Re: 1930s house -- very thick cedar shingles
your painter is right typically when wood siding keeps blistering its do to moisture.. water is getting into them and only drying from the outside.. the moisture comes out through the face blistering the paint.. if the painter is using oil based paint it will continue to blister. latex will breathe and let hte moisture out..
the other option is to strip the wall and install a proper rain screen for the cedar shakes to go over.. allowing them to dry both on the face and back by creatin ga air space. thick shingles are called shakes. typically 1/2" to 3/4" thick and 16- 24" tall with a 7 " exposure
fire up the saw and make some dust