5 Tips for Sealing Treated Lumber

A deck with treated lumber.
  • 2-6 hours
  • Beginner
  • 15-45

Treated lumber is wood that has been treated with chemicals so that it can be used as a support with heavy objects as well as stand up to the elements. You can use treated lumber for anything from building a deck and furniture to making a shed. Even though treated lumber has this added protection, it still needs to be sealed. The information contained in this article will share with you several tips on how you can properly seal treated lumber.

Remove the Old

Treated lumber is often used for decks, fences, and sheds. When the lumber is used, it is typically painted or stained. This is great for the time being, but after time passes the paint or stain will wear off and you will need to seal it again. It is not a good idea to seal the treated lumber on top of peeling paint or a blotchy stain. Use a paint scraper in conjunction with acetone to remove the paint or sand it down to remove a layer of stain. You can then begin to treat the wood and reapply paint or stain.

Always Clean it

If your goal is to seal treated lumber, it is always a good idea to make sure it is completely clean. Normal soap and water will not be adequate enough. Cleaning the lumber removes any dirt or debris on the surface as well as any paint that may be left behind from a previous removal effort. In order to properly clean the treated lumber, use a pressure washer set between 1,200 and 1,500 PSI. Allow the board lumber to dry completely before attempting to add a sealer.

Dry the Lumber

The process used to treat lumber adds a lot of extra moisture to the wood. This can be troublesome when you are trying to seal it, as most sealers do not work properly in those conditions. You can, of course, purchase a sealer that does require moisture. In order to properly seal treated lumber, you need to dry it out. You will need to place the lumber in a dry room with a dehumidifier. This will remove the moisture from the air and eventually the wood. You can also place the lumber outside under direct sunlight for several hours a day. If you are unable to do either of these things, you can use a hairdryer set on high and place it close to the wood.

Don't Believe Myths

You may hear people saying you should let your treated lumber alone for a few months to weather before sealing it. Although weathered wood looks good, you should not allow treated lumber to weather because it will be left vulnerable. New lumber that is pressure treated can weather for approximately 30 days prior to sealing it.

Seal the Whole Thing

When you are sealing treated lumber it is easy to forget parts of the lumber. Make certain you seal the edges, front, back and the ends of the lumber. This is especially important for fences and decks.