Plaster Man's Q&A
Question: When plastering over a basecoat, how do you stop the smooth coat finish from drying so rapidly? Also, if you notice a bubble or blister while applying the smooth coat, what is the best way to deal with these problems?
Answer: I've found that doing the smooth coat the same day I apply the basecoat gets the best results. The basecoat still has moisture in it and this makes the smooth coat easier to apply and spread over the surface. The smooth coat also takes up slower. Dry basecoat is the biggest challenge as it tends to pull the moisture out of the smooth coat, making it stiff faster and hard to finish out. If you have to go over dry basecoat, fog it down with a pump sprayer to add moisture to the surface before applying the finish. That should help quite a bit.
As far as blisters or bubbles, these usually occur when the surface has a lot of moisture in it. Different smooth finishes will react differently. One important point to keep in mind is that it's best to concentrate your energy on getting the finish coat as smooth as fast as you can. In other words, don't spend a lot of time trying to trowel out the blisters or bubbles. These can be troweled down at the very end when the smooth coat sets. Get the smooth coat smooth, then you can do a final troweling to make the bubbles or blisters disappear. I wish you much success!