plywood deck? instead of deck boards

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Old 07-19-15, 11:30 AM
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plywood deck? instead of deck boards

my upstairs deck (5' x 12') coming off the back of the house has always been a hassle. Since it is exposed underneath as well, even tho it is enclosed, precip and temp doesn't agree with finishes, and I've tried many.
the other issue is how water from the roof and direct exposure drains between the deck boards and drips on the items stored in the enclosure underneath the deck. i've seen products that are installed under the deck to divert water, but what a hassle... why not just install some 3/4 pt plywood on the deck and coat it?
 
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Old 07-19-15, 12:34 PM
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Coat it with what? Too simple a solution. It can be done, with the proper materials, but it isn't "coating" it. Once you apply your Advantech, you will be putting on at least 3 layers of fiberglas resin and fiberglas, then a final walkable coat to make it not rot in 2 years . The edges next to the house as well as the edges around the perimeter must be treated as well. Probably more expensive than under decking.
 
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Old 07-19-15, 01:23 PM
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Probably a lot less weight being added to the deck with the under deck material.
Geo
 
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Old 07-19-15, 03:04 PM
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Back to maarkr's question,
Chandler, it is common up here with our older housing to have porches made of pine, simply coated with a gray deck paint. I would think a T&G 3/4" exterior grade plywood painted on all sides to minimize moisture absorption would work just fine. Just don't paint the T&G area so they will still push together.

Any problems with that?

Bud
 
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Old 07-19-15, 03:30 PM
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Bud, porches, yeah, but not decks. I have done T&G on numerous older homes' porches, but I don't think paint alone will handle the traffic nor the weather associated with an outdoors situation.
 
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Old 07-19-15, 04:24 PM
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If you even consider using plywood you would need to use Marine grade plywood and once you see the price of that you will change your mind anyway.
 
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Old 07-19-15, 10:56 PM
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The last time I priced some marine-grade plywood, from a mail order outfit on the east coast, it ran just a tad under $120 a sheet, with almost a third of that being shipping costs. Decided I didn't need it that badly, as the chickens were perfectly happy with conventional plywood covered with a sheet of salvage vinyl flooring in their new coop.

Our local Home Depot discontinued selling its so-called marine-grade plywood. Apparently the stuff was delaminating almost as soon as a rain cloud appeared in the sky.
 
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Old 07-20-15, 06:03 AM
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I still have some pieces of 16" x 4' 1/2" exterior plywood that has been outside for over 6 years. I would get moved around but never put away for protection. It started out as 4 pieces and I have nibbled it away to one and a half or so, but I use it because it is still flat and almost perfect. That's just regular exterior grade.

I ordered 2 sheets of 1/2" pt for a location where I wanted the extra protection. After two days outside, 4 men and a boy could not hold that flat enough to use. It turned into a big potato chip. I have never since bought pt plywood.

As for needing marine grade, not needed where it will be well coated with a good deck paint. The por4ches we have up here have steps and entrance areas that are fully exposed and heavily traveled, for a house, and all they need is another coat of paint every 4 or 5 years. I can't imagine the deck described as being heavily traveled and regular exterior grade should be fine.

Bud
 
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Old 07-20-15, 06:16 AM
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The problem with any plywood as decking is the plys on the end are next to impossible to keep sealed and if/when the moisture gets into the plys - the plywood is apt to delaminate. Moisture is a coatings worse enemy and keeping plywood well sealed is challenging while PT deck boards are more forgiving if the maintenance is lax.

While there are always circumstances that defy the odds, they aren't in your favor when using the wrong material. Just like masonite siding, it paints well, looks nice and will last a long time as long as it never gets wet - easier said than done!
 
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