Cracks are simple to repair. You will need a four, six and 10 inch flexible drywall taping knife and/or broad knife. A drywall mud pan or flat plaster?s hawk will be necessary as well. These two things hold the plaster so you can work with it.
Start the repair process by removing all loose plaster. Mix up some joint compound. Mix until all lumps have disappeared. Pre cut pieces of paper or fiberglass tape to cover the cracks. If the crack is curved (many are!) then you will need several smaller pieces to make the curve.
Apply a 1/8 inch thick layer of joint compound over the crack with your four inch knife. Embed the tape into the wet compound. Drag the knife across the tape and remove half of the compound you applied. If you remove too much the tape will blister on the second coat! If you leave too much, you will have a giant hump!
Once the compound has set up (becomes hard) you can apply a second coat to hide the tape. I like to use the six inch knife for this job. I also use the 10 inch knife as well. You are trying to add just an additional 1/16th inch over the top of the tape. The larger length knife allows you to taper the compound so the hump is disguised.
When this coat hardens you can apply the third and final coat. Before you do this, it may pay to scrape off any high spots or use a ceramic tile rubber grout float to smooth out high and low spots. Slightly wet the dried or hardened joint compound and glide the rubber float over the patch. With just the right touch you will get ultra smooth results.
