Should You Apply Thompson’s Water Seal Over Paint?

Thompson’s Water Seal is a popular sealant and waterproofing agent for outdoor surfaces like wood, concrete, masonry, and brick. Its versatility and efficacy make it an attractive option for maintaining and protecting painted exterior surfaces. However, most sources advise against applying Water Seal directly over painted wood or other materials.

Thompson's Water Seal Over Paint

Overview of Thompson’s Water Seal

Thompson’s Water Seal is a water-based, clear sealer that protects porous exterior vertical surfaces from water damage. Key features include:

  • Works on various common building materials – wood, concrete, stucco, brick, fiber cement, grout, mortar, and more.
  • Contains polymers that penetrate porous surfaces and bind to form a hydrophobic barrier resistant to moisture absorption.
  • Dries to a clear, matte finish that resists UV damage without altering the surface appearance substantially.
  • Available in tinted versions that provide color while sealing.
  • Water-based formula is low odor and easy to apply with a brush, roller, or sprayer.
  • Very affordable and accessible at most hardware stores.

On bare wood, Thompson’s Water Seal is highly effective at preventing cupping, cracking, swelling, and the growth of mold and mildew. It’s great for wooden fences, decks, sidings, and outdoor furniture.

However, its usage on top of painted surfaces is more nuanced, as discussed next.

Using Thompson’s Water Seal on Painted Wood

Applying Thompson’s Water Seal over painted wood is possible but not always advisable. There are a few factors to consider:


  • Water Seal does offer an extra layer of protection on top of paint against moisture, sun damage, and mildew. However, quality exterior paints already contain similar water-repellent properties.
  • For severely weather-beaten painted surfaces, a fresh coat of paint likely provides better protection than applying Water Seal on top.

Paint Adhesion

  • Water Seal bonds to bare wood effectively, but not as well to surfaces with existing paint or finishes.
  • The waxy polymers in Water Seal may interfere with proper adhesion of paints.
  • Later paint touch-ups or new coats may not adhere optimally over layers of Water Seal.


  • Water Seal provides a low gloss sheen that can alter the original look of painted wood.
  • Makes the surface slightly darker and enhances the wood grain visually.
  • Later paint touch-ups may visibly stand out from the faintly glossy Water Seal layer.

Best Practices

  • Allow paint to cure fully, around 30 days, before applying Water Seal on top.
  • Clean and lightly sand the surface to improve adhesion.
  • Test on a small area first to check compatibility with the existing paint.
  • Reapply Water Seal annually prior to repainting for optimal results.

Overall, Thompson’s Water Seal does offer supplemental protection over painted wood, but may slightly alter aesthetics. It’s advisable to rely on high-quality exterior paints instead for wood that’s already painted.

Using Thompson’s Water Seal on Painted Decks

Deck surfaces are particularly prone to weathering and often benefit from Thompson’s Water Seal application. Water Seal can provide an extra barrier against moisture absorption and associated warping, rotting, and mold growth on painted deck boards and railings.

Points to note when using Water Seal on painted decks:

  • Allow paint to cure fully before applying Water Seal. Most deck paints require 1-2 weeks drying time.
  • Clean deck thoroughly and sand lightly to improve adhesion.
  • Apply Water Seal evenly according to manufacturer’s directions, usually 1-2 coats.
  • Reapply Water Seal annually, before re-painting for best results.
  • Use a compatible paint if touching up painted decks treated with Water Seal.
  • Alternatively, use a high-quality deck stain/sealant instead of relying on paint and Water Seal separately.
  • Water Seal may work better on vertical painted deck surfaces like railings and skirting vs. horizontal deck boards prone to scuffing.

Using Water Seal to fortify painted decks can be worthwhile. But as a general rule, it’s better to pick a quality stain or exterior paint when finishing a bare wood deck.

Proper Process for Applying Thompson’s Water Seal

To achieve the best results from Thompson’s Water Seal on any surface, proper preparation and application is crucial:


  • Surfaces should be clean, dry, and free of dirt, dust, oils, and existing finishes/sealants.
  • Clean with an all-purpose cleaner and rinse thoroughly. Let dry 24-48 hours.
  • Use a mildew remover and scrub brush for moldy areas, then rinse and dry.


  • Lightly sand to roughen up the surface. This improves Water Seal absorption and adhesion.
  • Repair cracks, holes, and defects before applying Water Seal.
  • Mask off areas like windows, plants, siding not intended for Water Seal.
  • Stir the container well before starting.


  • Use a brush, roller, or pump sprayer to apply Water Seal liberally and evenly.
  • Work it thoroughly into the pores of the material.
  • For horizontal surfaces, apply in sections and maintain a wet edge to prevent lap marks.
  • Allow 2-3 hours drying time before reapplying a second coat, following the same process.
  • Two coats are ideal for sufficient protection.

Curing and Cleanup

  • Let Water Seal cure 24-48 hours before exposure to moisture.
  • Clean equipment with soap and water after application.

Proper prep and application ensures maximum effectiveness from Thompson’s Water Seal.

Effect of Thompson’s Water Seal on Paint Adhesion

The key caveat with using Thompson’s Water Seal over paint or applying paint over it is potential adhesion issues stemming from Water Seal’s composition. Key factors:


  • Water Seal contains silicone water repellents that deeply penetrate surfaces.
  • Silicones don’t provide a surface to which typical paints and finishes can bond well.

Petroleum Distillates

  • Solvents like mineral spirits facilitate penetration but leave a waxy residue.
  • This wax interferes with proper adhesion of paints.

Water-Based vs. Oil-Based

  • Oil-based primers may have better compatibility with Water Seal residues.
  • But water-based latex paints and stains will not adhere well, tending to peel or chip.

Competing Protection

  • Water Seal and quality paints both offer weather protection through similar water-repelling mechanisms.
  • Applying both on the same surface is somewhat redundant.

Preparation for Painting

  • Allow Water Seal to cure at least 2-3 weeks before painting over it.
  • Thoroughly clean and sand the surface to improve paint adhesion.
  • Use an oil-based bonding primer meant for slick surfaces before repainting.

Proper prep work can mitigate some adhesion issues. But avoiding overlap of Water Seal and paint is best.

Recommendations for Using Thompson’s Water Seal and Paint

To summarize key points on using Thompson’s Water Seal in conjunction with paint:

  • Apply either Water Seal or a quality stain/paint on bare wood, but not both.
  • For already painted surfaces, rely on repainting for renewal rather than applying Water Seal.
  • If using Water Seal on painted surfaces, prepare the surface well and test adhesion first.
  • Allow sufficient drying time before painting over Water Seal – 30 days or more.
  • Opt for an oil-based bonding primer when repainting over Water Seal.
  • Or consider removing existing Water Seal coatings through thorough cleaning and sanding before repainting.
  • For best adhesion results, avoid overlapping separate paint and Water Seal applications.
  • On any surface, maintain regular reapplication of whichever protective coating you choose for optimal weather resistance.

Proper surface prep and test patches are advised when dealing with potential adhesion issues from Water Seal usage over paint. Optimal results come from selecting one preferred protective coating and maintaining it consistently.

Maintenance and Reapplication of Thompson’s Water Seal

To maximize the longevity of Thompson’s Water Seal protection, proper maintenance and reapplication is crucial:


  • Sweep or wipe down surfaces periodically to prevent buildup of debris.
  • Use a pressure washer on fencing, siding, and decks to remove dirt and grime.
  • For mold/mildew, use a cleaner and stiff brush to scrub affected areas.
  • Check for and repair any cracks or damage that allow moisture intrusion.

Reapplication Frequency

  • Reapply Thompson’s Water Seal every 1-2 years for optimal protection.
  • Reapplication for decks and outdoor furniture may be needed yearly subject to heavier use.
  • Horizontal surfaces usually require more frequent recoatings than vertical surfaces.

Reapplication Tips

  • Allow the previous coat to dry 2-3 days before reapplying.
  • Clean and lightly sand to help adhesion before reapplying.
  • Spot treat any visibly worn or bare areas before applying a full coat.
  • Maintain adequate coverage by applying Water Seal liberally over the entire surface.
  • Shake or stir the can frequently during application for consistency.

Enhancing Appearance

  • Reapply tinted Water Seal in the original hue to maintain color uniformity.
  • Or use a fresh color for an updated look.
  • Consider applying a clear coat of Water Seal over tinted sealant every few years to refresh the vibrancy.

Complementary Protection

  • Use Thompson’s Water Seal in combination with deck stains and wood preservatives for enhanced protection.
  • On wood siding, applying exterior paint over Water Seal boosts durability.
  • Concrete and masonry sealers used along with Water Seal offer added water repellency.

With the proper maintenance regimen, Thompson’s Water Seal can protect exterior surfaces for years before requiring a full removal and reapplication.

Removing Thompson’s Water Seal

If Thompson’s Water Seal begins to exhibit diminished performance or excessive aesthetic changes over time, full removal and reapplication may become necessary.

Testing Water Seal Condition

  • Check for darkened, patchy areas that indicate worn sealant not shedding water effectively.
  • See if moisture is causing swelling, warping, rotting or mold underneath.
  • Confirm need for removal if paint or stains applied over Water Seal exhibit poor adhesion.

Removal Methods

  • Use a paint stripper or solvent like acetone applied generously over Water Seal and let it sit before power washing.
  • Harsh chemical strippers may be necessary for removing multiple layers of Water Seal.
  • For full removal, rigorous sanding or media blasting may be required after using chemical strippers.
  • Properly contain, collect and dispose of dissolved Water Seal residues after removal.

Preparing for Reapplication

  • Allow surface to dry completely after removal before reapplying Water Seal or paint.
  • Make any necessary repairs to restore the bare substrate after removal.
  • Lightly sand and wipe down the surface with a clean rag before reapplying.

Thompson’s Water Seal is designed for longevity, but renewal will be needed. Proper removal prevents adhesion and appearance issues.

Frequently Asked Questions

Should you apply Thompson’s Water Seal before or after painting?

Applying Thompson’s Water Seal before or after painting is not generally recommended. It’s best to use either Water Seal or paint alone when finishing bare wood. Water Seal can be applied over fully cured paint, but may cause adhesion issues for future paint touch-ups.

How long does Thompson’s Water Seal protection last?

On most properly prepped and sealed surfaces, Thompson’s Water Seal can last 1-3 years before needing reapplication. Decks and outdoor furniture may need yearly resealing due to heavier use and exposure. Proper maintenance extends longevity further.

What is the best method for applying Thompson’s Water Seal?

Using a pump sprayer, roller, or brush allows applying Water Seal liberally over surfaces. Maintaining a wet edge on horizontal surfaces prevents lap marks. Let each coat dry 2-4 hours before applying the next. Two coats are recommended for sufficient protection. Proper prep and cleaning prior to application also improves results.

Can you apply Thompson’s Water Seal over pressure-treated wood?

Thompson’s Water Seal is well-suited for application over pressure-treated lumber once it has dried completely after installation. The wood preservatives do not block Water Seal’s protective capabilities. But proper surface prep is still needed before applying.

Can you put Thompson’s Water Seal over painted wood?

Applying Thompson’s Water Seal over previously painted wood is possible but not ideal. It can provide extra protection, but may alter the surface appearance while posing adhesion issues for subsequent paint touch-ups. It’s better to rely on high-quality exterior paints alone on painted wood. Proper prep helps if using Water Seal on painted surfaces.


Thompson’s Water Seal can effectively protect painted exterior surfaces from moisture damage. However, potential adhesion issues exist when applying over paint or painting over it. Following best practices for surface preparation along with proper product application and maintenance extends the protective benefits it offers on both bare and painted substrates. But relying on either a quality exterior paint or Water Seal alone provides optimal performance on any surface. With the right expectations and processes, Thompson’s Water Seal can be a versatile waterproofing solution for painted and unpainted wood, concrete, masonry, and decking.

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