the painted surface
How To Repair Water Damage and Stains On Drywall
Water damage and stains on drywall are usually the result of a leaky roof or plumbing fixture. Minor damage and stains can easily be repaired. When the damage is not severe enough to require the replacement of the damaged wallboard the following steps will lead you through the repair. The photo to the right shows a water stain but there was also loosened drywall mud and paint which is hard to see.
First make sure the drywall is still attached to the studs or framing. If the wallboard is sagging or broken it will need to be replaced. There may be blistered paint or loose layers of drywall mud but the wallboard itself is solid and secured to the studs. If the wallboard is sagging slightly try to snug it up using drywall screws. Start at the outer edge of the sag. Make sure the screws go into the studs and try not to break through the surface of the wallboard. Work slowly toward the worst part of the sag using the screws to pull up the board.
With the wallboard secure scrape off loose layers of drywall mud and paint. The moisture will have caused the mud and paint to lose its adhesion. Scrape outward until you feel these coatings are solidly attached. A putty knife with a sharp edge is a good tool for this job.
If any mold or mildew is present wipe the surface with alcohol or a solution of chlorine bleach and water to kill the mold. Check out “Mold In the Home” for more help with mold and mildew problems.
Water damage will cause a stain to appear on the drywall. This is usually the the first sign of a problem. The stain will bleed through the finish paint if not sealed. Several paints will seal drywall and are labeled for this purpose. You will find paints or primers in water, oil and alcohol(shellac) bases for sealing water stains. It has been my experience the oil and alcohol(shellac) base sealers work the best. They can be brushed or rolled on and usually dry quickly. Most stains will cover with one coat. Two coats will cover for sure and it is easier to apply the second coat now than later when the stain has come through the finish coat. The seal coat not only prevents bleed through but also provides a clean, dust free surface for any patching materials. The photo below shows how the stain was sealed over prior to applying the first coat of mud. The drywall mud shows up dark while it is wet.
To smooth the surface multiple applications of drywall compound are applied. Drywall compound can be bought pre-mixed or in a powder(also known as "setting type") that is mixed with water. There are disadvantages to both but I favor the powder. The pre-mixed will take longer to dry, shrinks more and may crack as it dries. The powder type must be mixed when needed and has a shorter working time. The advantages of the powder are:
- Mix only what you need.
- Stores well in a dry place.
- Dries quick enough to apply additional coats the same day.
- Shrinks and cracks very little if any.
- Sands easily when dry and leaves a smooth surface.
- Use for small and large repairs.
- Has good adhesion.
- One product with many uses such as filling cracks and nail holes, texturing, repairing drywall and more.
- Costs less, a bag goes a long way.