Plaster-ceiling finish coat

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  #1  
Old 03-22-05, 11:19 AM
Brendan
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Plaster-ceiling finish coat

Wire netting stapled over wood lath

(1 part gypsum to 2 parts sand)

The next step was the gypsum & sand mixture was applied almost flush to the rest of ceiling.


(1 part Red Top slow set gauging plaster to 2 parts Ivory autoclaved finish lime)

Then, ceiling was sprayed with water and this mixture was applied flush with ceiling in most areas. After sanding, the ceiling needs a thin finish coat. However, I am not sure which product(s) to use. I have tried several times to finish with the same mixture of 2 parts lime, 1 part plaster, but it will not apply over previous coat of the same mixture. It simply crumbles and falls off leaving rough patches, which are far from a smooth finished coat. What should I use to achieve a thin, smooth finish coat?
 
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  #2  
Old 03-22-05, 04:38 PM
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It sounds like you did everything right. When you stapled the mesh over the lath you used long enough staples to go into the joists didn't you?

Did you mix the lime a day or two before and let it soak? This isn't strictly required with autoclaved lime but it does make it more workable. Now I mean the lime only. You should gauge the whitecoat on a board or in a bucket. You must not have done it quite right if you needed to sand. Probably you didn't trowel the whitecoat through the set. Had you done it right it would have been as smooth as glass.

But you want to know what to do now. I think go over the patch with some EasySand. Give it a pretty tight coat then after it has set give it another coat. Then let it dry completely not merely set Then sand with fine sand paper or screen. Then wipe it down with a smooth damp rag and prime and paint. The hard part is getting the lap from the new to the old work smooth and down to microscopic nothing. That is what the whitecoat finish was supposed to do. You were supposed to work it exactly flush with the existing finish by troweling it and keeping the old work clean.


FYI the mixture of lime and gauging is known as whitecoat.
 
  #3  
Old 03-24-05, 10:12 AM
Brendan
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Over whitecoat

Thank you for the response. This project has been my first experience working with plaster. However, I'm experienced with modern day techniques of drywall tape and mudding. Which is what I intent to use as a final coat over the whitecoat. I would like to use the premixed 5-gallon. It gives a smooth coat, and requires little sanding, even though it takes a little while to dry. I have never applied this over a whitecoat. Would this be okay or would you suggest a different product, prime first, etc.?
 
  #4  
Old 03-24-05, 07:34 PM
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I defer to the drywallers among us. I think, however that once the plaster is dry that you should prime first. Awesome or Coops will tell you better. I would have the lid ready to paint with nothing other than the plaster.
 
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