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


Before You Start

Tools & Materials You’ll Need:
Tape measure, Level, Utility Knife, Carpenter’s Pencil, Circular Saw with Carbide Tip Trim Blade, Jig Saw with Carbide Tip Trim Blade (for any notching), Cleaning Rag, Plastic or Wood Window Shims, Adhesive & Gun, Caulk & Gun, Protective Mask, Protective Gloves, Protective Goggles, Ear Protection.
Cautionary Note:
When cutting or applying adhesive, please ensure the area is well-ventilated. Wear protective mask, gloves, goggles and ear protection. For those who lack the proper tools or the experience working with such tools, consider using a construction professional to install your new SILTECH® windowsill.