Spray gun newbie

[Stamper]

Am ready to ditch the brushes and start spraying but I need a little advice. I have an HVLP gun with the cup on top. Can I spray Min-Wax Poly with this ? Do I need to thin it or can I spray it right from the can?

[Snipe Hunter]

So every gun is different as is every finish. Not knowing anything about your gun or the tip, needle or air-cap size there is no way to really answer your question. Even with that information, I still wouldn't know the answer till I stuck some in the gun, played with the settings and tried to spray it. Assuming it is a solvent based, off the shelf poly, I would think it's a little thick to spray well. Water based poly might spray better as it's a little thinner and less sticky by nature. The products that are made for spraying have slower evaporating reducers (thinners) and spray better because they aren't drying in the air before the spray hits the target and thinning them with household (fast evaporating) thinners like acetone or lacquer thinner may make them atomize better and spray better but the result on the target may not be better. It may tend to have a rough or "grainy" finish.

But, that shouldn't stop you from trying to spray a product not necessarily designed for spraying. I've done well spraying clear Deft Brushing Lacquer (Home Depot) with about 10% little lacquer thinner in it. Too much lacquer thinner would probably spray better but leave a grainy finish.

Believe it or not, spray finishes have lubricants built into their (slower) reducers to help them pass through your gun and especially out of your spray tip without a lot of friction and without gumming up your tip and needle point. Brushing type finishes tend to be stickier and not as well suited for spraying. The reducers are too fast and they're too thick and sticky for most spray applications.

All that being said... There are lot of products made for spraying which have slower reducers in them which will give you a better finish. You just won't find them at the hardware store but you will find them or be able to order them at wood working suppliers and good paint stores like Sherwin Williams.

[jteneyck]

You can spray many waterborne finishes through a gravity feed HVLP gun with a 1.8 or larger needle.   If what you have is oil based I recommend not even trying to spray it.  You can spray it OK, with enough thinning, but the overspray will make a sticky mess on anything it lands on.  

John

[Rob Young]

Am ready to ditch the brushes and start spraying but I need a little advice. I have an HVLP gun with the cup on top. Can I spray Min-Wax Poly with this ? Do I need to thin it or can I spray it right from the can?

As mentioned, don't plan to spray oil based products unless you are prepared for the overspray mess. Not to mention the gun cleaning and personal cleaning required (wear a bunny suit!).

If you know the brand of gun, we might be able to help you find the manual which should have hints about the N/N size as well as starting points for pressures and CFMs. I'm assuming you mean a conversion gun to go with a compressor and not a turbine system. For what its worth, I use a 4 stage turbine HVLP rig. Compressors also should have an oil trap and dryer on the air line as well as the regulator.

But knowing nothing else, if you have a N/N of between 1.2mm and 1.8mm you are pretty much good to go for waterborne clear coats, shellac and lacquer. Spraying other stuff like dyes or acrylic paints you'll want smaller (1.0mm and smaller) and larger (2.0mm and larger) N/N sets. You can practice with water and cardboard to get techniques & gun adjustments figured out. And a "cheap" finish like the waterborne Minwax in the blue can is also a good one to practice with (and frankly is OK for stuff that doesn't need kitchen cabinet toughness). A few scraps of plywood so you can practice spraying vertically and horizontally is helpful.

[jcclark]

The biggest problem with HVLP guns is having a compressor big enough to handle it.
HVLP's take a lot of air and you don't want the compressor running a lot to keep up,
which makes heat and creates moisture problems.
A conventional gun uses less CFM and can help with that.
I have sprayed poly with a HVLP and find it works better to 
thin it a little.

[jteneyck]

The biggest problem with HVLP guns is having a compressor big enough to handle it.
HVLP's take a lot of air and you don't want the compressor running a lot to keep up,
which makes heat and creates moisture problems.
A conventional gun uses less CFM and can help with that.
I have sprayed poly with a HVLP and find it works better to 
thin it a little.

I use a 60 gal compressor that can generate about 10 cfm.  That's big enough to run the guns I have, but not enough for some HVLP guns.  There are LVLP guns that only need 4 - 6 cfm and supposedly spray just as well, just a little slower.  Those guns would a good option to consider if you have a smaller compressor.  Whether or not you need to thin a finish depends a lot on the size needle that's in your gun.  The guidelines from Homestead Finishing are a good place to start.  

I've never had a problem with moisture getting to my spray gun.  I use nothing more than the stock regulator/separator on the compressor, and another 20 feet from the gun where I step down the pressure.  I have a disposable inline moisture/oil filter at the gun inlet.  I'm sure additional measures are needed in humid sections of the country, but where I am in NY it hasn't been a problem, even in summer.  

John

[Snipe Hunter]

The biggest problem with HVLP guns is having a compressor big enough to handle it.
HVLP's take a lot of air and you don't want the compressor running a lot to keep up,
which makes heat and creates moisture problems.
A conventional gun uses less CFM and can help with that.
I have sprayed poly with a HVLP and find it works better to 
thin it a little.

A lot of the cheaper (non turbine) HVLP gins are really "Conversion" guns. Traditional spray guns converted to HVLP by adding a regulator. Take off the regulator and back off the air volume knob and you have a regular old spray gun. The popular $17.00 HF Purple gun is a good example.