I use spray foam to fill the gaps on a wooden frame that I built to display a piece of artwork that is painted on metal and is warped in a bunch of areas. The art is hung using a French Cleat system.
Here’s the step-by-step process for framing the metal sign and using spray foam to fill the gaps:
Start by making a rectangular frame with 3/4″ birch plywood and cut a 35 degree angle on the inside pieces for the French Cleat system. Then, screw the artwork to the frame and trace the artwork onto the wooden frame.
Use a jigsaw to cut the pattern of the sign on the wooden frame
Before using the spray foam to fill the gaps, wrap the metal sign in plastic to prevent it from sticking and screw it down to the plywood. I added some weight on top just to make sure the metal doesn’t rise up from the expanding foam. Once the metal sign is in place on the frame, use Minimum Expanding Foam to fill the gaps between the metal sign and the wooden frame.
Let the foam cure overnight, remove the metal sign from the wooden frame and use a hacksaw blade to cut away the foam squeeze-out.
Sand the foam and use 2-3 coats of joint compound to create a nice smooth finish on the built-up area, sanding between each coat. I used a paint roller with some white paint to finish the new edge.
Use a torch and vinegar and water solution to antique the hardware and leave the screws outside for a few days to built up some rust. Before mounting the metal painting to the finished frame, I added a little Bry Wax to the screws to help preserve the finish.
Attach the cleat to the wall using four 3″ long deck screws