How to Sink Mount a Canvas Board

Begin by measuring the canvas board and then subtract a half inch from each dimension.  This will provide you with the window size for your mat.  Cut a mat with a window of that size.  Cut a second matboard to the same overall size as the window mat, but don't cut a window in it.  This will be your mounting board.

From a sheet of foamboard you are going to cut some strips.  To figure the size of those strips, subtract the width of the canvas board from the overall width of the window mat and divide the difference in half. 

Cut strips of foamboard in the correct sizes.

Apply double sided adhesive tape (ATG tape) to each foamboard strip.

Assemble two strips on either side of the height dimension of the mounting board, aligning each along the edge.

Assemble the other two strips on the width dimension of the mounting board, creating a recessed area in the center.

Place the canvas board in the recess created by the strips of foamboard.

The surrounding area is now flush with the surface of the canvas board.  The canvas board is trapped in the sink top-to-bottom and right-to-left.

When you place the window mat over the sink mounted artwork, the overlap of the mat's window onto the edges of the artwork trap it front to back.

Stack the glazing over the matted, mounted artwork and you are ready to load it all into the frame.