MITRA Forum Question Details

​Hi Aude,

This is more of a woodworking question, perhaps - which I used to do but haven't for decades, so I'm hoping a conservator will respond as well.  Thicker panels are less vulnerable to flexing and warping; the more stable a panel, the more durable the painting - so your concerns are warranted for your larger sizes paintings.  Frankly, I wouldn't make any painting, even a 5" x 7", on an 1/8" board - it's just as simple to work on a 1/4" thick panel for more stability. However thicker panels (over 1/4") weigh more at large sizes, and are harder to frame.  So if a painting is small (a very rough estimate being less than 9" x 12") a 1/4 panel, gessoed on both sides (this improves stability), should work well enough. (Tho', to be clear - if weight and framing aren't concerns, a 3/8" or 1/2" panel is always more stable - just likely not necessary ​for very small sizes).

For larger panels, you are correct that 1/2" HDF is hard to find.  I've seen 3/8" more commonly, and it seems stable enough (if gessoed on both sides) for paintings up to, perhaps, 12" x 16'" (again, a rough estimate).  However once I'm into that size range I prefer 1/2", high grade plywood, covered with linen (anything with wood grain - solid or ply - must be coated with cloth to prevent the grain pattern from telegraphing through).  Applying cloth is simple: wash and then line dry the cloth; place into warm animal glue to saturate cloth; apply to face of panel, with weave parallel to panel edges; press cloth to surface, squeezing out excess glue (work over wax paper); let dry 24 hours; trim excess cloth (or warp around the sides using the same steps described above); coat with gesso.  All wood-based supports have drawbacks; still, cloth-covered, high grade plywood seems a pretty good option - and simpler, to me, than gluing together two, 1/4" HDF panels.

If you still want to glue panels together, my experience as a woodworker was that a good glue bond is as strong, if not stronger, than wood. So while I've never done what you're suggesting, it seems like it would work (but I'm not sure and hope others will chime in).   A good glue bond means prepping your surfaces (sanding lightly, to create some tooth, then wiping with alcohol to clean); using a good quality wood glue (not white craft glue) to completely coat both sides (i.e. don't just put drops of glue here and there); applying wood clamps every 6" or so (applying a similarly sized scrap board atop the HDP, between it and the clamps, prevents the clamps from marking the HDF); gradually tightening down on the clamps until glue squeezes out all sides; cleaning up excess glue with a wet rag; letting it cure for 24 hours.  Pardon if I'm explaining something you already know how to do - I just want to be sure you know the proper steps to make a really good bond.

One more option, if you want an even more durable panel, is to coat the back (atop the gesso) with house paint - this protects it from ambient moisture entering in.  The higher quailty the house paint, the more protective it will be.  

​Koo Schadler

Koo

Your advice is sound. As to using thinker boards, I really prefer a good quality hardwood ply to hardboard as long as it is covered with a fine fabric before the gesso is applied. It is far less likely to warp and does not suffer as much as hardboard if bumped on a corner. Applying ground to both sides also helps mitigate warping although many Old Masters did not take this precaution.

If sealing the back I prefer a solvent borne coating as opposed to a water borne one but certainly a high quality acrylic dispersion paint, including a house paint would work.

​​To clarify: gessoing both sides of any wood-based panel increases stability, and is particularly helpful to do to fiberboards.  However I probably would not gesso the back of 1/2" or 3/4" plywood (particularly a medium to small panel). That size plywood is already a fairly stable board, and it really does add time and effort to gesso two sides.  Regardless, I always coat the back of any painting panel with alkyd housepaint. ​