3 Ways to Waterproof Wood

That natural beauty demands protection! Choose the products and techniques that work best with your wood.

By Bob Vila | Updated Aug 11, 2020 3:26 PM

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How to Waterproof Wood

Photo: istockphoto.com

Some of the most delightful furniture, cabinetry, and trim work are crafted from wood, the world’s oldest and best-loved building material. Without protection, however, most wood will suffer from exposure to moisture and high humidity, resulting in swelling, warping, or even rotting. Fortunately, you can easily avail yourself of products that protect wood while enhancing its natural beauty.

How to Waterproof Wood

There are three surefire ways to waterproof your wood for years to come.

  • Use linseed or Tung oil to create a beautiful and protective hand-rubbed finish.
  • Seal the wood with coating of polyurethane, varnish, or lacquer.
  • Finish and waterproof wood simultaneously with a stain-sealant combo.

When choosing the approach that’s right for you, keep in mind that some methods of waterproofing are better suited for interior or exterior items, while others are geared towards dark- or light-grained wood.

For the full details on each of the main ways to waterproof wood, continue reading below!

How to Waterproof Wood

Photo: istockphoto.com

METHOD 1: Create a warm, hand-rubbed oil finish

Linseed oil, derived from the seeds of the flax plant, and Tung oil, extracted from the Chinese Tung tree, are the basis for nearly all hand-rubbed (a.k.a. wiping) oil finishes.

Employed for centuries, these oils beautify and protect such dark-grained woods as walnut and mahogany, and they’re still in use today—with a few improvements. Blending the oils with other ingredients hastens drying times and eliminates stickiness. You can purchase pre-blended Tung oil and linseed oil products— or you can mix your own for a custom finish. A standard hand-rubbed oil blend consists of one-part oil (either Tung or boiled linseed), one-part mineral spirits, and one-part polyurethane.

Here’s how to apply yours:

  1. Stir thoroughly.
  2. Apply with a natural bristle paintbrush to dark-grained wood that’s been sanded and cleaned. (If looking you’re waterproofing wood that is lighter in color, such as pine or ash, skip this method in favor of one of the next two; hand-rubbed oils have a tendency to yellow over time.)
  3. Let the oil soak into the surface, and reapply to any spots that look dry.
  4. Wipe off the residual oil, rubbing well with clean dry rags to remove all excess.
  5. Allow the wood to dry completely. This can take anywhere from a few hours to overnight, depending on the degree of oil in the mixture.
  6. Sand lightly with a fine-grit sandpaper.
  7. Repeat the process with as many additional coats as required to obtain your desired finish.

As you become familiar with oil-rubbed blends, feel free to experiment with the formula. For a thicker product, reduce the amount of mineral spirits. If you’d like more working time before the finish dries, reduce the amount of polyurethane. Or, on the flip side, add more poly for a glossier finish and quicker drying time. You can create a multitude of custom blends!

Note: Oily rags used to rub away excess oil can spontaneously combust—yup, even without being near flame, because as the oil dries, it generates heat. Take precautions by keeping a bucket of water handy while working; as a rag becomes oil-saturated, drop it in the bucket while and continue with a clean rag. Later, hang rags out to dry separately. When completely dry, you can throw them away without risk, but rags should not be reused.

How to Waterproof Wood

Photo: istockphoto.com

METHOD 2: Use sealants for best protection

Polyurethane, varnish, and lacquer are tried-and-true sealants with excellent waterproofing properties. They’re either brushed or sprayed onto clean, sanded wood and then allowed to dry completely, prior to the piece being lightly re-sanded and recoated.

For best results, apply your finish in a “room temperature” environment. And never shake or briskly stir sealants before application; doing so can cause air bubbles that would remain on the surface, even after the sealant dries.

Though relatively quick drying (some in as little as 15 minutes), these sealants often contain chemical solvents, so ventilation is necessary during application.

These are the pros and cons of the most popular types of sealants:

  • Polyurethane sealants contain, in addition to acrylic and polyurethane resins, various other solvents, helping you choose your favorite finish effect—anywhere on the spectrum from a high-gloss shine to a gentle, soft sheen. Today’s polyurethane won’t yellow, so it’s a good choice for light-toned woods. Oil-based polyurethane offers the greatest durability, but brush cleanup requires mineral spirits or turpentine. With water-based polyurethane, cleanup is a snap with soap and water.
  • Varnish, a combination of resin, solvent, and drying oil, gives a hard-shell finish that resists scratches without yellowing. To waterproof wood that will be placed outdoors, choose marine varnish, which contains UV absorbers to resist sun damage. For interior use on end tables and coffee tables, spar varnish is a good choice to resist pesky cup rings. Clean brushes with turpentine or mineral spirits.
  • Lacquer, a mixture of dissolved tree resin or synthetic resin in alcohol, is the sealant of choice for wood furniture. While it can develop a yellowish tinge over time that’s considered unattractive on lighter woods, lacquer brings out a rich, warm, and uniquely scratch-resistant finish on deep-toned wood. It’s available in a variety of sheen choices and can be thinned with lacquer thinner. For optimum results, apply lacquer in multiple light coats. Note: Lacquer emits off strong fumes, so ventilation is absolutely essential; work outdoors or open windows and use fans.
How to Waterproof Wood

Photo: istockphoto.com

METHOD 3: Work fast with stain-sealant combos

When time is of the essence or you’re protecting a large project, such as a wood deck, go for a quality stain-sealant combo. These multitasking products add color while providing water resistance in a single step. Stain-sealant products contain color pigments with the addition of binders, which can be oil-, water- or alkyd-based. Depending on the concentration of pigment in the product, the final result can be transparent, opaque, or in-between. If applying a stain-sealer to exterior wood, you’ll want to reapply every year or two to keep the wood protected.

With the exception of alkyd-based products, stain-sealants don’t build up on the wood surface; instead, they soak in and any excess evaporates. Alkyd-based stain-sealants leave a light surface coating on the wood, making them better suited for interior wood items, such as indoor exposed beams or rustic furniture, that won’t require future applications. Outdoors, alkyd-based stain-sealers have a tendency to peel if the wood isn’t perfectly clean and dry when applied.