MITRA Forum Question Details

If the environment cannot be controlled, we generally recommend putting a backing board on the back of the stretcher bars to slow down the suffusion of moisture and buffer the response. The aluminum foil idea is probably not disastrous, but is no longer recommended. The metal foil is more likely to be a source of condensation as compared to a cellulosic backing board.

Additionally, it is always best to keep paintings on the walls that are within the building proper and not those in contact with the outdoors. There is far less suffusion of humidity/moisture on interior wall and the RH would be more stable.

Finally, I am surprised that the humidity is worse in the winter. Generally the reverse is true due to the effects of the central heating. I suppose that in southern climates, the air conditioning in the summer would cause dryness and the lack of air conditioning in the winter months could elevate RH.

​I wonder if this is a situation where repair of the installation area might be worth considering, before doing something to the painting. If there is a lot of condensation on the interior, or that much moisture is penetrating the wall, it's surely a significant issue anyway that should be addressed.  (*edit* I know this isn't the comment section of the Home Depot website, but as usual, I can't resist stating the obvious!)

​Usually, air is more humid during the night than it is during the day. Even if the humidity rises way above 65% at night, that can be okay in terms of mold growth, as long as the space behind a painting can dry during the day, so that mold cannot grow. (see online: Michalski, S. (2004). Risk analysis of backing boards and paintings: damp climate vs cold climate.) If the backing boards have sufficiently big ventilation holes, to allow the moisture to escape then that could be a good solution for your student. This article has simple instructions for mounting backing boards: Backing Boards for Canvas Paintings