Old Dry wall and wood lath ceiling - how to restrain
Old Dry wall and wood lath ceiling - how to restrain
(OP)
A portion of the plaster of an 80 year old house ceiling suddenly fell down. There has never been any leakage or other apparent signs of distress, although I won't know for sure until I go into the attic on Wednesday to look around.
I think the most probable cause is the age, shrinkage of the wood lath and the fact the there is AC equipment installed in the attic maybe 15 years ago that is annually serviced by someone who goes into that attic. Perhaps the small deflection of the joists under his weight was eventually enough to break the palster to wood lath interlock.
I think the ceiling in all the rooms could give way and I can think on no way to test them for this. I tried hammer tapping the ceiling but does not tell me anyhting.
Assuming that the wood ceiling (attic floor) joists are sound, I was thinking that instead of removing all the existing plaster (a messy job while people are living in the house), we could install new 5/8" thick drywall to form a new ceiling and thereby confine the old plaster. However this will mean the new drywall will be supporting more load than would usually be the case.
Now the Question:
Does anyone know the size and spacing of screws normally used to fasten drywall, and how I can calculate the "pull-over" strength of the drywall on the screw head, so that I can determine the required screw spacing for a safe instalaltion?
I think the most probable cause is the age, shrinkage of the wood lath and the fact the there is AC equipment installed in the attic maybe 15 years ago that is annually serviced by someone who goes into that attic. Perhaps the small deflection of the joists under his weight was eventually enough to break the palster to wood lath interlock.
I think the ceiling in all the rooms could give way and I can think on no way to test them for this. I tried hammer tapping the ceiling but does not tell me anyhting.
Assuming that the wood ceiling (attic floor) joists are sound, I was thinking that instead of removing all the existing plaster (a messy job while people are living in the house), we could install new 5/8" thick drywall to form a new ceiling and thereby confine the old plaster. However this will mean the new drywall will be supporting more load than would usually be the case.
Now the Question:
Does anyone know the size and spacing of screws normally used to fasten drywall, and how I can calculate the "pull-over" strength of the drywall on the screw head, so that I can determine the required screw spacing for a safe instalaltion?






RE: Old Dry wall and wood lath ceiling - how to restrain
Drywall screws same spacing as cooler nails.
Mike McCann
MMC Engineering
RE: Old Dry wall and wood lath ceiling - how to restrain
The a/c is what is called a "split system", as I am told by a mechanical engineer, and is used on old houses that do not have ductwork. I believe that all that is in the attic is a fan, not the condenser. I believe the condenser is outside. I will be going into the attic to look around this morning. My question is where to find the "pullover strength" of a standard coarse drywall screw with bugle head. I need this information because the new drywall will be put on tight to the underside of the old existing plaster ceiling on old wood lath, to restrain any more plaster from breaking free from the wood lath and falling to the floor. This will be a plaster remediation project. Don't want to spend a lot of money and then have the new ceiling fall down. By the way, inspection to date gives no indication that water is any way involved, but will see better when get into the attic.
So any idea of where I could find the "pullover strength" of drywall screw on the drywall?
I will try calling Hilti this morning, but so far I do not see this particular data in their literature on line, or anywhere else on line, but I am not that great with the computer. I suppose I could rig up a test to measure this, but is a fair bit of work to do so. Someone somewhere must know the answer.
RE: Old Dry wall and wood lath ceiling - how to restrain
RE: Old Dry wall and wood lath ceiling - how to restrain
RE: Old Dry wall and wood lath ceiling - how to restrain
Another option is to put metal lath up below the existing plaster and re-plaster the ceiling. Follow ASTM C1063 for the application of the lath, but reduce the fastener spacing, again to accommodate the weight of the existing plaster.
RE: Old Dry wall and wood lath ceiling - how to restrain
QUESTION: The idea of washers is very interesting but can you tell me whether the washers are going to be visible in the finished installation or are they totally hidden?
Thank you for you help. Much appreciated.
Ron - the length of the fastener has to accommodate new drywall (5/8") plus existing plaster (0.38" measured with electronic calipers) and wood lath (0.46" measured with calipers) for a total of 1.5" plus at least 5/8" penetration into joists = 2.09". My better judgement tells me we should aim for more that 5/8" penetration into the wood, so my feeling is that we need 2.5" long dry wall coarse screws with bugle head.
I was coming to the conclusion that we should put the screws at 8" centres (based on sme pull over data I found for plastic fasteners, so it looks like we are thinking the same way, although I still have no definitive strengths for pullover with the steel drywall screws.
Your other option of metal lath and plaster sounds very interesting. Perhaps we should ask the contractor to price it that way too, as an option. How long would it take the plaster to dry...the residence are planning in staying with elsewhere whil the work is in progress.
Thank you for your help. You always have good and interesting comments. Much appreciated.
RE: Old Dry wall and wood lath ceiling - how to restrain
RE: Old Dry wall and wood lath ceiling - how to restrain
RE: Old Dry wall and wood lath ceiling - how to restrain
RE: Old Dry wall and wood lath ceiling - how to restrain
AELLC- I found no evidence of mositure staining or damage and the house occupants say there has never been any known leakage. I did notice that the heads of the nails holding the lath were slightly rusted, but I suppose this may be from the wet plaster when it was applied when the house was built in 1934. About the condenser, i will ask a mechanical engineer with whom I have worked about that. Thank you for you comment.
RE: Old Dry wall and wood lath ceiling - how to restrain
BA
RE: Old Dry wall and wood lath ceiling - how to restrain
RE: Old Dry wall and wood lath ceiling - how to restrain