Paint bubbling on concrete block wall

hammmer13

I painted an existing wall in a lani that has a flower bed in front of it made of concrete block as well. The flower bed wall inside and outside was previously painted. Upon inspection before repainting there were no imperfections or blistering visible. The flower bed was cleaned and pressure washed. Almost to the year the inside lani area started to blister. It blistered all the way to the block. I scraped away several of the spots and could not find any moisture. Behind the block where the blistering has occurred, it is chalky like. I did repair a crack in the front of the flower box that extended almost to the base. What do I need to do to stop this from happening in the future?

jsheridan

Hammer, the blisters are caused by moisture passing through the block. The chalky "stuff" is efflorescence, a salt that is brought to the surface by the moisture and deposited there when the moisture evaporates and blisters the paint. Why it is so and what you need to do is hard to say without seeing it. Start here. Prior to your painting the walls, was there any failure at that time? When did you repair the crack? Is it possible that the wall is cracked inside the flower bed and the dirt is hiding it? Would the dirt be directly outside where the interior failure is occurring?

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concretemasonry

I assume much of the older, sound paint was not removed completely. Applying a second layer (even if it is supposed to "breathe") can create a non-breathing wall wall surface, especially when there is a source of moisture from the planter area. - Does the planter have metal, pvc or vinyl tub to prevent moisture from entering from the back side.

It is common for additional coats of "breathing" paint to build up and create a vapor barrier that moisture can force off easily. The vapor pressure from evaporation can have high pressures. - I have seen epoxy paint come off in 3'x3' sheets with the concrete attached.

The process of forming crystals (efflorescence) also creates high pressures.

Just a guess without seeing a photo or having more details.

Dick

jsheridan

I'm glad a mason came by. For just being a painter Dick, did I do okay?
That's an interesting point about the additional coat creating the tipping point. Is it possible that there is no crack, and that prior to the additional coat the first coat of "breathable" paint was handling the transfer, and that OP actually turned a stable situation into a problem by repainting?

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