Walls – Fix a gap in flashing

The right answer is to fill them with spackling compound or taping compound.

Spackle dries hard - applied with a putty knife and then has to be sanded to remove excess and flatten surface. There are various flavors including lightweight, fast drying, purple-stained until it dries, etc.

Taping compound is also applied with a putty knife. It is water soluble and can be wiped with a sponge to level and remove excess (probably the easiest correct solution). Not as hard as spackle, but in a hole of that size, not an issue. Slightly harder to get a perfectly smooth surface.

If you are really in a bind and cannot go out and buy the right stuff, a common quick fix is plain white toothpaste. It consists of about 50% aluminum hydroxide and/or calcium carbonate - the kind of stuff you find as filler in real fillers. Won't cause significant problems, but does not set up as firm as correct patches. Can be applied with a finger, a butter knife or whatever. Not pro, but fast.

All such patches will be white or off white. They may stand out unless painted (depending on wall color). Most of these fillers can be tinted but if painting will follow, not an issue.

SUPPLEMENT: Two other variants on spackle are painters' putty and painters' caulk. Both are less hard than traditional spackle and usually come in bigger containers or caulk gun tubes.

There are a few options that can be used to repair this damage. You can use standard joint compound (non-lightweight), and apply it in thin coats to avoid cracking due to shrinking, joint compound mixed with plaster, or professional grade oil based drywall spackle.

The first step would be to dry the wall and inspect it for mold. If there is any surface mold present, you can kill it with a bathroom cleaner that has bleach in it. After the surface has been cleaned and dried out thoroughly, you would want to apply a stain blocking primer like Kilz. This will give you a good surface to bond the repair to. You can then apply the drywall filler of your choosing. You may need to apply it in several layers to get a good result.

Once you are satisfied with the repair, then you can begin to prepare the wall for paint. I suggest priming the wall with an interior/exterior grade primer that will be able to stand up to the moisture. 2 - 3 coats should be enough for good coverage. I also recommend that you extend the primer past the damaged area to ensure that the same problem won't reoccur. If you can, prime the whole area around the shower. After it has been primed, then you can apply the top coat. A good idea would be to repaint the entire bathroom with paint that is made for kitchen and bathrooms. This kind of paint will resist water, and can easily be cleaned. Many brands are also resistant to mold.