# Thinning poly for HVLP sprayer



## Bob Willing (Jul 4, 2008)

What is the ratio for thinning poly for a HVLP sprayer. I purchased a HVLP sprayer from HF and they do not give thinning info!


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## HowardAcheson (Nov 25, 2011)

If you are referring to oil based poly varnish let me suggest that spraying that type of finish is problematic. The overspray is in the form of a liquid droplets and mist. The overspray will get on every surface in the area leaving a crust that will not be easily removed. Only spray oil based finish if you have an efficient spray booth or can spray outdoors.

If you are spraying a waterborne finish, contact the manufacturer if the label does not answer your question. Water is not a thinner for waterborne finishes. Water is a carrier of other chemicals keeping them apart until the water evaporates. Too much water will impede the mixing of the chemicals and prevent the curing pricing.


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## cabinetman (Jul 5, 2007)

You can spray oil base finishes if you have some experience and are familiar with the gun. They are heavily bodied and it's easy to get runs. They stay wet long enough to be a landing zone for debris. Overspray will stay airborne and land on everything. Unless you have a certified spray booth, or have configured a DIY booth to be efficient, wiping on would be an alternative.

Waterbased polyurethane is an easy media to spray. I've used many brands, and the directions for application should be followed. I've found that adding 5%-10% water hasn't affected the curing of any of the brands. Spraying thin coats works best.










 







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## jleep (Oct 27, 2011)

10% and light thin coats...almost every can of material is vague I thinning.....it changes the product and the voc's


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## BWSmith (Aug 24, 2010)

Probably shouldn't post......oh well.

No thinning,get a bigger hose...uhh,I mean tip.And work on gun adj.BW


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## Bob Willing (Jul 4, 2008)

Thanks for all the comments but just as confused as before. I found this on a google search http://www.woodweb.com/knowledge_base/Applying_oilbased_polyurethane.html and still no one can agree on a method. I guess it is back to trial and error.


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## wildwood (Jan 25, 2011)

Pretty much a trial and error proposition spraying consumer grade polyurethane, most designed for brush application. Think your manual says:

*“Proper thinning varies with the material being used and local temperature and humidity. In most cases, thinning will be approximately 10% and not more than 30%.”*

So if have a 20 oz. spray bottle, try 2 oz of thinner to 18 oz poly, run through filter for 10%. (10% of 20=2) remember stir don’t shake! 

15% mix = 3 oz. thinner to 17 oz poly. 

Buy or steal a measuring cup that lets you read ounces and do some math to figure what percent of thinner to poly you need. 

Do some testing on scrap until poly/thinner ratio, adjustments on air pressure and gun give optimum performance.


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## BWSmith (Aug 24, 2010)

Its one of those subjects that,ask 100 finishers..........get almost that many answers.Can be quite daunting.

I know Howard A. above has gobs of info....just keep digging....or uhhh,ask?

I'm with C-man on the use of WB,for us it was the alternatives toxicity(BTDT).We just had to make WB work here.I differ from most in that,we run med. to heavy coats....but the learning curve and equip doing so,can get right dang complicated.

Andy Charron has a book that comes highly recomended...if you can find it.

And you might try digging around this site http://www.homesteadfinishingproducts.com/index.html

Further,JMO...but alot of folks subscribe to the notion:

You're gonna pay for information.Now,that can come in several ways.Might pay for a finishing class?Might spend some time in a commercial finishing job?Might go out and buy a bunch of equip and hope for the best?Might try just jumping in....finding 100 ways NOT to spray a finish?

Even after you have "all the right stuff" equip wise....theres still a ton of things that have to be learnt.Lighting,and its effect on the spraying process could have books written on it.But,would say that its(light)one of the biggys...after the hardware(paint,AC's,guns/adj)have been nailed down.Oh well....better stop there,it sounds like a bunch of negativity.And that certainly isn't the intent.BW


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## WillemJM (Aug 18, 2011)

Bob Willing said:


> What is the ratio for thinning poly for a HVLP sprayer. I purchased a HVLP sprayer from HF and they do not give thinning info!


First, I have to admit that I have only tried spraying one WB Poly, internal/external said to be marine grade with a UV blocker. It's Deft's new product.

I spray with a Devilbiss Finishline III HVLP gravity fed gun.

Started with a 1.5 tip and had to be extremely careful not to get sags, once I get a wet coat. Tried a 1.8 tip and it got worse. Called Deft, they said dilute with 5% to 10% water. Tried 5% and the sags got much worse, still tough to get a wet coat.

Tried a 1.3 tip, no dilution with water and the magic happened, can put the coat exactly as wide as I wish, exactly where I want with almost no over-spray and adust the fluid control to give a perfect wet coat without sags.

The finish is crystal clear and sanding is fair. Final coat after 400 grit paper looks like glass.

Negatives are extreme grain raising after the first coat, and a bit more sanding.

In short, you will have to experiment, unless you can find someone with the exact setup same as yours who worked out the kinks.


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## cabinetman (Jul 5, 2007)

WillemJM said:


> Called Deft, they said dilute with 5% to 10% water.


Good advice.



WillemJM said:


> Tried 5% and the sags got much worse, still tough to get a wet coat.


You might work on your technique.










 







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## wildwood (Jan 25, 2011)

When buying a HF HVLP gun better have good idea on type nozzle required for work you do. They don’t have supply of different nozzles for their guns. Learning to spray or occasional use and price make these guns attractive. Before running down to HF store with coupon flyer, check reviews online for gun interested in. 

Some guns list thinning instructions provided above, some say consult coating manufacturer for thinning instructions.


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## harmonpa (Mar 4, 2016)

For HVLP material usually needs to run about 20 - 30 seconds in a zahn 2 to be able to break it up well you can always pick up a zahn cup on amazon for a few dollars and they make knowing how thin material is much more precise. However you want to try to not over thin as that can cause performance problems in the finish. Here is more details on using an hvlp spray gun.


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## Bob Willing (Jul 4, 2008)

This is a very old post but I think now I would add Japan Drier to the mix.


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## highfigh (Oct 8, 2017)

Old thread, but the problem/solution could still help others.

I asked a painter who worked with many high end finishes about thinning poly and he told me to use Naptha because it skins over faster, so I tested it. Sure enough- it worked. I shot my kitchen cabinets in my garage, when the air temperature was around 50 degrees F, using a Harbor Freight HVLP conversion gun and Minwax Satin Floor Poly- very happy with the finish and I didn't need to re-spray anything. No sags, either. I mixed it with about 1/3 Naptha.

I bought the gun with "If it works, great and if not, no big deal"- it was cheap enough that either case wouldn't cause a problem. I have since used it for several other finishes with good results and it's a case of finding its happy place WRT amount of material vs air volume and pressure.


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