Siltech ® Solid Surface Windowsills Installation Instructions

Step 1 - Preparation

• Window Sill Opening must be free of dirt, dust, water, etc.
• Dry Wall must be cut level to bottom of window frame

Step 2 - Measuring

• Measure Window opening length
• Take measurement at rear and front of opening
• Cut windowsill to smaller of two measurements
• Option: If tabs/ears are selected add 1 ½” to each side of the sill. (3) Inches more than the window opening

Step 3 – Reveal (Ripping sill may not be needed if sill tucks under window frame)

• To obtain same reveal on both sides of windowsill, measure from window to corner bead on each side (Add amount of reveal desired to this measurement).
• If measurements on both sides are the same, rip sill accordingly.
• If return depths are different on each side, scribe cutting is recommended (This involves marking to measures on the sill, and marking a line to cut on as a guide).

Step 4 – Setting the Windowsill (against frame)

• If the windowsill is to be set against the window frame, use plastic shims where needed to make level.
• Be sure that the windowsill is level before using adhesive.
• Once the windowsill is level add liquid nail / QB-300 over shims.
• Set windowsill, check to make sure the windowsill is still level.
• Some installations may require a cleat under the lip of the windowsill until adhesive is set.
• Adhesive usually dries within 24-48 hours

Step 4 – Setting the Windowsill (tucking under frame, on concrete block or pre-cast only)

• Use a thin set floor mortar, making sure that consistency is not wet or to dry.
• Run a bead of adhesive onto concrete block.
• Place a dollop or scoop of cement every 12” – 16” apart on top of adhesive.
• Run a bead of adhesive on backside of windowsill.

• Tuck back of windowsill under the window frame.
• Tap front of sill down until level, keeping back of sill against frame.
• Clean any mortar that may have come out from under front edge of sill.
• Check windowsill for final level.
• Let dry for 24-48 hours
• Place stacks of shims until sill is raised up to window frame.
• Put liquid nail over top of shims making sure liquid nail also is on wood framing.
• Place sill back in opening and then level front to back with cleat if needed.

Do not remove blue tape for at least 4 days for all adhesives to cure properly

1. Adhesive recommended – OSI QB-300 pro series Multipurpose construction adhesive
2. CRL – Shim stack Shims CAT. # KRS16 – 1-800-262-3299