We are looking at a 1920's single story house in CA. There is one crack in every ceiling in the house. They all run the same direction, in the middle of each room, the full length of the ceiling and appear to be straight down the tape line. I'm assuming the ceilings are plaster. Does this house have structural problems, it's just settling or what do you think is going on? If it's cosmetic what's the suggested fix?

 

Plaster houses don't have "tape" lines since there is no tape. Plaster is mixed similar to the way cement is and it is applied with a trowel over wood lathe which runs perpendicular to the joists. If there is a crack right down the middle, I would suspect that it was a lazy lathe installer back in the 1920's who probably lined up all of the lathe seams along one joist in the middle of each room. As the joists deflect (sag) it cracks the plaster along the common seam between all the lathe. All the joists are sagging, but the worst of the sag will be in the middle of the room, and it's likely that if there is a seam in the lathe, it allowed that particular joist to sag even more than it ordinarily would have.

If someone was in the attic his weight probably didn't help matters any. In older houses, dimensional lumber is usually undersized and overspanned by today's standards. So the ceilings are probably all sagging under the weight of the plaster, which is heavy. Houses with plaster walls and ceilings all have cracks somewhere. It's just a matter of how many.

Best solution would be to tear the plaster off, shore up the weak, bowed joists, then drywall and insulate.

If you can live with the cracks, by all means do so.

 

Thanks XSleeper! It appears that it is cracked where each "panel meets". The interesting part is I don't see any bowing in the ceilings or any other cracks, just a clean crack down the center of each room. Can the cracks be filled with plaster or mud? A tear down would be a BIG job.

 

Like I said, on a plaster ceiling, there is no tape... and no "panels." The entire surface of a plaster wall was once wet plaster that has been trowelled on. If it cracked in a straight line, it is a safe bet that the line is where all the butt joints of the lathe all line up in a straight line down the middle of a stud. I would be willing to bet that if you had a 78" level and placed it perpendicular to the crack, it would probably teeter-totter back and forth. It may not be bowed bad, but it is definitely bowed a little... at least enough to crack.

Tearing down plaster is not a big job, just a messy one. You can patch plaster cracks, but they will reappear. By patching the crack, you will be trading a crack for an even wider "patch" that will not match the texture of the surrounding area. You would have to be really skilled in patching plaster to completely hide it, or else you would pretty much have to skim coat the entire ceiling with an additional layer in order to have it blend in. And then it would crack again, soon thereafter.

If you just want it to look "better", a simple (though not perfect) solution is just to caulk the crack with a good latex caulking like White Lightning siliconized latex or Big Stretch elastomeric latex, then wipe it with a damp rag. Doing that will probably last just as long, if not longer than a plaster repair.

If the ceiling has "drywall" then yes, that would be a tape joint, most likely at a panel edge. But you said the ceilings were "plaster", not drywall. There is no way for me to tell the difference from where I'm sitting... I can only go by your description.

 

I usually scratch out cracks like that and fill them with a setting compound like durabond. Sometimes it pays to use drywall tape on the cracks although as X stated, tape isn't normally used on plaster. Caulking will last longer than any mud that could be applied but you can't make the repair disappear with caulking.

 

I looked in the attic and it doesn't appear to be lathe. It looks like old drywall and the structure is standard 2 x 4 joists. The texture is definitely plaster. Weren't they using drywall in that period in CA? Anyway, I assume the right repair would still be to remove all the plaster and put up drywall.

Any guess about approximately how much it would take to have all the work done: tear down, installing drywall, tape, texture and paint on a 1,700 sq ft single story house in CA?

 

At one period in time the wood lath was replaced with a gypsum lath which is likely what you have. Today's plaster is just a plaster veneer applied over blue board. I don't think drywall became commonplace until the 50's or 60's.

 

In the 40's and 50's they started to use the gypsum that marksr mentioned. I believe the sheets were only 24" wide, then the plaster was applied over that. So if you are in the attic and can see seams on 24" centers, that's probably what you have. If the seams are on 48" centers, that's drywall.

 

I think you are correct about the gypsum lath only being 2' wide. If I'm not mistaken when they first started using gypsum lath it had holes in it to key in the plaster brown coat but then they decided it wasn't needed and went to a solid 2' wide gypsum lath.

I don't know if they used gypsum lath in the 20's maybe tightcoat will have time to respond as he probably knows more about plaster than any other member. It's also possible the house was remodeled at some point.

 

My house was built in 1928. It has 3/8" gypsum board (4'x8') on the walls and ceilings covered with plaster. This was certainly not common of the period. It is possible that the ceilings were plaster at one time and replaced with drywall. Plaster ceilings are the most prone to failing from activity occurring on the floor above them. This certainly wouldn't be your case because you have an attic. If they were replaced, it could have been from seismic activity or a roof leak.

 

Gentlemen, gypsum drywall was available in the twenties and even earlier. Taping of the seams was not really common in the early days of use, most joints were spackled over with a hard compound mixed on site from powder and water.

Nails were usually the same nails used to attach wood lath or a size very close to those.

If the cracks in the ceiling are straight line and extend for some distance then I would be more willing to bet the material is drywall and there is no tape.

If the board is relatively tight to the framing and does not have sagging issues you can certainly tape the joints and perhaps skim coat the entire surface of the ceilings affected to get a consistent surface appearance for the next painting.

The use of gypsum lath for plaster has, over the years, included a variety of sizes from 2'x4' to 2'x8' to 16"x4' and in today's world 4'x8' sheets and larger of blue board can be used for veneer plaster as well as conventional scratch and brown coat applications of gypsolite, structo-lite or sanded basecoat.

It is amazing to me that I frequently hear the phrase "no one does that anymore", referring to traditional plaster. This is a trade that certainly has seen a decline but the materials are still available although some of them can be a little difficult to get at times.