Weird water bubble in paint

[andyvh1959]

I remodelled the main bath in our 1973 built home back in 2018. Added a shower where previously was a bathtub, so there is a lot more water use in there since 2018. I repainted the walls with Behr interior paint, applied over the cleaned previous paint on the walls. Two sinks on the vanity, like before.

My wife's sink is nearest the door. Over the past year, above the door a bubble developed on the wall. I thought it was just paint peeling for whatever reason. Well, I pricked the bubble and out came about a meauring cups worth of water! The wall is solid behind the bubble. The Behr paint that had bubbled is very elastic. Above the bathroom is a loft directly under a shed style roof. No water penetration up there that would have leaked onto the area above the bathroom door. The vent line for the sinks/bathtub/toilet is away from the area over the door. No water trace or trail anywhere. Near I can figure is the Behr paint was porous enough in one spot that water/condensate could eventually accumulate, lift the paint and create a bubble. Wierd.

 

[gsmith22]

I'd recheck the area above for either a very slow water leak at a pipe or more probably a leaking/dried/cracked rubber boot at the roof around a vent. Had the exact same issue - bubble in paint (also happened to be Behr!) i pricked it and out came a bunch of water. Went into attic coudln't find anything until I crawled around with a flash light and I found a very very slow drip from a vent boot, it ran down pvc pipe, and even turned with pipe (non 90 turn) over to a 90 int he pipe where it dripped off the pipe onto the framing/drywall immediately above my bubble.

 

[rancherbill]

Was it a gloss paint. They are designed for baths and kitchens.

The second thing is preparation and what was there before. I have had Behr paint come off certain brands of paint. Ordinary painter tape will pull it off with certain previous paints. Other areas it did not pull off. It has been a while and forget the brands involved.

If you are changing types of paint did you prime the wall?