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Using wood in a bathroom requires some thought to prevent pooled water from leaving water stains or high humidity levels causing decay. If you don't use the correct finishes, your wood will incur damage, mold, and rot, which can be bad for your health, unpleasant to look at, and costly to fix. In this article, we'll discuss several methods to waterproof wood for a bathroom to ensure you get the maximum life from your decor. Despite the huge variety of products on the market, there are three principal methods of making wood resistant to water. Surface sealants - this envelope the wood in a plastic-like coating that prevents water ingress. Oils - we know that oil and water don't mix and that oil soaks into the timber, so when used as a surface finish, oils nourish the timber while repelling water. Nano-sealants - These sealants work at a microscopic level, penetrating deeply into the wood's pores to block capillaries, preventing moisture ingress while allowing the wood to breathe. Some products can use all three methods to provide the desired protection. So how do you choose? Looks, cost, and durability are three factors driving product selection, so let's look at each wood treatment method and discuss its pros and cons. Surface Sealants for Waterproofing Wood You'll hear several names used to describe these products, including polyurethane, varnish, lacquer, and shellac. The difference between these products is due to the resins and solvents used in their manufacture. Therefore, each offers different advantages and benefits based on its constituent parts. Shellac Shellac is a natural product made by mixing alcohol with the resin secreted onto trees by the female lac bug, sold in flakes. Comprising various acids and waxes, it provides a natural stain, sealant, and high-gloss varnish. Primarily used on fine furniture, antiques, and interior woodwork. Photo: Amazon Pros Non-toxic -Food safe Dries quickly - Is easily repaired Adds a warm amber color to wood - Applies to almost all surfaces Most finishes can be applied over shellac Cons Not particularly waterproof - Can be damaged by heat and chemicals Lacquer Modern lacquer comprises cellulose treated with nitric and sulfuric acid and uses plasticizers, pigments, and other resins (such as acrylic) to enhance specific properties like durability, sheen, or color. Commonly applied by spray and used on indoor furniture. Photo: Amazon Pros A reasonable level of water resistance, as long as exposure is not prolonged Dries very quickly Durable, scratch-resistant finish Cons Degrades or clouds on prolonged exposure to water High volatile organic compounds (VOCs) Can yellow over time Not resistant to UV Polyurethane Polyurethane is a synthetic resin made by reacting a polyol with a diisocyanate or a polymeric isocyanate in the presence of certain catalysts and additives. Manufacturers include additives to modify properties like flow characteristics, drying time, durability, and resistance to UV light. You can buy oil-based or water-based polyurethane. It is commonly used for floors, kitchens, bathrooms, and outdoor furniture. Pros Forms a hard, plastic-like layer over wood, sealing it from moisture and water - damage Flexible finish Superior waterproofing capabilities Very durable Resistant to chemicals and heat It can be purchased in various finishes, from matte to glossy. Water-based polyurethane dries quickly to a clear finish with fewer odors Oil-based polyurethane can last ten years before a reapplication is required Cons Oil-based polyurethane can yellow over time, has more odors, and takes longer to dry Varnish Varnishes can be natural or synthetic, combining wood oils, resins, and solvents. The inclusion of oil nourishes wood and helps repel water. Varnish dries through the oxidation and polymerization of the oils, meaning it cures by reacting with oxygen in the air. It is often used for outdoor projects and surfaces exposed to water, like boats and outdoor furniture. Photo: Amazon Pros Highly resistant to water and moisture Provides a hard, durable finish Adds a warm amber hue to the wood Cons It can be hard to apply it smoothly Takes longer to dry than shellac and lacquer Applying Surface Sealants To Wood Lacquer is normally applied by spray, while polyurethane and shellac can be applied with a brush. Ensure the wood is sanded smooth, all sanding dust is removed from the area, and the wood is dry. Apply several thin coats in a well-ventilated room, allowing each coat to dry before reapplying. Lightly sand between coats with fine sandpaper. Remember to observe the manufacturer's recommended drying times. Oils for Waterproofing Wood Two types of oils are used in woodwork: drying and non-drying. If we want reasonably persistent water protection, we need a drying oil that hardens to a tough surface film in contact with air. Let's be clear, however: oils are not as good at water protection as sealants, but they do provide some protection while nourishing the wood. When drying oils are exposed to oxygen, the hardening process occurs through polymerization or crosslinking. Drying oils that are commonly available are tung oil, linseed oil, and walnut oil. You'll also see people quoting products like Danish Oil and Teak Oil; these are not pure oils but mixtures of the previously mentioned drying oils with some additives; however, they're readily available, and some are good products, so we'll include these in our discussion. Let's look at the properties, pros, and cons. Tung oil Tung oil is produced by pressing the seed from the nut of the tung tree. The tree is of Chinese origin and has been used for centuries to produce oil, originally to waterproof ships' hulls. Raw tung oil can produce a wrinkled finish as it dries, but today, the oil is heated during manufacture to increase its viscosity, prevent the wrinkling effect, and improve its film-forming characteristics. Photo: Amazon Pros The best water resistance of the drying oils Finishes can be satin through to glossy, depending on thinning Has a slight golden tint Dries very hard Less prone to mold than linseed oil Cons Takes 1 to 4 weeks to cure, depending on the temperature Linseed oil Linseed oil is manufactured by pressing dry, ripened flax seeds. Its edible form is known as flaxseed or raw linseed oil. However, it does not dry well in this state. To be useful for wood application, raw linseed oil is mixed with linseed oil that has been boiled to undergo chemical change, and drying agents are added. Boiled linseed oil is not edible or food-safe. Photo: Amazon Pros Light yellow or amber color Slow drying Low shrinkage Cons Not very resistant to water Easily scratched Known to mildew or turn black over time when in the presence of moisture Walnut oil Pressing walnuts produces walnut oil, a lightly colored and scented food oil. Like all food oils, pure walnut oil will go rancid over time, so the oil we use on wood is heat-treated to remove the proteins, alter the chemical characteristics to prevent deterioration and make the oil hard-drying. Photo: Amazon Pros Fast curing - half the time of tung oil Thin, so it deeply penetrates the wood fibers Foodsafe for wooden objects used in food preparation Good water resistance - better than linseed oil and just behind tung oil Often mixed with beeswax for finishing timber Cons You'll use more due to its low viscosity Danish oil Danish oil is a combination of oils and varnish. There is no specific recipe, so each manufacturer uses their own mixture and additives. If you wish to mix your own, a common combination is one-third varnish, and the balance is a mix of linseed oil and tung oil. With Danish oil, you get the best of both worlds by nourishing the wood while getting greater water resistance due to the varnish. You’ll see some woodworkers claiming Danish oil is food-safe. However, that is incorrect if it has boiled linseed oil as a constituent. Photo: Amazon Pros Better water resistance than pure drying oils due to the varnish Reasonably quick drying time Easily applied Matte or low-sheen finish Cons Scratches easily Not food safe due to the linseed oil Teak oil Teak oil is another hybrid oil that's even harder to pin down than Danish oil. A great study was done some years ago by a woodworker and boatbuilder who analyzed many proprietary products on the market at the time; he found teak oil to be so varied in ingredients as to make the name meaningless. Different manufacturers used either wax and turpentine, pure linseed oil, pure tung oil, a mix of mineral oil and dehydrated castor oil, pure varnish, or an oil and varnish blend. This variety makes it impossible to make a statement about the efficacy or otherwise of teak oil when we don't know what it may contain. You'll need to be guided by the manufacturer's claims. Photo: Amazon Pros Depends entirely on what your particular brand contains If primarily oils or waxes, it nourishes the wood Cons No certainty on whether it is water-resistant or food-safe Applying Drying Oils To Wood Caution must be exercised when using drying oils, as oil-soaked rags may spontaneously ignite as they dry due to the heat generated by an exothermic reaction with air. Wash them in soapy water and hang them out to dry individually. Apply to properly sanded wood with a natural bristle paintbrush. Allow it to dry before lightly sanding it with fine sandpaper, then apply another coat. Apply as many coats as you need to get the desired finish and coverage. Nano-sealants for Waterproofing Wood This type of sealant has been used in the construction industry for years but is relatively new to the retail market; however, it's catching on fast. The principal behind nano-sealants is using chemicals like silane, siloxane, or silicone as a waterproofing ingredient. These products have small molecular structures that penetrate the gaps and capillaries in wood or other substances and fully or partially block them. They prevent the large water molecules from entering, permitting smaller water vapor molecules within the timber to evaporate. Engineers refer to this as a breathable membrane. Some products combine these nano-sealants with polyurethane or varnish to get a double effect, sealing the wood's pores and the surface. Photo: Amazon Pros Highly water resistant Don't yellow Natural finish Environmentally friendly Cons Some products can be costly Not UV resistant Applying Nano Sealants To Wood Ensure the wood surface is clean and dry Apply the sealant by spraying until you get pooling or run-off If some areas dry more quickly than others, apply a second light coat The surface is normally touch dry in 1 hour, although full cure takes a week. A Note On Stain Sealants You’ll often read advice that shows stain sealants as a fourth waterproofing method. It isn’t. As the name suggests, it’s simply a sealant with some pigment added to apply color to the wood. Stain adds no waterproofing capabilities, although the color can provide limited UV protection. Stain sealants are ideal if you want to seal your wood and apply some color simultaneously. Otherwise, you can stain the wood separately and then apply your chosen sealant over the top. Photo: Amazon The pros and cons of stain sealant are largely related to the type of sealant being used, with the added bonus of applying a desired color at the same time as you seal, saving you some time. Conclusion It's worth noting that while we speak about waterproofing wood, no surface covering or sealant is truly waterproof without ongoing maintenance. It degrades in sunlight, gets scratched, or the wood swells, moves, and cracks. Whatever surface coating you select, there will come a time when you will need to maintain it by lightly sanding it back and reapplying the surface finish. I trust the information in this article has helped you decide the surface finish best suited to your bathroom and provided a finish that protects your wood and suits your decor. Frequently Asked Questions