Preventing Deck Joists From Rot

by Dennis Ward
(Toronto, ON, Canada )

Would you put tar paper over deck joists to minimize rot or would it tend to hold moisture ?

Would you also leave a gap between butt joints for the same reason ?

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Aug 27, 2018
Joist Anti-rot Anti-split Info
by: pauljack

1. Cheapest anti-rot is anti-freeze, the best kind is concentrated. You can use a little warm water and boric acid solution to add to the anti freeze. Paint or roll on the tops of the joists then soak all nail holes and splits. It will dry out overnight.

2. When joist is dry enough coat top with Behr or Thompson's water resistance deck 'stains'.

3. Cut strips of synthetic shingle underlay. say 3" wide and lay them on top. You can tack if necessary. Let edges droop to shed water.

4. Using old but structurally/aesthetically acceptable deck boards. Remove and reinstall the old bottom side up fresh finish surface but before removal coat with a deck sealant from Thompson, Behr etc. Then relocate boards to re-use the old nail holes for new screws. Shorten deck boards when ends are split beyond re-use. Pre-treating the old board weathered side with antifreeze sprayed on is a quick drying rot deterrent. Place coated old weathered side down. Use 3" deck screws to reach sound wood.

5. Pre-treat deck board ends with antifreeze for rot. Then seal with deck sealant. Fill any imperfections/small holes with glue/sawdust or other wood past. Coat entire exposed upper surfaces of deck boards with water resistant stain/sealant.

The upper third of the joist is in compression and simply holds the deck boards down. The lower third is tension. The lower third is rarely weathered enough to warrant replacing. Rot treat with antifreeze and spray bottle spray on some sealant. Good for another 35 years. :)

Editor's Comments
This sounds like it might just work. Thanks for the suggestion. Try at your own risk.

Oct 06, 2013
Deck protector clips look good
by: Michael R

I think there is a less expensive and simpler option.

Those little deck protector clips they sell on this site look like they would actually move the water and debris away from settling on the joist in between the boards.

Even if you use those deck joist protector rot not or whatever it's called, the joist may never rot but the debris can still get caught in between the decking and rot the boards out.

The clips I am talking about are right here.

I think it's a good idea if that is what you are worried about.

Apr 19, 2008
Rot Proof Your Deck Joists
by: Editor - Rich Bergman

There are a couple great products that I think you might want to look at to preven the joist from rotting over the long term.

Take a look at Deck Flash barrier from Cofair and joist caps from RotNot. I think they both are innovative ways to approach solving this problem.

As far as worrying about the butt joints at the ends of each deck board rotting, I must say it is not really a huge problem. However, I suppose it could be depending on your weather.

The only think I can think of is some kind of sealant that maybe can prevent water from being wicked up by the end grain.

Hope this helps you out.

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