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
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
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, bin
seal the knots, 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.
Alternatively you can try Goo-be-Gone. I have heard people have had
excellent success removing sap from deck boards using this product.
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. Again, the Bin
sealer will slow down the flow but not necessarily entirely prevent its
Photo by Mark Donovan
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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