Cement render internally - off or on?

[mrwood]

Hi,

My first time here and the forum looks great and very helpful for our new purchase of an 1840s Dorset stone house.

In a number of rooms the lime plaster from the internal walls has been removed to a height of around 1m and replaced with a thick cement render which has then been skimmed. I am working through the usual contributory damp issues and am resolving them where possible and believe this to be another issue/factor.

I want to return the walls to lime but the render is stuck fast in most places and removing it is spalling the bricks and it is a complete pain on the stone sections. What should I do? Damage the bricks or leave on the damp holding render? I'll now be totally redoing the rooms anyway and don't want to have to re plaster again at a later stage

Thanks for any help.

 

[plasticpigeon]

Oh dear, and that treatment is erroneously thought to stop damp. Thousands of old houses are getting the treatment you describe every week in what is essentially a fraud caused by lazy surveyors, ignorant mortgage companies and fraudulent damp proofing companies.If you can stop the cause of the damp, then I'd have thought leaving the cement would be the best option. The masonry will probably take longer to dry by I think why bash the old building around any more than is necessary. Make sure the cement render doesn't extend down to any damp earth on the floor, my mum has this in her house and the paint is always bubbling off the lower sections of the walls.

 

[MatthewC]

I had that sort of stuff up a couple of feet on all the downstairs walls, and it was a nightmare to remove. We persevered with removal and eventually did it all, before re-plastering with lime. The cement is only another factor in terms of what is does when there is dampness. If you tackle everything else and the floor isn't damp now, then you should be all right if you leave it. On the other hand, there must have been dampness to make them do it, and if it's still damp now then in time you will regret leaving it.

Personally I wouldn't worry about spalling the bricks or even damaging the stone as you are going to cover them all with the lime mortar!

Photos?

Matthew

 

[mrwood]

Thanks for the replies.

Definitely a case of misguided approach to damp prevention, as the ground levels were really high and gutters leaking etc. I'm still expecting some damp issues however as when the winter hits again then it's undoubted that we'll get some condensation even whilst actively trying to prevent it.

A tricky decision to make as I don't want to bash the old building about anymore than needed but am keen to let it breathe as much as possible and I don't want to have to revisit the walls and damp issue regularly if I leave the cement in place. I guess you're right about the brick and stone surface damage Matthew as it'll be covered again. I guess this brick/stone damage won't cause any further issues, other than to my back!!

A couple of pics attached of the brick and stone.

 

[TheForge]

We had exactly this in most of our downstairs rooms and spent a long time painstakingly removing it with minimal damage to the substrates.

The walls behind the cement were unbelievably wet, some of the stone had turned to cake and you could push a finger into it like rotten timber. Once we left it to dry the wall became almost totally dry over time.

I wouldn't be too concerned with causing minor damage in removing the cement. If saturated, old bricks will have probably lost their face and more anyway - it's just you can't see it as its hidden behind the cement now.

There's also a tendency for moisture to track up behind the cement and blow the plaster above the line where the cement finishes.

I found that percussive tapping with a fairly light hammer helped detach the cement from the wall and made getting a chisel behind it much easier - it also allowed it to come off in bigger chunks as areas delaminate.

 

[jocelyn plummer]

A couple of pics attached of the brick and stone.

No pictures!!

 

[mrwood]

Sorry, pictures should now be attached

 

[Lime]

We had exactly this in most of our downstairs rooms and spent a long time painstakingly removing it with minimal damage to the substrates.

The walls behind the cement were unbelievably wet, some of the stone had turned to cake and you could push a finger into it like rotten timber. Once we left it to dry the wall became almost totally dry over time.

I wouldn't be too concerned with causing minor damage in removing the cement. If saturated, old bricks will have probably lost their face and more anyway - it's just you can't see it as its hidden behind the cement now.

There's also a tendency for moisture to track up behind the cement and blow the plaster above the line where the cement finishes.

I found that percussive tapping with a fairly light hammer helped detach the cement from the wall and made getting a chisel behind it much easier - it also allowed it to come off in bigger chunks as areas delaminate.

Yes I agree with that.
Seen exactly the same many times before.
IME the cement is far more likely to collect condensation too and lead to mould problems.

 

[mrwood]

Thanks for the replies. The majority seem to indicate that it is best to be removed. I'm just concerned that even though the brick and stone will be rendered that I will cause some other damage in relation to strength, lifelength or stability of the brick/stone.

Am I being overly nervous or is there an issue?

 

[noj]

The physical removal of the render must cause some structural damage/weakening but my best guess is that this is less fudamental than the brick/stone/original lime mortar remaining in a state of perpetual dampness.

Once it can dry out it'll maintain whatever structural integrity it has, but repointing and potentially replacing any bricks that have turned to mush before re-plastering will help too.

Hacking cement off damp cob is a whole different story!

 

[Hobden]

Hacking cement off damp cob is a whole different story!

Ah, we might have to do just this - could you expand on the problems?

H

 

[noj]

I read a horror story somewhere about the cob behind cement having effectively reverted to wed mud and then gently collapsing once the 'structural' render was removed. I suppose it's a case of going slowly, starting at the top where there's least weight baring down on the walls and assessing the condition of the cob as you progress

 

[Hobden]

Scary! Thanks <worries>