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Exterior paint bubbles

we are struggling with recurring bubbles in the paint on our 1868farm house exterior wall on south-facing side. This has been an on going issue, even after the whole house was scrapped, primed, painted. We have scrapped the bubbles, primed, and painted only to have more bubbles over the winter.

The bubbles seem to appear randomly, sometimes in repainted places, sometimes in new places. The problem is only on the south wall, and seems to be limited to the lower (1st story) section.

Would appreciate any thoughts as to cause, and potential prep, prime, or paint solutions.

Re: Exterior paint bubbles

Davery -

Your problem is most likely mosture within the wall cavity and siding. I would suggest you get hold of a moisture meter and test those walls which are blistering. A reading of about 12% and above will bring paint failure, especially on the hot southern exposure. Vapor pressure is blowing up those bubbles. Your color selection might aggravate the problem too. Dark colors result in a much higher surface temperture.

The question is how the moisture is getting into the wall. A home of this age seldom would have fire blocks in the wall or horizontal braces to keep the 2 x 4's from bowing. Moisture is free to travel upward. What type of foundation does your house have? Does it have a damp cellar? A brick foundation if not sealed against exterior water can wick water upward into the wall cavity. High humidity from the cellar can also enter the insulation-less cavity. You must determine from where the moisture is coming and take efforts to block it.

How much moisture are you and your family generating in your home? Long hot showers, cooking, laundry, even people breathing give off a gallon of water per day per person. Perhaps more ventilation is neccessary in baths and the kitchen. A humidifier might be adviseable in the cellar.

No paint will stick permanently to this wall until you solve this moisture problem, although acrylics will breathe better than an oil based paint letting moisture pass through it.

Your problem reminds me of a house I painted which had had problems with peeling on its south side. The house was a reproduction of a Williamsburg , Virginia colonial house and had a high brick foundation. When I threw a glass of water on the bricks, all the water got sucked into the brick. The peeling was on the lower level of the first floor, generally below the horizontal stud bracing. We sealed the brick with silicon brick sealer to stop moisture from getting into the brick and wicking up into the wall cavity. I don't know if the builder had used a vapor barrier between the foundation wall and the wall sill. None could be seen. Certainly, your house of such an age would not have had such a moisture barrier.

Just a few thoughts of where to look. Good luck!

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