Re-bonding old lime plaster

[Big Stewy]

Hi everyone, its my first time on this forum, Ive read some of the posts and I feel lucky!

I have a 1920's house, much knocked about and extended by me and much loved by our family. Its nothing grand but its our home. I have lots of old lime plaster on the walls and quite a bit of it has de-bonded from the brick walls behind - usually in two foot diameter circles. In a couple of places there are some moundings in the plaster that I dont want to lose and its not like its falling off (Yet!). I am therefore keen to re-bond it and was thinking of drilling a number of small holes (6-8mm diameter) in a grid-like pattern and injecting a resin or acrylic adhesive to soak in via capilliary action and glue the plaster back on. I understand that there may be a conservation technique along these lines for really old plaster and wondered wheher anyone has experience of it, what should I use as rein/adhesive etc.? Its got to be less trouble doing this than stripping it off and patching in. In any case I like the old plaster and want to keep it.

Thanks for an help guys and gals,

Stew

 

[biffvernon]

I don't think so. Sticking the plaster back on with resin does not seem a good idea. I would remove any that is loose enough to be pulled off with just fingers and then patch up with new lime plaster. If you are not very good at plastering it is easy to get it to look like old plaster. Expert plasterers find this more difficult.

 

[Ian Bond]

Sounds like some nice plasterwork there Stew.

I tend to agree with Biff on this one - if it isn't cracked and actually falling off on its own accord, I'd leave it alone. Lime plaster tends to sound hollow in places, but if the surrounding plaster is firmly attached it can be OK.

I've not tried the grouting method myself - too specialized for my limited skills and rough walls, but I know it is used as you say to save fine plasterwork.

I think that the method involves making holes top and bottom, then carefully flush out dust and debris from behind the plaster.

You then inject a liquid lime plaster into the holes to re-bond the loose stuff. The guide I read warned that great care was needed to support the repair area otherwise the pressure of the injected grout could push it off the wall. It's not something I'd want to try out on an area of precious plaster myself - not until I'd been shown how to do it all properly.

 

[chuckey]

In my victorian house, about 50 % of the bonding coat plaster in the hall, has lost its bond to the brick substrate. The surface behind the pieces of plaster that have actually fallen off is a very thin film of lime dust just sitting on the brick faces. The bits that have fallen off are a perfect(?) lump of bonding plaster with its coat of finish. I can't explain what has gone on, could be acidic bricks, rising damp or settlement ?
I have experimented with trying to stick down the edge of the plaster and have found that due to impurities/ molecule size/ ionic polarity(?) that the bonding coat just will not wet out without mechanical abrasion i.e. water sprayed on to its surface just falls off as in a ducks back, so any water based adhesive will not work cos' it will just sit there between the dust particles till it dries out leaving minute bits of adhesive dust sitting in the lime dust in the plaster/brick interface.
If you have a large bit to rescue, drill through it, and using large stainless steel washers and stainless steel screws literaly, screw the bit back to the wall. fill the holes around the washers. I would use a fixing 3 " from the lumps edge and every 6" round its perifery.
Frank

 

[Big Stewy]

Hi Fella's,

Thanks for the advice. I was aware of the big washers and screws solution and this was my last resort option!. I am grateful for the guidance regarding water based adhesives - I can understand the problem with them now that you have described it. I think I will try a resin like the sort used in anchor fixings. The house is made of locally fired coarse clay bricks with a good key. If the resin is slightly thicker than water and can soak into the imperfections in the bricks and the back face of the plaster then it might work. I will probably try this with washers then i can use the washer screw holes to inject the resin. I'll let you know how I get on.

Stew

 

[Nemesis]

Try PVA.

 

[Big Stewy]

Hi Fellas,

Been spanking the net and came accross a specialist in Devon who restores old plaster. He said the following:

"Hi Stewart
As you are aware conservation of plaster surfaces is a fairly skilled job,
but the principal involves the possible flushing of any voids behind plaster
layers to enable injected lime grout to adhere to surfaces. The grout will
flow more easily if the surface tension is broken by using some kind of
alcohol in dilution injected before the lime grout. The composition of the
grout (whether it is pure lime or mixed with fine aggregate) would depend on
the depth that the grout needs to fill or bond. The other important factor
is that the area behind which grout is injected is supported on the face to
prevent the pressure of the grout from forcing off the plaster."

Think I'll give it a try.

Stew

 

[Ian Bond]

Hi

The doc I found mentioned alcohol to help clean out the debris.

I recommend using some cheapo blended whisky for the lime plaster rinsing (diluted), and of course a nice Ardbeg or two (undiluted naturally) for yourself.

hic!

 

[Nemesis]

I'd still give PVA a go, trial of a small area - recommended on a SPAB course along with washers. Worth a try and sounds far less bother.

 

[MdB]

I thought you where joking when you said PVA. It would guess it would work OK but it would but a nice non breathable layer in the middle of your nice breathable wall.

 

[Nemesis]

Well, I would consider the structure and other ways it may need / be able to breathe.

If it's wet PVA won't dry of course.