KDAT vs ADAT

[LeftyTom]

The search function found a thread about decking, but a better explanation will benefit me.

For my porch railing project, I had the choice of #2 KDAT (phone call, I didn't verify it was really KDAT)at one business, and #1 ADAT at another. It is a 30 minute drive to either place.

I went and got eight 12' 2x4's in the #1 ADAT flavor. The boards are mostly straight, a knot in each board, none twisted. All boards are drier than anything I have found at the big stores.

Am I in for any surprises working with ADAT wood? My plans are to cut a 1 1/2" dado. 1/4" to 1/2" deep, down the length of the boards, and roundover the edges on the sides which face up once assembled.

Like most woodguy (or gal) Neanderthals, I usually work with the lumber available from large retailers, in the lovely "wet green" shade. (insert knuckle-dragging emoticon)

 

[DaveO]

Tom, basically they mean the same thing. Both are re-dried to 19% MC, either in a kiln or stacked and air dried. I would suspect that the manufactures have greater loss with the air drying, but incur much less costs in the process. The final result will provide you with the same product, more stable stock at 19% MC and generally a higher grade #1. I think that you did better by getting the #1 grade, no matter what the method of re-drying. #1 lumber is going to be more structurally sound, than #2, and will be clearer stock.
Dave

 

[LeftyTom]

Thanks Dave. I know you posted good info in my other thread, steering me toward the #1. I tried to Google ADAT, but to no avail. I think your reply will help all who are confounded by the designations.

:eusa_clap for DaveO, :eusa_clap

 

[scsmith42]

Tom, let me add a couple of comments in addition to Dave's. Regarding potential surprises lurking for AD, the short answer is yes.

KD softwood (such as pine) is typically sterilized and has the pitch set at the end of the drying process.

The advantage of sterilization is that it kills any insects that may be resident in the wood, along with their eggs and larvae.

Setting the pitch will crystalize the sap in pine, so that it does not bleed out and create future problems in the finished product. Once crystalized, the temperature that the wood experiences has to meet or exceed the sterilization temperature for it to flow as a liquid again.

The temperatures that the sterilization takes place at varies depending upon the kiln and the operator, but are usually somewhere around 140 degrees or above.

I've used both types of wood in my farm projects, but of the two, I prefer KD because of the reduced risks.

Regards, Scott

 

[DaveO]

Scott, I could be wrong here, but I was always under the impression that the lumber that is pressure treated is kiln dried before the treatment process. Then if you get either KDAT or ADAT, it is re-dried. If that is correct wouldn't the initial drying set the pitch and sterilize the wood?

Dave

 

[scsmith42]

Dave, you raise a good point and one that I don't know the answer to. Typically I would think that the lumber would have been KD before treating, but I know that there are some places that do pressure treating that do not KD prior - they AD for a few weeks first (mainly agricultural fencing related wood).

Theoretically the pressure treating would kill any bugs, therefore the main concern would be setting the pitch if it were not KD prior to treating. However, on a porch it shouldn't be that big of a concern.

 

[DaveO]

I did a little research after making my last post on this subject and found several sources that stated if the stock wasn't kiln dried first it wouldn't be able to uptake enough of the treatment solution to pass the grading requirements and would get stamped "Treated to Rejection". That basically means they tried to get enough treatment solution into the wood to the point that it rejected any more. I can definitely see this method (AD then treated) used for large quantities of low cost fence material, to keep the costs down.

Very interesting subject...I'm learning something every day :eusa_danc :eusa_danc

Dave


Dave