Conversion Varnish Turning Wood Panels Pink
Investigation reveals that the catalyst in the varnish reacts with the wood to create a pinkish hue. Solution? Start by applying some kind of barrier coat. June 28, 2013
Question
I recently finished veneered acacia panels (acacia melanoxylon) with ML Campbell clear satin CV. All of the panels came from a single sheet of veneered MDF. The panels left my shop looking good. They spent some time at the jobsite prior to the cabinet maker installing them. At some point, some of the panels took on a pinkish hue.
My two theories are light exposure or chemical reaction. The case against light exposure is that the entirety of each panel that turned pinkish has done so uniformly, including the panel edges that likely did not get much light. The case against a chemical reaction is that all of the panels were sprayed with the same batch of CV at the same time - and they left the shop looking good. Does anyone have any other possible explanations or thoughts on this?
Forum Responses
(Finishing Forum)
From contributor O:
It is my opinion that what you’re experiencing is a reaction between the wood and the acid in the care catalyst. If you have any extra wood try some samples. Spray one with a vinyl sealer and a cv. top coat and try another sample out of 2k urethane. Try to use a urethane system that contains an Isolante barrier coat of which is used on oily wood.
From contributor G:
Over-catalyzing a CV can cause the coating to turn pinkish.
From the original questioner:
Contributor O - that's a good thought, thanks. I'll do some experiments.
From contributor M:
Here are a couple of articles from the Knowledge Base that may be of help.
Pink Maple Mystery
Overcatalyzation
From the original questioner:
From reading your responses and from reading the Knowledge Base responses (thanks Contributor M) it looks very likely that the problem is over-catalyzation. We're very careful with our catalyzation, but it's always possible to make a mistake. It turns out that the panels were not all sprayed in one batch as I had originally thought, which lends additional credence to this over-catalyzation theory.
From contributor G:
That's going to be a lot of work to re-do. At least all of them aren't affected and they are flat panels and not something with intricate details.
From the original questioner:
Actually I feel pretty lucky, as this was a small project (one sheet of material). It could have been a whole kitchen.
From contributor G:
So what's the plan? Just buy a new sheet and do them over or try to strip the others and re-spray? I'm not familiar with acacia panels (acacia melanoxylon) and their costs.
From the original questioner:
New material. The old material when sanded does not return to the color of the original wood. I prefer to fix this just once, so cut some new panels, spray, and be done.
From contributor G:
That's what I would have done myself - just curious.
From the original questioner:
There’s a new twist to this issue. It turns out Contributor O was right in suspecting that the pinkish hue was a result of cv catalyst (acid) reacting to the wood. A few days ago I poured pure catalyst onto the acacia. When I came in this morning it had turned the wood reddish.
As I mentioned in an earlier post, it turns out that the panels were sprayed in two separate batches, so a difference in the acid catalyst concentration would cause a difference in the extent of the red effect. I can imagine that even different weather conditions/dry times would cause the acid to react differently. I'm curious to see if the catalyst has similar effects on any other wood species.
From contributor P:
A coat of MLC's Vinyl Sealer before the catalyzed topcoat could prevent your problems.
From contributor U:
Acids will often pink up timbers, particularly the heartwood, where there is a greater concentration semi-soluble chemicals in the timber. Softwoods and fruitwoods are particularly prone, so vinyl or shellac sealers are often used. I used to be a tech advisor for Sadolin in the UK, selling Synteko Classic under the name PV67 for floors. Up to 2007 there were no problems, as there was a vinyl sealer for the first coat. In 2007, the solvent level of the sealer meant it could not be sold in Europe (VOC legislation). The marketing people didn't bother suggesting a replacement, so we techies had to field no end of complaints of floors going red or pink. In the end I started suggesting Zinsser SealCoat as an isolator.
