Gary - what extender do you use?
I use XIM with latex paint. Will that work?
Jim, do you notice a difference in how the finish lays out with and without extender?
Also - do you ever dilute the conversion varnish with water? I usually dilute WB poly a little.
I never cut a water borne finish with water. That spreads the actual finish molecules out...remember, the water is just a carrier. While there's unlikely to be an issue with a very small amount of thinning with water, it should never exceed 10% or whatever the manufacturer specifies as the limit, but preferably "none". Viscosity is best handled by a gun setup that's suitable for the finish being used. I have added a small amount of the GF extender to a particularly thicker finish like tinted Target EM6500 as well as to SW KemAqua to get them to lay down better, however.
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The most expensive tool is the one you buy "cheaply" and often...
Adding to what Jim said, Extender makes a huge difference for me with some products, especially Kem Aqua Plus which I could never spray well until I added 3% Extender. Then it sprayed very easily and flowed out to a thin, smooth film, something it just would not do without it. I also use Extender with GF's EnduroVar and EnduroVar White Poly; again, the improvement is dramatic after adding Extender at 3%.
Unlike Jim, I often added water to WB products. Before I had a pressure assisted HVLP gun I had to add 6% water to GF's HP Poly to get the viscosity down into the 45 second range in order to spray it well with my 1.8 mm N/N gravity gun. It cured fine. To spray SW's ProClassic I had to add 18% water, far more than I wanted to, but that's how much it took in order to spray it with that gun. The finish dried and cured just fine, not that I'm recommending you do the same. I eventually bought a pressure assisted gun so that I could spray paints and other higher viscosity WB products with no or little thinning. But even with it I sometimes added 3 - 5% water in order to spray thinner coats. Then I found Extender. I haven't added water since I started using Extender.
FYI, Benjamin Moore makes an Extender, too, and it works very well with WB paints and stains. BM does not specifically say it can be used with clearcoats, however. It's white in the can so that would make me suspicious about trying it with one.
John
Here's one that looks like it would be worth a trial for table tops that need to be easily repairable: https://www.rubiomonocoat.com/en/home?country=us