12:06PM | 11/10/02
Member Since: 06/21/02
5 lifetime posts
Posted this on the mis. board with no answers. Will try it here.

Just finished a new deck(14'x32'). Beams, Joist and posts all PT. Would it be a good idea to use a water Repellent on the PT or would it be a waste of money?

Thanks for your help..Bob..

Jay J

01:47PM | 11/12/02
Member Since: 10/26/00
782 lifetime posts
Hi BigMuz,

Well, as simplistic as this may sound, PT wood is for the purpose of protecting the wood where you can't get at it to maintain it. And depending on the 'application' you're referring to, you need to be sure you're using PT wood that's rated for Below-grade use vs. beams and joists and the like, which is for Above-grade use. Just be sure the Grade of PT wood you're using is for its 'intended use'.

Personally, I think it would be a waste of $$$ to use a Repellent. I would do this - Make sure you don't have much around the deck to obstruct airflow. You know, lattice skirting and 'bushes' and such. Keeping the underside of the deck dry AND ventilated is the best thing you can to to retard insects and aging. This is what I do for my deck, and around the entire house.

My best to ya and hope this helps.

Jay J -Moderator

PS: What rpxlpx says in your other Post is correct. Yes, I'd seal the ends AND the decking. But if I read your post correctly, you're referring to the PT posts, beams and joists; not the ends and decking ...

PPS: God Bless America!

[This message has been edited by Jay J (edited November 12, 2002).]


02:35AM | 12/02/02
Member Since: 11/19/02
59 lifetime posts
Using a topical water repellent on your decking, handrails, etc = a big YES! It's not such a big deal on the joists and posts though. Not necessary there.

As a treater, I manufacture and sell pressure-treated lumber for a living. Please excuse me for the length of this, but we don't usually get this sort of a platform.

There are basically two types of pressure-treated that are currently on the market:

CCA treated lumber, which we (the treated lumber industry) are voluntarily ceasing production of for virtually all uses by December 31, 2003-


CCA alternatives that are copper variants, which include Copper Azole and ACQ.

When the previous poster spoke about above ground and ground contact applications, he was referring to the latter type of material. CCA treated lumber doesn't carry the same designations that the alternatives do. This boils down to CCA being spec'ed by level of chemical retention (usually .40 pounds per cubic feet or .60 pounds per cubic feet of retention) -versus the 'new' way of spec'ing things for particular applications. The general reason for this is that the new chemical costs more than CCA and is more effective in smaller doses.

No matter which chemical your new PT is processed with, YOU ABSOLUTELY SHOULD use a topical water repellent. The brand really isn't important, but giving your deck extra protection from UV rays and weathering is. The notion that pressure-treated is a 'put it down and forget about it' type of product is an incorrect one; and it's something that we as an industry have been trying to combat for years.

Pressure treaters are basically licensed pesticide applicators. And the reason for that is that we are treating material with a pesticide. The primary reason we treat is to prevent insect infestation in lumber. Our processes do very little to improve or maintain the actual appearance of lumber. Some of our products contain a parafin wax-based additive that is designed to help shed water off of the lumber and enhance dimensional stability, but this additive wears away with time.

Your deck's worst enemy is being outside every day. Rain, wind, ultraviolet light, and everyday use take it's toll by causing the deck to swell and then dry out and shrink all year long as the lumber seeks out its equilibrium moisture content. Those processes are all responsible for the checking, cracking, twisting, and weathering that people experience with their decks on a routine basis. That's why fasteners that hold the material firmly in place (galvanized hot-dipped screws on the decking and galvanized hot dipped nails on the superstructure) and routine maintenance (applying a water repellent or sealer every other year) are so important for your deck.

Pressure-treated lumber was never intended to be, nor is it in any capacity, low maintenence. If people are looking for something that they don't have to maintain to keep up its appearance, then they ought to be looking at plastic decking.

I hope this helps.

[This message has been edited by JayF (edited December 02, 2002).]

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