney breast was removed and then blocked up, would this require filling for structural or thermal mass reasons ?

Cracked sandstone repairs.

tony — Mon, 22 Aug 2022 13:10:45 +0100

I would fill with eps beads if it was mine to ceiling level plus insulation, ventilate any flue above that

Cracked sandstone repairs.

Peter_in_Hungary — Mon, 22 Aug 2022 14:38:18 +0100

Wot Tony said +1.
Certainly don't do anything that involves dismantling the wall to do any filling

Cracked sandstone repairs.

renewablejohn — Wed, 24 Aug 2022 12:32:15 +0100

Nothing wrong with that wall that a good mix and repoint of lime mortar will not fix. Would suggest you do what I did and book in on a lime mortar and lime plaster course at Ty Mawr. Would highly recommend it and once you get used to using lime mortar you wonder why you ever used sand and cement. Personally I would hack off all that screed and do a proper repoint with lime mortar. The aim of these walls is to allow them to breath as a dry wall is a well insulated wall. The trick then is to use insulated lime plaster on the internal walls my preference being cork and install MVHR like the Partel systems to protect the internal fabric of the building by removing internal moisture.
I am no expert but it has certainly worked for us on our grade 2 listed building.

Cracked sandstone repairs.

Davycrocket — Thu, 15 Sep 2022 07:48:56 +0100

Thanks for all the advice guys, really appreciate it.