All,
I am working on a large renovation utilizing a variety of plywoods, veneer on MDF and solid materials, all Rift White Oak.
Everything is receiving a water based flat finish. The RWO veneer on MDF (kitchen doors/drawer fronts, etc.) has small black "stuff" appearing from inside the grain as the first coat of finish dries. I'm waiting to hear from my supplier/the mill regarding what this might be. None of the veneer on veneer core (plywood) or solid wood have any issues at all AND not all of the RWO on MDF is affected, maybe 50%.
I am hoping someone here might have seen something like this and have an idea.

Thanks for any input.

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That looks like white oak. It has a porous grain structure. Perhaps their glue is leaching.

I think you are seeing a reaction between the tannins in the oak, the water based finish and iron from somewhere. Where the iron is coming from is the mystery.

I'm with Tom... this is tannin bleed and a reaction to your waterborne coating... humor yourself and seal the same material with a solvent borne finish and i bet you don't get the same result.

Steel Wool will supply the iron for a ferrous metal reaction.

Thank you all for the responses.
I spoke with my finishing supplier this morning and he seconded the glue issue.
Apparently he has seen this only one other time in years of selling this finish. The instance was when a very thin veneer was used (as in over an MDF core). The water based finish makes contact with the panel adhesive through the deeper parts of the grain and reactivates. His solution is a wash/barrier coat as well. Going to be looking for a different mill for supply as well as testing the barrier coat.
Again, thanks for the responses.

So no one used steel wool in the finishing process? I'd experiment on a piece of scrap and I'm thinking someone is lying if no one fesses up to the steel wool. I know of no adhesive that would reactivate with the small amount of water from the finish. Take a piece of scrap and submerge it.

I'd put money on it as tannin bleed and not the adhesive used to apply the veneer face to the core/substrate. A lot of waterborne finishes contain a high amount of ammonia which in turn will react with woods such as oak.... What your seeing in the pores is the high ammonia concentration reacting with the tannins in the oaks pore structure. There is no one making veneered goods layed up on core that is using a "rewetable" glue for veneer press lines. Look up fuming oak... ammonia is the key ingredient to make the reaction happen... your particular coating used just may have a higher concentration than other finishes as well as the particular flitch of veneer you have must have a high concentration of natural tannin... perfect storm...

Update:
I met with my field rep. from my plywood supplier. He also believes this is a reaction between the glue and finish. He took a sample that the mill will analyze.

No steel wool or any other metal has been near these panels..at least in my shop. Also, this problem is apparent over various pieces from 12 different sheets, ordered and received over two weeks apart.

In the meantime....

I found an unfinished off-cut in the shop. Visible glue seepage through the grain.
Taped of a portion and applied full strength coat of Bullseye Sealcoat. Dried, sanded and applied a coat of finish. Issue is still apparent in both areas, regardless of the barrier coat.

Still searching.

Material coming in from another mill next week (Columbia Forest).

Thanks for the continued interest and contributions.

Cub:

It is interesting that in the bottom photo the staining is heavier on the left side of the panel, and seems to diminish towards the right side. I would think glue seepage to be more consistent across the entire panel.

It makes me wonder if either:
A.) The veneer has some kind of mold on it already, and the sequence matching lets the mold intensity trail off as the veneer cutting gets farther away from the mold.

or B.) It is a reaction to steel, which could have come from many sources, such as from someone grinding steel near the panels, with the residual dust being hard to remove.

I would think that an ammonia reaction would be more consistent. Fuming oak would certainly not leave isolated pockets of reaction in the pore structure, with the rest of the surface untouched; it would be more consistent across the face of the entire piece.

I would be curious to know. Hopefully you will post results.

TonyF

I really like reading everyones guesses.
Too bad you didn't take Shane up on his money bet. ;.)

lol..... Maybe I was a little overzealous... Yeah maybe there would be more graying effect if it was an over ammonia issue... I was banking the pores were lighting up with a tannin bleed since it's a waterbone finish and the pores would be full of that solution longer than the surface to create that condition ... if the coating was shot too heavy and the humidity was high it could be a possibility. That being said i have seen glue seep through the pores of our own shops veneer dept pressing veneer on core at too high of a pressure with veneer that may have been too thin.... causing a glue bleed... i've never seen a veneer glue that rewetted though... not in years anyways.. I could always send that money via gift card to the coffee house of your choice if proven wrong though! ...Lol

All,
Perhaps a light at the end of the tunnel...
I just spoke with a rep. from the mill who received and reviewed my sample panel last week. He confirms (or at least agrees) that this is glue bleed through. The story goes that about 6 weeks ago they discovered a bent shaft on one of their glue spreaders. This was causing an uneven application of glue to the panel...heavier by a couple .000" on parts of the panel. This in-turn led to the bleed through on the panel, which he acknowledges shouldn't have left the mill.

As for the interaction with the finish, this was most likely the fault of a "dye" they use in the adhesive. As he put it, once it comes through the grain you will never remove it, and, it is activated by the finish. He noted that he doesn't "like" the stuff.

I've re-cut the whole job using sheet goods from another mill. All material looks exceptional, for what it is, and there is no sign of any glue anywhere....yet!

I'll let you all know if I'm in the clear.
Thanks again for all the interest.

A bent shaft? I can't wait for the responses. ;.)