A bathroom can provide a difficult environment for paint to perform as well as we would like for it to. A half bath without a shower or tub can be treated pretty much like any other room. Most of the time you would want to use a paint other than a flat just so that you have more washability. This could be as shiny as a gloss or as dull as an eggshell. This would depend more on personal preference than environmental demands. However, a shower and its accompanying steam and splashing create a much harsher environment for a coating to contend with. Even with a ceiling fan, many bathrooms remain relatively moist a good bit of the time. This can create the perfect place for mold and mildew to thrive. If the paint is not allowed to totally cure before the shower is used, a situation can develop in which the resin(the part of the paint which hardens and holds the pigments in place) remains soft and bleeds out of the coating every time the bathroom gets steamy. This can appear as shiny spots or runs which feel sticky to the touch. In extreme cases the entire wall may feel sticky after the shower is used. To prevent this from happening to your newly painted bathroom, follow these steps when prepping and painting:
1. Start your prep(and/or priming):Situation A: If you are painting a brand new bathroom for the first time, prime the water-resistant drywall with a 100% acrylic primer and allow it to dry completely. This will from several hours to overnight.
Situation B: If you are repainting a bathroom previously painted with an oil paint, wash the walls with a mild solution of bleach and detergent(no ammonia since this will produce a toxic gas) and allow to dry completely. Then lightly sand the old paint to dull it and remove any dust that may have dried in the previous coat. Wipe the walls with a damp sponge and allow to dry. Apply a coat of oil based primer and allow to dry overnight.
Situation C: If you are repainting a bathroom previously painted with a latex or acrylic paint, follow the directions in the above paragraph except you won't need to prime.
2. Once all of your prep(and/or priming) is completed, proceed to one of the following:
Option A: The absolute top-notch, 100%, very best, hands-down coating for a bathroom of this type is an oil based paint, because it dries the hardest and is not susceptible to resin bleed from excess moisture. Two coats are required if new work, even over the primer. If one coat looks good over a previously painted bath, you can stop there. (Benjamin Moore's Satin Impervo is a great choice for this application).
Option B: A close second best in my opinion is a premium grade Acrylic Paint designed to be used in bathrooms with potential moisture issues. This coating should be resistant to moisture and thus to resin bleed. It should also have good mold & mildew resistance.
Lastly, it should dry and cure quickly so that the bathroom can be put back into service in as short a time as possible. Benjamin Moore's Aura Bath & Spa is perfect for this job. It dries in 1 hour, is mildew resistant. and can be put back into service in 24 hours under most conditions.