Although not the most durable option, a widely employed method to waterproof plywood is the application of water-resistant paints, such as latex paint varnishes. Through painting over plywood, latex paint creates a protective layer on the surface; preventing moisture from seeping into the wood.
Painting plywood can provide some water resistance, but it does not make the plywood completely waterproof. For better protection, you would need to apply a waterproof sealant or use marine-grade plywood, which is designed to handle prolonged exposure to water.
To waterproof plywood, an epoxy, waterproof paint, oil, varnish, latex or PVA can seal the wood for both indoor and outdoor use. These can come in either a paint-on or spray form, and they all bond easily to the wood to seal it and protect it from moisture.
Top quality acrylic latex paints are the best choice for exterior surfaces. For best performance, use MDO plywood if it is to be painted. Paint on MDO will not fail from checking of the wood or from peeling because of the wide dark bands of summerwood. One primer coat and two top coats may last up to 10 years on MDO.
The most affordable way to waterproof wood is by starting with a natural wood oil and following with a coat or two of outdoor paint. Though more budget friendly in the short term, you will need to redo this method more frequently, as it is not as long lasting as, say, a pricier, high-quality sealant.
Applying a waterproof top coat
You can waterproof most types of paint by coating them with clear polyurethane or acrylic.
With proper upkeep and maintenance, you can extend your furniture's lifespan for years beyond what wood could handle on its own. Another benefit is that polyurethane keeps moisture away from wooden surfaces to prevent rot.
The most durable and effective option to waterproof plywood is by applying Type-A waterproof glue sealant. Most reputable plywood suppliers will already adopt this approach and as such, it is the type of sealant you will find on marine and heavy-duty plywood.
Sealing, Painting, and Staining to Prevent Wood Rot
Use high-quality stain, primer, and paint on all exposed wood surfaces to create a protective barrier against moisture. Seal cuts, joints, and end grains, and even the back sides of boards where water can get in and cause damage.
Many manufacturers boast a lifespan of treated wood up to 40 years with proper care. That being said, regularly maintained untreated wood can last forever.
Marine plywood is recommended for any plywood application where the timber will be directly immersed in water for a period of time such as boat building and other marine activities.
Plywood can typically withstand rain exposure for a day or two without significant damage, depending on the type of plywood and the severity of the rain. However, long-term exposure can lead to serious damage such as warping, cracking, or rotting.
The short answer is yes, to a certain degree. There are several factors that make some polyurethanes more absorbent than others. Depending on the physical properties and material, thermoset polyurethanes can practically have zero water absorption compared to other known materials.
Prime your plywood.
Using a primer before you start painting will seal off the surface of the wood, stopping your paint from soaking in.
Untreated plywood must not be used externally or in high moisture areas. H3 treated plywood must not be in contact with the ground. It is not recommended to use smooth face plywood as a cladding - refer to IBuilt CoreClad which is manufactured with a textured face veneer specifically for exterior use.
Oil-based paints are unaffected by extreme temperatures and humidity, and they repel water as well. Water-based paints dry more quickly but do not apply well in challenged weather conditions.
Two or more coats of exterior paint are already sufficient outdoor protection. As long as the paint and underlying wood are in good condition, the paint can remain as-is. The best sealer for wood painted in exterior-grade paint is another layer or two of exterior-grade paint. No clear coatings are necessary.
These treatments include wood paints, wood stains, wood oils, wood waterproofer & wood sealers, which all vary in a number of ways. Wood paint – an opaque coloured finish that completely covers the grain of the wood with a uniform finish. Available in matt, satin & gloss finishes.
Untreated wood is the most susceptible to rot, fungi, and general weathering. It's extremely important that you use a wood preservative first. You can either use a wax enriched preservative for an all-round coating or alternatively use a wax-free preserver if you want to then use a stain or a paint on top.
The cheapest way to waterproof plywood is by applying a waterproof sealant or paint. Using water-based polyurethane or oil-based paint/varnish offers effective moisture protection at a low cost.
Epoxy Sealer: Epoxy sealer is an oil-based thick coat that penetrates wood pores, making plywood waterproof from the inside. It effectively blocks out moisture and air infiltration, preventing mould growth.
Latex paint
Latex-based or polyurethane-based paint is one of the most accessible forms of waterproofing plywood. There are plenty of colours to choose from, which can be applied using a spray gun or painted with a roller. You must apply two to three coats of paint for maximum effectiveness.
Massaging a generous layer of oil into the surface of your wood furniture enhances its waterproofing abilities. Wood oil can only be applied to wood furniture that has not already been sealed. It can yellow over time so it is best used for darker wood grains.
Water-based oil-modified polyurethanes are an excellent choice for outdoor applications as they provide good durability while being less harmful to the environment.
How do you keep untreated wood from rotting? Treat it with outdoor wood preserver to protect it from biological growth that causes wood rot.