I'm replacing my rotted out deck that's old tongue and groove fir planks. I'm treating them with Borate mix today and tomorrow and would like a natural finish in the end. It's a covered deck.

I've seen some competing advice here on when to seal: should I seal before I install the planks? Or seal after when they're all in place?

Appreciate the input!

  • It's really a matter of opinion. It's better to have wood sealed all the way around, but pressure-treated or cedar decking isn't usually sealed before installation, for example. I tend to seal siding on all sides, then re-coat the outside after installation.
    – isherwood
    Jan 5, 2021 at 20:09
  • Or are you really just asking about timing, and not technique?
    – isherwood
    Jan 5, 2021 at 20:10
  • both. installing makes new holes, but it's hard to do the underside once layed.
    – dandavis
    Jan 5, 2021 at 21:23
  • Thanks this is helpful! Sounds like I should seal, cut, install, then seal again in place. Jan 6, 2021 at 1:17

1 Answer 1


If you have the opportunity, I'd seal the sides/ends of the boards before placing them down, then seal the tops once they're mounted. Avoids the whole bit of getting a brush down between them, and provides a cleaner finish. You can do the tops twice if you like, but I suspect that either way they'll not match the existing deck unless your Borate treatment has aged them properly.

You can put down an adhesive bead on the joists before mounting the boards. I normally don't, but some people do. If you plan to live there another 20 years, I would use the adhesive, just to keep things a bit tighter, and lock out a bit more of the water.

  • You're suggesting putting caulk between the deck boards and the tops of the joists? I've never heard of anyone doing that and cannot fathom what it would buy you. It would either limit wood movement (and outdoor wood will move) or simply fail as the wood moves. There would be no value in "sealing" out water, as water will be everywhere anyway. If you really want to use it as additional attachment, then a construction adhesive would be better than caulk, but again, I cannot see any advantage to the added time & expense of doing so.
    – FreeMan
    Jul 8, 2021 at 13:27
  • @FreeMan Good catch. I was meaning to say adhesive. I will edit my answer.
    – Bee Kay
    Jul 13, 2021 at 16:34

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