How to Caulk a Wooden Sailboat

You need to caulk both the decks and the hulls on all wooden boats, whether they are propelled by wind, diesel, gasoline or oars. Decks are usually raked, scraped, sanded, primed and caulked with marine grade putty caulk. Some manufacturers claim that hulls can also be caulked only with putty if the seams between the boards are not open all the way through the hull. Seams in plywood hulls can usually be caulked with putty. In general, wooden plank hulls should be sealed with caulking cotton, topped with marine caulking compound and then painted. Sometimes, after all that, they still leak.

Things You'll Need

  • Hull scraper
  • Dumb iron
  • Medium and fine grit sandpaper
  • Marine grade primer or wood sealer
  • Cotton caulking
  • Putty knife
  • Shears
  • Marine caulking compound for hulls
  • Marine grade paint for hulls
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Instructions

    • 1

      Remove the sailboat from the water and put the boat where you can work on all sides of the hull, including the bottom.

    • 2

      Scrape the hull with a hull scraper. Clean out the seams between the hull planks with a dumb iron. Dumb irons have a broad blade attached to a stout handle,

    • 3

      Sand the hull and the seams with medium, then fine grit sandpaper. Prime the hull and the seams with marine grade primer or wood sealer. Allow the primer to dry overnight.

    • 4

      Push cotton caulking into the seams between the hull planks. Cotton caulking resembles rope or string, and both cotton and wood swell when they get wet, so do not overstuff the seams. Push the cotton about two-thirds of the way into the seams with a putty knife or dumb iron.

    • 5

      Pay the cotton caulking roll into one seam at a time, starting at one end of the boat. Cut loose ends with shears. Connect rolls of caulking by rolling, rather than tying, the rolls of caulking together.

    • 6

      Work marine caulking compound intended for hulls (not decks) into the seams over the cotton with a putty knife. Follow the manufacturer's instructions for removing excess caulking compound.

    • 7

      Sand the seams flat if necessary. Follow the manufacturer's instructions for re-priming the hull over the caulking compound. Paint the boat with marine grade paint intended for use on hulls.