A hairline crack in a soffit board is not only an eyesore but an open door to water damage from inclement weather. The moisture seeps into the wood and causes the soffit board to deteriorate. It is possible to fix a hairline crack without removing the board. Fill the crack with a cyanoacrylate glue, epoxy putty or paintable wood caulk. Each process is less time consuming than replacing the entire board and more cost effective.
Clean the hairline crack with a rag. Sand to remove any paint chips or splinters. Sand the area around the crack if necessary.
Put on rubber gloves. Cyanocrylate glue will stick to your skin and any other area it may touch. Wear old clothing to avoid spoiling your good clothes.
Position the end of the open bottle of cyanocrylate glue directly over the hairline crack. Squeeze the glue into the crack while moving the bottle along the length of the crack.
Position the end of the bottle of cyanocrylate activator over the hairline crack. Squeeze a line of activator over the glue while moving the bottle along the crack. The chemical reaction between the activator and the glue will cause it to set in about 10 seconds. It will be completely cured within 30 seconds.
Allow the glue to cure 30 seconds. Sand the area with 180-grit sandpaper until smooth. The area is now ready for paint.
Clean the hairline crack by dragging a putty knife through all areas large enough to enter. Sand the surface with 180-grit sandpaper until the surface is smooth with the remaining board. Sanding will remove any small chips of paint from the surface.
Wearing rubber gloves, squeeze the epoxy putty to activate. Continue to work the putty until it is malleable. Create a long slender snake-like roll.
Place the snake-like roll over the hairline crack. Press the roll into the crack with your fingers.
Scrape over the surface with a putty knife immediately after pressing the roll of epoxy putty into the crack to remove excess.
Allow the epoxy putty to cure five minutes. Sand the surface with 180-grit sandpaper until smooth.
Paintable Exterior Caulking
Clean the area of the crack with a rag. Sand the surface until smooth. This removes any small paint chips and splinters.
Cut the end of the tube at an approximate 45-degree angle and insert into a caulking gun.
Place the end of the tube parallel with the soffit surface. Position the tube over the hairline crack. Squeeze the trigger and move the caulking tube along the surface of the soffit board until the entire hairline crack is covered.
Wet your finger. Pull your finger over the crack to press the caulk as far into the crack as possible. Remove any excess with your finger.
Allow the caulk to dry 30 to 60 minutes.