The use of polyurethane is fairly common among woodworking projects. It provides benefits that lead to a more durable material, extending its lifespan. However, there are certain things to consider, and you should know when dealing with this material.
Our expert painters provided this guide to address the most asked question— “is polyurethane waterproof?” So, let’s find out!
Does Polyurethane Make Wood Surfaces Waterproof?
Applying polyurethane does not make wood surfaces waterproof, but what it can do is make them water resistant. The polyurethane still has minor holes in it. Applying a polyurethane coating will prevent water from going through the pores found on the wood’s surface.
What Does Water Absorption Mean?
Water absorption can be measured by the concentration of water molecules that can penetrate a material. Furthermore, the size and number of pores dictate the rate of water absorption of the material.
Water Absorption Testing
Simple water absorption testing is a sure way of measuring a material’s percentage of water weight gain. The testing of water absorption compares a material’s wet and dry weight for one week.
The water absorption values will differ based on the ambient temperature, polymer, length of exposure, and additives. Consistent results can be achieved through the ASTM Standard D570 test.
Also, you can assess the weak points of a material through water absorption testing.
Can Polyurethane Protect Wood from Water?
Polyurethane coats are thin and thus require multiple coats. These layers reduce its porosity which will help protect the wood making it more resistant to water. Polyurethane creates a plastic finish once dried, but a solid coat creates a semi-gloss or glossy finish.
What Happens to Polyurethane Over Time?
If you consider using polyurethane on your furniture, you might also ask yourself does polyurethane increases water absorption over time.
As time goes by, wood expands and contracts. This wood character leads to natural abrasions, which wear the protective layer of the polyurethane over time. Furthermore, more exposure to moisture will weaken the layer, showing more weak points.
Waterproofing Properties Compared to Other Materials
There are some factors to consider to gauge whether polyurethane can absorb water compared to other materials. In reference to the different physical properties and source material, the water absorption capacity of polyurethane is less than other supplies or materials.
Making Wood Waterproof Using Polyurethane
Knowing how to turn plywood surfaces waterproof is important, and waterproofing repels water and other elements. Since poly cannot 100% protect wood from water, you must apply other formulas and processes to make it completely protected.
Here are the steps you need to follow to turn wood waterproof using polyurethane.
Step #1: Sanding the Surface
Sand down the entire exterior of the wood’s surface. Sanding the surface will help the sealant adhere to the exterior. This process removes scratches and other imperfections. This process will also lessen the formation of air bubbles.
Step #2: Removing the Dust
After sanding it down, considerable dust will be produced. Make sure to clean off the dust using a lint free cloth or a damp rag before proceeding with the next steps. Allow the surface to completely dry before applying a sealant to it.
Step #3: Sealing the Wood Surface
Apply your sealant  using a paintbrush. Make sure to use long even strokes from end to end. Catch any drips with your brush and smoothen them unto the exterior.
Step #4: Applying the First Polyurethane Coat
Use a high quality brush, spray, or roller to apply the first coat of the sealant. Make sure that you get an even coat.
Step #5: Shaving the Bumps Off
Once the surface is dried up, examine the wood and remove any observable drips. You can do this using a razor.
Step #6: Wet Sanding Your First Poly Coating
Once you have allowed it to dry for a certain time, wet sand the first application to remove any blemishes. Use circular motions when performing this step.
Step #7: Applying the Second Coat
Once the layer is dry, you can now apply the second coat. In this step, you need to know how long you should wait between coats of polyurethane on hardwood floors, walls, roofs, etc.
Step #8: Applying the Final Coat
It is not enough to have just one layer. It will take additional coats or about three coats. Make sure to the first coat to dry completely before applying the next. Refer to the instruction guide to determine the recommended drying time of polyurethane.
Step #9: Polishing the Wood Surface
Polish the exterior after at least forty-eight hours.
You might be interested in: Ways to Waterproof Wood for Bathroom Floors & Walls
How to Make Wood Waterproof: 3 Methods
To preserve and make your beautiful furniture last longer, it is recommended to waterproof them. Here are methods with the corresponding waterproofing products to help you.
Method #1: Use Sealants
Different types of products are sealants for waterproofing wood. Some products, such as polyurethane, lacquer, and varnish, are proven to work. They have excellent waterproofing properties.
Sealants are considered finishing items that have very good water-resisting qualities. Consider each type of sealant for the specific application you intend the product to be subjected to.
Polyurethane sealants have polyurethane and acrylic resins in combination with other solvents. The current formulation will not give a yellow color on the wood. Oil-based variants provide the greatest durability; however, they require turpentine or mineral spirits during clean-up.
Varnish results in a hard finish that is resistant to small scratches and does not yellow over time. It is best to apply marine varnish to outdoor furniture. It is formulated to contain UV absorbers that resist sun destruction. This keeps wood protected for outdoor use.
Lacquer is a formulation that involves natural resin and synthetic resin in alcohol. It gives yellow discoloration over time. Despite this, lacquer is the sealant of choice among many. It brings out a warm, scratch-resistant coating on the wood.
How to Use Sealants
- Stir the sealant but do it gently.
- Apply the sealant on the surface as even as possible.
- Allow the coat to dry
- Sand the exterior once it is dried out
- Clean off the dust
- Repeat these steps until you get three coats of the sealant
Method #2: Apply Wood Oils
Using wood oils such as linseed or tung oil can be utilized to result in waterproof wood. Linseed oil is extracted from the flax plant, whereas the Tung oil is from the Chinese Tung tree. Applying wood oil can also lead to a beautiful coat that restores the wood’s natural beauty.
You can get pre-blended Tung oil and Linseed oil or make your own custom finish. Here are the steps for applying wood oils to the wood surface.
- Stir the oils thoroughly.
- Using a natural-haired paintbrush, apply a thin layer of the oil to the wood that has been cleaned and sanded down.
- Allow the oil to be soaked unto the surface of the wood. Examine the surface and reapply the oil on the exteriors that look dry.
- Remove any excess oil from the surface.
- Make sure to give ample time for the oil to dry.
- Sand the exterior with a fine grit sandpaper
- Repeat the process to get the coat number necessary
Method #3: Use a Stain-Sealant Combination
A third method to waterproof wood is by applying a stain sealant combos. The stain sealant combo can be used especially in cases when you have limited time and you have a large area to cover.
Stain sealant is formulated to have color pigments and binders. These binders are either water, alkyd, or oil based. The resulting exterior is either opaque, transparent or anything in between. Make sure to reapply the stain sealant annually or every two years.
- Stir the stain-sealant combination thoroughly.
- Using a natural bristle paintbrush, apply a thin layer of the mixture to the wood that has been cleaned and sanded down.
- Allow the mixture to be soaked unto the exterior of the wood. Examine the exterior and reapply the oil on the exteriors that look dry.
- Remove any excess mixture from the exterior
- Make sure to give ample time for the mixture to dry.
- Sand the exterior with fine-grit sandpaper.
- Repeat the process to get the coat number necessary.
Making Hardwood Floors Waterproof: 7 Effective Ways
Using hardwood for your next project does not guarantee that it is waterproof. Here are seven effective ways to turn hardwood waterproof.
Tip #1: Choose Harder Woods
Plan your woodworking project to include hardwoods as the raw material for construction. Hardwood floors have water-resistance properties since their fibers are packed more closely together.
Whereas softwoods such as bamboo are porous and absorb more water. Thus, they do not have water-resistance properties.
Tip #2: Opt for White Oak Instead of Red Oak
Make sure to choose White oak over Red oak. Due to its cellular anatomy, white oak is more resistant to water than other oak types. The white oak’s cellular structure consists of pores with tyloses, making it water resistant. Furthermore, its wood fibers are compact.
Due to White oak’s cellular structure, it is commonly used in canoes and boats. If you use white oak for your home, place it in areas prone to moisture and high humidity, such as comfort rooms and kitchens.
Tip #3: Add Multiple Layers of Polyurethane
It is also best to add multiple layers of polyurethane on the exterior. The more layers you add, the more protection it can provide. Three coats are enough. Too many coats can make the exterior yellow.
(But, you might wonder if you can apply polyurethane on chalk-painted surfaces. Read next!)
Tip #4: Seek Professional Help in Sanding and Refinishing Hardwood
Not all wood projects can be done as a DIY job. Seek professional help in sanding and refinishing hardwood. This route leads to additional costs, but it is worth every penny. Professionals have years of experience and skills and use top-of-the-line machinery.
Tip #5: Screen and Recoat the Floors Periodically
Perform preventive maintenance to help the floors become more durable. Preventive maintenance can also be considered as screening and recoating or buffing. Do not worry since this process only needs one day of work.
Tip #6: Wipe Off Spills
Make sure to wipe off spills from the exterior immediately. Clean the surface as often as you can. And if ever the substance get on you skin, make sure to wash polyurethane off your hands, as well.
Tip #7: Don’t Just Rely on Waxes or Products to Restore Sheen
Do not apply waxes or products to restore the sheen of your wood surface. These products may result in a glossy finish, but this product can degrade the polyurethane on the floors. If you need to restore the surface’s sheen, you can use a regular hardwood clear.
You might be interested in: Recommended Polyurethanes for Outdoor Applications
Can you make wood waterproof by staining it?
You cannot waterproof wood by staining it. Staining the exterior of wood can only give the surface a certain color.
Are water-based polyurethanes waterproof?
Water based polyurethane is not waterproof. However, water-borne poly makes wood water resistant.
Are oil-based polyurethanes waterproof?
Oil-based polyurethane is not waterproof. Oil-based poly is water resistant.
Are polyurethane foams waterproof?
Polyurethane foams are waterproof up to a certain extent. You need to consider certain factors, such as material, to assess whether it allows water penetration or not.
Are urethanes waterproof?
Urethanes are waterproof to a certain extent.
Do shinier floors mean they’re more durable and waterproof?
Shinier floors do not mean that they are more durable and waterproof. This is a common misconception claimed by a lot of people. Different sheens are all equally durable.
Is varnish waterproof?
Varnish is a tried and tested sealant making a material waterproof.
Now, is polyurethane waterproof? Simply, it can decrease the water absorption rate and repels standing water. Since it’s always best to give your wood the best protection from the elements, adding oil or water-based poly on furniture is a common practice.
We hope this article clarifies the confusion and now you understand the benefits of polyurethane to woodworking.
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