HVLP needle/cup sizing and other details

[Carlos Alvarez]

I'm brand new to HVLP. I've used normal high pressure guns in the past but mostly for automotive type catalyzed paints which have consistent viscosity. So it's all pretty new to me. I found a nice Amazon open-box deal on a Fuji Semi-Pro2 which has an M-Series gun and comes with a #3 or 1.3mm setup. It says this is good for most things like lacquer and "modern waterborne finishes" but not latex. And elsewhere they allude to some latex being a modern waterborne finish and some not? My primary wood use will be lacquer, but I currently need to spray some household latex on a small shed, and will occasionally want to do some indoor latex. So should I get a #4 (1.5mm) set also? Or the #5?

It didn't come with a whip, and that's another $50. Does it make a big difference? I'll be shooting small furniture pieces and the like a couple times a month, in a warm environment. So that also brings me to retarders like Floetrol for latex, and others for lacquer and such. Should I be using retarders all around? I'm in AZ so temps will vary from cool to damn hot.

I've read all the docs and watched some videos, but any little "secrets" to making this work better would be appreciated.

[Patrick Chase]

I'm brand new to HVLP. I've used normal high pressure guns in the past but mostly for automotive type catalyzed paints which have consistent viscosity. So it's all pretty new to me. I found a nice Amazon open-box deal on a Fuji Semi-Pro2 which has an M-Series gun and comes with a #3 or 1.3mm setup. It says this is good for most things like lacquer and "modern waterborne finishes" but not latex. And elsewhere they allude to some latex being a modern waterborne finish and some not? My primary wood use will be lacquer, but I currently need to spray some household latex on a small shed, and will occasionally want to do some indoor latex. So should I get a #4 (1.5mm) set also? Or the #5?

Latex paints are typically much thicker than waterborne woodworking finishes, and require either a lot of thinning, or both a larger nozzle to let the finish through and higher air pressure to atomize it effectively.

Moving to a large N/N therefore allows less thinning, but only if you have enough air to atomize the resulting increased volume of thick finish, which you probably don't. The Semi-Pro2 is a 2-stage, 5 psi system which most would consider to be pretty "weak" for Latex.

One significant "plus" to the Semi-Pro2 is that it has a pressurized cup, which allows it to push thick finishes like Latex through a relatively small nozzle. That in turn keeps the flow rate low so that the (limited) air pressure/flow can atomize it, and is probably your best bet to get a good finish.

If I were in your situation I'd consider adding a low-end airless rig to take on Latex duties, and use the HVLP for fine finishes (clears, stains, etc). Between them they will cover everything you've listed, and probably do so more cheaply than any single system can.

IMO the underlying problem here is that air isn't a very efficient way to atomize latex. The most powerful HVLP rigs (for example my 5-stage, 10-psi Fuji Q5) can get creditable results from minimally thinned Latex, but such setups are several times the price of an airless rig that can shoot Latex equally well straight out of the can with no fiddling required.

[Carlos Alvarez]

I wouldn't do enough latex to warrant buying another device. Since it's really a matter of doing a few feet of it here and there, not huge areas. For example, my dust collector shed needs to match the house...

https://i.imgur.com/oINfAPJ.jpg



A secondary thought was that I'd be able to get some really cheap and trivial practice with this gun. If I screw it up, no big deal.

[Patrick Chase]

I wouldn't do enough latex to warrant buying another device. Since it's really a matter of doing a few feet of it here and there, not huge areas. For example, my dust collector shed needs to match the house...

You can rent airless rigs at your local home center if it's just for sporadic use like that.

[Carlos Alvarez]

So I guess what I'm saying is that I *will* be using this gun for it, and what is the best choice of cup and needle? I get that it's not the perfect setup, yet the manufacturer claims it will do a reasonable job and I believe them.

[Bill McNiel]

Carlos,
Patrick know significantly more about this stuff than I do so I will only comment on your question about a whip. Yes it is worth the money.
Regards - Bill

[Wayne Lomman]

Do you still have a high pressure gun kicking around? If so, use that instead of trying to beat the Fuji into submission for this. Its waterborne latex. It is not going to fill your atmosphere with VOCs.

With regard to retarders, use them only as needed. You will need them at different rates and for different reasons. If its too cold, you need a bit to avoid blushing. If its too hot, you need a different amount to keep the job wet long enough. Cheers

[Mike Henderson]

I've used a conversion HVLP gun with a 2.00mm tip, thinned the latex and it shot great - flowed out really nicely. Can't say what you'll need for the Fuji but you could try a 2.0mm or larger tip.

Mike

[Patrick Chase]

Do you still have a high pressure gun kicking around? If so, use that instead of trying to beat the Fuji into submission for this. Its waterborne latex. It is not going to fill your atmosphere with VOCs.

This is spot on. On a related note, the OP's Fuji Semi-Pro2 only delivers 5 psi at the tip. LP (as in HVLP/LVLP) is defined as no more than 10 psi, so that 2-stage turbine is "latex-challenged" even by HVLP standards. It's a great setup for woodworking finishes though.


I've used a conversion HVLP gun with a 2.00mm tip, thinned the latex and it shot great - flowed out really nicely. Can't say what you'll need for the Fuji but you could try a 2.0mm or larger tip.

I assume you ran your conversion gun with an inlet pressure approaching or perhaps even exceeding its upper spec limit when you did that, in which case the nozzle pressure would have been around 10 psi. I agree that if you have that much atomizing pressure to work with then a large N/N can be just the ticket for latex (and that's exactly what I would do to spray latex with my 5-stage Fuji turbine), but I doubt the OP's 5 psi turbine is going to be able to atomize that thick of a stream. I suspect that his best bet will be to stay small and rely on the turbine's cup pressurization to get the finish to flow. It won't be fast, but it should atomize adequately.

[Curt Harms]

So I guess what I'm saying is that I *will* be using this gun for it, and what is the best choice of cup and needle? I get that it's not the perfect setup, yet the manufacturer claims it will do a reasonable job and I believe them.

I have an Earlex 5000 which sounds similar to your machine. I find a 2 mm needle/cap set works okay. Not great, it's pretty slow compared to an airless rig and needs quite a bit of thinning but it does work. I guess the answer is as large tip as you can get. I think the key to getting it to work at all is the pressurized cup.

[Rob Young]

I'm brand new to HVLP. I've used normal high pressure guns in the past but mostly for automotive type catalyzed paints which have consistent viscosity. So it's all pretty new to me. I found a nice Amazon open-box deal on a Fuji Semi-Pro2 which has an M-Series gun and comes with a #3 or 1.3mm setup. It says this is good for most things like lacquer and "modern waterborne finishes" but not latex. And elsewhere they allude to some latex being a modern waterborne finish and some not? My primary wood use will be lacquer, but I currently need to spray some household latex on a small shed, and will occasionally want to do some indoor latex. So should I get a #4 (1.5mm) set also? Or the #5?

It didn't come with a whip, and that's another $50. Does it make a big difference? I'll be shooting small furniture pieces and the like a couple times a month, in a warm environment. So that also brings me to retarders like Floetrol for latex, and others for lacquer and such. Should I be using retarders all around? I'm in AZ so temps will vary from cool to damn hot.

I've read all the docs and watched some videos, but any little "secrets" to making this work better would be appreciated.

Get a 2mm N/N or 2.2mm if available for the latex. It won't be as efficient as an airless and will still require thinning. And as mentioned, you can rent those for larger one-off jobs around the house.

Find the $9-ish Ford #4 cup on Amazon and get one of those. At the very least, you use it to make your own notes on how to prep the finishes so they flow correctly.

Floetrol helps with shooting latex but it really doesn't alter the viscosity all that much, you still need to stir in water. I've had pretty good luck with even the thickest primers mixed such that I get about a 2-minute flow from the #4 cup. Then either a 1.8mm or 2.0mm N/N on my 4-stage turbine rig. You may need to get the viscosity down below 2 minutes for the 2-stage Fuji.

Retarders for other finishes are probably going to be important to you given the ambient conditions in your area. Experiment and keep good notes.

[Patrick Chase]

I have an Earlex 5000 which sounds similar to your machine. I find a 2 mm needle/cap set works okay. Not great, it's pretty slow compared to an airless rig and needs quite a bit of thinning but it does work. I guess the answer is as large tip as you can get. I think the key to getting it to work at all is the pressurized cup.

Interesting. The Earlex 5000 is a 2-stage ~5 psi design like the Fuji Semi-Pro2, but IIRC the Fuji uses a larger, higher-power turbine (1400W vs 600W spec). The Fuji will likely require roughly the same amount of thinning, but it may be able to go a bit faster if the increased power translates to more cfm.

To the OP: Of all of the feedback here including mine, Curt's is most relevant to your situation. He's right on about the pressurized cup, which both the Earlex and your Fuji have. A 5 psi gun without pressure feed would be a lost cause for Latex.

Curt, how much do you need to dilute with your Earlex (and which brand/paint?)

[Patrick Chase]

Floetrol helps with shooting latex but it really doesn't alter the viscosity all that much, you still need to stir in water.

IMO it helps indirectly with viscosity in two ways: First, adding floetrol helps to retain adequate surface tension and flow-out with relatively large amounts of thinning. Second, because it helps the paint flow out it makes it more tolerant of imperfect atomization, such that mild orange-peel will tend to self-level before drying. In other words it simultaneously allows you to thin more, while also reducing the amount you need to thin to get a flat finish from any given setup.

On the minus side it flattens the sheen of gloss paints.

[Carlos Alvarez]

Do you still have a high pressure gun kicking around?

Only a small cheap detail gun. I also don't have enough hose to reach some of the areas to paint, and the compressor is a floor-mounted monster.

I guess what's emerging here is that Fuji basically lied about it being reasonable to spray latex?


Find the $9-ish Ford #4 cup on Amazon and get one of those. At the very least, you use it to make your own notes on how to prep the finishes so they flow correctly.

Sorry, I'm not understanding how this is different from how the included viscosity cup works?

[Patrick Chase]

I guess what's emerging here is that Fuji basically lied about it being reasonable to spray latex?

Far from it.

If you read their literature they're pretty blunt about HVLP not being the preferred technology for that. For example, here's what the manual for the Q series (http://www.fujispray.com/User%20Manual%20T-Model%20201602.pdf) says, on page 10:

"Although it is possible to use our equipment for house painting(walls), and many end users do, we feel that an airless gun or powerroller is better suited for that kind of job".

They also spell out the recommended configuration. For fine work they recommend a 1.5-1.8 mm N/N. Presumably they chose that for the reasons I spelled out in previous posts: The fact that their guns have pressure assist means that they can push thick finish through small nozzles, and doing so allows for better atomization with lower-pressure turbines.

[Carlos Alvarez]

Right, I guess the line to be drawn is "painting small stuff" which they say is fine, and "painting walls." I believe I'm painting small stuff, no? The biggest thing I'd do is that shed. Otherwise it will be trim and such, or small areas.

[Patrick Chase]

Right, I guess the line to be drawn is "painting small stuff" which they say is fine, and "painting walls." I believe I'm painting small stuff, no? The biggest thing I'd do is that shed. Otherwise it will be trim and such, or small areas.

The shed is in between IMO :-).

Seriously, the bottom line that everybody is telling you is that you can make it work with enough thinning and patience. I would recommend sticking with Fuji's recommended nozzle size, which will give you reasonably good atomization at the cost of lower speed.

[Carlos Alvarez]

LOL, fair enough. The dust collector shed will be my practice with this gun. It has almost zero impact, because it's in a place that will never be seen. I'll get the larger n/n set for latex on trim and for the shed. Thanks everyone.

[Curt Harms]

There's really no substitute for experimenting. I thin more than recommended but it seems to cover okay and I coat with unthinned or lightly thinned water based Poly for additional protection. I've never sprayed walls, just trim and small utility cabinet type stuff.

[Rob Young]

Only a small cheap detail gun. I also don't have enough hose to reach some of the areas to paint, and the compressor is a floor-mounted monster.

I guess what's emerging here is that Fuji basically lied about it being reasonable to spray latex?



Sorry, I'm not understanding how this is different from how the included viscosity cup works?

Wasn't sure your kit came with a #4 cup or not. Use what it came with.

[Julie Moriarty]

So I guess what I'm saying is that I *will* be using this gun for it, and what is the best choice of cup and needle?
When I need to know what air cap will be needed for a particular finish, I try the website of the finish manufacturer first. General Finishes is great for this. I have a Fuji HVLP with an XPC gun and downloaded all their info on the specifics of air caps for the XPC. With that information in hand, the right air cap size is a no brainer.

If the paint manufacturer doesn't have spraying information, maybe you can find a website that has a product with a similar viscosity and go from there.

[Patrick Chase]

When I need to know what air cap will be needed for a particular finish, I try the website of the finish manufacturer first. General Finishes is great for this. I have a Fuji HVLP with an XPC gun and downloaded all their info on the specifics of air caps for the XPC. With that information in hand, the right air cap size is a no brainer.

If the paint manufacturer doesn't have spraying information, maybe you can find a website that has a product with a similar viscosity and go from there.

Fuji provides viscosity-based guidelines as well in their manuals, though they're generic for each gun so you have to scale a bit based on your turbine. Jeff Jewitt also has pretty good guidelines (http://homesteadfinishingproducts.com/wp-content/uploads/2014/05/paintspraying_ver3.pdf) on his site (at the end of the doc). One thing I like about his is that he addresses pressure-assisted guns (like your XPC and the OP's Semi-Pro) as a separate category. They really do behave a LOT differently than unassisted gravity or siphon guns as in most conversion setups.

One gotcha with viscosity-based guidelines is that because they're generic they don't take individual finishes' flow-out characteristics into account. A finish that self-levels after spraying can tolerate worse atomization (and therefore higher viscosity with any given setup) than one that doesn't. The guidelines typically assume that the finish has to be flat "as sprayed", so they often end up being conservative.

To the OP: Jeff Jewitt's doc (linked above) is directly relevant to your situation. Your gun falls into his "pressure-fed" category. At 5 psi it's on the weak end of HVLP, so you'd probably want to skew towards the low end of his ranges.

[Carlos Alvarez]

That was very useful also, thanks.

[Curt Harms]

Interesting. The Earlex 5000 is a 2-stage ~5 psi design like the Fuji Semi-Pro2, but IIRC the Fuji uses a larger, higher-power turbine (1400W vs 600W spec). The Fuji will likely require roughly the same amount of thinning, but it may be able to go a bit faster if the increased power translates to more cfm.

To the OP: Of all of the feedback here including mine, Curt's is most relevant to your situation. He's right on about the pressurized cup, which both the Earlex and your Fuji have. A 5 psi gun without pressure feed would be a lost cause for Latex.

Curt, how much do you need to dilute with your Earlex (and which brand/paint?)

Brand was whatever was on the shelf, I don't recall. As for how much, I'd estimate 15% - 20% with floetrol and a little distilled water. I know the maximum recommended dilution is 10% but the higher dilution seems to be holding up. It did turn out quite flat but it was overcoated with a water based poly that didn't need much dilution and brought back some gloss.