Another Deck Related Question...

Building ground level deck... Concerns: short lifetime expected due to lack of space for proper air circulation under deck, plus high moisture levels from both sky and ground (i.e. rainy Vancouver weather and high water-table clay soil, respectively). I've put much thought and research into how to best counter this... Now I've finally arrived at my final choices of strategy/design/materials, as follows: Ipe for the decking material, drain rock down to a depth of 9" to 12" below grade (in conjunction with pre-existing landscape drainage), thorough sealing of PT frame joists and beams with double wet coat oil based paint/sealer.
Now, here's my question: How can I _keep_ the frame (i.e. joists) sealed against moisture in spite of the fact that the screws (for fastening the decking) will be piercing whatever sealer/paint I've put there?
I've read that dipping the deck screws in hot paraffin wax prior to use will cause the screws to form a water-tight seal (as well as, primarily of course, facilitate the screw's entry into the wood). But I'm having difficulty visualizing how this would actually be accomplished ... Unless there is maybe some kind of simple and portable hot-wax-applicator-gun or similar device available that I am just not aware of (...?).
Ken
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If you're putting a sealer on PT lumber, you should wait at least a year before applying it - PT lumber is "wet" when new and needs to dry out before any sealers are applied - if you do apply a sealer, it won't go on very well.
With good PT lumber, though, you shouldn't need a sealer unless you're concerned about appearance (and for the joists, why would you be?). The PT lumber shouldn't rot for decades, even if exposed to moisture. That's the whole point of PT lumber.
What you need to make sure you use, however, is fasteners that are DESIGNED to work with the type of PT lumber you're using. The chemicals in ACQ PT lumber (the most common kind) will corrode most types of fasteners - use hot-dipped galvanized screws or stainless steel.
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We use "re-kiln dried" treated lumber because the "wet" stuff tends to warp & twist. The kiln dried is more expensive and yields more usable pieces. TB
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Thanks. I wasn't aware of this. I'll be sure to get the kiln dried PT lumber.
Ken

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I'm leaning towards screws made of stainless steel. I had previously thought I'd use polmer coated screws. I got this idea after reading thru the web site of a deck building outfit that claims to use only the best materials, including "poly-coated screws". (See http://www.deckspecialists.com /) But I've found no other references to support this idea, and using stainless steel screws appeals to me intuitively (provided the stainless steel used is of the of proper type and quality, etc... see http://www.key-to-steel.com/Articles.asp ).
Ken
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How low is your deck to the ground?
We just replaced our previous deck. The old deck was relatively structurally sound -- very little, if any, rot. (the wall behind the ledger board, left unflashed, was another story). The builder didn't seem to take any precautions at all other than using PT lumber, and the deck seemed fine after 25 years (we wanted a larger deck with a stairway).
Ours is about 7' off the ground to the deck surface, so that might make a difference. But I've never heard of anyone doing anything like dipping screws in wax or anything like that...
-Tim
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The bottom of the joists about 6 inches off the ground.

I got this tip from http://www.woodsthebest.com/ipe_decking/ipe_fastening.htm
"Dipping the screws in paraffin wax, prior to installation, will allow for easier insertion, and the wax will seal the hole."
There are many references that describe using wax to lubricate wood screws. But this is the only reference I know of that describes this use of wax on screws as also serving to "seal the hole" . I was hoping other people here had heard about or knew something more about this and could therefore comment.
Ken
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On 10/1/2005 3:33 AM US(ET), Ken Moiarty took fingers to keyboard, and typed the following:

I built a 19' wide x 16' deep deck with the joist bottoms about 2" from the dirt on one end and about 8" on the other end. The ground beneath sloped slightly to the one end. I did not seal the PT joists but put a black plastic moisture barrier on the dirt underneath with holes punched into the plastic in the low spots (for water drainage for those parts where the water could not run out from beneath the deck. I used rocks to hold the plastic down. The deck was up for about 17 years before it was torn down to be replaced with a sunroom. The joists were in such good condition that I was able to save and use them for other projects, including a small deck on the side of the sunroom. A few, that were going to be exposed on the new projects, needed a little sanding to remove dirt and deck staining that had dripped between the decking. After sanding, they looked like new wood. This was the old PT formula, so I don't know how well the new stuff holds up.
--
Bill


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On 10/1/2005 3:33 AM US(ET), Ken Moiarty took fingers to keyboard, and typed the following:

I built a 19' wide x 16' deep deck with the joist bottoms about 2" from the dirt on one end and about 8" on the other end. The ground beneath sloped slightly to the one end. I did not seal the PT joists but put a black plastic moisture barrier on the dirt underneath with small holes punched into the plastic in the low spots (for water drainage for those parts where the water could not run out from beneath the deck). I used rocks to hold the plastic down. The deck was up for about 17 years before it was torn down to be replaced with a sunroom. The joists were in such good condition that I was able to save and use them for other projects, including a small deck on the side of the sunroom. A few, that were going to be exposed on the new projects, needed a little sanding to remove dirt and deck staining that had dripped between the decking. After sanding, they looked like new wood. This was the old PT formula, so I don't know how well the new stuff holds up.
--
Bill


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This is a question for me as much as it is for you. Why use any sealer at all on the PT joists/frame? I built a deck with PT and EON (plastic) deck boards. I did seal end cuts with wood preservative but I thought PT would not need anything else even with direct ground contact? Kevin
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The question of sealing a wood member, then poiking holes in the sealing coat is worth consideration. Moisture might be let in through the punctures, then held in the wood by the sealing coat.
An Example: Government facility was designed with cypress hand rail around large court yard. After installation, handrail was painted except for counter sunk bolts. Three months (as I remember it) later, fungus was growing out of the hand rail. Steel tube was substituted. TB
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Two more considerations: (1) The fact that my deck is going to be hemmed in almost completely around its circumference by pre-existing landscape planters. (A certain lady of the house, and master lanscape architect for the yard, is responsible for this arrangement; not my choice...) This means that (unless I were to install industrial duty fans underneath - not likely), air circulation underneath the deck will be 'unacceptably' poor. (2) With the recent change in PT wood specifications from arsenate based preservative to less toxic alternative(s), I won't be surprised when/if in a few short years it gradually becomes apparent to consumers that "PT lumber don't last as long as it used to". I don't *foreknow* this will be the case, of course. But I see no basis to place much faith in lumber makers' and/or the governments' present assurances to the contrary. For one thing, they just don't have 30 or so years experience with the newer stuff having been used _in the field_ to be able to properly compare it to the conventional product, in my opinion. And afterall, the lumber makers just want us to buy the stuff, and our governments, well, they have their own bottom line too. So they each tell the public, "all the public *needs* to know" (for the time being, that is). In summary, I'm trying hard to err on the side of caution here.
Ken
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Use Penofin Oil to protect it.

Some sealers won't do anyting on PT wood because there is so much surface oil on it anyway. I'm not usre it will help at all.

It won't. But PT will is saturated through and it whould not be needed.

I don't know about that. You may want to go to www.mcfeelys.com as they have a lot of information on deck screws and materials.
IMO, you can eliminate most of this by putting in a concrete patio instead. Less maintenance and will last 200 years.
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wrote:

Thompsons Water Seal works well on PT wood. But its an every year or so project.

HM
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