Frequently Asked Questions

Proper surface preparation is necessary for the best waterproofer application and performance. All exterior wood — from decks to fences to siding — should be cleaned before sealing, staining or painting to remove dirt, stains from mildew and mold, waterproofers, wood stains, paint and other contaminants. Even new wood can have dirt or other invisible barriers to the penetration of a coating. For instance, new wood can have an invisible mill glaze, caused when the heat of the milling equipment reacts with the natural oils in the wood. For step-by-step instructions on cleaning your outdoor surfaces, visit the How-To section and read the Expert Advice articles.

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

For Wood and/or Composite Surfaces

If you need to remove:	Use:
Stains from dirt, mildew, algae & fungus and there is little or no trace of a residual finish.	Thompson's® Water Seal® Deck Wash
Weathered clear & tinted waterproofers 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
On REDWOOD/ CEDAR/ HIGH EXTRACTIVE Wood: Tannin staining and restore lighter color of redwood/ cedar/ mahogany or other high extractive wood species in addition to removing stains from dirt, mildew, algae & fungus and/or, as instructed, to neutralize any wood species after using other cleaners.	Thompson's® Water Seal® Deck Cleaner & Brightener

For Exterior Multi-Surfaces

If you need to remove:	Use:
On EXTERIOR SURFACES such as Wood & Composite Decks, Fences, Concrete & Masonry, Outdoor Furniture, Roofs & Siding: Stains from dirt, mildew, algae and fungus with a non-bleach, chlorine-free oxygenated foaming formula.	Thompson's® WaterSeal® Oxy Foaming Action Exterior Multi-Surface Cleaner

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 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, Thompson's^® WaterSeal^® waterproofers 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.

Yes. Thompson's^® WaterSeal^® Advanced waterproofers, which are water-based, offer the highest level of waterproofing protection available. In fact, they far exceed the industry standard for waterproofing wood. In addition, they have the benefits provided by a water-based formula, as well as their own unique benefits (see question below).

Water-based waterproofers have easy soap and water clean-up, are generally low odor and are environmentally safer. Thompson's^® WaterSeal^® Advanced waterproofers have other unique benefits - these products can be applied just hours after cleaning the deck and offer immediate protection for new pressure-treated wood. This breakthrough formula seals out 99% of the water, right from the start. Plus, it lets you clean and treat in one day.

It's a matter of personal preference. All stains differ from paint in that they provide color while also allowing the wood's character to show through. A "solid" product is the most opaque and allows texture, but little grain detail, to be seen. Also, opaque products usually last longer because they block out a greater proportion of damaging ultraviolet rays.

A "semi-transparent" product allows some grain to be seen. Keep in mind that the more transparent the product, the more its color will be affected by the underlying wood. Variations in wood color, then, will be more obvious with transparent products, as will any natural blemishes such as knots and tannin. Please note, we do not recommend using a semi-transparent stain on wood that previously has been treated with paint or a solid color stain.

Only one coat of Thompson's^® WaterSeal^® Deck & House Waterproofing Stains is recommended. However, a second coat can be added if desired. If it's been a few years since you last stained, or you're going to a lighter (opaque) color, you may need two coats. Make sure to follow the directions on the package.

The air temperature for applying any Thompson's^® WaterSeal^® Deck & House Waterproofing Stains should be between 50°F and 95°F. Avoid staining in direct sunlight or in windy conditions as the stain will dry too quickly. Also, it is best to avoid applying in windy conditions as overspray problems may occur.

It depends on your preference. Latex Waterproofing Stains are water-based, making them easier to use. Latex Waterproofing Stains have low odor and clean up with soap and water. If you would like a more traditional exterior stain, try using an Oil Waterproofing Stain. No matter which formula you choose, Thompson's^® WaterSeal^® Deck & House Latex or Oil Waterproofing Stains provide our complete wood protection heritage.

We have seen no evidence to support this claim. In fact, linseed oil is just a filler and provides very little - if any - waterproofing benefit. We also know that linseed oil is "mildew food", as it is susceptible to mildew growth; particularly in warm and humid climates. Extra mildewcide is required in products which contain linseed oil, and this is not usually provided.

Yes. Pressure-treated wood is pretreated with chemicals to prevent insect damage and rot. It is not waterproofed. 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 cycles cause wood to crack, warp and split - this is typically what is meant by "water damage." Thompson's^® WaterSeal^® brand offers the most powerful protection against water damage, guaranteed.

Silicone/siloxane-based waterproofers do not waterproof wood and do not pass widely accepted industry waterproofing tests such as ASTM D-4446.

All fences need to be protected from water damage. Even pressure-treated wood may protect a fence from insect damage while allowing water damage to occur. Fences that are properly protected will last longer and look better. Whether it's a fence, deck or outdoor furniture Thompson's^® WaterSeal^® Wood Protectors give you superior, long-lasting protection against water damage and its durable coating resists mildew and UV damage.