Lime mortar outside / Cement plaster inside - could this be causing the damp?

Status
Not open for further replies.
O

OddLion

New Member
We recently did a full rehab or our 1890's house in South London, including removing old cement render, replacing S&C-based mortar with lime, and new plaster (was lime, repaired and skimmed with cement) inside. A couple of the walls are now having some stubborn damp problems, and I fear the combination of lime mortar outside and non-lime plaster inside is causing problems.

Can anyone advise on what might be happening?

Thanks!
 
The pictures are only in my computer, not online. Is there some way to cut and paste here? (I only see a button to insert a URL...)
 
OddLion said:
We recently did a full rehab or our 1890's house in South London, including removing old cement render, replacing S&C-based mortar with lime, and new plaster (used to be lime plaster, now repaired and skimmed with cement-based) inside. A couple of the walls are now having some stubborn damp problems, and I fear the combination of lime mortar outside and non-lime plaster inside is causing problems.

Can anyone advise on what might be happening?


Thanks
Click to expand...

Have i got this right?
On the exterior you've replaced cement based render with lime based materials.
On the internals you've replaced lime based plaster with cement based materials.
 
Yes, you've got it right bubbles65. The outside render was removed, as it was cracking and ugly. The work was done by different people a few months apart, so this was not the "plan" (indeed, there was no plan per se), though neither person mentioned anything about there being an issue.
 
Apologies OddLion, I didn't have much time last night, but basically we need more information to try and help find you a solution.

1. Is it a solid wall?
2. Is it below ground level or partially below ?
3, Were there any damp issues prior to the re-vamp?
4. What type of lime was used and what mix?
5. Was there any time allowed for the walls to dry before re-plastering?
6. Internally, what materials were used and in what order, how much time was left between each coat?
Can you provide any more pictures? The whole of the exterior would be good (to eliminate any obvious points of water ingress etc,)
and some more shots of the internals please.
Cheers.
 
I would think that the walls are still wet from an ingress of moisture from the poor render and now the cement based plaster on the inside isnt allowing the moisture within the walls to evaporate. The internal picture looks like penetrating damp
 
bubbles65 said:
Apologies OddLion, I didn't have much time last night, but basically we need more information to try and help find you a solution.

1. Is it a solid wall?
2. Is it below ground level or partially below ?
3, Were there any damp issues prior to the re-vamp?
4. What type of lime was used and what mix?
5. Was there any time allowed for the walls to dry before re-plastering?
6. Internally, what materials were used and in what order, how much time was left between each coat?
Can you provide any more pictures? The whole of the exterior would be good (to eliminate any obvious points of water ingress etc,)
and some more shots of the internals please.
Cheers.
Click to expand...

Thanks Bubbles65. I can only answer some of your questions, but here goes: The plastering was done first
1. Is it a solid wall? I was told it was a cavity wall, but searching around on the web it seems like 1890 homes were mainly solid2. Is it below ground level or partially below? No, and the damp is nearly all upstairs (1/F)
3, Were there any damp issues prior to the re-vamp? Some condensation on windows, but no wall damp. After the re-plastering was done (approx April 2013) there was some damp, but minor.
4. What type of lime was used and what mix? I'm really not sure, but we're only talking lime mortar, not render or plaster. I believe it may have been St Astier hydraulic lime.
5. Was there any time allowed for the walls to dry before re-plastering? The plastering was done quite early on (March-April-May 2013), while the outside walls were not started until July.
6. Internally, what materials were used and in what order, how much time was left between each coat? I unfortunately was not supervising and do not know the precise type of plaster used (though of course there were at least two coats). There was definitely drying time between coats, and much complaining by the contractor about delays costing him money.
Can you provide any more pictures? The whole of the exterior would be good (to eliminate any obvious points of water ingress etc,) I will try to add those to the photobucket.

Interestingly, there were some damp issues after the plastering but before the brickwork. The contractor brought in a dehumidifier for a few days and they seemed to be resolved. There were cracks visible on the render outside that wall, and as the render was in pretty bad shape (and we never liked it). We feared water ingress through those cracks.

Our photos of the internals all seem to be a bit shadowy - damp is hard to photograph - but no telltale black spots, just big splotches of damp.

Cheers,
 
oddlion ! you are right the outside has lime, and can dissapate any dampness through the mortar but as you have stated inside has a sand and cement float and a gypsum finish which of course is not allowing the dampness to be brought through the wall and thus gathers in the wall causing dampness over a period of time a common fault in lots of work when people see the price of lime plastering !!!!regards stuy
 
stuy said:
oddlion ! you are right the outside has lime, and can dissapate any dampness through the mortar but as you have stated inside has a sand and cement float and a gypsum finish which of course is not allowing the dampness to be brought through the wall and thus gathers in the wall causing dampness over a period of time a common fault in lots of work when people see the price of lime plastering !!!!regards stuy
Click to expand...

Thanks Stuy, for your reply. Actually we were quite ignorant, and the builder didn't even mention the difference or need to consider cement vs. lime. I'm seriously considering just running dehudifiers, as tearing the walls apart again is almost too much to face right now.
 
Artisan998 said:
I would think that the walls are still wet from an ingress of moisture from the poor render and now the cement based plaster on the inside isnt allowing the moisture within the walls to evaporate. The internal picture looks like penetrating damp
Click to expand...

Indeed, this seems to make sense. We are running a couple big dehumidifiers non-stop now, and the moisture seems to be reducing, but I was hoping to find a better solution.
 
Not with silk paint? Does your roof not have a softer around it or does the facia sit flush to the brickwork?
More pictures would be good
 
flynnyman said:
Not with silk paint? Does your roof not have a softer around it or does the facia sit flush to the brickwork?
More pictures would be good
Click to expand...

More pics here. There is facia, flush to the brickwork, but it was checked by the guy who did the brickwork and should be in good shape.
Rear_roof_top-shot.jpg Photo by ocouzin | Photobucket
Outside_Chimneys-wall.jpg Photo by ocouzin | Photobucket
Rear_elevation2.jpg Photo by ocouzin | Photobucket
2F_BR_clean.jpg Photo by ocouzin | Photobucket
 
I meant has the exterior been painted ?

I have been to property that has bare render transmitting damp through the wall.

Usually suggest painting the exterior with a good masonry paint.
 
Sorry just seen the pics, forget about the painting.

Is the dampness only on the exposed walls, I mean the ones more prone to get the most of the wind and rain ?

Really you should of sealed the brickwork after repointing

Rain Penetration Through Masonry (Penetrating Damp).

It could be lateral penetration because there is no cavity, I bet the place was dry before you repointed it, good old lime its great for sucking up the moisture lol.
 
adapt said:
Sorry just seen the pics, forget about the painting.

Is the dampness only on the exposed walls, I mean the ones more prone to get the most of the wind and rain ?

Really you should of sealed the brickwork after repointing

Rain Penetration Through Masonry (Penetrating Damp).

It could be lateral penetration because there is no cavity, I bet the place was dry before you repointed it, good old lime its great for sucking up the moisture lol.
Click to expand...

Yes, the brickwork was supposedly all sealed with "silicate primer" - is this correct?

It wasn't particularly dry before the repointing. In fact, there was some damp - though much less than now - after the plastering that took a long time to go away.

Yes, the damp is only on the exposed walls, SW walls that were subject to wind and rain, so this explanation makes sense...still, what is the solution??
 
Well if I was you I would try putting a good few coats of a brickwork sealer on the walls, because there Is no cavity it means the moisture is transmitting through the wall.

Why not seal an area that is easily accessible and see if it cures that area, then you can do the rest of the areas, if its only had one coat of sealer then maybe it should have had at least two, personally I would put at least two coats on a wall.

I would never put a lime product on an external wall, seen far too many problems with lime based products causing dampness.

times have moved on from the 1800's so why do people still use outdated products.

Try that anyway Oddlion and I hope that helps.
 
adapt said:
Well if I was you I would try putting a good few coats of a brickwork sealer on the walls, because there Is no cavity it means the moisture is transmitting through the wall.

Why not seal an area that is easily accessible and see if it cures that area, then you can do the rest of the areas, if its only had one coat of sealer then maybe it should have had at least two, personally I would put at least two coats on a wall.

I would never put a lime product on an external wall, seen far too many problems with lime based products causing dampness.

times have moved on from the 1800's so why do people still use outdated products.

Try that anyway Oddlion and I hope that helps.
Click to expand...

Thanks for your reply adapt. I think there are many people on this site who would disagree though. Lime is not "outdated", and given that my house is made of bricks from the 1800's, I prefer to use materials that are appropriate for them.
 
Well we all have an opinion, mine is based of experience and seeing lime based products fail, I don't want to bore you with the science of materials but we will agree to disagree.

Hope that helps and please let us know how you got on :RpS_thumbup:
 
adapt said:
Well we all have an opinion, mine is based of experience and seeing lime based products fail, I don't want to bore you with the science of materials but we will agree to disagree.

Hope that helps and please let us know how you got on :RpS_thumbup:
Click to expand...
I have never heard so much s..t in all my life
 
Status
Not open for further replies.

Share this page

Back
Top