How To Waterproof & Seal Plywood for Outdoor Use (Step by Step)

Disclaimer: Obsessed Woodworking is reader-supported. I may receive a small commission if you purchase anything through my site.

Waterproofing plywood is essential for outdoor projects since moisture exposure causes swelling, warping, and rotting that compromises the wood’s structure and longevity.

This article provides instructions on how to do it effectively to protect outdoor structures for years.

Choosing the Right Products for Waterproofing

Selecting the right waterproofing product is essential for effective protection of plywood in outdoor settings.

  • Paint: Offers basic moisture protection and is ideal for projects where appearance is important.
  • Polyurethane: Known for its durability and clear finish, preserving the wood’s natural look.
  • Epoxy: Provides a strong, durable finish, perfect for heavy water exposure areas like boat decks.
  • Rubber-like Sealants: Extremely water-resistant and flexible, ideal for sealing irregular surfaces.

Epoxy is my top choice, but it’s expensive and harder to work with. If you decide to use epoxy, I highly recommend Total Boat products.

Step-by-Step Guide to Waterproofing Plywood

Properly waterproofing plywood is key to ensuring its longevity and durability, especially in outdoor settings.

1) Selection of Plywood and Waterproofing Products

  • Choose the right type of plywood for your project, considering factors like water exposure, desired finish, and durability.
  • Avoid the mistake of using the wrong type of plywood or waterproofing product for your specific environment.

2) Preparation of Plywood

  • Cleaning: Ensure the plywood is clean and dry. Remove any dirt, grease, or debris.
  • Sanding: Sand the surface with medium-grit sandpaper for better adhesion.
  • Filling Gaps: Use an exterior-grade wood filler for gaps or cracks to prevent water seepage.

3) Apply The Waterproofing Sealant

  • Following the manufacturer’s instructions, apply the chosen waterproofing product (paint, polyurethane, epoxy, or rubber-like sealants).
  • Avoid applying a too thick coat, which can lead to uneven coverage and longer drying times. Instead, apply multiple thin coats.
  • Pay special attention to edges and corners, as these areas are more prone to water penetration.
  • Work in a well-ventilated area and allow sufficient drying time between coats, as rushing this process can result in a tacky finish and reduced effectiveness.

Maintenance and Care

Maintaining waterproofed plywood is essential for its longevity.

  1. Regular Inspection: Periodically check for signs of wear, such as peeling, cracking, or discoloration of the waterproof layer, and for any soft spots or swelling in the wood.
  2. Clean Regularly: Keep the surface free from dirt and organic growth. Use mild detergent and water, avoiding harsh chemicals.
  3. Prompt Repairs: Address any damage or wear immediately to prevent further deterioration.
  4. Reapplication of Waterproofing Products: Look for signs like water absorption or loss of water beading on the surface to indicate that it’s time to reapply the product.
  5. Avoid Standing Water and Sun Damage: Design structures to prevent water pooling and consider UV-resistant sealants for sun-exposed areas.

Proper techniques to seal and maintain plywood ensure durable, long-lasting outdoor structures.

Please leave a comment to join the discussion