Sticker Thickness

Three quarters of an inch is the practical minimum. April 10, 2005

Question
Have there been any studies or does anyone know how to calculate (not assume or speculate) on what the minimum sticker thickness can be based on - loading depth, fpm, moisture loss, operating temp or RH%, etc. Primary incentive would be to maximize kiln capacity without risking quality and/or productivity concerns.

Forum Responses
(Sawing and Drying Forum)
From Dr. Gene Wengert, technical advisor, Sawing and Drying Forum:
What species and thickness? What initial MC in the kiln? I do recall a study that showed that 11/16" was the thinnest possible (in a specific situation). Most kilns are designed for 3/4", so that is what is used. You did see the recent posting about sticker thickness, etc.



From contributor A:
To Dr. Gene Wengert: I posted the earlier thread about sticker thickness. I made airflow sticks at 3/4" and they dried the first load of pine no problems. You responded to a post about electric kilns and I'd like you to clarify the part about needing "1500kW or 150kw per day average". That didn't make sense. Is it watts and kilowatts? I am using electricity for heat in one kiln, and am unsure whether to hook it my boiler, since heating oil is going to go through the roof. Perhaps this is the year to finally build that sawdust burning boiler.

To close with something to the point of the original question - the possibility of having degrade and uneven drying made the sticker thickness question easy for me I opted to be a little conservative and avoid the problems.



From Dr. Gene Wengert, technical advisor, Sawing and Drying Forum:
1 kWh = 3,413 Btu = 1 kilowatt hour. Does that help?



From contributor B:
I feel if you go under 3/4" stickers, you're pushing your luck. It seems like everyone is trying to push everything to the edge. I have a friend who has seventeen 80,000 bd ft kilns, and they use 7/8" stickers. Their family has been in business for nearly 100 years. That told me all I needed to know.


From Dr. Gene Wengert, technical advisor, Sawing and Drying Forum:
With 7/8" stickers, compared to 3/4", you will reduce the kiln capacity by nearly 10% (which means you have more heat and venting per BF), you will increase the volume of air between the stickers (making drying more uniform) but will slow the overall air velocity (slowing drying at MC above 30% MC), and will increase air drying in a yard that is short on space and uses piles over 6' wide. With air dried lumber, there is no benefit in using thicker stickers and in fact there are several production losses.


From contributor B:
Do you feel that 3/4" stickers are the best way to go? I do not air dry much, and when I do, it's only in the winter. Usually my lumber, mostly red oak, comes off the mill and goes directly into the kiln. I am running DH kilns. When I air dry during the warmer months I get too much degrade and poor color. I seem to get a lot of bug damage also.


From Dr. Gene Wengert, technical advisor, Sawing and Drying Forum:
Yes. You probably can improve your air yard to avoid most damage.


From contributor C:
I am in the process of building my first solar kiln. Should the stickers be same height and width ( 3/4" x 3/4" ) or does width make a difference?


From Dr. Gene Wengert, technical advisor, Sawing and Drying Forum:
As 3/4 x 3/4 is fairly weak, many people will go with 3/4 x 1-14 or 1-1/2.