Sandpaper and Fisheye

Another finisher confronts the dreaded fisheye problem, and a discussion of sanding materials ensues. November 8, 2007

Do silicon carbide sandpapers or fine finishing screens have stearates in the coatings? I'm not speaking here of the gray non-loading versions, which I know have stearate coating, but rather the black wet/dry papers. Same question for abralon or abranet. I'm having a between-coat contamination problem with General pre-cat 181 waterbase. 3m Frecut gold is not alleviating the problem. I know it's an inter-coat problem because I can shoot multiple cats starting with bare wood just fine... Fisheye problem only starts after any intercoat sanding of previous coats.

Forum Responses
(Finishing Forum)
From contributor M:
Would silicon carbide have silicone in it? That would cause a fisheye problem. I use Carborundum Premier Red Aluminum Oxide Resin Bond and Carborundum EZ Touch sanding sponges. Best finishing abrasives on the market.

From the original questioner:
Actually, it's silicon carbide, i.e. the element silicon. Silicone is a complex compound, and according to Wikipedia, the two - silicon and silicone - are completely different.

From contributor D:
I work for Webb Abrasives. Your problem could be the result of all sorts of variables. It could be a problem with storage/temperature/mixing of the 181 waterbase. If you're using any steel wool at all, that could be a problem, too, as it's full of oils. Sometimes people blame the stearate, when really it's a different problem altogether.

From contributor G:
Cleaning of the sanding dust before recoat could be one problem. Try using Crystalac Surface Conditioner to clean any residue after removing the dust.

From contributor K:
Jeff at Target recommends cleaning the surface with 50% alcohol and H20.

From contributor R:
I use General's pre-cat and their high performance all the time, and one thing I love about these two products is that they are rarely, if ever, problematic. I am refinishing old pieces, so I should see fisheyes every once in a while, but I don't. I use Mirka gold discs, and Mirka gold flex sheets between coats, and foam pads I buy from Wal-Mart (Mainstays is the brand name on the package). My guess is it's either the sandpaper or whatever you're backing it with or lubricating it with.

From the original questioner:
I don't get it... I'm basically jumping ship on these General Finishes...completely frustrated. It does seem that pre-cat 181 is a relatively problem-free finish for most shops... Beats me.

The fisheye effects I am seeing don't appear obviously until the third coat, and are happening even without intercoat sanding. I tried targeting the spray rig as perhaps pumping oil into the line, but I borrowed an oil-free compressor, used new supply lines, and the same thing happens: 1st coat bare wood 2-3mils, okay. 2nd coat without cutting off raised grain from 1st coat 2-3 mils, okay. 3rd coat fisheye starts to become apparent.

If I continue without sanding, the fisheye continues to get worse, and if I sand, it becomes much worse. The only thing I'm wondering about is whether the bare wood sanding is causing the problem; perhaps the fisheye is in fact appearing immediately in the first seal coat, but it's too small to see until 2 and 3.

Bare wood prep always uses a stearated (white) random orbit pad. I haven't bothered to try changing the bare wood prep, because if the prep throughout the whole process is that unforgivable, I wouldn't be able to trust my ability to keep things uncontaminated throughout the fabrication. (Never had contamination issues with any other products including NC.)

Contributor D, no steel wool used at all. Each test used brand new Frecut gold and new paper towels to clean. I am curious about your storing/temp/mixture point. It's brand new stock, stored in the shop. Right now temp in the shop is in the 80's, and mixing is just a light stir, careful not to raise bubbles before using. The ultimate goal was to shoot pigmented 181, which is what their colored finishes are, using Degussa 896 2 oz/quart. Maybe mixing the pigment into the 181 needs to be done in a particular way, but the experiments used both pigmented and straight 181, all with the same results.

From contributor D:
What I was getting at is that the fisheye effect may have to do with the coating, not the abrasive. Your problem is contamination if you are sanding a partially-cured lacquer. Please make sure that the lacquer is completely cured before scuffing. If you sand before the lacquer is cured, you will get contamination, because the very thin layer of lacquer underneath the surface is still in a partially uncured state.

I suspect that you could be applying the lacquer at a temperature that is too high. Read the can. Most water-based lacquers will tell you to apply at a lacquer temperature of 70 degrees F. If you are applying your finish at the wrong temperature and you do not wait long enough before sanding, you will get fisheyes. My advice to anyone reading this, and I hope I haven't been stating the obvious to you guys, but... buy a thermometer and take the temperature of the lacquer prior to application, applying the finish as per the instructions on the can. If the temperature is too low, try storing your finishes on a table (not on the floor) where the ambient room temperature is higher, etc.

Of course, my area of expertise is sanding... This is just a bit of knowledge I've picked up in talking to people like yourself and I thought it would be good to pass it along.

From contributor A:
I'm confused. You are knowingly using zinc stearated (white) paper on wood prep, then coating with a waterborne. Then wondering why you end up with fisheyes even though you started using the correct stereated products (gold) after you started spraying. Why not use Mirka or 3m gold paper for everything?

From contributor K:
If you are sanding with the stearated papers, then definitely clean the surface with AL and H20 before staining/finishing

From the original questioner:
Well... I think you're correct about the bare wood/stearated paper issue, although I haven't tested it out. The present large project was prepped with stearates before I realized this was going to be such an issue. So it's too late unless I seal with shellac, thus obviating my hope of ditching the solvents.

That aside, after speaking with a waterborne product designer, it seems that the stearate contamination problem would not be that hard to fix in these coatings. So why make such an issue out of stearates when it can be addressed in the chemistry?

Anyway, for now I'm going with Pianolac for this project. It allows any type sanding medium and flows out over reasonably minor contaminants.

Contributor D, when I am running test boards they often get rushed in a way the actual project does not get rushed. But in talking with the General technicians in working through this (who were, by the way, eager to help) we discussed the 80's temps, and they didn't feel there was a temp problem. That said, I still think your point makes sense, and will pay attention to it in the future.

From the original questioner:

I had given the alcohol/h2o wash a shot previously, with no improvement.

From contributor P:
I have seen the same problem with ML Campbell WB products (Ultrastar and Polystar). I doubt it's related to sandpaper, because I use the same sandpaper (Norton discs) for everything. I spray with AAA and turbine equipment. Campbell themselves have stated that they don't know what causes it.

The best I can tell is that it appears to be related to a specific batch of product, maybe a shelf life issue. For the record, I still use those products regularly, and I haven't seen the problem recently, but I know other guys in the same area who have.

I can say that I've never seen it with other WB products, including Target, Fuhr and Minwax. Maybe some formulations are just more prone to fisheye. Maybe try General's Enduro. It can be custom tinted, too.

From contributor A:
Crystalac offers a wash for fisheye removal. I have some, but don't know what's in it. I have used it with success in the past. It's a good idea to have some around just in case you or someone else unknowingly throws a wrench in the works.

From contributor T:
I've never been a firm believer that sandpaper causes fisheye in coatings. Fisheyes are usually caused either by defoamers (some are silicone based) that have floated out of suspension, or surface contamination from oils or waxes or silicones. We [General Finishes] incorporate several different defoamer packages into our coatings to prevent this from happening. We very rarely have fisheye problems with our coatings. All manufacturers of waterbase coatings have encountered fisheyes at some point in time. Why they show up after the 3rd coat is the mystery. Temperature can cause orange peel more than it has an effect on fisheye. You mentioned you were tinting with Degussa 896 series pigment. Have you tested the clear product without the pigment? Have you sprayed any other product with the same tint with different results? One last item: the batch date on the container will let me look at retains and draw cards to verify the quality of the product. After time, defoamers can float to the surface of the container and if it is not mixed properly back into suspension, it can cause fisheye from the get go.