Step 11Caulk the window grooves.
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Begin by laying out the pieces of the frame in a row with the grooves facing up. Open the tube of caulk and load it into the caulking gun. Small squeeze tubes work also. The best caulk for this is probably the GE Silicone Window and Door available at home improvement centers. Run a bead of caulk in each of the grooves; no need to fill up the whole groove as then it will squeeze out too much, but ensure each of the grooves has a light even coating the whole length.