I remember visiting a job site some time ago during the plastering stage. I noticed that the plastering crew had removed the protection around the windows and the floor where it meets the wall. They had done this so that they could remove any debris from around the tape that was in place from the scratch and brown coats and thus apply a clean finish coat to the wall.
This is a good idea as the little bumps of dried plaster can actually contaminate the finish coat quite easily. Remember that when you scratch the first coat, there will be a lot of debris left on the surface once those scratches dry. Similarly, when floating the brown coat, sand grains and other material can ball up and dry on the surface.
If you don’t knock those pieces off of the wall, especially where they might be stuck to the tape around windows, etc… you can end up with these dry contaminants in your finish coat. Now, removing the tape as mentioned above is a great idea, yes; however, the plastering crew had begun applying the finish coat of plaster without replacing the window and floor protection. This is not a good idea at all.
In the areas the plasterers had already applied the finish coat, I found a number of places where the plaster had landed on the windows (wood frames with clear coat finish) and on the finish concrete floor (yet to be stained). I informed them that they would need to clean up the mess they had made under the supervision of my project manager and that they needed to tape everything off before they continued to plaster.
It seems common sense to tape off before plastering, but don’t always count on common sense prevailing when you are not on the site to supervise. I make it a rule to be on site at least three times a day if I do not have my own crews there with a project manager. In other words, either my project manager or I will visit each site in the morning, after lunch, and in the afternoon before quitting time. Catching a mistake while it is still small is well worth the effort.