How to Waterproof Painted Wood Furniture for Outdoors

Outdoor furniture must stand up to the elements year round. If ice, snow, and rain are given the opportunity to penetrate your wooden furniture, moisture can quickly cause significant damage. Ensuring your painted outdoor furniture is properly finished will help it last for seasons to come. It is possible to waterproof your painted outdoor wood furniture.

How to Waterproof Freshly Painted Outdoor Wood Furniture

If you have recently spent time lovingly painting your outdoor furniture, you need to finish the job by waterproofing your wood furniture. Being able to waterproof your furniture hinges on the type of paint you used to paint it.

Necessary Materials:

• Polyurethane
• Lint-free cloth
• Fine grit sandpaper (#220)
• Polyurethane applicator
  • For oil-based polyurethane: natural bristle brush or lambswool roller
  • For water-based polyurethane: synthetic bristle brush or synthetic roller 
• Drop cloth to protect area around furniture from drips or overspray
• If using oil-based polyurethane: mineral spirits

Waterproofing with Oil-Based Paint

Oil based paint is commonly used to seal outdoor furniture. Oil-based paint stands up to moisture well and provides a classic glossy look. 

However, this type of paint takes significantly longer to dry. Low temperatures or high humidity can slow down the curing process. Oil-based paint can take up 24 hours to dry.

Oil based paint provides a degree of waterproofing, but at least two coats of polyurethane should be applied after the paint has dried. This provides added layers of protection to prevent water from causing potential damage to the wood.

As oil based paint dries, it releases moisture. If the paint on your furniture has not cured when you apply polyurethane, peeling and cracking may occur as moisture is off gassed beneath your polyurethane seal coat. 

This is especially common with water-based polyurethane applied over oil-based polyurethane.

To waterproof your freshly painted outdoor wood furniture:

1. Ensure that the paint has been given ample time to cure thoroughly.
2. Lightly sand your furniture with fine grit sandpaper. This will help newly applied polyurethane adhere to the cured oil-based paint.
3. If possible, apply polyurethane in an area protected from the elements. This will allow for predictable dry times and reduce the risk of dust and debris spoiling your finish.
4. Prepare the surface of the furniture to receive polyurethane by cleaning all areas with a clean, lint-free cloth moistened with mineral spirits.
5. Allow the surface to dry completely.
6. Apply polyurethane in a thin even coat.
7. Allow polyurethane to cure per manufacturer instructions.
8. Lightly sand, then wipe down furniture before applying a second coat of poly.
9. Apply the second coat.
10. Additional coats may be necessary depending on your environment and chosen polyurethane.

After your coats of polyurethane have cured, your furniture should be waterproofed.

Waterproofing with Water-Based Paint

Water-based paint has traditionally not been favored in outdoor settings. Early formulations of water-based paint had less durability and were more susceptible to damage from water and heat. 

However, advances in water-based paint technology has created viable options for long lasting outdoor paint.

To waterproof your outdoor wooden furniture that is freshly coated with water-based paint:

1. Make sure paint is not tacky and has properly hardened. 
2. Use fine grit sandpaper to gently abrade the paint surface. 
3. If available, move furniture to a dust-free, temperature controlled area.
4. Use a lint-free cloth dampened with water to remove all dust, grease, and oil from the surface of the water-based paint.
5. Let the surface dry completely.
6. Apply a thin layer of polyurethane with long, even strokes.
7. Polyurethane should be allowed to cure according to the manufacturer’s recommendation.
8. Gently sand with fine grit sandpaper, then wipe away dust with damp cloth.
9. Allow the surface to completely dry.
10. Apply a second coat.
11. Applying additional coats may be necessary depending on environment and chosen polyurethane.

How to Waterproof Old Outdoor Painted Wooden Furniture

Perhaps you scored nice patio furniture at your local Habitat for Humanity Restore or from a yard sale. The style of the furniture fits your aesthetic, but the paint needs help.

Damaged paint on outdoor furniture provides moisture a pathway into the interior of your wooden furniture. When water penetrates into your wooden furniture, mold, fungus, and rotting can occur.

You will need to follow these steps for restoring the furniture, and THEN waterproof it.

Supplies Needed

Rehabbing your old outdoor painted wooden furniture will require time, work, and safety gear. Unless you have access to a lead-based paint test, it is better to be safe than sorry. Wear a respirator, goggles, and work in a well ventilated area. 

In addition to the necessary supplies listed above, more items are needed to waterproof old outdoor painted wooden furniture:

• Wood sealer or oil
• Exterior primer
• Exterior paint
• Paint Scraper
• Medium grit sandpaper (#80)

Fixing Paint Problems Before Waterproofing

To restore your old outdoor wooden furniture, look for all imperfections in the paint. Each imperfection is an opportunity for water ingress and the eventual ruin of your furniture. 

1. Inspect furniture for paint that is cracked, peeling, chipped, or bubbled.
2. Place furniture on drop cloth or plastic sheeting.
3. Put on goggles and a respirator.
4. Use a paint scraper to remove all damaged paint. Try to keep paint chips on drop cloth or plastic sheeting to make safe disposal easier.
5. Sand all areas where wood is exposed. The goal of this step is to smooth the transition between paint and wood.
6. Wipe away all dust with a damp rag, then allow to dry.

Dispose of paint according to EPA recommendations or local ordinances, especially if there is potential your paint scrapings are lead-based paint.

Preparing Surface for Waterproofing

At this point your old furniture should be completely prepared to receive new layers of wood sealer or oil, primer, and paint.

1. Apply wood sealer or one of many wood oils according to manufacturer’s instructions. Depending on the choice of sealer or oil, this can take as long as a week.
2. Let the sealer or oil cure.
3. Sand the entire piece of furniture lightly and wipe clean with damp cloth.
4. Allow the surface to dry.
5. Apply exterior primer to your furniture. 
6. After primer dries and sets, then gently sand with fine grit sandpaper.
7. Free surface of all debris by wiping with a clean, damp cloth.
8. Apply two coats of paint, sanding and cleaning after each coat has set.
10. At this point your old furniture should look brand new with exposed wood having been sealed, while the entire piece of furniture has received new primer and paint. 

With your freshly painted outdoor wood furniture, you can follow the steps outlined at the beginning of the article to finish waterproofing your furniture with polyurethane.

Choosing Your Waterproofing Materials

Here is a brief guide for selecting materials to waterproof outdoor wooden furniture.

Sealer or Oil

For outdoor furniture, all exposed raw wood should be sealed or oiled before being primed, painted, and polyurethaned. 

Natural oils such as tung oil and linseed oil can be used to seal your raw wood. These oils contain no VOCs and readily accept paint, as opposed to most sealers which contain chemicals.

Natural oils will work for waterproofing your furniture, but won’t provide as strong of a barrier as chemical sealers.

Here are some great resources to pick a natural sealer for your project:

• Tung Oil vs Teak Oil
• Tung Oil vs Danish Oil
• Danish Oil vs Polyurethane
• Raw Linseed Oil vs Boiled Linseed Oil
• Mineral Oil vs Linseed Oil
• Mineral Oil vs Tung Oil

Polyurethane or Spar Varnish

With your furniture painted and oiled, I still recommend adding a wood finisher that will protect it from the elements.

Polyurethane has long been used as high quality sealant for outdoor furniture. This specialized varnish creates a plastic like coating overtop of your wood piece, protecting it from sun and precipitation.

Compared to polyurethane, spar urethane or spar vanish is an even better sealant, as it is designed specifically to protect against water.

Both will leave a slight yellowing, but will do a better job of protecting against outdoor elements than lacquer or polycyclic.

You can brush polyurethane or spray polyurethane. The same application methods exist for spar varnish.

Conclusion

Waterproofing painted wood furniture for outdoors requires putting several solid, durable layers between the wood of your furniture and the elements. I recommend finishing raw wood with natural oils, then applying at least two coats each of water-based primer, paint, and polyurethane. Following these steps and monitoring your furniture for signs of distressed paint will lead to lasting outdoor wooden furniture.