How to Treat Bathroom Mold Before Painting

Updated February 21, 2017

Almost every homeowner contends with mould and mildew. In particular, mould can build up in bathrooms, where air tends to be humid and walls become damp. If you paint over the mould without removing it first, the mould eventually will seep through the paint. If not properly removed, mould can induce asthma, allergic reactions and other respiratory problems, according to the U.S. Environmental Protection Agency. To help prevent mould growth in your bathroom, regularly turn on the fan, if you have one, and use a dehumidifier to reduce air moisture.

Mix 1/4 cup of trisodium phosphate (TSP) with 1 gallon of warm water. Scrub the mouldy area and leave the mixture on the wall for several minutes. Rinse thoroughly with warm water and dry with a soft cloth.

Combine one part water with one part chlorine bleach in a spray bottle. To prevent contamination with different chemicals, use a new spray bottle. Spray the contaminated area with the mixture. Allow to dry then prime with an alcohol-based stain-blocking primer that also includes a shellac.

Mix a mildewcide additive---available at most hardware and building-supply stores---into your paint. Mildewcides inhibit the growth of mould and do not affect sheen or colour.


TSP is a cleaning agent that you can find at most hardware stores.


Wear gloves and a mask when cleaning with chlorine bleach. Do not mix chlorine bleach with other chemicals or cleaning agents. Doing so can produce lethal fumes.

Things You'll Need

  • Trisodium phosphate
  • Chlorine bleach
  • Spray bottle
  • Alcohol-based stain-blocking primer
  • Mildewcide paint additive
Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author

Angela Brown has been a book editor since 1997. She has written for various websites, as well as National Public Radio, Pacifica Radio and more than 20 fiction anthologies. Brown earned a Bachelor of Arts in theater and English from the University of Wisconsin.