Wood stains give amazing color but no waterproofing, so the finish is prone to water damage. So, can you apply Thompson’s water seal over stained wood to protect it?
You can apply Thompson’s water seal over stained wood. It will protect the wood from water damage and mold growth. However, whether this is a good idea or not depends on the type of wood stain.
You can apply Thompson’s water seal over water-based and some oil-based stains, but you can\t apply it over varnish or gel stains. That’s because varnish or gel stains are sealants that won’t allow penetration.
Do You Need To Remove Stain?
You don’t have to remove the wood stain before applying Thompson’s water sealer. That’s because the sealant will stick over a stain as long as the coating is cleaned and sanded.
However, you shouldn’t apply it over a sealed stain, such as a varnish or gel stain. These two finishes have water resistance and a high volume of oils. As such, they will not accept a topcoat properly. If you have a sealed finish, you need to remove it before applying a new topcoat.
Waterproof and water-resistant wood stains especially the oil-based types don’t accept top coats properly. If you apply the sealer directly on a waterproof or water-resistant finish, the sealer will not stick. Asides from this, the finish will develop problems later such as peeling and chipping.
However, if the existing finish is water-based or oil-based, then you can apply the sealer directly over it. In this case, sanding it with fine sandpaper is enough.
How To Apply Thompson Water Sealer Over Stained Wood?
Sealing stained wood isn’t hard, but you need to follow the right steps and have the right tools.
Here are the tools you need:
- Thompson’s water seal
- An airless paint sprayer
- Sandpaper of different grits
- Masking tape
- Microfiber cloth
- A pair of gloves
- Denatured alcohol
- Breathing protection
- Drop sheets
1. Prep The Work Area
First, prep your work area. This is important if you want to get a perfect finish. Start by removing all items around the wood. If you have items or furniture that you can’t remove or lift, you should cover such items with drop sheets.
Next, wipe and clean the surface using a lint-free rag. The purpose of wiping and cleaning it is to remove dust nibs from the surface that can prevent good adhesion.
2. Wipe The Finish With Diluted Alcohol
Next, degrease and remove oils on the wood stain. To do this, mix equal parts of denatured alcohol with water. You can also use mineral spirits if you don’t have denatured alcohol. Use a microfiber cloth and the diluted solution to wipe down the surface. Use only a little of the solvent so the finish isn’t damaged or removed.
Inspect the finish using the water test. This is to know if the finish has an existing sealant or not. If the finish has an existing sealant, you need to strip it with a chemical-based paint stripper.
3. Sand The Wood Stain
After removing the existing sealant, sand the finish with 320-grit sandpaper. If there was no sealant, you should sand directly with 320 or 400-grit sandpaper. When you are done sanding, wipe off and remove the dust.
The next step is to prep the Thompson water sealer. To do this, follow the manufacturer’s instructions. You might need to stir or shake it before application.
4. Apply The Thompson Water Sealer
To apply Thompson’s water sealer, use a paintbrush, roller, or sprayer. You can apply up to two thin coats of the water sealer for good coverage and protection.
After applying the sealer, leave it to dry for at least 48 hours before normal service of the surface is resumed.
Stain Dry Time Before Sealing
You should let the wood stain cure or dry fully before sealing it. This takes 24-48 hours depending on the type of stain.
The solvent (oil or water) must evaporate from the coating before you can seal it. If you seal it too soon, the solvent will get trapped between the sealant and the stain and will turn the finish sticky.
The solvent will prevent the existing coating to dry, and also prevent the sealant to stick. This is why you must wait until the coating fully dries (cures) first.
When wood is damp, you can apply a sealant because the moisture in the wood can’t damage it. However, this is a very different case when dealing with stained wood.
Wood stains don’t just contain water. They also contain oils, solvents, pigments, and additives. Some of these compounds can ruin the sealer. So you need to allow all of these solvents, additives, and moisture to evaporate before sealing it.
How To Know if Stained Wood Needs Sealing?
All outdoor stained woods need to be sealed because wood stains won’t protect them from outdoor elements. Wood stain just enhances the color of the surface, but doesn’t protect it.
On the other hand, the sealant will produce a glossy moisture-resistant layer that will protect the surface underneath from water, moisture, and other damage.
For indoor surfaces, you don’t need to seal them, unless they’re exposed to constant water. Indoor or decorative surfaces usually aren’t exposed to water and don’t need protection.
In summary, you can apply Thompson’s water sealer to water-based and oil-based stains, but you can’t apply it to gel stains. The sealer will produce a glossy moisture-resistant coating over the finish and protect it from different elements, such as water or rain.
Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,