Q. We are a cabinet shop that is having a problem with end checking in red oak pieces, not at the glue joint, but in the wood itself. The cabinets are finished and in boxes, stored in a warehouse at 65 degrees with 27 percent RH, which is 5.8 EMC. That is low but not extremely low. This problem appeared when the contractors started complaining on the job site while installing the cabinets, or soon after. Then we opened boxes in the warehouse and found some there also. We did a moisture check on couple of pieces (oven test) and moisture was at 7.6 percent. These are small end checks that penetrate inwards up to 1 inch. The finish is cracked, so the separating was after it was prefinished.
 
My take on this is that these were preexisting surface checks that opened up again in a drier environment. Is this correct or am I missing something?
 
A. You are perfectly correct. Dry wood is too strong to easily develop a new crack. Plus, the finish slows down any moisture change, so stress levels will be lower than with unfinished wood. And you do have the moisture values and do have good storage conditions—humidity is good.
 
Assuming that the lumber you purchased was at the correct MC, then it is likely that the checks you now see developed when the lumber was dried. (We do have end coating that can be used on fresh lumber ends to eliminate virtually all end checks in drying, but not all mills use this inexpensive protection.)
 

NOWLEDGE CENTER

Find more Wood Doctor at FDMCdigital.com

Gene Wengert, aka The Wood Doctor, troubleshoots wood related problems, and explores lumber and veneer qualities and performance, species by species, in Wood Explorer, inside FDMC's Knowledge Center.


So, when you get the lumber, you visually examine an end and cut off an inch or two to eliminate the visible end check. However, the end check is often so small in dried lumber that it cannot be seen perfectly. So, the estimated end trim taken can sometimes be too little; that is, there is a very small crack in the end that was not cut off.
 
Unless your facility is fairly dry (many are quite dry during the heating season, but not when it is warm outside), then this crack will remain invisible throughout manufacturing. Now, when the finished piece is exposed to slightly drier conditions (but not unreasonably dry in your case), the end shrinks a tiny bit and this shrinkage re-opens the end check. If it is really dry, the check can increase in length.
 
As you know now, the cost of repair is quite high. It is too bad that properly applied high quality end coating was not used on the lumber. The cost to do so is under $5 per 1000 BF.
 
Special note: Sometimes we can have surface checks that will be invisible in manufacturing when the manufacturing facility is not real dry. But, then these checks will open after finishing. It is the same story: Preexisting checks that re-open.
 
Certainly, this is one reason why it might be incorrect to have a high humidity manufacturing facility; 30 to 35 percent RH is as humid as we want in the wintertime so we can catch any preexisting end or surface checks before finishing or, at least, before shipping.
 
Gene Wengert, "The Wood Doctor," has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.

Have something to say? Share your thoughts with us in the comments below.