Is Pressure Treated Wood Waterproof?

Image of a treated wood, but is pressure treated wood waterproof?Pressure treated wood is a popular construction material, and you can attribute that to the fact that it offers strong resistance to destructive insects such as termites that eat away wood, causing rotting in the process. This wood type has chemicals infused into its cells during the treatment, which plays a role in inhibiting infestation by the insects. You might have already known its qualities against termites, but is pressure treated wood waterproof?

NO! Pressure treated wood is not waterproof and is not resistant to rot. However, this wood contains chemicals that resist infestation by insects such as termites that eat away the wood and contribute to rotting. Therefore, ensure that you protect your treated wood with water repellant stains and sealers to enhance its durability.

The fact that pressure treated wood is safe from insects must not give you the confidence of not giving it further protection against elements such as water and the UV light from the sun. The two, especially, can contribute to more accelerated degradation of your wooden structures. Therefore, ensure that you use the best deck stains and sealers to give your pressure treated enhanced wood protection.

How Long Does Pressure Treated Wood Last?

Pressure treated wood can last up to 40 years with proper care and good maintenance practices.

As you are already aware, you can impregnate wood with preservative chemicals as a way of preventing rot and infestation by insects, especially in the exterior surfaces and structures such as decks. 

You will find pressure-treated lumber ideal for outdoor construction projects. This is because of its ability to defy time and serve you for many years compared to other alternatives. Additionally, pressure treated wood comes with affordable prices, which explains why they are very common for construction projects.

Large numbers of wood are put inside a huge cylindrical chamber called a retort during the treatment process. This chamber has a door on one end, which is usually sealed so that it is airtight, after which waterborne chemicals are forcefully infused into the wood under high pressure.

How Long Should You Wait for Waterproof Treated Lumber?

Following the pressure treatment of wood, you need to allow the preservatives up to 30 days for the wood to dry properly and be ready to soak up the sealant. After 30 days, you need to carry out a test to see if the wood is dry or needs more time. The best and simple test that you need to do is the sprinkler test. 

Here’s what you need to do in the sprinkler test, pour a few drops of water over your wood’s surface, and observe how it behaves. If the water absorbs immediately, it means that the wood is dry, and you can stain it right away. However, if you notice bubbles coming from the sprinkles, it means that the wood is not dry; you should allow it more time to dry thoroughly.

Is It Better to Stain or Paint Pressure Treated Wood?

Having tried to do both painting and staining pressure treated wood, I can confidently say that the exterior paint is not very likely to adhere to treated wood and would not last long before it peels. I’d advise that you stain or seal your treated wood instead of painting. With that, I’m not saying that you cannot paint your treated wood. It is possible; however, you need to take extra precautions to ensure that you get it right.

Can You Waterproof Pressure Treated Wood?

Image of ready seal, a formula to waterproof your treated woodYes, you can make your pressure treated wood by sealing or staining it with a finish with waterproofing features such as Ready Sealwhich is both a deck stain and sealer. Even as you prepare to waterproof your pressure treated wood using a stain, sealer, or a formula that serves as the two combined, ensure that you have made proper preparations of the surface. Start by cleaning the surface and sanding, especially if the surface has a previous finish. Sanding etches the surface, which in turn helps increase the adhesion between the surface and the formula.

How to Waterproof Pressure Treated Wood

Pressure treated wood is not waterproof; however, you can make it repel water using any of the three methods highlighted below. 

  • You can use linseed or Tung oil: Either of the two creates a beautiful and protective hand-rubbed finish.
  • Sealing the Wood: You can do this using a coating of polyurethane, lacquer, or varnish.
  • Staining and Sealer in One: Some formulas serve the two roles in one finish to give your surface-enhanced protection against water and moisture.

Even as you consider the above methods, you should know that not all are applicable in every situation. Some of the techniques best suit certain conditions such as the external environment, type of grains, among other factors.

Materials Needed

  • Linseed oil
  • Mineral spirits
  • Polyurethane finish
  • Natural bristle paintbrush
  • Rags/Cotton Clothing
  • Fine-grit sandpaper
  • Polyurethane sealing finish
  • Wood varnish
  • Lacquer
  • Deck stain and sealant

Method One: The Use of Sealants for Enhanced Wood Protection

Sealing is one of the very best ways that you can use to give your treated protection against water penetration. The use of polyurethane, varnish, as well as lacquer provides excellent waterproofing properties. You can choose to brush, spray your polyurethane finish on an adequately prepared wood surface. Allow the finish to dry before you sand and apply another layer. 

Water-based polyurethane takes about 6 hours to dry while the oil-based one will need up to 24 hours for it to dry to touch. The curing time of the two extends to as long as 30 days.

If you desire to have the best results possible, I advise you to apply your finish at room temperature. Also, avoid shaking your finish before using it; this will help prevent the bubbles’ formation over the surface once the sealer dries.

Polyurethane formulas are fast-drying. Some may take as little as 15 minutes to dry. Even so, they still contain volatile organic compounds, especially the oil-based poly products, and that’s why you should ensure that you are working in a properly ventilated environment during the application.

Below are some of the advantages of formulas commonly used in sealing.

  • image of polyurethane sealer for waterproofing woodPolyurethane sealants contain different ingredients that allow you to select your favorite finish other than the acrylic and polyurethane resins. You get to choose any from a high-gloss shine to a soft sheen. One good thing about the polyurethane finishes manufactured recently is that they won’t yellow easily, a quality that makes them great on light-toned woods. 

In particular, oil-based polyurethane comes with so much durability; however, it takes mineral spirit to clean the brushes following your application. Water-based polyurethane is easy to clean as it only requires the use of water and soap.

But brush cleanup calls for the use of mineral spirits or turpentine. With water-based polyurethane, cleanup is a snap with soap and water.

  • Varnish Sealants come as a combination of resin, solvent, and drying oil to give a hard-shell finish to resist scratches without turning yellow. If you are looking to waterproof your wooden structure, especially the ones on the exterior environment, it would be best if you can use the marine varnish to seal your surfaces. These varnishes also come with UV absorbers that help minimize the damage by the sun. 

In case you intend to seal your interior structures such as coffee tables, then go for spar varnishThey resist pesky cup rings. If you are doing after cleaning following your application, use mineral spirits or turpentine.

Lacquer is, in most, if not all cases, a mixture of tree resin or synthetic resin dissolved in alcohol. It is the best sealant, mostly for wood furniture. Much as this formula can develop a yellowish tinge with time, it is not very pleasing on lighter woods. Even so, it brings out a rich and extraordinary finish that can resist scratch if used on a deep-toned wood. This product is available in indifferent sheens, and you can use lacquer thinner to thin it. Lacquer has strong fumes, and therefore you must ensure that you are working in a properly ventilated room.

Method TwoThe Use of a Warm, Hand-rubbed Oil Finish

Linseed oil is a product of the flax plant’s seeds, plus Tung oil, which is extracted from the Tung tree of the Chinese and is excellent for the creation of virtually all the hand-rubbed oil finishes.

This oil has existed for several centuries as it helps beautify and protect dark grained wood like walnut and mahogany. Linseed oil is still in use today, though with so many improvements. Most manufacturers blend these oils with other chemical ingredients, which hastens the drying times and minimizes stickiness. Additionally, you can buy the pre-blended Tung oil and other linseed oil products, make your custom made mixture to come up with a finish. 

You will find that a standard hand-rubbed oil blend comes with one-part oil (usually Tung or boiled linseed), the other part -mineral spirits, and one-part polyurethane formula.

Here’s the procedure of applying your finish:

Stir Properly

If you are looking to seal your pressure treated wood using this approach, ensure that you first stir your formula properly then apply it using a natural bristle paintbrush to dark-grained treated wood that’s well prepared. 

Allow the oil to soak inside the wood, and if you notice spots that still look dry, you can reapply the formula.

Once you have applied your formula, wipe off the residual oil and rub the surface well using clean, dry rags- this will help remove all excess.

Give your wooden structure enough time to dry. Usually, this takes 24 hours, depending on the amount of oil present in the mixture.

After the surface dries, use fine sandpaper for sanding the surface lightly.

Feel free to repeat this process, adding coats as you require until you get the finish that you want on your structure.

Note: The rags that you have used for wiping extra can spontaneously combust even when there is no flame, and this is attributed to the fact that these oils generate heat when drying.

Therefore, you must take extra precautions, such as having a bucket ready around your working area to help put off the flames in case it happens.

Method Three: Use of a Combination of Stain And Sealer In one 

If you are looking to protect your pressure treated wood with both stain and sealer, you can do it on one go using a formula that serves as both. These formulas save you the time and cost of having to acquire and apply the two separately.

In virtually all the stain-sealant products that you shall use, you will realize that they contain color pigments that have extra binders. These binders can be oil-, water- or alkyd-based. Therefore, your final finish can vary from transparent, semi-transparent, or opaque, depending on the concentration of the formula’s pigments.

For exterior structures, I advise that you refinish after every year to ensure that you keep your wood in the best condition possible.

All the stain-sealants formulas do not build up on the wood; instead, they soak in, allowing excess evaporates except for alkyd-based products. Alkyd-based stain-sealants usually leave a light surface coating on the wood’s surface, which makes them best suited for interior wooden structures, such as rustic furniture, that don’t necessarily require future applications. 

If used on the exterior environments, you will notice that the alkyd-based stain-sealers will likely start to peel, especially when the wood is not well prepared to apply the formula.


The pressure treatment of wood is not a new thing, and it is not about to end because these woods are reliable for construction projects. They resist infestation, which is a plus, especially if you hope that your structure can serve you over an extended duration. One question that people keep asking… 

Is Pressure Treated Wood Waterproof?

You must be aware by now that pressure treated wood is not waterproof. Suppose you choose to use it to construct structures, especially in the exterior environment, where it comes into extended contacts with destructive elements such as water and UV rays. In that case, you should seal the wood with a formula that features UV inhibitors and water repellency.

Watch the video below on how to waterproof your treated wood:

Have you found this article helpful? Have I answered all your questions regarding the pressure treated wood? Do you have a question, opinion, or suggestion? Kindly feel free to share any concerns with me in the comment section below.

Image of a woodworker wearing hearing protectors for woodworking

Tyron Otieno

Tyron is an avid woodworker and writer. He founded this website to help other woodworkers, whether hobbyists or professionals by sharing his knowledge and experiencie after a decade of woodworking.