Stripes in Fir Plywood

A cabinetmaker's finisher notices a strange defect in some Fir plywood, probably caused by grain compression that happened at the plywood mill. October 13, 2012

I just sent a batch of VG Fir slab plywood doors to the finisher, and got a call that he noticed lighter stripes running perpendicular to the grain. I went to check it out, and sure enough there is a straight 3/8" stripe each 3" that is a shade lighter. It only shows in the right angle of light. I sanded through a scrap, and there is nothing showing on the MDF jacket or in the glue. No amount of sanding would eliminate the lines. The finisher shot a coat of sealer and it made no difference. We left it in the sun to see if it would even out. The lines are subtle, but I'm sure the client will notice. At this point I have to decide whether to stop the finishing and remake all the doors, or forge ahead and hope for the best (and possibly have to eat $2,100 in finishing costs).

Forum Responses
(Cabinetmaking Forum)
From contributor F:
Something happened in processing or storage, either in the finisherís shop, your shop, or the mill. Do you have any unprocessed sheets or long strips back at the shop that you can look at and see if they have the same defect? If the defect is in a long strip of fall-off that hasn't been through any machines and you don't have any storage on those centers then get the distributor to look at it. You need to determine the cause of the problem before spending any more money.

From the original questioner:
The problem is in the unfinished wood. I got back to the shop and looked at more pieces and itís all there. Either way itís tough - I'm out of town for the next week so I can't remake everything. It's either risk paying the finisher twice or possibly lose a very good (general contractor) customer for holding up the job.

From contributor U:
Were these doors run through a widebelt sander? This sounds like a common defect from using an old belt where the splice is leaving a mark perpendicular to the grain. Even sanding over it with a random orbit sander is tough make those lines go away. Usually, a light pass with a fresh belt will take care of that problem.

From contributor F:
If it happened at the mill then you need to get the distributor up to speed fast and get them on the hook for some of the costs. Also tell the GC youíre going to need to remake some items and you will work as fast as possible. Your other option is to get the GC and the customer to come look at the defect and give them a credit based on what the distributor and you want to give up in order to make this go away. Then see if they will accept the defect with the credit. Moving forward at this point without a solution will only cost you more money and more ill will in the future.

From contributor G:
I had a problem with some hickory veneer and it turned out that the veneer knife had dents in it that would compress the wood fiber. Although the veneer was sanded smooth, the compressed sections would take less stain and would appear lighter in color. The lines were more on an angle in the direction of the knife cuts than straight across. This may not be the same problem you are seeing.

From the original questioner:
To contributor G: I think you're right that the grain is compressed. It's only visible from certain angles and goes all the way through the veneer. I'm guessing some feed roller at the mill had a ridge in it as the lines are very regular and straight. Of course the "B" side of the panels has no such marks.