Repairing lime plastered ceiling

[graypark]

I have a large lime plastered ceiling I'm restoring. The plaster is generally in goodish shape though with some lengthy (2-3m) cracks (some hairline, some double cracks but nothing particularly stepped) running throughout. These join up with hairline cracks in the surrounding cornice which appear to be quite ancient since having stripped off the emulsion and distemper (which I should guess has been up there for the best part of 50 years) some of these cracks appear to have been repaired in the past. On one side of the larger double cracks in the ceiling the plaster appears to have very slightly blown with a mm max of play if pushed. The ceiling appears to be painted in a thin coat or two of emulsion.

Fundamentally, I'm not too worried about the situation as I take the view that the ceiling has almost certainly been up for some 125 years (the house was built in 1880) and is unlikely fall down now (unless I cause it to!)

My "do the minimum" plan is:

- rake out the double cracks and fill with lime plaster (lime putty to sharp sand in 1:3 ratio).

- paint ceiling and cornice with soft distemper.

Two further options occur to me:

- try to strengthen the slightly blown bits of plaster by using washers. But I'm concerned it might do more harm than good;

- remove the emulsion layer and apply a layer or two of limewash before painting with distemper (as I've heard limewash can strengthen the ceiling and that distemper might not like to be painted directly onto emulsion - also could this stop the ceiling from breathing?).

Very grateful for any thoughts.

 

[Ian Bond]

Limewash will help fill fine cracks, and consolidate plaster to a degree.

But it won't fix more serious problems, obviously. Things like broken keys, sagging plaster, large cracks, failed plaster, loose laths etc...

I use washers a lot, particularly to strengthen the margins of patch repairs. With care you can screw the washers into the lath alone, although it's better if you can find a stud or joist.

Some care is needed, as I sometimes find that beneath the finish coat, the old coarse plaster is very crumbly and weak. Sometimes however careful you are, as soon as you start working on the very weak areas the plaster crumbles away to dust. What starts of looking like a tiny bit of damage can become a huge hole very quickly. And the mess from even a tiny hole in the plaster is horrendous!!!!

Having said that, a few washers have worked miracles, and I've saved more than 70% of ceilings that others have condemned as beyond repair.

A lot of the damage and decay to my ceilings has accumulated gradually over time, and I expect that just left to its own devices parts of it would fall down at some point.

I stripped the emulsion from all of the walls and the ceiling of my front bedroom. I won't pretend it was easy work, but it did allow me to limewash onto a suitable background. The limewash doesn't rub off either, which was a concern. And it really does help fill those tiny cracks, and hide my repairs somewhat.

If you've got bags of time, energy and patience then it may well be worth stripping off the old emulsion. The rest of your 'do minimum' plan sounds OK to me, so long as the ceiling is secure.

To get the emulsion off the walls (several layers) I tried:

* Chemical strippers (an eco friendly one) pretty useless

* Klingstrip (effective, but would have cost £££hundreds) May bring bits of the ceiling down with the paint if the plaster is very weak - the layer of Klingstrip is heavy, and it will fall off by itself if left.

* Hot air gun and scraper - got a lot off, but some stubborn patches remained, and it was a tedious job.

* Sharp stripping knife (like a large Stanley blade) OK, but tended to dig into the wobbly plaster

* Smaller stripping knife with a 2inch blade, sharpened regularly with abrasive paper. Got all of the paint off the ceiling with this, a single layer of emulsion that I did in my ignorance

* Steam stripper (hose only, plate removed) and scraper. Wear heavy duty gauntlets, and protective clothing. Probaby a very dangerous thing to be doing. But it worked. I got most of the stubborn paint off with this method.

The steam also blasted off the gypsum skim, and desolved old gypsum repairs!!

If I ever tackle emulsion again, I'll would go for the steam and scraper method. It was cheap and very effective. But I'd make sure noone else was in the immediate work area, and that I had all the protective gear on to help prevent a scalding.

 

[graypark]

Thanks Ian,

having inspected the double cracks further (they were causing me a little disquiet) I've discovered they are filled with gypsum therefore suggesting they are the consequence of a predecessor's attempt to rake out and fill what were originally finer cracks. The plaster underneath the skim layer is in pretty good shape and indeed requires quite a firm raking to remove. I'm still slightly concerned about the blownness of some of the plaster next to the double cracks - could this be the result of having filled with gypsum (which I gather expands as it dries?) - in particular it's hard to tell quite how far it goes before becoming sound again.

Did a trial run of painting a small patch with a crack running through it with distemper, seemed to cover the crack a treat and doesn't seem to have objected to the emulsion, which after your eloquent discription of stripping methods I'm inclined to leave where it is unless someone can set out convincing reasons otherwise!

 

[Ian Bond]

I don't blame you for leaving the emulsion. It tested my already fragile grip on sanity to the limit!!

Good luck, and let us know how it goes. The distemper sounds like a good idea.

 

[Ian Bond]

If gypsum patches are sound, I leave them alone. You can remove the gypsum without breaking the lath, but sometimes it isn't worth the risk.

To remove the gypsum, I use my small plasterers' tool to score a line between the laths, then carefully break the gypsum off. If the gypsum is rock hard and well bonded, I don't bother - too risky.

With de-bonded finish, I carefully remove it to a sound edge and replaster. It's a compromise, but I do try and save as much as possible, not least because it is so hard to replace!!!!

The plasterwork in my fairly rough and humble cottage has done well to survive 170 years. It is not the best quality work, but still impressive by today's standards. There's just a single backing coat of 'coarse stuff' which is not scratched, just left with a rough texture. The fine coat varies considerably in thickness, to give a smooth but wobbly finish. Hold a torch against the wall and you see how uneven it is - no dot and screed methods used at all. Still, it looks fine in day and candlelight.