I'm now at the stage of planning the interior lime plastering for my renovation. Some of the walls have a cement + gypsum plaster coat about 10mm thick, which is in generally good condition, except for the edges and some holes. I'd like to put lime plaster over it, but do I need to get all of the cement/gypsum off? Is it practical to scutch the surface ( I scutch, he scutches, they knock a bleedin' great hole in the wall....) and then apply lime plaster over that?
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Lime plaster over cement/gypsum
- Thread starter rosbif
- Start date
skier-hughes
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- 3,414
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- Staffs, UK
If the wall originally had lime plaster and needs lime plaster to enable it to breathe, then removing the cement is the only proper option.
If this isn't the case, then you could lime plaster over the gypsum.
If this isn't the case, then you could lime plaster over the gypsum.
Penners
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- 17,294
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- Suffolk, England
Not much point in lime plastering over gypsum and cement. To do the best for the building you should remove all the gypsum and cement before lime plastering. But if you can't face that, then judging by your description you might as well just patch up the edges of the gypsum with gypsum.
Is the wall damp?
Is the wall damp?
How long has the gypsum plaster been up? Has it been applied to the inner face of solid 'exterior walls which are built and pointed with lime mortar? I had this problem on one exterior wall where previous owners had used gypsum instead of lime plaster and to my expense, the gypsum started to fail sucking water out of the solid wall causing the gypsum to fail and crumble away. I believe the gypsum had only been up about 2 or 3 years. I had the gypsum hacked off and the wall re-plastered with lime /horsehair and a finish lime coat. Problem solved. Nice dry breathable wall.
P.S. - The cement might be forming an impervious barrier thereby protecting the existing gypsum but probably not doing the bricks/stone any good behind. If we're talking about the inner face of an exterior wall, do the holes you talk about go straight through the cement to the inner face of the brick or stone. If so you might experience the same problems as me (at least in patches) if you simply fill the holes with gypsum
So, after some further excavation, I've discovered the following: the cement/gypsum is directly onto an exterior single skin brick wall. The wall is actually part of a throughway passage dividing my ground floor from the next door property, so is not exposed to the rain, except in one corner. Guess what - that corner is damp....
I've now started stripping the cement/gypsum off and I'm going to put a hemcrete layer on for some insulation, then lime plaster over that. Now, where did I put that diamond blade for the angle-grinder.....?!
I've now started stripping the cement/gypsum off and I'm going to put a hemcrete layer on for some insulation, then lime plaster over that. Now, where did I put that diamond blade for the angle-grinder.....?!
Lime
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- East of England
Just a further bit of advice.
With single brick walls in particular, but also in general, it is best when using a hammer and chisel to have a sharp chisel and always aim the blows in a downward direction.
That way the force is transmitted down through the brick wall in compression and into the earth with minimum damage. Any other direction stresses the mortar which in single brick walls is not intrinsically strong.
With single brick walls in particular, but also in general, it is best when using a hammer and chisel to have a sharp chisel and always aim the blows in a downward direction.
That way the force is transmitted down through the brick wall in compression and into the earth with minimum damage. Any other direction stresses the mortar which in single brick walls is not intrinsically strong.