A wooden door sill plate must be sealed in order to prevent water damage to the floors, the door frame, and the joists beneath the floor surface. Follow these steps to seal your exterior door sill plate.
Step 1 - Ensure a Snug Fit for the Door Sill
Ensure that the door sill fits snugly over the base of the door frame. The door should swing over it without making contact. Secure the sill plate to the door frame base with galvanized nails to prevent corrosion and gaps.
Step 2 - Coat the Sill Plate with Epoxy Paint
Spread a thick, smooth coat of epoxy paint all over the sill plate. Allow the epoxy paint to dry for several hours. Test the fit of the door over the sill plate, and lightly sand any ridges that catch the base of the door.
Step 3 - Seal with Silicone Caulk
Seal any visible gaps between the door sill and the door frame with a water-resistant silicone caulk. Press the caulk firmly into the gaps.
Step 4 - Add A Screen Door
Install a screen door to your exterior to minimize exposure of the door sill plate to inclement weather.