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undercatalyzed conversion varnish6/2/19
About 2 years ago I built a large conference table (1 1/2" baltic birch exposed edge plywood, cypress veneer with solid wood inlay details). Apparently it didn't get used much until recently, but now there are major finish issues. My used-to-be-trustworthy finisher apparently undercatalyzed the conversion varnish finish, as it seems to have never fully cured/hardened. If you write on a piece of paper on the table, then lift the paper, you can see the faint outline of the writing in/on the finish. It gets dirty easily and seems to have a slightly gummy feel to it (looked great when it was originally delivered).
Stripping is your only real option.
The catalyst needs to be able to force crosslinking *everywhere*, not just a thin layer on the top/etc.
It's basically impossible to turn it back into a completely liquid form and have the catalyst mixed and agitated into the result in the right ratio.
Even if you could somehow guess the ratio right enough to not cause white spots due to overcatalyzation, the thinner is highly unlikely to melt it all the way through and thoroughly mix it.
If you had screwed up one thin, small, coat, you might be able to get away with something here because you may be able to melt the entire film.
But a conference table would normally have whatever the max allowed is :)
So unless you have a magic way of guaranteeing your thinner is going to melt *all* of it, *all* the way down, and then a way of ensuring the catalyst makes it thoroughly into the result, all the way to the bottom as well, you are screwed here.
Wish i had better news.
Usual approach is to go get xylene and strip it all.
I'm assuming your "used to be finisher" will not take any responsibility for his mistake? Did you have a contract w/him?
Plan B might be to slap the whole thing with laminate (buries face in hands). Iím hopeful the customer will have mercy on me and share the cost. Anything peculiar about contact cement sticking to conversion varnish?
Staring at a bunch of SDS for Magic 555, i don't think most will work.
Depending on how fast you want to do it, xylene or acetone will be your fastest way.
If it was not catalyzed properly, acetone should go right through it and be cheap in bulk.
It's also VOC exempt.
If you want something "less dangerous", something NMP based will probably work, and do a more thorough job, but it will take a while to work.
Citristrip is NMP based (right now) as an example.
There are other variants you could use.
I honestly would try to just pay someone to dunk tank strip it or something (depending how big a conference table we are talking)
I'd build from scratch before I went down that path... IMO
For stripper, get a couple of gallons of Dad's. It's got a decent amount of methylene chloride in it, so it's potent. It has no ammonia in it and no lye, so it won't darken any of the woods.
Score the existing finish with 100 grit, just to create a scratch pattern in the finish. This allows the MC to work its way into the finish film to break it apart and to cause it to want to unbond (mechanically) from the substrate.
Use a boatload of woodshavings to clean off the sludge instead of rags, instead of steelwool, instead of Scotchbrites.
Wear thick neoprene gloves. If stripper gets on your skin, it will sting. Remove the stripper from your skin with a rag soaked in water. A solvent-soaked rag drives the stripper into the skin.
Before stripping, yes, do try the over-catalyzed conversion varnish. Lightly scuff your existing finish, first.
The extra-hot CV will often -- not always -- kick the undercatalyzed finish underneath. Been there, done that, with proper success.
The over catalyzed conversion varnish will either wrinkle the existing coating or it will fail prematurely because it's over catalyzed.
Either put a correctly catalyzed conversion coating on it (after light scuff) or put a vinyl sealer coat on it, catalyzed (ask your rep for percentage. I know 1% is good for MLC vinyl sealer). And then apply the properly catalyzed conversion varnish coating on top of that after a light scuff.
I realize a lot of us have dealt with this issue at one time or another. Sure some of us may have shot another coat on it and called it good... the customer was probably pleased.... but the chemistry isn't going to lie... Sure the coating you put on top happens to lay out and cure on the surface...Ö. what's underneath is still a problem.... we all know a hard finish on top of a layer of soft finish is going to be the weakest link... it will fracture.... just when will it start? If you can sleep at night knowing it's wrong that's your deal..... Strip it and start over or remanufacture the product...
Two thoughts, cypress is really soft and are you sure the writing isn't showing in the wood. Second, was some odd kind of cleaning chemical used by a new cleaning crew lately? Hard to imagine that in 2 years no one complained about sticky feel. It should have felt sticky when it left the shop if it was under catalyzed. Don't waste the time and money to apply something on top. Strip it down, do it right.
Thanks all- I really appreciate the responses! I too thought about the softness of cypress, but the same effect occurs in the hard edge grain of the baltic birch ply. The possibility of a cleaning crew's wax cleaning product would be a welcome discovery (to put it mildly); I plan to do another site visit to investigate more thoroughly. It's hard to describe the feel- it's not sticky, but kind of waxy. Fingers crossed someone just put a dumb cleaning product on it that can be easily removed.
After reading your last post, another cause of the issue could be the varnish was over catalyzed. What you are feeling is the excess catalyst leaching out and laying on the surface. This doesn't always show up right away like you mentioned during the initial delivery and it also depends on how much it was over catalyzed. If this is the issue, it's an easy fix. Take 1 gallon of water and mix in a box of baking powder. Wipe the area with a damp cotton rag of the water/baking powder mixture. And dry off the area with another rag. You may need to do this a few times to get it all off. Don't reuse the damp rag, only use it once. And don't redip the dirty rag, always get a clean one.