KDAT Decking

[shana@1]

Hello
I need some information - My company manufactures boat docks/marinas.
Recently we had a customer who wanted KDAT lumber for his decking on his dock. We installed the lumber on the substructure. We used Galv fasteners. The product set in our yard about 1 month prior to installation on the water. The lumber has cupped, shrank and pulled away from the fasteners. What should we have done? This is the first time we've used KDAT we normally use, regular treated lumber, composite and concrete - we've never had this problem.
Thanks for your help
Shana Hess

[HayZee518]

any lumber, treated in direct contact with the earth will stay supple for a while. KDAT or Kiln Dried After Treating will reduce the moisture content by 75% and will be susceptable to cupping and excessive warping. the wood when removed from the treatment tank is literally dripping with water and the chemical. it is sold "wet." only way you could have done anything was to keep the wood in a controlled atmosphere which could be cost prohibitive for just one job.

[shana@1]

Thank you so much!
Yeah, I think it was just one of those things, next time we will probably seal it immediately to minimize the exposure.

Shana

[pushkins]

The biggest problem I see with the clients choice is even though it is over water it is basically high and dry with full air circulation under it ...over it....and around it. The moisture under it (water level) is sorta like a tease to the wood, it can absorb it from underneath but it's getting baked out on the top.
TO have even stood a chance you would have to seal all four sides of the timber decking (very difficult to do) and this would have to be done on a regular bases.
Last I read as well said that galvanized screws weren't recommended for KDAT.

[shana@1]

Thanks so much...We hope this is the only customer that wants KDAT for this application, as it is "illegal" to "treat" any lumber on the lakes around here, so the customer I believe is going to have a headache...I thought Galv screws were approved? Is there a website you can link me to? What I have read says it is ok> but I might have misunderstood?

[pushkins]

There’s an unfortunate side effect to the new formulations of treated lumber: They’re extremely corrosive to certainly types of nails, screws, and other hardware. The culprit is the same copper that gives the wood its green hue. Both ACQ and CA use higher amounts of copper to replace the arsenate in CCA wood. The problem is that water (from rain or your hose) will pick up trace amounts of copper and, if it comes into contact with plain metal screws, it will begin to corrode them. Obviously, corroding screws holding your deck railing in place can be a serious hazard.


Stainless steel is the number one recommendation for fastening PT wood. Next down the list (though likely more popular because it’s significantly cheaper) is hot-dipped galvanized fasteners.

(The zinc coating on electric galvanized fasteners is too thin to last the typical lifetime of a deck.)
The easiest way to make sure you’re getting the right stuff is to look for packaging that indicates the product is “ACQ approved” or specifies that it is hot-dip galvanized.
For connectors like joist hangers and post anchors look for brands that say “triple zinc” coated or G185.


Hope this helps.

[shana@1]

That's what we have been using is a "coated" or "Galv" quick drive screw that says it is approved for ACQ lumber ??

[pushkins]

As long as they are ACQ approved and or hot dipped (not plated) gal. screws your good to go.
I think the only screws they (Quick Drive) supply are hot dipped gal. screws, I think they changed over a year ago.

There are a few places now requiring that only concrete piers be used in direct contact with water areas like lakes, it's not just the risk of the arsenate or copper leaching into the water it's more to do with the lack of distribution, lakes don't have currents (not counting the Great Lakes) so the leaching of chemicals is much more concentrated immediately surrounding the dock...etc...
2x12" lumber and 4x4,6x6,8x8 (etc) posts are the only treated lumber approved for direct contact with the ground. So a 2x12" can be used to retain dirt in a below grade crawlspace opening but not a 2x10.