one of the victorian ceilings in my house is slightly sagging causing a small crack about 1mm wide to run across. i would normally just bring the ceiling down dryline it and skim but this ceiling has really ornate original plasterwork which i cannot contemplate losing! i have heard of a method of propping the ceiling in the middle and pouring plaster of paris from above over the laths and nibs of old plaster. has anybody tried this? any experiences /advice/warnings etc would be very useful
I did it on a plain Edwardian ceiling as a temporary measure - when I came to bring it down it was dead tough! I jacked it flat with chip board and acrow props and used finished plaster poured in from above - smoothing out between joists with a pointing trowel. I classed it as a total sucess but it was only needed for a few months to delay pulling the ceiling down prior to more major building works
Is the ceiling actually sagging or is it just the joists that have relaxed over time ? An old lath and plaster ceiling can begin to sag in areas that have become nail sick, this means that the original nails have rusted and broken away from the joists with the movement on them over the years. A common repair is to either re-fix the laths by screwing nails through them again, or to bare small areas along the full length of the joists and fix thin timber strips along them and screw them through to the joist. You then hide the timber strips with a new coat of bonding and finishing plaster over top and match it to the original plaster work.
I've never attempted this type of repair myself, but have seen it done many times on the old historic buildings we get work at. It has always seemed very effective.
if you can inspect it from above, survey it to see if it is the joists sagging or the lathe has come away from the joists. If it is the latter then you can try propping it up and then screw the lathes, perhaps using washers too to stop from splitting the lathe and then skim. if it is the former, then you are down to reboarding at the very least and if you want to save the ornate plaster work you could take a mould off of it before pulling it down so that you can repeat it on the new ceiling.
A couple a years after moving into my last house (1994 ?) the washer in the ball valve in the loft water header tank split and water started coming out of the overflow. Fixed the washer, but the solvent weld joint in the overflow pipe from the tank had never been solvent welded (house made in
1971), so water dripped from the joint onto the insulation and onto the plasterboard. This produced a pronounced sag of the plaster board. In fact it just sagged the board more than it was when I moved in. implying this had happened before.
I got a piece of 18mm spare MDF bigger than the sagged area, covered one side with thick polythene (as there was now a crack that would allow plaster through)., vacuumed area in loft, applied PVA in loft and propped the MDF against the ceiling using a length of 2x2. Also put 4 screws in the MDF to stop my prop sliding off the MDF. Then poured some finishing plaster, with PVA added for good measure onto sagged area, spread around and left to set.
Left a day or two, removed prop, removed odd bit of plaster that got through the crack, painted crack and good as new. Oh and remembered to solvent weld the overflow pipe.
Because of this when I bought my new house, whilst doing the snagging I purposely overflowed the loft tank and guess what, it leaked at the joint in the overflow pipe, not joined correctly !!! Shame I didn't check the toilet overflows, as they all leaked, in one case flooding the new bathroom due to plastic shreds in the ball valve preventing it closing !!!
You should contact a restorer. I helped repair victorian friezes and ceilings all the by injecting epoxy resins into them and propping them into position as the resins cured.
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