FAQs

GENERAL

In order to get maximum penetration and performance of the waterproofer or stain, it is important that the surface is cleaned of any stains from mildew, dust, dirt, oil, soot, grease or other contaminants. The Thompson’s® WaterSeal® cleaner line has a product for every exterior wood cleaning need.

Yes. Although pressure-treated lumber is pre-treated with chemicals, preventing insect damage, it is NOT waterproofed. In fact, the chemical treatment actually causes the lumber to dry out quicker and absorb more water than untreated lumber. When wood absorbs water, it swells; as the wood dries it shrinks. These wet/dry cycles cause wood to crack, warp and split.

No. There are standardized industry tests developed and adopted by both the Federal government and the American Society of Testing and Materials (ASTM) which measure the amount of water repellency a waterproofing product provides. Products for wood must be greater than 60% efficient at providing water repellency in order to meet the minimum water repellency criteria. Not all products provide this much protection, but nearly all Thompson’s® WaterSeal® products exceed this standard.

Yes. Stains are formulated to better penetrate wood and accentuate its natural beauty. With paint, you have a choice in the level of sheen you want while stains generally have a flat sheen. With stain, you also have a choice in the level of opacity. Transparent shows the most wood grain while adding subtle color. Semi-transparent allows some of the wood grain to be visible to the eye. Solid covers the grain, but still allows some of the wood’s natural texture to show through. Paint covers the grain.

Not with Thompson’s® WaterSeal® Wood Sealers. They are specially formulated so you get unsurpassed waterproofing protection and beautiful color at the same time. However, not all stains provide the same level of water repellency. If you are not using Thompson’s® WaterSeal® Wood Sealers, we can’t guarantee how much waterproofing protection you’re getting.

No. To determine if your surface is still protected perform the splash test. Sprinkle water on various sections of the surface to be sealed. If water absorbs and darkens color of surface within five seconds, surface is porous and considered ready to be treated. If water beads up or otherwise sits on top of surface, then the surface does not need protection at this time.

When wood absorbs water, it swells. As the wood dries, it contracts. These repeated expanding and contracting cycles cause small cracks which grow and expand over time. In cold climates, this cycle is exacerbated by freezing and thawing. Excessive moisture content in wood also supports fungi that cause wood rot.

Sunlight will turn the upper layer of wood cells silver over time, but it will not structurally damage the wood. It will also affect stains and finishes over time, which can then open the wood up to damage from water.

EXTERIOR WOOD SEALERS

Beading alone is not a measure of water repellency. It is just a surface phenomenon - remember, water will even bead up on a dirt field when it starts to rain. Some products are formulated to produce water beading on wood but do not effectively protect the wood from water penetration and damage. The best way to tell if a surface is waterproofed is to use the “Splash Test.” Pour a little water on the surface. If it darkens, the water is penetrating and the surface needs to be protected. If it beads, rolls off or stands on the surface, but does not darken the surface, it is protected. Thompson’s® WaterSeal® Waterproofers and Wood Sealers penetrate the wood so that even after the beading is gone, the waterproofing protection lasts.

Passing federal or industry tests IS NOT required for a product to be advertised and sold as a “waterproofer.” However, nearly all Thompson’s® WaterSeal® products exceed the widely accepted industry tests which measure the amount of water repellency a waterproofing product provides (these tests are developed by industry leaders and the American Society of Testing and Materials [ASTM]). On tests with a pass/fail standard, a score of 60% or higher means the product passes. There are many products on the market which do not meet this criteria yet still claim to be waterproofers.

One very important step is to remove all existing loose, flaking or peeling stain. Failure to do so will result in continued flaking and peeling. Other preparation steps include cleaning the surface thoroughly. Apply to a small sample section of the surface to ensure the color you want.

Clear
Provides long-lasting protection while helping enhance and maintain wood's natural color
Transparent
Provides complete outdoor wood protection by adding subtle color 
Semi-Transparent
Adds beautiful color while still allowing some wood grain to be seen
Solid
Hides the wood grain while allowing wood texture to show 

Drying time will vary depending on temperature and humidity. Under normal conditions, the product should dry to the touch within 2 hours.

Perform the splash test. Sprinkle water on various sections of the surface to be sealed. If the water absorbs and darkens the color of the substrate within five seconds, surface is porous and considered ready to be treated.

On new pressure treated lumber, please allow 30 days before applying Thompson’s WaterSeal Wood Sealers.   Always perform the splash test before sealing wood.  If water absorbs within 5 seconds after you’ve sprinkled it on the surface, the wood is porous and considered ready to be sealed.  If the water beads up or otherwise sits on the surface, then the surface is not yet ready to be sealed.

CLEANERS

It’s important to choose the right cleaner for your project to ensure the best adhesion during the waterproofing / staining process. Use the below guide as a reference when selecting a surface cleaning product.

For Exterior Wood Surfaces:

If you need to remove:
Use:
Weathered clear waterproofers & transparent or semi-transparent stains in addition to stains from dirt, mildew, algae & fungus
Thompson's® Water Seal® Heavy Duty Deck Cleaner
Oil & water-based solid stains and long-lasting, hard-to-remove semi-transparent stains & waterproofers in addition to stains from dirt, mildew, algae & fungus
Thompson's® Water Seal® Maximum Strength Deck Stripper

Proper surface preparation is necessary for the best waterproofing / staining application and performance. All exterior wood – from decks to fences to siding – should be cleaned before sealing, staining or painting to remove waterproofers, wood stains, or stains from dirt, mildew, or algae. Even new wood can have dirt or other invisible barriers to the penetration of a coating. For instance, new wood can have invisible mill glaze, caused when the heat of the milling equipment reacts with the natural oils in the wood, that needs to be removed.

The fastest way to apply is with a pump-up sprayer (using a coarse setting), but you can also apply with a brush or a roller. You should apply liberally. In the case of areas with heavy discoloration or dirt, apply a second coat, brush lightly with a broom and hose off.

Weather and environment can create various factors. Always follow the instructions on the waterproofer or exterior stain product label.

Even new wood can have dirt or natural sap/tannins on it, or something called mill glaze. Mill glaze is formed when the friction of planning machinery heats the existing sap in the wood, momentarily liquefying it. Once the surface cools, the sap re-hardens as a glossy sheen, which can interfere with a new coating. Anything that is on the wood can keep the new waterproof coating from being properly absorbed, and so the wood should be cleaned first.

There is no hard and fast answer on how long a project will take. The more dirt or old coating on a deck, the more thorough you will need to be in cleaning. It takes me about 3 hours to completely clean my multi-level, 400 sq. ft. deck, (with a set of stairs but limited railings/banisters) and I don’t use a power washer.

Again, there is no rule on how long to scrub each area of the deck. If an area has just light dirt or gray color, a few passes with the scrub brush may be enough. For more dirt or an old coating, you may want to spend 30 seconds on each area. But – you cannot “over scrub,” and you can always re-apply cleaner, if needed. 

The thing about power washers is that it is easy to damage the wood if you’re not careful. You can cause “feathering,” which is a fuzzy-looking surface. You can even “carve” into the wood if the pressure is extreme. If you do choose to use a power washer, begin with the ready-to-use cleaner, and use the power washer for extra rinsing muscle, keeping it at 1,200-1,500 PSI. The use of a cleaner is important: while the power washer can get rid of the stuff you can see, it leaves behind mold, mildew, and algae spores. The cleaner will help to kill those spores so that they don’t interfere with the new deck coating.

It may be hard to tell while the wood is wet. Allow it to dry at least partially - there should be no more gray color, mildew or old coating. You should see mostly a natural, brown wood color. Just remember that old coating or dirt left on the deck will keep the new coating from being absorbed by the wood.

You should not see any more “sudsing” once the cleaner is rinsed from the wood.

MULTI-SURFACE

No. Thompson’s® WaterSeal® Clear Multi-Surface Waterproofer applies white but dries clear and allows your wood to gray naturally over time. Prior to covering the entire surface, a test patch should be done in an inconspicuous place. The test patch will give you an indication as to whether you will like the look of a clear product.

Simply perform the splash test. Sprinkle water on various sections of the surface to be sealed. If the water absorbs and darkens the color of the substrate within five seconds, the surface is porous and ready to be treated. If the water beads up or otherwise sits on top of the surface, then it does not need protection at this time.

“More is not better”. The situation that you have described is an over-application of Thompson’s® WaterSeal® Clear Multi-Surface Waterproofer. The “excess” is due to the fact that Thompson’s® WaterSeal® Clear Multi-Surface Waterproofer was unable to penetrate into the substrate. Because of this, you need to make sure that the surface is completely dry and free of debris prior to applying. If over-application occurs and there is puddling of the product, redistribute product within 15 minutes to a dry area or wipe off.

No. These products will not change the surface’s feel or leave it sticky.

Thompson’s® WaterSeal® Fabric Seal can be used on many different fabrics, including canvas, nylon, polyester, and cotton.

Yes. In addition to providing maximum strength waterproofing protection, Thompson’s® WaterSeal® Fabric Seal also contains UV inhibitors in order to resist color fading caused by the sun.