You can repair water-damaged walls and ceilings yourself, depending on the extent of the damage. Signs of water-damaged walls and ceilings include cracking and crumbling, peeling paint or discoloration, or drywall tape that's hanging. You can repair this kind of damage easily. But, if there are large holes in your walls, clear down to the lath, which is the strip of wood that's nailed to the joists or studding, the repair is somewhat more complex.
First thing is to visuallly inspect the walls or ceiling to get an idea of the extent of the damage. If your walls and ceilings do show signs of water damage, it would be a good idea to first determine what is causing it so that you don't waste your time repairing the wall or ceiling only to have water seep back in and ruin them all over again. Water damage can happen for many reasons, and it would be prudent to pinpoint the source. For example, if you see water marks on the ceiling of your two-story home, the cause could be a bathtub, sink, toilet or vent above. Any drywall that has become spongy or soft will need to be replaced, whether it's a wall or a ceiling. That's not difficult to do because it's easy to work with drywall as it cuts and breaks easily. Drywall is the plasterboard panels that are used to make interior walls and ceilings. Drywall has largely replaced plaster walls and ceilings as a speedier and more cost-efficient alternative. But, it can become unsightly when wet because it has a paper backing that will crumble.
After you've located the source of the problem in both your walls and ceilings and have taken care of it, it's best that you waste no time in fixing the damage because other problems, such as mold and structural damage, can occur if you let it go too long. So, whether you decide to make the repair yourself or hire an expert, time is of the essence.
Your drywall repair kit should include, at the very least, a bucket, a sponge, sand paper, paper towels, a putty knife, utility razor knife, drywall tape and drywall compound (or mud as it is sometimes called), which comes in tubs. The two most common types of drywall compound are lightweight and all-purpose. The compound does have a shelf life, so make sure you don't buy more than you need. If you are unsure of the type of compound to use, ask the salesperson. Drywall tape can be either paper tape, which will need an undercoat of the compound so it adheres to the drywall, or self-adhesive drywall tape, which has the advantage of not needing a coat of spackle or compound underneath it. Also, you will need knives in a variety of widths (for instance, 3- , 4- and 6-inch knives for taping and finishing small patches, 8-inch for larger work, and a 12-inch knife for the final application of the compound). You can find everything you need in any home improvement store, such as Home Depot, Sears or Ace Hardware.
Depending on the extent of the repair, you may also need inside-corner and utility knives, hammer, screwdriver, a drywall saw, stud finder and drill. If you need to do extensive drywalling, which hopefully will not be necessary, you will also need the following:
For small holes and cracks in walls, a simple patching job is all that's needed. First, take your sandpaper and sand the area to be patched to remove the rough edges. Then, place a large enough piece of the mesh tape, the kind that does not need an undercoat of spackle, over the hole. Press the spackle along the edges of the tape. Finally, take a larger knife and roll over the area to smooth out the spackle. Allow to dry. Then prime and paint.
For deeper holes, it is necessary to patch it with drywall and tape, otherwise the hole could collapse due to lack of support. Cut a piece of drywall that will cover the hole. If you use the paper tape, apply a first layer of compound, making sure it is enough to make the tape stick. Then, apply the tape over the seams, which are the cut edges, and embed into the compound. While the compound is still wet, apply a second layer about 1/8-inch thick to cover the tape completely. Glide the blade of the knife tightly over the surface to squeeze the compound from under the tape so you end up with a nice, flat finish. Remember, fiberglass self-adhesive mesh tape does not need the undercoat. Simply apply the tape, then apply the compound, again taking care you create a flat, neat finish.
For more extensive jobs that require replacing drywall that has been ruined, the repair gets a little more complicated. First, you must locate the wall studs with a stud finder. This will determine where you cut out the drywall. Remove the damaged drywall with a saw in a shape that is easily replaceable, such as a perfect square or rectangle. At this point, you will want to look for the cause of the water damage and correct the problem. Remove and replace wet insulation (that pink stuff), if necessary, from walls and ceilings. Allow the walls or ceiling to dry out if wet. You can use fans for this.
After the wall is sufficiently dry, vacuum the debris and dust. Then, replace the drywall by cutting a piece that's the same size you removed. You can trace the old piece as a guide. For further reinforcement, you may want to insert a backing piece, such as a piece of wood, onto which to attach the new drywall. The backing piece should be screwed into surrounding studs or drywall.
Now, take the new piece of drywall you have cut and attach it, making sure that the fit is as tight as possible. Tape about 1-inch past the drywall seams (again, seams are the cut edges), and apply multiple coats of compound 1/8-inch thick and six inches out over the taped area. Allow each coat of compound to dry before applying additional coats. It could take up to 24 hours for each coat to dry, so this is not a one-day process. Once the compound is dry, it is ready to be sanded.
After you are done with the repair, it's time to finish the wall or ceiling with primer, then paint, wallpaper or other finish to match the rest of the wall or ceiling, unless it is a tile ceiling.