Tips for lime plaster on internal brick wall

[JBean]

hi

I'd be grateful for advice on exactly what is needed successfully to add lime plaster to an internal brick wall.

A chimney breast in our attic room had a small, persistent patch of damp, probably through the chimney being sealed. We've removed the old plaster (a mix of lime at the top and plasterboard lower down where the fireplace was covered over), replaced the old flashings, vented the chimney and are now happy that the problem is solved and the wall is dry. It is inside the house, but an external wall (if that makes sense), with brick on the inside and stone outside. The house is Edwardian. The rest of the walls are covered in an old, slightly rough lime plaster (maybe a scratch coat?).

Our builders have agreed to replaster the chimney breast with lime, but I am not entirely confident they will follow good practice - even if I knew what that was! So I'm hoping for some expert advice - for instance, Is there anything they should use / avoid using before applying the lime, what sort of lime should they use, how many coats might be suitable, and any other questions I don't even know to ask...

I have a meeting with the head honcho on Thursday to agree the work and want to make sure I know what to agree to / query / refuse.

Advice much appreciated!

 

[Chris-Burgess]

Three coat work, pricking up coat, floating coat and set. Just brush down the brickwork and give it a good wetting apply pricking up coat with a bit of hair in it, leave it 3/4 days to carbonate, there might or might not be any suction on the scratch coat a little bit of suction isn't a bad thing apply floating coat rule it off your beads on the angles. I'm presuming there's beading on there. rub up with a wood or poly filling in the slacks in the floating to bind it together and devil it. then leave 2/3 days to harden off then skim it. You'll have to use your own judgement to determine suction. If it's tight, coat and half work to bring it out to the beads same day. Then skim with putty based finish which is rubbed up then troweled finished unless you want a rough finish. You can buy small bags of render. We use Limebase 25kg bags. For jobs like this.

 

[Flyfisher]

Make sure they won't use any additives such as PVA to 'seal' the brickwork before plastering!

 

[Abi Cott]

Make sure they won't use any additives such as PVA to 'seal' the brickwork before plastering!

This was what I was going to say.

 

[MikeG]

Three coat work, pricking up coat, floating coat and set. Just brush down the brickwork and give it a good wetting apply pricking up coat with a bit of hair in it, leave it 3/4 days to carbonate, there might or might not be any suction on the scratch coat a little bit of suction isn't a bad thing apply floating coat rule it off your beads on the angles. I'm presuming there's beading on there. rub up with a wood or poly filling in the slacks in the floating to bind it together and devil it. then leave 2/3 days to harden off then skim it. You'll have to use your own judgement to determine suction. If it's tight, coat and half work to bring it out to the beads same day. Then skim with putty based finish which is rubbed up then troweled finished unless you want a rough finish. You can buy small bags of render. We use Limebase 25kg bags. For jobs like this.

I try to avoid beads if at all possible. To me, they are the thing which distinguishes period plasterwork from modern. Depending on the era, of course.

 

[JBean]

Thanks for the replies.

This makes me very dubious that they are planning 'proper' lime plaster. I'm pretty sure PVA has been mentioned and the plan was for a visit for some sort of sealant and then just one visit to do all the plastering.

Supposing they offer hydrated lime? I don't really know what that means and would like to understand whether that is an option.

 

[Chris-Burgess]

Three coat work, pricking up coat, floating coat and set. Just brush down the brickwork and give it a good wetting apply pricking up coat with a bit of hair in it, leave it 3/4 days to carbonate, there might or might not be any suction on the scratch coat a little bit of suction isn't a bad thing apply floating coat rule it off your beads on the angles. I'm presuming there's beading on there. rub up with a wood or poly filling in the slacks in the floating to bind it together and devil it. then leave 2/3 days to harden off then skim it. You'll have to use your own judgement to determine suction. If it's tight, coat and half work to bring it out to the beads same day. Then skim with putty based finish which is rubbed up then troweled finished unless you want a rough finish. You can buy small bags of render. We use Limebase 25kg bags. For jobs like this.

I try to avoid beads if at all possible. To me, they are the thing which distinguishes period plasterwork from modern. Depending on the era, of course.

Me too I like a hard arris done with a rule for a sharp edge. The op mentioned it was Edwardian so I assumed the staff beads where still in situ.

 

[JBean]

I'm not sure what staff beads are, but am pretty sure we don't have them. It is just brick and mortar. I'll post a photo later.

 

[MatthewC]

Supposing they offer hydrated lime? I don't really know what that means and would like to understand whether that is an option.

No. Hydrated lime is often used as a plasticiser with cement, and that is all it does. But people try to tell you that somehow it magically makes cement breathe and so on. It doesn't, it just helps them to apply it.

Sounds like you might need to find a new plasterer!

Matthew

 

[livias]

Hydrated lime attracts moisture which makes it go off (ie turn back to limestone/chalk so its best use is for liming the veggie bed) so if it is used it must either be really fresh or have been stored in a sealed plastic bag

Good hydrated lime can be mixed with water to make lime putty or more usually with sand and water to make lime mortar

Advantage ... considerably cheaper than buying lime putty
Disadvantage ... Needs to be left underwater for some time eg 1 month to give the chemical reaction time to happen. Is then ok for rendering work but I would not touch it for my detailed interior plastering.

If your plasterers are planning to turn up on monday morning with a bag of hydrated lime to throw in to the cement mixer then I suggest you politely show them the door

Hydrated lime and hydraulic lime are NOT the same thing. Which all goes to show that the Marketing Profession was never involved in the naming

 

[livias]

Three coat work gives a smooth plumb flat lovely finish but you mention that the other walls are slightly rough and that this is an attic so two coat work would match better and be cheaper

The first coat is to fill in holes, level up the surface and bridge over changes in the substrate. The second coat beautifies it

 

[JBean]

Many thanks for all the advice. I now feel much more confident about my meeting tomorrow and can be clear on what is acceptable.

By the way, I've had a look and in fact we do have staff beads - or at least one of them. The one on the other side is presumably covered by the later wall and sloping ceiling in the eaves. You can't see it very well in this photo, but there is a clear wooden dowel running down the external corner. (The blanket is covering the recently re-openend fireplace, to stop any remaining debris coming into the room.)

 

[JBean]

This project was rather delayed but I'm pleased to report that all seems to be well. There was an attempt to introduce Limelite as an option, and then some discussion about goat's hair, and a plasterer was identified who has just lime plastered a church. He turned up this morning with two lovely big tubs of mature lime putty and seems to know what he's doing. More visits planned.

 

[skier-hughes]

That's hardly a delay, more like normal working timescales...........................

 

[JBean]

Ha. I was embarrassed to be posting 4 months after it sounded like we were about to start...

But the plasterer has done a lovely job and we are now letting it dry slowly - helped by the fact that we currently have no heating (which would be a suitable subject for a Grump of the Day post, as we have had snow most of the day, and the cause is a very recent piece of plumbing :evil: ).