“I’ve just gotten a home from the early 1900s in Philly, and I’m working on plaster patching. I’ve noticed with close inspection that the dining room ceiling (a 10-footer) is fairly loose in many places beneath the finish coat and paint, which is still pretty much intact, but with noticeable parallel stress lines all the way across (I assume these lines correspond with lath strips, since they’re perpendicular to the second floor joists above).

“I’ve read that one option for repairing this condition is to put new blue board and veneer plaster over the old ceiling. The sources I’ve looked at specify to attach 1-inch-by-3-inch furring strips to the joists, through the existing lath and plaster. I’m wondering whether those furring strips are absolutely necessary, if I can locate and mark the joist locations and then use long drywall screws to attach the blueboard directly to the joists. Also, should I be worried about the old plaster coming loose and adding weight stress to the new board?

“I also wonder whether there’s any other solutions to this problem. The ceiling isn’t falling apart, but I’ve managed to poke a considerable hole in one place just using my thumb and moderate pressure, and the old basecoat looks like it’s crumbling. I figure that stripping the paint, applying a bonder and then some veneer plaster could make the ceiling look better, but that this might add stress to the crumbling base and precipitate more problems. Still, I’d like a professional opinion on that. I’m just dreading the prospect of hoisting 4-feet-by-8-feet sheets of blueboard 10 feet in the air. Note that I can’t access the joists from above, since they’re beneath a finished second floor.

“Finally, if I do use blueboard, I know it should be 5/8 inch instead of 1/2 inch, right? And does it have to be of the type specifically manufactured for ceilings, or can it be a standard grade as long as it’s screwed into the joists on an acceptable schedule?

I want to thank Josh for writing and congratulate him as the winner of the Plaster Man T-shirt for August!

Stress lines

Plaster separation: This is where the plaster, for one reason or another, has come loose from the wood lath above it. It could be water damage or vibration or settling over time that causes the plaster to separate. No matter the reason, this can lead to a dangerous condition where part or all of the ceiling can fail and fall.

Faulty mixture: Companies today have made an art out of the process of mixing gypsum products for board and plastering. This, unfortunately, was not the case in times’ past, especially in the times of full coat plastering. It was mixed by hand, and though the majority of buildings have a solid interior, there are many occasions that I personally come upon that fit the description Josh talks about. It has to do with the mix being over sanded. Too much sand in the mix can lead to the basecoat eventually becoming “crumbly.” When repair is attempted to this type of wall or ceiling area, many times the basecoat will continue to crumble and almost become a powder. The strength of the plaster has been lost.

I would say this is the condition Josh is dealing with. With the loose, crumbling condition that the plaster is in, I would not suggest resurfacing as a solution. Resurfacing is going to be as solid as the base over which it’s put.

Re-hanging with board

Q: Are furring strips necessary?

A: If the wood lath and joists are sound, I would suggest hanging the board directly to the old ceiling, without the use of furring strips. I like to use construction adhesive on the board so that it bonds directly to the old plastered ceiling, and use this in combination with 2-inch screws; one on each edge and three in the field.

Q: Should I use 5/8-inch board?

A: Re-hanging over a ceiling this way, with 16-inch centers, I would say you could use 1/2-inch standard blueboard. It’s rare that I’ve come across an older home with 2-foot centers, so I’m going to say it’s either 12- or 16-inch centers.

Q: Will the new board add stress to the old plaster and make it loose?

A: If the old plaster on the ceiling is bulging or hanging down, and there is a question as to whether the new board will bring the old plaster back up into its original condition (tight against the wood lath), then it might be best to tear off the old plaster. I am all for keeping as much of the original building intact as possible. So, I would suggest taking off only the loose plaster and leaving the wood lath in place. Again, this is only if the wood lath is fairly straight and is sound and solid. If it’s OK, then you have both the joists and the wood lath to attach the new board to with screws.

As far as the board adding additional weight to the ceiling, the key issue is making sure it is fastened securely with long enough screws, to the joists. If this is the case, then this won’t be an issue. An example of where it becomes a problem is the case of one ceiling I came upon where the board being hung was 1/2-inch thick, over 1/2-inch thick plaster, through 3/8-inch wood lath, with the joists being above this. Someone used 11⁄4-inch screws, which barely got into the wood lath. This caused stress to the entire ceiling, as the weight of the board and original plaster were now being transferred entirely to the wood lath, which, by the way, was not in very good shape at all.

One additional point: If a plaster molding is present around the edge of the room, then the decision also has to be made as far as if the new board is going to cover up part of it. Hanging 1/2-inch board over the old plaster, you’ll lose a 1/2 inch of such a molding. In this situation, some plasterers have put in nails around the edge 1/2- to 1-inch out from the molding.

They hang the board up against the nails and then put an L-bead all the way around the edge. This gives an effect that the original ceiling was designed this way and is acceptable to some people. Others will remove the original plaster and wood lath and install the plasterboard, with the finished plaster coming out even against the molding where the original plaster was worked out to originally.