Troubleshooting "Craters" in 2K Poly

Is it fisheye? Solvent pop? Water in the lines? A finisher gets help with a finish defect. March 12, 2015

Question (WOODWEB Member) :
Iím troubleshooting craters in 2k poly and my problem is on the final coats. I wipe everything down with a silicon remover and then using silicon free tack rags wipe it down again. Now the first coat goes on fine but the following coats tend to show some very small craters which makes wet sanding that much longer. I use a wall filter and also a gun filter. They are not very deep but I am hoping to get rid of them as the finish the gun puts on is very good.

Forum Responses
(Finishing Forum)
From Contributor S:
Did you add fish eye flo-out to you finish? I would do just that at this juncture.

From the original questioner:
No I haven't added this as I am in the UK and can't seem to find this product. I will ask the supplier.

From Contributor S:
It's a standard additive. It might also be better known as fish eye remover. If your supplier doesn't have this additive then many places which sell car finishes will carry it.

Since you're not familiar with this here are some suggestions:

- Don't add more than what the bottle suggests. It's usually just several drops or squirts per liter of finish. Adding too much softens your finish, the additive starts to behave like a pasticizer.

- It's silicone oil. Once you add it your pot and fluid passages and lines now have it. Some people use dedicated lines or guns. I think that's overkill. A repeat and thorough flushing with lots of lacquer thinner will clean everything in most cases - sometimes not, in which case you might just consider to always use this additive from here on out.

- The additive makes your finish feel slicker. It raises the sheen just slightly, sometimes too slight to notice.

- If you're going to use it from here on out then you add it in to all the parts of your finish system, your sealers, primers, topcoats, etc. Think of it like this: just as ketchup solves a multitude of food problems, so will your fish eye remover/flo-out.

From the original questioner:
I have been in touch with the supplier and he is going to supply me with some.

From contributor C:
Are you sure it is fisheye? Are you wiping the raw wood with the cleaner? I would do your final sanding and then apply sealer. After that I would dry sand. It is a lot quicker and there is no risk of adding moisture. Does it happen on all the woods you use? Sometimes on walnut I get mini pinholes but I will dry sand and apply a second sealer which fills any pinholes. Get a piece of glass and clean with denatured alcohol and then try spraying it. If you get fisheyes then your air supply or material is your problem. I only wetsand after the final topcoat.

From contributor J:
If they are really small, it sounds like it could be solvent pop. If it is, then slowing down the finish is what you need to do and not pile on the coats.

From contributor M:
Your contamination sounds like its native to your wood (in other words, it was in the wood before you got started). Like said above - you need something like fish-eye killer added to the finish. I've gotten this sort of thing with 2K poly on refinishing kitchen tables. It can be nerve-blowing.

From the original questioner:
Itís not the wood as these are final coats after the wood pores have been fully filled. I have a feeling it is water in the line even though I have two filters one at the gun and one on the wall (see image).

Click here for higher quality, full size image

From contributor J:
If the filter on the wall is not refrigerated then it needs to be 50' away from your compressor. That 50' will give your water vapor time to cool off and recondense. Your water trap won't stop vapor. I use that system even onsite when away from the shop. Compressor, 50' hose, filter, then hose to spraygun.

From the original questioner:
Ok that could be my problem as my compressor is about two feet away from the filter - not too sure what to do as my finishing shop is only 15x15.

From Contributor S:
Your best solution is to run hard pipe around the perimeter of your shop. It ought to be canted back toward your compressor. The hard pipe with its appreciable length allows for the condensate to form and to drip back toward the compressor where you drain your air tank. Condensate forms best on smooth surfaces such as iron or copper piping. It will form with PVC pipe but using PVC pipe for pressurized air is the height of poor judgment, it's too unsafe.

Rubberized air lines (air hose) also tend to provide some kind of insulation from the outside ambient air temperature from what's taking place inside the hose. Long hose is better than a short run but it's not as good as using a long run of hard pipe. The disadvantage of using iron versus brass is that eventually rust and slag develop inside the pipe. I prefer copper for that reason.

Either way, whether itís hose, iron, or copper, you need a long run so that you do cause precipitate to form, and drip back where it can be drained. Filters go at the end of your run to capture moisture and any oils that might survive the long run. Fish eye remover won't help you with pock marks created by moisture in your lines. They help you with contaminated surfaces, issues in need of dealing with surface tension. That depression in the film of your finish looks to me more like it's some contamination. Oil in your air? (Proper air pipe runs are part of the solution, good filters, and additives are the other fix-its).

From the original questioner:
Thanks for the advice - would a long line also prevent oil in the line?

From contributor C:
I have had similar looking issues with my 2k urethane. I just had to replace my compressor as it was blowing too much oil. I now have an oil removal filter at my compressor and two more in the spray area. Now I can monitor if oil is getting in my hoses.