Sink mats are made in much the same way as a standard mat, but the sink must be made before the window mat is hinged onto the backboard. The sink layers can be made of matboard scraps (if the object is small) or B-flute or E-flute board can be used for larger items to keep the mat lightweight.

1. After cutting your window mat, position the object correctly under it and weight the object down on your backboard. Decide on the board you will use to make your sink by lining it up along the side of the object. You can use the “ruler test” to determine how many layers or how deep to make the sink: the sink should be high enough so that if you place a ruler across the surface of the sink, it will clear the object.

   

    

   • If you need to use more than one layer, stagger the arrangement of the boards in the layers (so they overlap or meet in different places). For example:

     

   • Mark the edges of your object on the backboard (aligning it properly under the window mat when boards are lined up) and then remove it from the area while you safely construct the sink. Leave a slight border around the object (many people leave about 1/8” to 1/4” around all sides). Then cut sink layers in strips to fill the borders. Use double-stick tape, dots of PVA, or other approved adhesive to attach the strips to the backboard (applying PVA overall to layers is likely to make the mat curl). These strips can be wrapped with a soft paper before being attached if needed for delicate objects.
2. You can leave one or two sides of the sink off until after you insert the piece, for ease of installation. Be sure to move the sink pieces around the sides of the piece, not over it, when you have the adhesive exposed, to avoid accidents. (As a variation, one of the sides can be hinged along the outer edge, so it flips out for object access and folds in securely when the window mat is closed).

   

3. Now hinge on the window mat and cover as in the instructions for a simple storage mat. You will want to add some layers of scrap board under the window mat side to raise it to the same level as the sink when you are hinging the window mat to the backboard.