I have attached deck guardrail posts in a way shown on page 3 of Simpson Strong Tie's T-C-GRDRLPST22 bulletin.

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There are couple of places where water could be trapped:

  1. Between double blocking or blocking and joists (along the length of blocking).
  2. Between guardrail post, rim joist, and blocking butts. Highlighted below.

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For (1) I plan to use wide enough butyl joist tape to prevent water from getting in-between the boards.

I am not sure how to protect against (2). Is there a recommended approach to this?

  • What are the posts made from? Are they pressure treated? Cedar?
    – matt.
    Commented Aug 28, 2023 at 0:42
  • Posts are made of cedar. Not pressure treated. Commented Aug 28, 2023 at 3:18

3 Answers 3


I use hollow 5 1/2" KDAT pressure treated posts. I coat the inside and out with West Systems 105 epoxy. Usually with 206 catalyst. Also all blocking and inside of the deck whereto blocking will be. The blocking is beveled at about 30 degrees to allow water to run off. Now I also add deck tape to cover the blocking. Water will still make its wayn into the joists through the screw holes. But this has lasted for about 15 years for an older deck.



Not sure how you're finishing the exposed portion of the post, but, if you stained the bottom portion that will be below the decking that would help prevent any water absorption for quite some time.

Oil and water don't mix, a quality oil based stain could potentially help quite a bit.

Sherwin Williams SuperDeck oil based stain is a great product, I have used it quite a bit in the past.

Image Credit: Sherwin Williams Sherwin Williams SuperDeck stain

  • Yes this! Even the cheapest protective oil, boiled linseed oil. would work.
    – Jasen
    Commented Sep 29, 2023 at 3:28

use joist tape there too but fold it so it goes half-inch up the post.

  • 1
    "half-inch" or more. You probably don't want it to show, but more is better than less.
    – FreeMan
    Commented Aug 21, 2023 at 14:20
  • Wouldn't the joist tape detach with time, trapping the water between the joist tape and the post, creating even better conditions for rot? I suspect the glue is not something that will hold up with time very well. Commented Aug 21, 2023 at 16:25
  • Thinking more about it, would some sort of pressure strap around the joist tape work to prevent detachment? Commented Aug 21, 2023 at 16:27
  • the tape is pretty sticky stuff.
    – Jasen
    Commented Aug 21, 2023 at 20:37
  • 1
    The joist tape has a useful life span. so does the wood. Neither will last forever. The idea of the tape, or any prevention method is to extend the amount of time that the wood will last before decay becomes an issue. Yes the tape will degrade. Water will find it's way into the wood. What you are hoping for is an extension of time before the natural occurrences are such that you must take action. That is all that you will get.
    – RMDman
    Commented Aug 23, 2023 at 12:29

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