Stopping and Removing Sap from Deck Boards

Sap Bleeding Deck Boards and How to Stop and Prevent its Occurrence

By Mark J. Donovan

Question: Mark, I would like some information on how to stop sap from bleeding through our deck boards and how to remove sap from deck boards. We bought weather treated wood and sealed it when we built our deck, but still have some deck boards bleeding sap. What can we do to prevent this from happening, and how do we go about removing sap from deck boards? Any information would be greatly appreciated. Thank you, SM.

Answer: SM, Pressure treated deck lumber commonly oozes sap from knots and the immediate area surrounding the knots. 

Pressure treated deck lumber is regularly made from White pine, Southern Pine and Ponderosa pine tree species which are replete with organic sap resins.

The sap typically will crystallize and show up as white patches on your deck after it has dried out. Unfortunately the sap will continue to ooze until it bleeds itself out. This can take a number of years depending upon the amount of sap stored in the wood and the weather conditions in your area. Hotter drier temperatures cause the sap to ooze out of the deck boards more quickly.

This said, you basically have three alternatives to stop and remove sap from deck boards. You can clean and/or scrape the sap off of the deck boards and re-stain, bin seal the knots and re-paint, or you can outright replace the offending deck boards.

Cleaning Sap off Deck Boards

To clean the sap off of deck boards there are a couple of products that you can use. Turpentine works quite well and will not damage your deck boards. Use a coarse plastic sponge pad to work the Turpentine into the affected areas and to scrape away the old sap resin. You can also try sandpaper to scrape away the sap, but the sandpaper gums up quickly. Watch this video on sanding a deck.

Alternatively you can try Goo-be-Gone. I have heard people have had excellent success removing sap from deck boards using this product.

Sand your deck and restore it to looking like new!

Watch this video on using a deck cleaner on a pressure treated deck.

Once you’ve cleaned the sap off of the deck you can re-stain it. Read this article on how to apply deck stain properly. Also make sure to choose the right deck stain type for your deck .

Bin Seal Deck Board Knots

If your deck boards are painted, you can first use the Turpentine or Goo-be-Gone to remove the sap from the affected deck boards. Then lightly sand the affected areas after they have fully dried. Next, apply a Bin sealer to the knots and their surrounding area. The Bin sealer will help retard the flow of sap bleeding out through the knots in the deck lumber.

Finally, apply a fresh coat of paint over the deck boards. See how to apply a solid acrylic deck stain properly. Again, the Bin sealer will slow down the flow but not necessarily entirely prevent its occurrence.

You may still need to apply a new coat of Bin sealer every couple of years until the sap has completely oozed out of the deck lumber.

Replacing Knotty Deck Boards Bleeding Sap

Finally, the most aggressive approach of stopping deck boards from bleeding sap is to simply replace them with new deck lumber, preferably with knot free deck lumber.

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