Plaster Misc Questions

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Old 04-11-09, 01:56 PM
J
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Plaster Misc Questions

Hello;

Does it matter how long plaster sits between coats, i.e. Scratch to brown to finish, is it ok if it sits a few days between coats as long as it is keyed, will the next coat just grab into the keys? Should it just be sprayed down a little bit to make sure the next coat doesn't get all the moisture sucked out of it?

Are Gauging plasters just Finely ground pure Plaster of Paris with a Retarder and some sand added? I have that moulding plaster, which is suppose to be just finely ground POP and nothing else. I also have a retarder. I may be able to get someone to order some Gauging plaster for me to use as a base for my other rooms. Kal-Kote has gotten to be kind of expensive at $17 a bag. My understanding is that mixing up gauging plaster on site with sand is much cheaper.

Is it ok to use Ivory Lime for Portland Cement plaster? How is the finish coat made for Portland Cement plaster? The Portland Cement plaster is just something I am playing with for landscape work and possibly for my basement walls. The Portland Cement bag has direction for making scratch and brown coats with Lime and sand, I did that and tried it, and it seems to have worked. But I can't figure out how to make the finish coat or what to use for a finish coat over Portland, can you use a lime / portland mix, like you would with lime and gauging for inside walls?

Thanks again,

Jamie
 
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  #2  
Old 04-11-09, 04:00 PM
T
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Hello;

Does it matter how long plaster sits between coats, i.e. Scratch to brown to finish, is it ok if it sits a few days between coats as long as it is keyed, will the next coat just grab into the keys? Should it just be sprayed down a little bit to make sure the next coat doesn't get all the moisture sucked out of it?

Within reason it doesn't matter except it will suck the moisture out too quickly if it sets too long. Too long might be overnight or a few days As long as the plaster is clean it can keep weeks or months. Yes you can spray it down a little. If you can, do it a while before you finish so it has time to even out a bit. Now are you putting this over a thin coat of VP base over blue board or a thick coat of scratch and brown? The two coat system can soak up more water than the thin one coat system. Get it moistened evenly. That is most important

Are Gauging plasters just Finely ground pure Plaster of Paris with a Retarder and some sand added? I have that moulding plaster, which is suppose to be just finely ground POP and nothing else. I also have a retarder. I may be able to get someone to order some Gauging plaster for me to use as a base for my other rooms. Kal-Kote has gotten to be kind of expensive at $17 a bag. My understanding is that mixing up gauging plaster on site with sand is much cheaper.

Most gauging plaster has no sand in it. It is intended for mixing with lime putty to make whitecoat. The moulding plaster will work for that but it will set awfully quickly. Use retarder with care. A little goes a long way. I don't have any experience in retarding moulding plaster. If someone can order gauging they should be able to order hardwall plaster like RedTop or Two Way Hardwall. That is a better basecoat than trying to use gauging. I don't know what kinds of working time or what sand ratios would work for scratching and browning with gauging. I bet it will get hard though.

Is it ok to use Ivory Lime for Portland Cement plaster? How is the finish coat made for Portland Cement plaster? The Portland Cement plaster is just something I am playing with for landscape work and possibly for my basement walls. The Portland Cement bag has direction for making scratch and brown coats with Lime and sand, I did that and tried it, and it seems to have worked. But I can't figure out how to make the finish coat or what to use for a finish coat over Portland, can you use a lime / portland mix, like you would with lime and gauging for inside walls?

To make a finish for Portland cement plaster you usually add a bit more lime than for scratch and brown and depending on the desired texture or finish you might want to use either a little less sand or finer sand.

For interior walls it works just fine. You don't use it over gypsum lath, however but over metal lath or over woven wire reinforcement like 17 ga stucco wire or 20 ga chicken wire, (a less preferable choice but it is done) with a moisture resistant paper behind the lath or wire. Portland cement plaster is called stucco on exteriors. You can also apply it over concrete block if it hasn't been painted. You might get different suction over the mortar joints and the field of the block. Straighten and float carefully to keep from getting holes and humps.

You can also plaster over Portland cement but not Portland cement over plaster. And Keenes does not work over Portland. I don't know why but I tried it once and the literature is right.

If you want to avoid painting the interior Portland cement plaster for at least a while you can color the finish and use white Portland to get a truer color or pastel shades.



Thanks again,

Jamie[/QUOTE]
 
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Old 04-12-09, 12:11 PM
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Originally Posted by tightcoat View Post
Now are you putting this over a thin coat of VP base over blue board or a thick coat of scratch and brown? The two coat system can soak up more water than the thin one coat system. Get it moistened evenly. That is most important

Thank you for all the information. In much of the Kitchen, where you saw the photos of the large area I patched (blue ceiling), I put plaster weld over this entire ceiling on Thursday morning, then put about 3/8" of Kal-Kote over the entire ceiling. The Larsen Plaster Weld said you must use a base coat that is a minimum of 3/8" thick if you are doing a 2 or 3 coat system. So we did 3/8", a few areas I can see we didn't make 3/8" thick, so I might have to put a new dap of plaster weld on thoses.

I am going to put some more Kal-Kote on this ceiling tommrow morning to get it all leveled out, it looks quite dry to me at this point. I think it all cured well, as it looks consistant and is quite hard. I kept the room very humid and around 70 for the first 48 hours after we aplied it, by that time it all looked well cured and dry. I brushed the entire ceiling with a wallpaper style brush while it was still wet.

Since I am dealing with about 3/8" thickness, am I going to need to get that fairly wet before I put the next layer of Kal-kote on it so it doesn't suck out all the moisture.

Once my brown coat is complete and the ceiling is completely true and level, and ready for the finish coat, do I still want to lightly brush the brown coat so the finish has something to bite into or is the sandy texture of Kal-kote good enough as long as it isn't over troweled?

Thanks very much,

Jamie
p.s. A couple things I learned about Kal-Kote that were helpful, National Gypsum told me I have to mix full bags at a time of Kal-Kote or thourghly dry mix it otherwise I will get inconsistant results. After numbers smaller batches, I do belive this to be true with there product. What I finally did that made the difference and allowed me to work with full bags was to get the retarder from National Gypsum and slow it down to about 1 hour of working time. I used the percise amount of retarder as directed by there technical services and it does not seem to have adversly affected the finished product.
 
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Old 04-12-09, 07:04 PM
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The reason you want a moist wall is to make finishing easier. If you can work it without wetting it so much the better.
The way I understand bonding agents work is by sticking to the substrate then slightly reimmuslifying when the moisture from the plaster softens it up a little thus gluing the new plaster to the bonding agent which in turn is stuck to what is there so it stays up. the risk is that when you wet down the brown coat the water will soften the bonding agent again and loosen the whole thing. I think that is why they want a minimum 3/8 of plaster so it doesn't soften from the moisture in the finish. Now if you are using keenes to finish with you will probably get along without wetting the base coat. Spread on a tight coat of Keenes to kill the suction then double back with a second coat to bring it to thickness and lay it down nice and smooth. you can go over it yet again to fill in the imperfections then water trowel it through its set and you should have a perfect job. Ideally, you do this with all one gauge. By now you should have an idea of how much gypsum plaster to add to how much Keenes to give you enough time to work it out so it sets and the same time you are finished with the job and still have some energy and shoulder left.

Now we haven't dealt with this but you can do parts of jobs in a batch then make a joining with the finished work. If you think you want to do this let me know and I can tell you how to do it. It takes a lot of words to describe it but it isn't that complicated to do. If there is the capability to search my posts here you can find where I have described how to do a patch and have it come out exactly even with the surronding existing work. You do a joining the same way.
 
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Old 04-15-09, 09:33 AM
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Originally Posted by tightcoat View Post
The reason you want a moist wall is to make finishing easier. If you can work it without wetting it so much the better.
The way I understand bonding agents work is by sticking to the substrate then slightly reimmuslifying when the moisture from the plaster softens it up a little thus gluing the new plaster to the bonding agent which in turn is stuck to what is there so it stays up. the risk is that when you wet down the brown coat the water will soften the bonding agent again and loosen the whole thing. I think that is why they want a minimum 3/8 of plaster so it doesn't soften from the moisture in the finish. Now if you are using keenes to finish with you will probably get along without wetting the base coat. Spread on a tight coat of Keenes to kill the suction then double back with a second coat to bring it to thickness and lay it down nice and smooth. you can go over it yet again to fill in the imperfections then water trowel it through its set and you should have a perfect job. Ideally, you do this with all one gauge. By now you should have an idea of how much gypsum plaster to add to how much Keenes to give you enough time to work it out so it sets and the same time you are finished with the job and still have some energy and shoulder left.

Now we haven't dealt with this but you can do parts of jobs in a batch then make a joining with the finished work. If you think you want to do this let me know and I can tell you how to do it. It takes a lot of words to describe it but it isn't that complicated to do. If there is the capability to search my posts here you can find where I have described how to do a patch and have it come out exactly even with the surronding existing work. You do a joining the same way.

Thank you, Now I see exactly what you mean about the dry plaster sucking the moisture out of the new coat. I just posted a new message in this forum with some photos of how the base coat is looking.

Thanks

Jamie
 
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