Plaster Help

I am repairing several plaster walls in my home due copper re-piping. The original plaster walls used a 3/8" drywall backing with random " diameter holes so that what looks like stucco could bond. Then the finish coats of plaster were then applied to what looks like stucco. This system resulted in a " thick plaster / stucco / wall. I have repaired some walls that were not visible by installing " and " drywall and then taping and mudding. However, the finished product does not look as good as the plaster. I want to repair the walls with plaster on the walls that are visible. My intention is to duplicate the same system that was originally used. However, I may use " dry wall to start the process. I have never done plaster but have plenty of drywall experience.
My question is this what do I use the build up the wall. Are my suspensions confirmed in that it is stucco that is bonded to the original drywall backing? If not what do I use the scratch coat? After reading several articles on how to plaster they state to use a scratch coat, a brown coat and then a finish coat (skim coat). I want to build the wall back up to match the others then using a bonding agent will apply a brown coat and a finish coat to the entire wall. I just do not know what material to use for the scratch coat. It does not seem right that I would use finishing plaster for the scratch coat.
Thanks in Advance, Jim
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I am repairing several plaster walls in my home due copper re-piping. The original plaster walls used a 3/8" drywall backing with random " diameter holes so that what looks like stucco could bond. Then the finish coats of plaster were then applied to what looks like stucco. This system resulted in a " thick plaster / stucco / wall. I have repaired some walls that were not visible by installing " and " drywall and then taping and mudding. However, the finished product does not look as good as the plaster. I want to repair the walls with plaster on the walls that are visible. My intention is to duplicate the same system that was originally used. However, I may use " dry wall to start the process. I have never done plaster but have plenty of drywall experience.
My question is this what do I use the build up the wall. Are my suspensions confirmed in that it is stucco that is bonded to the original drywall backing? If not what do I use the scratch coat? After reading several articles on how to plaster they state to use a scratch coat, a brown coat and then a finish coat (skim coat). I want to build the wall back up to match the others then using a bonding agent will apply a brown coat and a finish coat to the entire wall. I just do not know what material to use for the scratch coat. It does not seem right that I would use finishing plaster for the scratch coat.
Thanks in Advance, Jim
Jim,
If you're doing gypsum plaster over gypsum base, you need to use a plaster base like rocklath. You can't just use regular drywall because the plaster won't bond as good. For the scratch and brown coats I've used Red Top plaster from USG. For the scratch coat use 2 parts sand to 1 part plaster by weight. For the brown use 2 1/2 sand to 1 plaster. Be sure to rake the first coat ( scratch ). The brown coat doesn't need to be scratched. It should be level and straight but rough enough for the finish coat to bond. For the finish you can use either Red Top Gauging or Red Top Finish plasters. If you use the gauging plaster, you have to mix it with lime putty. The other you just add water. Hope this helps.
Tim
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