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Question DetailsAsked on 4/14/2016

I live in a 126 year old house. The original plaster on the ceiling is beginning to pull away from the lathe.

It looks like old water damage but we had a totally new floor put in in the bathroom above about 15 years ago and there is no sign of leakage in the bathroom. We did have a new roof with complete clean off done about 4 years ago and now have small cracks on many walls. Some I can fix but the ceiling needs help. It also seems that the water came in when a small overhang roof was added to this room. The water marks were never there until they did the overhang. The plaster in my house is horse hair and plaster.

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Obviously any generalization about 126 year construction is bound to find exceptions - but VERY generally, true plaster ceilings (and with the age this is likely 100% plaster of pairs/lime, not a cementatious mixture) tend to fail in 3 ways - breaking up into smaller pieces due to stress or being hit, collapse because the nails holding the lath in place rust away or the wood lath is eaten away by insects, or by softening and slumping of the plaster because it is soaking up moisture - either from direct wetting or exposure to continual very high humidity.

With improper construction, where the plaster was not well extruded into the spaces between the lath (or through wire mesh in newer work) or the lath was placed basically edge to edge without gaps, it can also just fall away with age - typically in large slabs, as it loses its bond with the wood.

The first type of failure you would see multitudes of cracks and small pieces falling away, and of course for the last if the plaster was just never extruded into the lath gaps or mesh you would have slabs falling away cleanly from the ceiling. Rusted away nails or rotted/eaten away wood you could easily identify where it is coming loose.

Sounds, like I think you suspect, that moisture is the problem. A good walk-around in the attic should resolve that question, though of course it would have to get down to the bathroom floor to appear in the next lower floor ceiling. Look for wetness of course, but also mildew growth and water staining, and matting down of any insulation. (Be cautious if very old - may be asbestos containing insulation).

Adding an overhang or patio / porch roof, especially if a flatter slope than the main roof in snow country, is a very common water infiltration point if it is not properly transitioned with ice and water shield and flashing. If you can get in under that point what you see should help a lot in identifying if that is the problem. If this overhang is at the top of the level with the plaster problem (like a porch overhang), rather than at house roof level, this becomes a more likely source.

Generally speaking, if that is the source of the problem, unless the entire attic is very high humidity from the leaks (plaster picks up water out of the air quite well), I would expect the damage to be limited to the leak area and a few foot zone around it, and would normally show water marks before it fails and starts falling down unless it is getting very wet and basically coming down because it is saturated.

Now - the alternative. Since this is below a bathroom, the first suspicion would always be a bathroom leak in lieu of other specific source having been positively identified. I would start with a rented color fiber optic camera scope (typically $25-50/day rental at Home Depot, tool rental places, some auto parts stores) or buy for under $100 at Amazon, Harbor Freight, some tool carrying stores. Takes about 1/2-3/4" diameter hole in ceiling (possibly at 2-3 places) to put the probe through and quite good for tracing stains and leaks. Or open up head sized holes for flashlight search. Once you find the staining (in framing or on top of plaster) you can then test for bathroom and ceiling leakage source by running various faucets/showers etc - or wait for rain or sprinkle roof for a good long time for roof leakage.

Of course if your piping is original any pipe could be leaking - if newer, shower floor would be most common source probably, secondly leak in drain pipe where it comes out of shower or tub. Or if you have resin/fiberglass shower/tub, cracking of that is pretty common.

Since you say there are water marks now, sounds like finding the drip/pooling point on the plaster would be simple, then trace back to source from there.

If plaster is pulling away, it may be possible to fix it - but unless historic house or on National/City Register, generally cheaper to just pull down and replace with drywall. If that is done, make sure floor is WELL protected (good contractors use 1/4" luan plywood over padding or canvas tarp to avoid scratches, all under tarps to catch and pick up the plaster debris and dust) because the plaster, lath, wire and nails ground around under foot will cut through canvas or plastic sheeting in no time and gouge/scratch up the flooring.

Answered 4 years ago by LCD

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