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I sprayed a water based polyurethane (Minwax) on a lot of cabinets, but it was about 15 years ago. It was relatively noxious, but it sprayed great out of my inexpensive HVLP gun and compressor. I'm guessing that it had higher VOCs than what I just bought, because I remember it being pretty noxious. Fast forward to today, I bought a gallon of the Varathane Ultimate polyurethane water based clear-satin and it would not go through the gun! Water goes through great, but not this stuff. I called Rust-Oleum tech support and they say that it shouldn't be sprayed or thinned!

My question, is whether this is really true, or are they just concerned that somebody might thin too much, etc., so it's easier to just say "no". The label says use a brush, but there aren't any comments about NOT using a sprayer.

I'm willing to go against their advice of not thinning if someone has experience with this, but otherwise, I need to find a new product.

Anyone have any experience with spraying this? Do you have suggestions about a clear water based product that is sprayable? Thanks for any advice that you can offer.

(I did call Minwax and Rust-Oleum, and neither carry a sprayable water based clear)

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  • This should be possible. Competitor products can be sprayed by HVLP with no dilution, but you must choose correct gun or nozzle.
    – Volfram K
    Commented Jan 18, 2022 at 6:21
  • Hi, welcome to Woodworking. Over the years I've done a lot of spraying and read lots more about it and it has become my mantra that everything can be sprayed. Even the stuff people say can't be sprayed someone will have found a way to spray it. And this includes when a manufacturer tells you it can't be sprayed, or gives a max dilution of X% and that's insufficient to get it to spray. Sometimes the gun, nozzle or pressure is the key, but in general dilution is what'll help so this is definitely worth investigating as the route to getting it through your gun. BUT, there is a caveat [contd]
    – Graphus
    Commented Jan 18, 2022 at 10:31
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    ...that's already been mentioned and that is the possibility that it could undermine the protection achieved. It's been my experience that this is not a certainty, not even likely in fact, but there is a chance. So while I think you should have confidence you can get this to spray I would first ask yourself some questions. First is arguably the most important, does this need the max protection offered by the Varathane product? Second, do you have to use this finish? Third, do you have to spray this project (could you roller it on instead and get acceptable results in a reasonable timeframe)?
    – Graphus
    Commented Jan 18, 2022 at 10:40

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In my experience, sprayers require the material to be thin enough to be sprayed, and many include viscosity cups to determine if the material is thin enough. I'd decant a portion into a separate container (say a pint), add measured amounts of water to thin it to the required viscosity, then do a test spray and see how it works. If you're satisfied with the results, thin the rest of the gallon with the same percentage of water that you used for the pint, stir well, then spray.

It is possible, though, that while the initial application may look really good, the thinned poly won't protect as well or last as long as it would have straight out of the can. If you chose to do this, any lack of life or protection is on you, as the manufacturer has clearly stated that this goes against the product's recommended usage.

The fact that neither company that you checked with makes a poly that's thin enough to be sprayed does give a strong indication that it just won't hold up as well as you'd expect or desire.

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  • +1. Re. the last para, Flexner is on record as saying the Minwax technical support basically don't know what they're on about. Apparently it goes far beyond the infamously poor instructions for their pre-stain product, which remain incorrect years and years after better guidelines have been out there in the public eye, including in multiple published articles.
    – Graphus
    Commented Jan 18, 2022 at 16:09
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    I took my gun apart, more than I ever have, and there is a plastic straw-like tube with a mesh filter that the cup feeds into. Evidently the water could make it through, but not the varathane. It was in pretty bad shape with gunk etc.. I saw a suggestion to just get rid of that filter which I'm going to do. With all of the suggestions, I'm confident that I will get this to work.
    – rebar
    Commented Jan 18, 2022 at 20:27
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    @rebar better to clean filter instead of remove.
    – Volfram K
    Commented Jan 19, 2022 at 6:23

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