Siltech® Solid Surface Acrylic Windowsills & Products


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




  • 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




  • To obtain same reveal on both sides of windowsill, measure from window to corner bead on each side (Add amount of reveal/overhang 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).
  • (Ripping sill may not be needed if sill tucks under window frame)



Setting the Windowsill

Butting against window frame, on concrete block, pre-cast or wood


  • 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 adhesive / Titebond Interior/Exterior construction adhesive to substrate.
  • 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


Tucking under frame, on concrete block or pre-cast only


  • Run a bead of adhesive onto concrete block.
  • Run a bead of adhesive on the underside 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 adhesive that may have come out from under front edge of sill.
  • Check windowsill for final level.
  • Let dry for 24-48 hours.


Tucking under window on wood framing


  • Place stacks of shims until sill is raised up to window frame.
  • Put adhesive over top of shims making sure adhesive also is on wood framing.
  • Place sill back in opening and then level front to back with cleat if needed.


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


  1. Adhesive recommended – Titebond Interior/Exterior construction adhesive

  2. CRL – Shim stack Shims CAT. # KRS16 – 1-800-262-3299