How to Repair a Gap in Wooden Exterior Trim

Gaps that occur on exterior trim are often caused by many things such as shrinkage due to temperature change, faulty installation and wood rot or decay. In any case, if left unattended, these gaps could further increase the damage to your trim and cause you more money and headaches.


  • Stiff Brush or Putty Knife
  • Silicone Caulk
  • Caulk Gun
  • Sponge
  • Rags
  • Sandpaper
  • Paint and Primer

Step 1: Cleaning the Area

Using a stiff brush or putty knife, carefully clean the gaps between the wood of dirt, dust and debris. Avoid pulling the putty knife or brush towards you while within the gap to avoid damaging the trim and making the gap bigger. Clean in the direction of the gap.

Step 2: Fill with Caulk

Open your silicone caulk and load its contents into the caulk gun. Fill the gaps with caulk giving it an even distribution. Make sure that all gaps are filled and that you don’t miss any.

Step 3: Smooth Out the Caulk

Get your sponge and wet it. Smooth out the caulk by running the sponge over the area. Make sure that you do not accidentally remove the caulk which would again reveal the gaps. You can actually smooth it out using just your fingers, as well. Clean the area with the rags.

Step 4: Finishing

Let the caulk dry according to the instructions on the label of the product. After the caulk has completely dried, sand the affected area if necessary to smooth it further. Then, prime and paint the exterior trim so it matches.