| Jim Burkhard |
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| #1 |
I'm in the middle of re-drywalling a kitchen (5/8" firecode) and was planning to again use Master of Plaster for skim coating when I am done. I've done this many times in the past (for 10 years now!) over *old* work (existing walls, both plaster and drywall) and new plaster (Structolite) and it's always came out great and lasted well. This time it's a little different in that I'm putting up NEW drywall and will be taping all those joints. [yeah, I'd rather build new plaster walls out of structolite as I've done in the past, but the Mrs. wants her kitchen back ASAP so I grudgingly consented to using drywall as long as I got to skim it with M.O.P...]
I see in the Master of Plaster instructions that they tell you to tape the joints & screws holes with mesh tape and bring everything to level with M.O.P. base coat first prior to overall skimming with M.O.P. basecoat again.
I'm wondering if it is *instead* permissable to tape the joints with conventional joint compound and when finished use M.O.P. base + finish for the OVERALL skim finishing of each wall? I wouldn't bother sanding the joint compound prior to this, since the final step will be to skim the whole wall with M.O.P. anyhow.
I ask for 2 reasons:
1. The joint compound is a good bit cheaper than M.O.P. I'd go through a lot of M.O.P. just bringing all the tapered joints to level. It seems like a waste of really good M.O.P for this part of the job...
2. While I wouldn't want to skim a whole wall with it, joint compound is pretty well proven for use on drywall *joints* and that's all these are really. If M.O.P. does fine resurfacing old drywall (which was been taped with conventional joint compound years earlier), why not over new construction that has also been taped with normal joint compound?
If this is a bad idea, please explain why.
Thanks very much!
Jim Burkhard
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| Clarence Bauer |
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| #2 |
Yes you can use joint compound for leveling and taping joints.
If this is what you do be sure to prime the compound areas with a primer so the MOP will not soften the joint compound and cause a failure.
I have used MOP with many products with very good results.
I even mix MOP with USG Structo-Lite and use it for leveling and joints works very well (mix 50/50) no primer required.
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| Jim Burkhard |
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| #3 |
Clarence, thanks for the speedy reply!
I forgot to mention it, but yes, I had thought about the risk of softening the joint compound by applying M.O.P. directly over it.
To avoid that risk, I had been planning to use a setting joint compound instead of a drying compound. If I use setting joint compound for leveling / taping will that get me out of the need to prime all the joints prior to M.O.P. overall skim? I'm thinking the setting compound should be safe from resoftening with water, right?
Also, if I use the setting compund, will bedding in paper tape be OK instead of mesh? I can understand not using paper tape with MOP itself, but with the setting compound, I was thinking it should be OK as long as it had a layer of setting compound over it, right? My general feeling when working with drywall joints is that the paper tape is a bit more long term crack-proof than mesh, so I should use it if I can.
Thoughts on this? Is it OK to tape and level with setting compound and paper tape, then skim the whole wall with M.O.P. without a primer step?
Thanks!
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| Clarence Bauer |
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| #4 |
Setting compound should work.
The only thing that would effect the bond or softing is the drying time if it is cool and moist it could soften the setting compound.Try a area first see if it works.
Yes you can use paper tape.
Tape and level with setting compound is ok.
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| Kevin McGovern |
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| #5 |
Ive used the mop many a time over new unprimed drywall with newer a failure.Even when the wall was taped with compound as a first or second coat the mop finished it off great |
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| Clarence Bauer |
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| #6 |
Yes Kiven is correct you can use MOP over many surfaces.
The reason I say to prime over joint compound or other fillers is the MOP product is not affected by water when it is being troweled it will only make it smoother.
But excess water could effect the the underlying material.
If you know what you are doing when using a true plaster material you can mix mop with most gypsum products and achive great results.
I have mixed it with Moulding plaster, Hydro-Cal and Hydro-Stone this will cause it to set rapidly and it will be harder.
I have mixed it with cement and used it on the exterior of buildings.
I mix it with Structo-Lite plaster and use it as a filler.
Keep in mind that MOP is lime and any gypsum or cement Product requiring the addition of lime, than MOP can be added which will also increase the bonding.
I have used many truck loads of MOP materials with no failures in the past 15 Years.
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| Brian |
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| #7 |
Does MOP bond properly with a flat sheet of drywall with no keys? |
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| Clarence Bauer |
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| #8 |
Yes Master of plaster will bond to sheet rock.
When you say drywall you do mean board with a gypsum center and a paper face.
Master of Plaster will bond to all of the following.
Sound painted plaster and gypsum board.
Cement board, new sheet rock,new or old plaster.
When patching plaster or gypsum board it is used to skim the complete area so as to conseal a patched area.
I have used Master of Plaster over new and old CMU.
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| Brian |
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| #9 |
Out of curiosity, why do people use a gypsum skim coat over blueboard when lime plaster over regular drywall will work? |
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| Clarence Bauer |
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| #10 |
The blue board is a USG product called Imperial board it has a special paper facing to receive USG Imperial base coat and a Diamond finish coat when a two coat veneer plaster system is called for.
You can also use the obove and omit the Imperial base coat and just apply the USG Diamond finish this would be a one coat system.
Gold Bond has the same type system called Kal-Kote and the Gold Bond board is called Kal-Board.
There are some brands of Veneer plaster that may be applied over regular gypsum board and some of these require a bonding agent or other primer over the gypsum board.
Master of Plaster is the only one that I know of that does not require a bonding agent and there may be others that don"t require the bonding agent I have not used anyother veneer plaster that is as user freindly as MOP.
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