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Plastering methods that create ~16"x24" pattern

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  #1  
Old 08-29-12, 06:48 AM
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Plastering methods that create ~16"x24" pattern

A bit of a plaster history question here....
The ceiling in the virtually untouched rooms on the second floor of my house have noticeable sections to them. The pieces are ~16"x24" and appear to make up the entire ceiling. This is noticeable in all the rooms I suspect never saw major renovations over the past 70+ years.
The house was built in ~1937 as a former nun convent.

Reading through a couple different sites I found on historical plaster and plastering techniques, I can't really see a method that would create these consistent shapes. None of the sites I reviewed had a real solid time line for various techniques or materials used. I'm pretty sure these differ from region to region. I'm pretty sure this is not lime based plaster (based on what I have read) and it's definitely not clay based.

At this point, I have not touched any of what I assume is original plaster, so I can't say if it's was done using the 3 layer method.

I'll post some photos tonight when I get home.
 
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  #2  
Old 08-29-12, 09:24 AM
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Are you talking sections as it small pieces of gypsum lath? or texture?
Hopefully the pics will clarify
 
  #3  
Old 08-29-12, 09:31 AM
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If you look at the ceiling, it looks like someone plastered right over a drop ceiling (with smaller pannels).
It kind of looks like it was small pannels that where placed, then mudded over.

I'll grab a picture or two tonight when I get home. Will be a bit later in the evening.
 
  #4  
Old 08-29-12, 10:40 AM
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I have an idea but will await the pictures. Try to get good contrast and get one showing a large section of the ceiling and if you can, one showing the joint detail.

You must be figuring on doing some renovation. Do you want to replicate the pattern? Do you want to remove it? Cover it up?
 
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Old 08-29-12, 11:40 AM
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You must be figuring on doing some renovation. Do you want to replicate the pattern? Do you want to remove it? Cover it up?
I don't think the visible pattern was something desired from the begining.
If I had to guess, it could have been the plaster sagging over time, but it's looking like a reasonably consistant pattern to it.
If it had been drywall, I would have said that someone used 16"x24" pieces and taped and mudded them together.
 
  #6  
Old 08-29-12, 02:00 PM
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I'll have a better idea when I see the pictures.
 
  #7  
Old 08-29-12, 04:57 PM
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Here are a couple quick photos.
The first is from one of the bedrooms on the second floor and the second is of the stairwell going from the main to second floor.
Above the bedroom is part attic, part room. Above the stairwell is all room.

From what I can tell. There is blow in insulation above the plaster (between the joists), floor boards, then more blow in insulation (in the attic portion).
The lines are a bit cleaner then they appear in the photos. The angle really makes them look un-uniformed.
If they wheren't almost exact spacing, I would say it was poor mudding, but they are almost exactly the same size, every section.
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Old 08-29-12, 08:43 PM
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Only the first pic is helpful. Are we seeing the straight lines at ~24" oc? Or ~16" oc? Near the center of the picture is a line perpendicular to the other more or less parallel lines. Are all of these lines depressed from the field? Or looking at it the other way are the lines tight to the joists and the field projecting downward?

I've seen this before when gypsum lath was used and the joists were spaced 24"oc. Typcially gypsum lath AKA RockLath or button board was 3/8" thick and came in pieces 16" X 48" It was nailed perpendicular to the joists and the joints were staggared usually in a running bond but occasionally another pattern was used.
Gypsum plaster was applied 3/8" to 1/2" thick with a finish on top of that. If you think about it a sheet 4' long will be nailed on edges only on the ends and only on one joist in the middle. It was straight when the plasterer was finished but in time gravity won and humidity and insulation contributed to the sagging. Gypsum lath and plaster seem to stay just fine when the joists are 16" oc. Now if your joists are 16" oc I wonder if the lath was installed parallel to the joists. That would sag with the weight of the insulation and the action of humidity over the years.
Something else I have seen in houses of this vintage is gypsum plaster applied over some kind of fiber board similar to Celotex. It has little to no structural strength and will sag like I think I am seeing.

Now it is also possible that you have plaster over wood lath and the joists are 24"oc. I have never seen that but I imagine it would also sag under the same conditions.

Now tell me if I am right about what I described. If so, that is probably your problem and you know the contributing factors.

So now what to do about it. Or is this merely academic curiosity?

One other thing I'd like to know before I suggest a treatment if that is your wish: How high are the ceilings?
 
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Old 08-30-12, 03:59 AM
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What you describe tightcoat makes sense to me.
I haven't measured the actual sizes of these pannels but I can say that the lines are almost perfectly square.
The house has been (as far as I know so far) wood heat back in the 1930's and moved to hot water boiler (eletric then oil) over time (possible 1970's when the nuns sold the property as all the pipe work appears to be soldered copper). With that, the house would be dry during the winter months, and probably somewhat humid during the summer.
As for the hight of the ceilings... I think the second floor is all 8-9ft tall (need to confirm). The stairwell is closer to 18-20ft from the landing part way up the stairs (12ft ceilings on main floor + joists + second floor height).

I would like to repair the ceiling once time and money permits.
I am thinking removal and replacing with drywall would be the simplest, but will be messy and expensive as I'll have to handle all the blowin insulation and replace it with fiberglass batt.
I'm guessing simply mudding over the lines will only last a few years before I'll have to address the issue further.
 
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Old 08-30-12, 05:52 AM
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I wonder if laminating over the plaster with 1/2" or 5/8" drywall would work. You'd need screws long enough to secure it to the rafters. Tightcoat is the expert so take his advice anytime it differs from mine
 
  #11  
Old 08-30-12, 05:56 AM
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My first thought on seeing the pictures was sagging, not an intentional pattern.
 
  #12  
Old 08-30-12, 06:36 AM
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mitch17,
I'm assuming the same thing. It's not nearly as bad as it looks. I had bounced the camera flash (off camera flash) in order to make it show up for the photo. The sun was going down so I was fighting with that nice orange lighting.

I was kind of wondering what technique would have been used to apply the plaster so that it would sag as it did. I could see sag between the joists, but the length of the sections is pretty consistant.
 
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Old 08-30-12, 04:42 PM
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If or when you remove this or some of it will you check back in and tell us what is behind the plaster? I am curious.

When it was plastered everything was flat. It stayed flat for a long time -- years. The sagging began gradually and took years to get as bad as it is. the insulation might have exacerbated the condition.

How much offset is there from the highest to the lowest peaks or valleys?

I am not sure that you can screw 5/8" drywall and pull the existing ceiling back into alignment, especially if the joists are 24". You might be able to fur it out with 1 X 3's or 1 X 4's. I say 1 X 3's rather than 1 X 2's just to give you a bigger target to screw to especially at your butt joints. You would need screws long enough to go through the strip, the plaster and the lath of whatever kind it is and into the joists. Then if it pulls everything into some kind of straightness you can drywall it.

I would sure try to avoid tearing it all down for the sake of the mess. There is not only the insulation but also 75 years' accumulation of dust up there not to mention the plaster and lath. Granted, that would likely give you the best installation.
 
  #14  
Old 08-31-12, 12:47 PM
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I've torn down an old ceiling twice, and the amount of dust, grit and dirt is unbelievable. In another room (w/o the sags you have) we laminated drywall over the plaster. Only the usual mess of finishing drywall there. No comparison.

I would go with tightcoat's suggestion of 1 X 3 or 1 X 4 stringers + 5/8" drywall.
 
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