We had a new deck put up at our cottage. It was done with pressurized wood, maybe spruce? Many of the boards have knots in them. Some of the knots were weeping a whitish green substance. What is that, and do I leave it alone? Looking at the other knots, will they eventually pop?—Don Whelan, Oliphant, Ont.
’Sup, Don? How’s your new(ish) shed holding up? (“What Kind of Foundation Does My Shed Need?,” Cottage Q&A, Mar/Apr ’20). How’s the flooring? (“Shed Flooring Fix,” Cottage Q&A, Mar/Apr ’21). But enough chit-chat. Back to your questions. We asked Cottage Life builder Wayne Lennox. (He’s built many pressure-treated decks over the years, including six for himself. The man loves him some decks!) He suspects that, indeed, the wood is likely spruce, though it could be pine or fir. Unfortunately, these softwoods are prone to weeping pitch, a.k.a. sap, from the knots or the area around the knots. (It can happen if the wood wasn’t dried properly.)
You can leave the deck alone. At least, that’s what Lennox does. “In my experience, the weeping will stop, and the only thing to do in the meantime is clean up the sap,” he says. There are lots of tricks to remove sticky tree sap (see “Talk Dirty to Me” in our Spring ’18 issue, or online here). You could also let the pitch harden and then scrape it or sand it off. If you’re left with a lot of white marks on the deck, you may want to then stain (or re-stain). Or, if there are a few particularly knotty boards (ooh, bad boards!), you could replace them.
As for the knots popping out? “I have never had that problem—but I’m not saying it ain’t possible,” says Lennox. “In the event that a knot did pop out, you could simply glue it back in with an outdoor-rated wood glue.”
In theory, knots can weep for many years before finally stopping. But hopefully that won’t happen with yours. Don’t cry, Deck! Don loves you.
Got a question for Cottage Q&A? Send it to answers@cottagelife.com.
This article was originally published in the Winter 2023 issue of Cottage Life magazine.
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