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Appreciate the help, restoring 1978 house on a slab in Texas - no shifting / settling history. Few years ago replaced 5/8 sheetrock ceiling section 10 x 40 by cutting out damaged setion, sistering a 2x4 to 2x12 joist, attached with screws and paper tape and regular mud. Got a minor crack where 10 foot section joins existing. Considering soaking/scraping existing mud away
and using fiberglass tape. Heard I should use "fortified mud" but don't know what that is and don't find it except as related to tile grout? Any ides will be appreciated.
 

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TomTom,
You'll probably get a dozen different ways to do this, but here's mine anyway. Scrape away the joint and try and get down to the original sheeting under the paper tape, in other words, get the paper tape out. Do you get any flex between your new section and the existing ceiling? If so, you really need to take care of that first. I use the ultra-thin nylon mesh tape. I have taped whole garages, basement remodels, and additions with it. I have not had any problems with it. I don't use paper tape at all anymore. The fortified mud is probably referring to the dry mix compound you can get anywhere. I use Easysand by USG. It is available in different setup times, 20, 45, 90, 120 minutes etc. You really have a bout half the time listed on the bag to work with it. It dries by chemical reaction and is harder and stronger than premixed compound. I generally use it for the first two coats of mud then use premixed USG 'Dust Control' for the final coat.
Mike Hawkins:)
 

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If it cracked then more then likly something moved.
Undersized joist, not enough screws, trying to use the area above it for storage, ect.
I've never once seen a pro sheetrocker use webbed tape.
 

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what is the spacing of the joists the ceiling is attached to? 5/8" is typically for 16" o.c. spacing ..... in my area 1x3 at 16" o.c. strapping is installed under the joists so that the ceiling is level (by shimming the 1x3) different strokes for different folkes
 

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I was wondering what was meant by fortified mud?
In reality, I think paper tape and regular mud should work fine.
If it cracked out again, this suggest something is moving and should be fixed.

I like to use Fiberglas tape and hot mud for first coat. Some 45 min mud gives you chance to get 2 coats first day.
It also has more body as it cures, just dries harder and works better in some situations.
But if a ceiling patch and it cracked out with regular mud, changing the mud is not the cure.
 

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"In the case of paper tape, approximately 30 lb./lin. in. of tensile force (pulling apart) is required to break the tape with no measurable movement or elongation (no stretching). On the other hand, glass-fiber tape elongates
(stretches like a rubber band) 0.03" before reaching maximum or breaking load of 70 lb./lin. in.
Research investigation has shown that hairline cracks or nail pops are visible at 0.01" of movement with veneer plaster system joints treated with glass-fiber tape. Actual load at that amount of movement is only 20 lb./lin. in. or about 30% less than the breaking load of paper tape (with no movement). As such, paper tape provides greater joint strength and is recommended where greater movement and shrinkage is anticipated." From; http://www.usg.com/rc/technical-art...laster-joint-reinforcement-systems-en-PM5.pdf

The cross-fiber construction are important in both fiber and paper tape strength: http://www.usg.com/rc/data-submitta...tapes-industrial-construction-data-MH1178.pdf

The setting-type compounds are unaffected by humidity, perfect for bathroom use; http://www.usg.com/sheetrock-durabond-setting-type-joint-compound.html

Gary
PS. welcome to the forums!
 

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In my experience I do not use mesh tape for anything but small repairs. I know there are guys out there that use it to mud whole houses. From what I have read and seen if there is ANY movement mesh tape will crack. on drywall talk there is a big debate on mesh versus paper maybe go there and use the search engine for mesh vs paper and see what the pros say. On the quick setting muds be careful if you get the stuff in the brown bags it is not sand-able and the easy sand only means it's easier than brown bag. On the times if you mix with warm water it cuts the setting time way shorter if you use cold water you pretty much have what it says on the bag or longer. And as for the strength of mesh that is for long ways if you pull corner to corner there is very little. There is a new product out called fibra fuse I have not used it personally but the reviews seem really promising. And of course this is all my personal opinion.
 
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