"Crawling" Problems with Waterborne Finishes

      Like fisheye but different, "crawling" or "cratering" is a pesky finish issue involving surface tension effects in fluids. December 10, 2008

Question
My schedule goes like this:
1. Two coats BM white acrylic primer
2. Sand 320 (Norton 3x)
3. One coat Agualente tinted white
4. Sand 320
5. Two coats Agualente tinted to Dunn Edwards Swiss Coffee
6. Sand 400
7. Topcoat Agualente clear satin

After every coat of Agualente, fish eyes have been appearing within 30 seconds to one minute of application. I'm almost positive that it is not from ambient dust. My gun is clean, my air is clean, and my clear coats come out fine. It's just the white tinted coats. What am I doing wrong?

Also, I need some advice on what the best water based paint system is. I have used Target products and found that it takes seven or so coats to turn completely white. White tinted Agualente is not much better, which is why I'm using the acrylic primer to kind of get a jump start on things. I have been doing stains/glazes and clears for many years, but whites and other solid colors are fairly new to me.

Forum Responses
(Finishing Forum)
From contributor P:
I had very similar problems with Polystar: they weren't fish eyes, more like mini craters, and always after the second coat. Haven't tried the Agualente line of coloured finishes, so can't comment on them, but it sounds familiar. My MLC rep, who is extremely knowledgeable, helpful and always ready to try and fix a problem with WB, had no answer despite putting in a lot of in-shop hours with me. So I switched to Becker Acroma WB pigmented, and all the problems went away, even when I sprayed over the offending Polystar.



From the original questioner:
You are right about the mini craters, but the problem remains the same. In regard to the Becker products, I live in California and so far have not found a good way to get a hold of their product line. In addition I was supposed to have these parts done by tomorrow, which doesn't look like it's going to happen now.


From contributor J:
I had the same problem with Polystar. Never found out why but I think they may have changed how the product is made. This might be a shot in the dark, as there are a lot of other things that can cause problems. No problems with Agualente yet.


From contributor B:
What is your gun/method for applying these WB products? Do you lay on a heavy coat like you would if you spray solvent laqs? Check out your technique of spraying... Try another type such as thinner (lighter) coats, lower pressure, etc.


From contributor T:
I've sprayed a bunch of Polystar (and Ultrastar) with the same problem, seemingly random. Never got a good answer from my supplier or MLC directly on the cause. My suspicions and testing pointed me to the recoat time as the likely suspect. Here's what seems to work for me: I let coats dry the minimum amount of time before recoating and I try to get all my coats done in a single day. Also, I never sand with anything finer than 220. Try that and report back.


From contributor D:
This doesn't sound like fisheyes to me but rather the unique waterborne issue known as crawling. It's a wetting phenomenon. Thinner coats often reduces this issue. There are wetting agents available for waterbornes that fight this tendency. For white you just can't beat solvent borne Global Ultra conversion varnish undercoater under their (Valspar's) white Global Ultra topcoat. Two to three coats and you're completely done. Yeah, I know I'm an environmentally insensitive solvent kind of a guy. Sorry.


From contributor P:
Contributor D is probably right that it's not fisheye in the traditional sense, which is typically caused by silicone or other contamination. But fisheyes, craters and crawling are all used to describe surface tension issues of some kind. I spray only WB finishes, and I've seen a lot of this problem with a certain manufacturer's product.

Because I've only seen it on second or later coats, I'm convinced that it has something to do with the recoat window. Since I have yet to see a knowledgeable response from a manufacturer (even when I've asked directly), I can only guess what's happening. I'm pretty sure it's some kind of chemical bond thing, rather than a mechanical bond issue, because I've experimented with different kinds and grits of sandpaper, with no success.

In my experience, the problem is far more likely to occur the longer the earlier coats have been allowed to dry. There are all kinds of additives (surfactants, for one) in WB coatings that are intended to do things like improve flow-out. My guess is that as the finish cures, some of these chemicals evaporate or migrate to the surface and affect the adhesion and/or flow-out of the later coats.

I'm not a chemist, so I welcome anyone who really knows what they're talking about to chime in here.



From contributor B:
The problem of cratering is as contributor D says - a wetting problem or crawling. I don't think it has anything to do with re-coat windows. (Do waterborne products have recoating windows? I've never heard that they have.) And the way to overcome the crawling is to apply thinner coats. And I do that by holding my gun a little bit farther away than for solvent applications... Of course I haven't used all of the pigmented waterbornes to experience this problem.


From contributor T:
I'm using the term "recoat window" loosely here. I realize it has something to do with catalyzed finishes and crosslinking. In my experience, the window of time that works best is somewhere between 1 and 5 hours to recoat. I couldn't find any manufacturers that call it a "recoat window," but Target says you can recoat their USL product any time after 30 minutes to 24 hours without sanding. So, in effect, it has a 23 1/2 hour window. For what it's worth, I've never had the fisheye/cratering/crawling problem with any of their products.

The problem is definitely not confined to pigmented products. Just got back from a friend's shop that had it bad with a WB clear.



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