ID plaster type/repair cracks

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  #1  
Old 08-30-16, 11:53 AM
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ID plaster type/repair cracks

My 1930s house has developed plaster cracks, plus I need to patch a few holes I drilled looking for leaks/mold. I'm confused about the different types of repair plaster: lime plaster, gypsum plaster, plaster of Paris (still gypsum?). I've even heard some plasters can be fixed with drywall joint compound.

My walls are 3/4" thick: 3/8" plaster coat over 3/8" rock lath. There's a visible paper layer at the mid point.

Given the age (1935) and type (rock lath), what repair materials and techniques should be used to repair the cracks?
 
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Old 08-30-16, 02:41 PM
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I generally scratch out the crack and fill it with a setting compound like Durabond.

There's a visible paper layer at the mid point.
Can you better describe that or better yet, post some pics.
 
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Old 08-30-16, 03:14 PM
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Can you better describe that or better yet, post some pics.
If one were to say cut a hole out of the wall with a hole saw and then look at the "cross section view" one can see a thin layer of brown paper at the middle (3/8" from either edge) which I assume is the backing paper of the lathe, just like modern drywall or blueboard (modern rock lath) has paper facing/backing.
 
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Old 08-30-16, 03:24 PM
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I don't know when it first came out but they used strips of 3/8" drywall for lath before blueboard, perhaps that is what it is. If so, the paper is the face of the gypsum lath.
 
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Old 08-30-16, 04:48 PM
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You are describing gypsum plaster over gypsum lath, a very good, durable system.

How wide and how deep are the cracks? Do they follow the lines of the lath?
Put up some pictures of the cracks and we can be specific on the kind of fix.
 
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Old 08-30-16, 09:53 PM
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Some are indeed along lath lines based on the spacing or around windows. Others seemed to form after leaks due to ice damming.

I'll try to get some pics up tomorrow.
 
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Old 09-02-16, 06:50 AM
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Sorry, I haven't gotten pics yet.

So given tightcoat's confirmation of gypsum plaster on gypsum lath and marksr's suggestion of durabond, would a procedure like this be appropriate?
 
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Old 09-02-16, 08:27 AM
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That's decent info I've never owned/used a crack opener, the edge of a putty knife or screwdriver has always worked well for me. I don't always tape the cracks as it isn't always necessary although that does provide more insurance that the crack won't come back.
 
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Old 09-03-16, 08:42 PM
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Good idea EXCEPT screws will not hold in gypsum lath. Where the crack is over a stud they will hold if needed. Countersinking the washer will make for a flat repair. At a cursory glance the rest of the information is right on.
 
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