How to Seal and Stain Pressure Treated Wood Decking

Last Updated: September 15, 2021 References Approved

Most decks are made from pressure treated pine. Here is how to keep your deck looking great and protected.

Steps

1
Remove staining, mildew and old finish with a commercial deck cleaning solution. Pressure washing is almost always a must on older decks, but be sure not to use too much pressure. You can damage the wood if it's turned up too high. Usually 1500-2500 PSI is adequate for pressure treated lumber. Stay between 1200-1500 PSI for cedar and redwood.^{[1]
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After cleaning the wood, let surface dry very well. Most coatings require that the wood should be dry before application. There are exceptions. Thompson's Water Seal Advanced Wood Protectors can be applied to damp lumber, so it's possible to clean and waterproof your deck in one day. Read the directions on the product you're using for temperature and weather guidelines, drying times, etc., and follow them!^{[2]
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Choose your finish. You can use an oil base or water base sealer or stain, solid or semi-transparent. The best method for applying the material is with a brush or a paint pad on a long handle, available at any hardware store. Most materials can be sprayed also, but you will end up needing a lot more product this way. For a large deck, spraying will save time but you should brush the material into the wood. This will help with uniformity and provide a better looking job.^{[3]
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Finished.

Community Q&A

Question

Can I use boiled linseed oil on treated deck wood before applying Thompson's Water Sealer?

Community Answer

Read the Thompson's MSDS, it is boiled linseed oil and some solvents. The operative chemical in Thompson's is linseed oil. For generations farmers used linseed oil to protect wood and metal. Thin linseed oil with paint thinner and apply it like Thompson's.
Question

When can I stain a new pressure treated deck?

Community Answer

If you treated it during the summer, wait two to three months. If you treated it in the fall, wait until spring.
Question

How do I handle a peeling, painted deck that has treated lumber?

Community Answer

Use a pressure washer to remove the paint. (Avoid focusing pressure in any one spot or you might end up ripping away some of your deck surface.) Follow with an opaque penetrating deck sealer to hide any remaining color you might have.
Question

I'm going to use a solid stain on my new deck that is made of pressure treated wood. Should I use a primer coat first?

Community Answer

It is not recommended to use solid color stain on any horizontal surface. If you do it it anyway, thin it a little and brush it in well, after the wood is well weathered. Keep in mind you will have set up an ongoing maintenance project, because solid color stain is basically just thin paint. Contact the maker of your stain for more specific advice. On shingles such stain lasts indefinitely.
Question

Can I use a roller to stain the deck?

Community Answer

Yes, you can use a roller, but you will find your job moves more quickly and efficiently with a garden sprayer. Also, avoid applying during midday heat and sun and avoid a day when rain is projected within 48 hours.
Question

How long should I wait to apply a water seal on new wolmanized lumber?

Community Answer

Wolmanized lumber is already treated with a deep penetrating water seal and should never require additional sealer.
Question

How do I fit my decking boards under the bottom of vinyl siding?

Community Answer

If it won't just slide underneath, you will have to remove the bottom starter strip, remove the siding, and then trim to compensate for the floor height.

Warnings

Be careful when using a sprayer and sealant on decks. The over spray may kill nearby grass and shrubs. To prevent this cover the adjacent greenery with a tarp or newspapers.

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FIRE HAZARD: Before disposing of rags, spread them out to dry completely. Heat generated from evaporating finish on a pile of rags can start a flash fire. If you are using latex stain, clean equipment with soapy water. If you are using oil-based sealers, clean with paint thinner or mineral spirits..

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Do not use varnish!

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The sealant may drip between the decking boards, so use tarps beneath the deck to avoid staining a cement pad.

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Treated lumber does not hold paint well, so avoid painting.

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A clear finish usually needs to be treated more often.

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If the deck is near a chlorinated swimming pool, check your selection of stains and oils because the chlorine vapors can cause some oils to become opaque.

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A deck that does not get a lot of sunlight is more likely to have mildew staining and green moss. This is a black staining or green fungus. Try to avoid oil-based products if the deck doesn't get a good amount of sunlight.

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Pressure-treated wood may contain arsenic, so EXTREME caution should be used when sanding it. Arsenic is known to cause cancer in adults and children.

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Use a light-colored stain if your deck gets a lot of sunlight. A dark stain will make the wood get hotter.

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References

About This Article

wikiHow is a “wiki,” similar to Wikipedia, which means that many of our articles are co-written by multiple authors. To create this article, 24 people, some anonymous, worked to edit and improve it over time. This article has been viewed 756,215 times.

206 votes - 90%

Co-authors: 24

Updated: September 15, 2021

Views: 756,215

Categories: Decks