Drying time for water-damaged lath and plaster ceiling?

[LondonR]

We recently had a big leak from the roofspace in our Victorian terrace which came through the lath and plaster bedroom ceiling below - about half the ceiling is affected. We're slowly drying it out and while the ceiling looks pretty awful it doesn't seem to give when we press it.

From what I've read on here, lath and plaster ceilings can recover from water damage and don't necessarily need replacing the way plasterboard would if it got wet. Can anyone advise on how long we should let the ceiling dry out before we'll know whether it's a redecorate job or needs more?

Insurance are involved but haven't sent an assessor yet. If work is needed on the ceiling we're keen to keep the lath and plaster but know it might not be what the insurance wants. I'm keeping my fingers crossed redecoration will be enough!

 

[Cubist]

Much will depend on how that room is heated and the efficiency of the ventilation of the void/loft above that ceiling but 1-3 months would be the likely range in my opinion. If it's a loft it would be wise to remove any insulation immediately above the ceiling as this would inhibit the drying process and, if it too got wet, this could lead to other problems. Pressing or pushing against the plaster at present may not reveal any sagging as the wooden laths are probably swollen with water and will have a stronger grip on the nails/pins. A test you can use to check how well the plaster is drying is to use a small 2-3mm drill to drill a couple of holes through the plaster to see if the flutes are full/packed when its withdrawn from the hole.

Good luck.

 

[Flyfisher]

We had the same issue many years ago, soon after taking on our house project. The house was empty and unheated and due to a burst pipe water and a sloping floor/ceiling water ran across the ceiling for most of a weekend before it was noticed. The lath & plaster ceiling was so saturated that the ceiling paper fell off!

Having had a lesser issue in a previous house with a plasterboard ceiling that turned to mush and collapsed, I was expecting this ceiling to follow suit. The entire room was due for complete renovation anyway so I just added it to the list, closed the door and tried to ignore it while I concentrated on fixing the roof.

To my amazement, it never did fall down. I can't remember now how long it took to dry out because it was an unused and unheated room for a couple of years but when we finally got around to decorating the room, the ceiling was as solid as it had ever been and required no repairs, probably because the slight slope prevented the water from pooling such that there was no localised damage. Anyway, the decorators only had to 'tidy up' the plaster (actually mainly the remains of the paper glue and bits of paper that had not fallen off) before painting. Ten years on, we've not had any further problems and it was a very welcome early lesson about the resilience of lime plaster!

It was also a lesson about not rushing things. Of course that's easier said than done, but I suspect that if I'd filled the room with fan heaters and dehumidifiers it might well have been a different story. It's just a guess though because there was no 'control experiment' for comparison, but I reckon that just allowing things to gradually dry out and reach a new equilibrium probably helped. But regardless of what I might think, the fact is that the ceiling survived intact - indeed, it turned out to be a very easy way to remove the rather awful textured ceiling paper. Physically easy, that is, although not so mentally easy at the time!