Attach one half of Velcro strips to the desktop in situations where you do not want to ruin the desktop finish. Set the strips parallel to each other and evenly spaced. Attach the other half of the Velcro strips to the underside of the countertop in a complementary pattern so the two sections of strips will contact each other when the counter is placed on the desktop. Remove the counter when necessary by applying steady, direct force upward on the counter edges.
Place the countertop on the desktop if attaching them together with wood screws. Pre-drill four holes up through the bottom of the wall-mounted desktop and into the counter from areas of the desk which are easily accessible, such as areas without drawers. Attach the wall-mounted desktop to the countertop with wood screws.
Secure ceramic or stone countertops to the wall-mounted desk using a special putty made for bonding those specific materials together. Spread the putty completely over the desktop surface and press the counter to the desktop, clamping the surfaces together overnight, if necessary, to allow the putty to harden.