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.