[Tom Edgerton]

Lisa--

Search this site, as there are other threads addressing this problem too.

I've had the same problem, and it's somewhat endemic to where we live. Most of my paintings sag a little when the season changes to winter and the humidity goes down. But if you restretch and over-tighten, when summer comes the canvas almost hums it's so taut. Usually when the paintings live in the same space for a year, they stop changing so drastically. I don't know how much sag you're getting, but use caution due to this seasonal variance.

Bill Whitaker has suggested stapling foamcore to the back of the stretchers, to even out the changes in humidity over time (protects the painting too). Others have sealed the back of the canvas itself with various preparations, but I'm somewhat timid to do so. It may be perfectly fine.

I especially wouldn't use alcohol...except to ply the artist.