Waterborne Finish Basics
An extensive and detailed introductory how-to on spraying water-based finishes. March 2, 2006
Question
We are looking at using a water-based topcoat. We are going to try Chemcraft. We have a Kremlin 10.14 pump and I’m wondering will it work well?
Forum Responses
(Finishing Forum)
From contributor O:
We haven't tried Chemcraft but had good success with Target, Fuhr, Cash Coatings, M.L. Cambell, Ronan, Camger, and Becker waterbornes. We had a problem with micro bubbles in the finish (not fish eye, solvent pop, contamination or gassing around open pores) using the 10.14 with the MVX gun until we used the 09-094 and the 06-094 tips. Until then we had used the 114 series which works great for solvent based material.
Here are some things to watch for:
1. Fluid 20 / Air 30 (strange but true)
2. Going between waterborne and solventborne - take the time to really flush everything adequately because any residue which mixes gets gummy
3. You may get a build up on the fluid tip while spraying. We kept a toothbrush and a cup of water nearby and stayed 100% clean all the time.
4. If you walk away from the gun for a while you can leave the tip/cap assembled and just let that part of the gun sit in water. Pick it up, blow it off and shoot again.
5. After cleaning the tip with water at the end of the day we left them in acetone.
6. This probably goes without saying but you still have to ventilate and wear
respiratory protection. Don't develop bad habits in the booth just because it doesn't stink as bad.
7. The waterbornes love IR light. We have a ceiling heater we got at Grainger's which has a quartz tube that glows red. We were able to put a 5 wet mil coat on, put it under the lamp with no flash time and let it come to about 120 degrees (used a RayTek point and shoot tester for this), let it cool and sand it. It works great for samples.
8. The waterbornes we tried all seemed to 'feel' the best when we shot them heavy. They don't have the slip agents (wax) that solvent based coatings do and didn't feel as nice to the touch unless we gave a heavy coat - this ranged from 3 mils (Target) to 5 mils (Fuhr). This is only anecdotal and may not be a necessary result but was certainly our experience. This became an issue with vertical spraying. Fuhr offers the higher viscocity coating to help with this. Overall we had the best success with Target's CV which dries a little slower but overall is an amazing coating.
9. Again, you are probably aware that shellac must be de-waxed if it is to be used as a sealer (Zinsser Sealcoat).
10. Don't ever shoot waterborne on paperbacked veneer which has been applied with contact cement. You will have a drastic problem every time. The only chance you have is to shoot really light coats, building up this way, then let it cure, sand and a full top coat. Waterborne on phenolic backed with contact ok or on paperbacked which has been applied with white glue, UF etc. and pressed ok.
11. You don't have the solvent content to help dissolve contamination on the panel so you may have to be more careful then you are used to about surface prep.
From contributor C:
I like the response above. The only thing I would add is to be careful of the sandpaper you use. I have had trouble using stereated paper, which most is. There are non-stereated versions available, just ask your rep. I know Klingspor's is PS31.
From the original questioner:
Arcdesign what were the problems with the sand paper?
From contributor A:
I've found the
Mirka line of stereated to be the most cost effective and it causes no issues with WB (Zinc stereate contamination) The 3M is more expensive and is not as good a paper.
From contributor C:
The problems I had resembled solvent pop and it was in my infancy of using water base. It might have been the coating, maybe the sandpaper or me, I don't know. I have heard of others having problems. When I had it I was recommended by the product manufacturer to switch paper - I did and haven't switched back since. I find the Klingspor paper to sand fast and well and while it may clog a little sooner, it works great for my needs.
From contributor O:
Another comment I wanted to make about waterbornes is that the various manufactures we tried insisted on intercoat sanding except Target (if you recoated within 24 hours). We did a very large refinishing job of 15 year old flat panel birch kitchen which because of the original coatings failure (cracking and crazing) required about 6 coats to fill to a smooth satin.
We rarely go that far but in this particular application the fact that we didn't have to re-sand the entire kitchen every coat really saved some time. Another observation is that most manufactures of waterbornes will tell you not to put them over solvent borne vinyl sealers. Exceptions are MLC and Target. Tech support at MLC told me it was out of the question but their lab told me it would definitely work. Target told me it would work and it did but in testing we had some fisheye like results on panels that we didn't sand and then wipe really clean. When we did sand the dried vinyl and cleaned appropriately we got perfect results with the Target.
Why shoot waterborne over vinyl? In our case the original coating we needed to go over had cracked all the way down to the raw veneer. Even after a careful sanding which leveled the surfaces somewhat the waterborne would then enter the cracks and swell the veneer so that we got an uneven surface. We used the vinyl to stop this and also as an excellent barrier coat. This type of solution could also help with spraying waterborne on paper back veneer applied with contact cement although it’s still too risky to attempt.
Using de-waxed shellac or solvent based vinyl as sealers seems to go against the whole notion of using waterbornes and I'm certainly not suggesting that it’s necessary. All I want to point out is that it can be done and overall any use of water is better than no use whatsoever even if that use is not 100%.
From the original questioner:
My rep suggested using vinyl. He said it would dry faster than using two top coats. I assumed that was the way everyone is doing it.
From contributor O:
I know it can be done, but haven't done extensive testing and (it seems) neither have either the waterborne manufactures or the solvent borne manufactures. I don't know enough chemistry to speculate about why it would or wouldn't succeed. It is best to test. You may well be doing testing and research at this point that has not been done before and I would encourage you to report all of your results - both positive and negative.
