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What are the Best Methods for Waterproofing Wood?

Autumn Rivers
By
Updated May 17, 2024
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A deep understanding of wood sealants is not essential for waterproofing wood. Although some people hire professional waterproofing contractors for large jobs, most simply buy a container of waterproofing solution to apply to their exterior wood. Others choose to create their own solution. The best method depends on the type of wood, personal preference, and possibly health and environmental concerns.

Reasons for Waterproofing

It is crucial to waterproof wood to protect it from rotting, warping, and cracking. Untreated wood will soak up water, causing it to expand, and then to contract as it dries. This cycle of expanding and contracting can cause it to crack or warp. Water can also wash the color out of certain woods and dampness encourages the growth of mold, mildew, and algae, which can damage or discolor the wood.

Deciding whether wood needs to be waterproofed is simple: if the wood is untreated, it is a good idea to apply a sealant. Where the wood structure has been waterproofed in the past, splashing water on the wood can help determine whether to apply more solution. If the water beads up when it hits the wood, the material is still protected and does not need another application.

Types of Wood Sealant

Products for waterproofing wood come in many varieties. They may provide a waterproofing membrane or surface barrier, or they may penetrate deeply into the wood, filling pores and spaces. Some products simply consist of a type of oil that repels water. Others contain a polymer or resin in a solvent that evaporates, leaving behind a solid, waterproof material.

Epoxy resin is one of the most common solvent-based products. It comes in two parts — the resin itself and a curing agent that hardens it — that are mixed just before they are applied. It is important to check the curing time, because if the resin cures too quickly, the person applying it might not have time to finish his or her work before it hardens. Products with a short curing time might not be suitable for larger projects.

Among waterproofing oils used to penetrate into the wood, linseed oil was often used in the past. Tung oil — another natural product extracted from the seeds of a tree — is now considered more effective. There are also some synthetic oils that provide even better protection. Penetrating oils have the advantage of giving a natural look that many people prefer, but usually need to be rubbed into the wood, which can be hard work. They also require several applications, and regular treatments every six months to a year.

Varnish and similar products provide a water repellant surface coating. Often, a single coating is enough, though for soft woods, a second or third coat may be required. These coatings are long lasting and there may be no need to re-apply them for several years.

Wood waterproofing products may be clear or tinted. The clear forms showcase the wood’s natural beauty, but mixtures tinted with natural wood shades can compensate for any loss of color as the wood ages.

It is also possible for DIY enthusiasts to prepare their own waterproofing mixtures. One example consists of polyester resin dissolved in acetone, a solvent that evaporates quickly. This mixture rapidly penetrates deep into the wood and leaves a strong, waterproof material behind. It is well suited to waterproofing wood that may be submerged in water, such as on wooden boats.

There is an increasing interest in nontoxic waterproofing solutions. These are better for the environment, and they are not harmful to children, pets and wildlife. While they may be harder to find and do not usually last as long as regular wood sealers, they are low-odor and generally safer than other types. In most parts of the world, information on toxicity, possible harmful effects, and environmental “friendliness” can be found on the container.

Applying Wood Sealants

Before applying the sealant, it is important to clean the wood well. This may involve sanding it down to remove old paint or other coatings. The wood should also be dry when the product is applied.

Some non-toxic oils, such as tung oil, are best rubbed in by hand — the warmth from the hand helps the oil to penetrate more deeply — although a cloth may also be used. Solvent-based products are best applied with a paintbrush. Some products can be applied with a garden sprayer; however, it is important to check this first as unsuitable mixtures may block the nozzle or may not penetrate the wood deeply enough if applied this way.

The number of applications of sealant that need to be applied depends on the hardness of the wood. Softer woods, like pine and cedar, will soak up more of the product, so two or three applications might be necessary. Harder woods, such as beech or oak, can often get by with just one coat, although it is important to read the instructions of the selected product and use it as directed.

Health and Safety Precautions

Many solvent-based mixtures are potentially harmful to humans and the environment. Some solvents, including acetone and petroleum based compounds, are classed as volatile organic compounds (VOCs). They can cause irritation to the eyes, nose, and throat, as well as headaches and dizziness if not used in a well-ventilated area.

Some petroleum-based solvents can produce serious ill effects if inhaled in large amounts or through regular exposure over a long period. These problems are unlikely to happen during normal use; nevertheless, all such products should be kept away from children and pets. Solvents are often highly flammable and products containing them should not be used near an open flame or other source of heat. It is essential to read the manufacturer’s guidelines before using any waterproofing product.

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Autumn Rivers
By Autumn Rivers
Autumn Rivers, a talented writer for About Mechanics, holds a B.A. in Journalism from Arizona State University. Her background in journalism helps her create well-researched and engaging content, providing readers with valuable insights and information on a variety of subjects.
Discussion Comments
By anon988850 — On Feb 14, 2015

I'd like to waterproof and seal house my foundation poles. They're already H4 treaded, just the part which goes into the ground. I looked at bitumen paints or wrapping it with some sort of heavy duty protection or seal. Any ideas? -- Alexander, South Africa

By toyresq — On Jul 15, 2011

I want to know if I can waterproof large wooden bowls so I can use them as bathroom sinks.

By anon106782 — On Aug 27, 2010

any suggestions for the most effective method of sealing softwood (pine) kitchen work surfaces?

By cmsmith10 — On Aug 17, 2010

@christym: If your wood is already painted, adding a layer of wood sealant works well for waterproofing. You should make sure to clean the wood very well first. You can mix ¼ cup liquid detergent with a gallon of water and scrub the surface well. It is of equal importance to rinse well.

Allow a couple of hours for the surface to completely dry before continuing. Apply a thin, even layer of wood sealant (either silicone based or polyurethane) using a paint sprayer. Allow at least a day to dry before touching the protected surface.

By christym — On Aug 17, 2010

Does it matter if the wood is already painted?

By calabama71 — On Aug 17, 2010

@alex94: It’s hard to say, not knowing what kind of sealer is already on your furniture. If it is oil based, you would want to use an oil based sealer coating. Most paint stores sell it.

By alex94 — On Aug 17, 2010

I have several pieces of wooden antique furniture. What is the best way to waterseal them? I don't want to do anything that would damage the furniture or decrease its value.

Autumn Rivers
Autumn Rivers
Autumn Rivers, a talented writer for About Mechanics, holds a B.A. in Journalism from Arizona State University. Her background in journalism helps her create well-researched and engaging content, providing readers with valuable insights and information on a variety of subjects.
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