How to Seal Wallboard to Use in a Damp Area

Most types of wallboard are strong when dry but lose all structural integrity when wet. The paper facing of wallboard wicks up moisture, spreading it over an area quickly. To avoid water damage, seal wallboard as well as you can, especially in moisture-prone areas. For example, dark, windowless basements and bathrooms usually have poor ventilation. If there's a flood or water leak, the moisture cannot escape. Since mold spores need moisture to grow, serious problems can develop quickly.

Constant moisture and water vapor can damage wallboard.
  1. Apply several coats of moisture-resistant drywall primer (also called wallboard primer or primer sealer). The product should be both moisture- and mold-resistant. The goal is to create a seal that will keep water from compromising the integrity of the paper facing. Keep in mind that damage to the wallboard will allow water to get under the primer, which may then peel away.

  2. Cover the drywall primer with semi- or high-gloss paint. Both these types of paint work well in bathrooms and damp basements. As with primer, water can cause the paint to peel and blister if it works its way underneath the layers of paint, so avoid damaging the wallboard.

  3. Seal all gaps around the wallboard with silicone caulk. Place a tube of caulk into the caulk gun. Snip the tip off the nozzle with scissors. Squeeze the trigger to advance the caulk. Fill all gaps completely. This will prevent water from entering the area behind the wallboard.


  • Semi- and high-gloss interior paints resist splashes of water, but there is a drawback: glossy paints reveal surface blemishes in the wallboard because they are so reflective. So if you plan to use glossy paints, fix any blemishes before you prime the wallboard. Use a 6-inch drywall knife and joint compound to fill any dings or dents, allow the compound to dry overnight, then sand the repairs smooth with 150-grit sandpaper.
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