Wood is very susceptible to water damage, which can reduce its age and life. This is why most wood finishes have waterproof or at least water-resistant qualities. But with so many options and confusing information, it can be hard to choose a finish. If you are trying to find the best waterproof finishes, you don’t need to look any further. In this article, we will tell you about the 3 best waterproof finishes to help seal wood.
The 3 best waterproof finishes are varnish, polyurethane, and lacquer. Oil-based varnish is composed of resin, which cures to a film finish that seals the wood and protects it from water. While polyurethane acts the same way, it is made of polymers, which are similar to plastic. Lastly, we have lacquer, which when made synthetically contains polymers, like polyurethane.
All three of the above finishes are synthetic in nature, in the case of varnish, it is usually mixed with naturally processed oils that are absorbed by the wood. All of these finishes dry to a clear film finish, there might be some hue due to the chemical processing. They are glossy and transparent which does not block the view of the beautiful wood grain.
Oil-Based Varnish
Oil-based varnishes are said to be the best waterproof finishes available in the market. Such varnishes contain natural oils, resin, and metal driers, which help them in drying faster. Each brand has a different composition, but the most important components are usually the same.
The way oil-based varnish works is pretty much like any other synthetic finish. The oil in the varnish is absorbed by the pores in the wood and the resin penetrates only on the surface. Once the finish is cured, the resin is hardened sufficiently and creates a clear coat that is durable. While varnish dries fast, it takes a similar time as other synthetic finishes to cure.
Spar or marine varnish seals wood like no other finish, which is why wooden boats from head to toe are coated with it and left to cure for weeks. After which it is protected from prolonged exposure to water for a year or two before you need to apply another coat.
The metal drier in varnish can be toxic so it is not a food-safe finish which in turn means it cannot be used in the kitchen. Though the metal driers usually evaporate with the fumes when the varnish is curing it is still wise to avoid it altogether in case some traces are left on the coat.
Pros
- Most durable sealant for protection against water.
- Once cured, it is super durable and protects the wood against any moisture damage.
- Dries to a clear film coat that allows you to see the wooden grain.
- Has a glossy mirror-like finish but can be found in satin as well.
- Lasts a long time if properly maintained.
- Some brands contain UV inhibitors to protect against the sun.
Cons
- Takes a long time to cure, longer than lacquer.
- Not kitchen safe and cannot be used on utensils and wooden countertops due to metal dryers.
Polyurethane
Polyurethane is very similar to varnish and it is stronger as well in terms of taking abuse. It is basically polymer or plastic dissolved in a solvent. There are two types of polyurethane, based on the solvent. One is oil-based polyurethane and the other is water-based.
These days most people prefer water-based polyurethanes as they dry really fast. But as the wood absorbs water, the grain raises a bit which needs to be knocked down before applying another layer. Oil-based polyurethanes on the other hand are better at layering but take a lot of time to dry and cure, which might be a deterring factor.
Also, the quality of the polyurethane mostly depends on the kind of polymer resins present in it. Since polymers have different grades, some polyurethane finishes look better compared to others. Cheaper ones have a more plastic feel and look to them. While the more expensive brands will give you a better look and feel depending on the grade of the polymer present in it. This Arm-R-Seal from General Finishes has a high-grade polymer in it and is slightly more expensive than a rub-on poly like this one from Minwax.
Polyurethane is the most used finish these days because of its quick drying times when it contains water solvents. It is less flexible than varnish, so it is great for sealing static objects like flooring, etc that are static. But for furniture that might flex or for boats you will want to stick to varnish or spar.
Pros
- Water-based polyurethane dries fast.
- It is very durable and can take a lot of abuse.
- Seals wood pretty well and makes it waterproof.
- Dries to a clear glossy film, but can also be found in satin.
- Has UV inhibitors to protect wood against sun degradation.
Cons
- Cheap varnish feels like cheap plastic.
- Oil-based varnish takes very long to dry.
- Fumes are toxic and can linger until fully cured.
Lacquer
Lacquer is a quick-drying finish that is usually sprayed on wood. The term lacquer is often misunderstood as any finish that can be applied by spraying it on the wood. But lacquers can also be applied with a brush, so any finish that can be sprayed on shouldn’t be considered one unless it fits the description.
Lacquers consist of synthetic polymers like acrylic resin and lacquer thinners, which are solvents. Once it is applied to any wooden surface it hardens very fast. Though lacquer consists of VOCs and should only be applied in an open space and with a respirator on. If you have any pre-existing breathing conditions, it is advised to not apply lacquer at all.
Lacquer not only dries fast, but it also cures faster than any other finish. It hardly takes 7-10 days for lacquer to cure to its full hardness. This means that all the chemicals that are in the mix, solvents, will have evaporated by then and only a layer of synthetic polymer remains to coat the surface of the wood.
If you are spraying on lacquer, you will need to apply at least 3-5 coats for a durable finish. Once it is fully cured, it will seal the wood completely and make it waterproof. The only issue with lacquer is that it is more brittle than the other two finishes mentioned above. So it cannot take a lot of abuse and is not flexible so should not be applied to any projects that might require flexing.
Pros
- Dries faster than any other clear coat film-based finish.
- Cures in a week or two at most.
- Glossy clear coat finish that really brings out the beauty of wood.
- Can be sprayed on making it easier to apply.
- Makes wood waterproof once it is fully cured.
Cons
- Extremely hazardous and contains VOCs that should not be inhaled at any cost.
- Not food safe in the least so never use it on any kitchen or food-related wooden item.
- Brittle that most other finishes and not flexible.
Theory Behind Waterproofing Wood
Wood absorbs water very fast and can crack due to rapid expansion. Even if you dry wood quickly once it gets wet, chances are it might warp and never retain its original shape again. To avoid that you must seal wood properly so that it does not absorb water from its surface. This is where sealers come into play, they completely cover the surface of the wood so that water cannot penetrate inside.
When any finish dries and cures to a film that just sits over the wood it repels water. Water usually gets into the wood through its pores, so if the surface is covered, there is no way for moisture to penetrate into the wood and damage it.
A good waterproof finish seals wood entirely, it repels water instead of resisting it. If you just need a water-resistant finish, you can apply a natural processed oil that will also dry to a film and cover the wood. But it can only resist water to a degree and so, it does not make it completely waterproof.
Something like spar or marine varnish, which when applied completely repels water from entering wood even when the wood is floating on a waterbody is what we call the best waterproof finish. But a good finish should not only prevent water damage, but also be durable, and our list of the best waterproof finishes fit the criteria.
How to Apply Sealer for Ultimate Water Protection
Applying a sealer is pretty easy, but generally requires a long time. So it is a time-consuming process, which cannot be rushed, due to the nature of waterproof finishes. To apply a sealer, you need to prepare the wood to accept it. You need to sand the surface of the wood from 80 grits up to 180 grits. This will help open the pores of the wood a bit and scuff the surface so that the finish bonds itself more strongly.
Once you are done sanding, clean any remaining dust, and apply a coat of your finish. Wait for it to dry now, if you are applying lacquer, it will dry rather quickly. So you can apply a second layer of lacquer over the first one and apply up to 3 this way.
If you have used polyurethane or varnish, just apply one layer and wait for it to dry. Once it has dried completely, there is no trace of stickiness or such, you need to scuff it once more. The reason for applying more layers of lacquer compared to the other two is because lacquer is thinner and would have completely worn off if you sanded it with one layer only.
Once you sand the layers, apply another coat and wait for it to dry. Rinse and repeat the process depending on how many coats you want to apply. Once the finish has cured depending on which one you used, it should have sealed the wood completely and made it waterproof.
If you want more information on how to apply a sealant to waterproof wood, check out this article.
Tips to Preserve Your Wood from Moisture
Here are some tips and tricks you can use to preserve wood from any moisture:
- If you own a house with complete wooden flooring, try to ensure that there is a waterproof cover in the area where there is a chance of water spilling over. For instance, the dining room, kitchen, and laundry room.
- In case of water spillage, dry it off immediately.
- Use a dry/wet vacuum to take out water from crevices between the wood.
- If you spill water on any wooden furniture, use a lint-free rag to wipe it dry, then just fan dry it.
- Don’t use a hairdryer or heat gun to dry water, let it dry under the fan.
- Keep wood indoors so that it does not get wet from any exterior sources like rain.
- If you have outdoor furniture, use finishes that have UV inhibitors to help prevent sun degradation while keeping the wood waterproof.
- Reapply finish to wooden flooring every two years to preserve it from water damage.
- The same goes for indoors and outdoors wooden furniture, reapplying the finish every year or two to help prevent it from taking any moisture-related damage.
Is Waterproofing Wood Indoors and Outdoors Different?
Indoor furniture does not get prolonged exposure to moisture or sunlight. It gets cleaned and maintained every so often, in some cases every day. This is why indoor furniture does not require thick coats of finish. Wooden flooring needs to be buffed and polished because of the abuse it takes though. But otherwise, most indoor wooden items do not require frequent recoats of finish.
Meanwhile, outdoor wood and furniture are constantly battling against UV rays from sun exposure. Not to mention it might get wet and remain wet for a long time due to rain. It can be days before the rain stops, and if you live in a cold region, the snow does not melt for days either. So your outdoor furniture and wood will be battered with moisture from rain, snow, and the environment.
For that, you need to give it proper care and maintenance every so often. You will need to reapply coats of waterproof finish that also have UV inhibitors to battle sun degradation because UV rays weaken the finish and it starts to peel off very fast. Wood also starts to get grey with prolonged UV exposure.
So the reapplication of finish will be much more frequent and you will need to be careful of the finish you choose, whether it is suitable for outdoors wood or not. Also, you will need to apply a thicker coat than usual for outdoor furniture so that it can be protected from the elements in the open better.
Oils for Waterproofing Wood
While oils do not completely waterproof wood, some oils are highly water-resistant and can protect the wood from moisture even under prolonged exposure.
Tung Oil
Tung oil is said to be the best for waterproofing wood, which is why it is the main component in some brands of Danish oil and even some oil-based synthetic finishes. It is the most durable amongst other oils, and more water-resistant than even shellac.
Tung oil is extracted from the seeds of the nuts of the tung tree which is commonly found in Asia, specifically the Chinese region. The tree can also be found in South America but very little compared to the Asian countries. This is why it will be hard to find pure tung oil at reasonable prices.
Being the best amongst natural finishes, it dries to a film after it is cured properly. And once it is cured, it is food safe and non-toxic, which makes it a great finish for kitchen countertops, cabinets, and utensils that you may have carved out. Not to mention, during the drying process, there are no toxic fumes coming from it, making it environmentally safe as well.
Amongst all the oils, tung oil makes wood waterproof to a certain degree. This is why it is one of the best natural oil finishes for outdoor furniture. However, you will need to frequently reapply coats if you want to keep your wood protected from the elements.
Not to mention tung oil actually deepens the tone of the wood and its grain without altering its color. It is transparent and gives a wet feel to any wooden surface it is applied on.
Polymerized Linseed Oil
Perhaps the second-best oil for waterproofing is boiled or polymerized linseed oil. It is made after processing and boiling natural linseed oil, which allows it to dry faster. Linseed oil is made by squeezing linseeds and preserving their extract. Raw linseed oil can also be used as a finish but it does not cure fast in the least and still leaves a sticky feel to it even after drying and curing completely.
So it is boiled at high temperatures under a vacuum to make it polymerized, which is thicker, dries way faster, and does not have that sticky feeling to it once it cures. The only issue with linseed oil is that it has a yellowish hue to it, it is not transparent, and while it does deepen the color of the wood and its grain, it does alter its tone slightly.
Some Danish oil brands use either tung oil or linseed oil as their main component. Which speaks volumes about its quality as a finish. It is, however, slightly less durable than tung oil and a bit less water-resistant. Though if a few coats of it are applied to any wooden furniture, it will repel water to a great degree.
Reapplying Sealers and Maintenance
After you apply a sealer to wood, it does not mean that it will be waterproof forever. The elements can be harsh and they will cause the previous finish to slowly degrade and wear off. So reapplying wood finishes is important if you want it to last for a long time.
Usually, finishes come with instructions on how long they will last under the most duress and how often you should reapply a coat. But you can also check signs of any cracks on the surface of wood which can be the finish peeling off. Sometimes the finish starts to fade and the difference is pretty visible as the wood looks either grey or dull.
When you see these signs, it is time to reapply a coat of your sealer on the wood. First, you need to remove the previous finish using sandpaper. This is important because if one area or section of the wood has its finish fading or peeling, it means that the other areas or sections will also face similar issues in near future. So by sanding the whole piece and removing the previous finish you are readying it for a full new coat.
Once sanded, just apply the finish as you would on a fresh piece. When you are done, let it cure and the maintenance is finished. If you feel that one part of the wood is more worn out due to certain conditions like prolonged sun exposure or water exposure than other parts, you can just sand that area and reapply the finish there.
FAQ
Is oil-based varnish better than polyurethane?
Oil-based varnish is definitely better than polyurethane. It is more durable against the elements but requires more time to dry and cure, which is why some people avoid using it.
Can tung oil be used as a wood sealer?
While tung oil has the highest water resistance properties compared to any other natural oil, it does not seal wood entirely. It repels water and makes wood waterproof to a certain degree, but it will not block water from penetrating wood if you submerge it for a long time.
Can you submerge wood that has been sealed using a waterproof finish?
Boats usually float over a body of water and stay on a watery surface for their whole lives. Once the wood has been sealed by a waterproof finish, it will not allow the wood to absorb water from rivers or the sea.
Final Thoughts
Waterproofing wood is an important part of keeping it safe. For wood to see long age, maintenance and care are of utmost importance, and waterproofing wood is part of it. With the finishes mentioned above, you will be able to waterproof any wooden object, furniture, or even a boat. Though before choosing a brand or finish, don’t forget to see whether it is suitable for a certain application or not.
