How do you attach canvas to masonite?
My first question would be why? Masonite is a wonderful surface for painting on with either oils, Genesis, or acrylic paints. You can purchase pre-gessoed masonite (known as gesso board) or you can prepare it with gesso yourself. You can also paint directly on the board without gesso if you basecoat it with a couple of coats of acrylic paint first.
That said, if you really need to apply canvas to masonite, then you need to use an acid-free glue. Cut your canvas slightly larger than the piece of masonite. Spread a thin layer over the entire surface of the masonite and then lay on your canvas. Use a brayer or your hands to smooth the surface so that you get all the air bubbles out. Let it dry and then trim the edges of the canvas flush with the edges of the masonite or wrap the edges around the masonite and glue them down on the back. If you are going to do this, it is very important to get all the air bubbles out. Otherwise you will have a lumpy, ugly surface which will be visible in your finished work.
I have not done this myself as I prefer to paint on as smooth a surface as possible. If you are just looking for a rigid backing for canvas as an alternative to stretchers, then you can purchase canvas boards which are canvas wrapped around a cardboard support or canvas already attached to hardboard.
Hope this helps.
Judy Leasure, TDA