Frequently Asked Questions
Q: How important is it to properly clean my deck before applying a waterproofer?
Proper surface preparation is necessary for the best waterproofer application and performance. All exterior wood, even new 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. Thompson's® WaterSeal® Oxy Foaming Action Exterior Multi-Surface Cleaner is a great cleaner that can be used on a wide variety of outdoor surfaces — wood and composite decks, fences, concrete, masonry, brick, stucco, outdoor furniture, roofs, siding and some fabrics such as awnings and vinyl plastics. It will remove stains from dirt, mildew, algae, and fungus.
To find the perfect cleaner for your specific project check out our quick product finder or read more about our cleaners.
Q: How do I know which type of cleaner to use for my wood before applying a waterproofer?
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|
Q: Does water beading prove a surface is waterproofed and protected from water damage?
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.
Q: If a product is labeled "waterproofer" doesn't that automatically mean that it will protect against water damage?
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.
Q: Can water-based waterproofers work as well as oil/solvent-based 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).
Q: What is the difference between a solid and semi-transparent stain?
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.
Q: I'm getting ready to re-do the stain on my house. How many coats will I need?
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.
Q: What are the ideal weather conditions for staining?
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.
Q: Which is the better stain — Latex or Oil?
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 Waterproofing Stains provide our complete wood protection heritage. Before beginning the staining process, be sure your deck is clean and ready for treatment.
Q: Does linseed oil strengthen wood fibers?
We have seen no evidence to support this claim. In fact, linseed oil is just 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.
Q: Does pressure-treated lumber need waterproofing?
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.
Q: Do silicone products protect best?
Silicone/siloxane-based waterproofers do not waterproof wood and do not pass widely accepted industry waterproofing tests such as ASTM D-4446.
Q: Do fences-including cedar, pine and redwood fences-need protection?
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.
Q: What is the difference between softwoods and hardwoods?
The terms hardwood and softwood have nothing to do with the overall strength of the wood. As it turns out, several softwoods are harder and stronger than a number of hardwoods. However, both hardwoods and softwoods have the same basic chemical composition and both are susceptible to weathering and biological degradation. Softwood comes from trees that carry needles and seed-bearing cones and usually remain green throughout the year. Trees with broad leaves that shed at the end of a growing season are known as deciduous hardwoods.