You can put certain types of plaster over other types, but doing so isn't always the best idea. For example, putting a coat of gypsum over lime plaster is possible, but doing so will limit the lime plaster's breathability and potentially affect its performance.

Since cement plaster tends to leave a textured surface, no matter how much you smooth it, some people prefer to use gypsum plaster as a topcoat over cement plaster, creating a smoother surface.

Depending on the place where the cutting error occurred, you may be able to fix it. Learning how to patch a hole in drywall is challenging, but if you can tape and mud drywall, you can do it. Having said that, patching is time consuming. Early in the installation process, you may find that it’s easier and far less time consuming to just start over with a new sheet of drywall, cutting a new hole in the right spot. You may be able to use part of the incorrectly cut piece elsewhere, so it’s not completely wasted.

You can technically just paint over hairline cracks in plaster since these cracks are often harmless, but this will mostly be a waste of paint. Paint will only hide the hairline crack for a few months before it shows up again. The best solution is to repair the crack with flexible filler or joint compound before repainting.

Although they are used for similar tasks, spackle and joint compound are not the same. Joint compound, also known as drywall mud, consists of limestone and gypsum and is primarily used for large-scale projects like taping and finishing seams on new drywall. Spackle is composed of gypsum and binding agents, making it a thicker compound best suited for small wall repairs like filling nail holes or cracks, as it dries quickly and is easy to sand. For small repairs, either product can be suitable. However, you can use joint compound for small jobs in place of spackle, but you cannot use spackle for large-scale taping and mudding projects.