HVLP Spraying Technique

[Ben Grefe]

I dove into the world of HVLP spraying a month ago after finding a Fuji setup on sale. So far I’ve been very happy with the quality of finish given my experience level, using Target Coatings EM1000 Sanding Sealer and EM6000 (Semi-Gloss) Lacquer. However I’d like to improve, which leaves me with my first question.

On this particular piece I’m spraying oak. I did a coat of EM1000, sanded with 180. 2nd coat of EM1000 and sanded to 220. Everything seemed acceptably smooth. Then I did two coats (maybe it was 3, I forget) of EM6000 and it seems like I have excessive nits on the surface. I sanded with 400 and did what I hoped was a 3rd/4th (final coat). The nits were reduced (in number), but still there. I was hoping for a glassy finish.

Should I expect a glass finish right off the gun? If not what should I be doing? Less finish? Tightening down the flow control (increase atomization?)? More finish? I know I can experiment, but it would be helpful to be pointed in the right direction.

Second, assuming that I should expect to have to sand after finishing to get a satin or true semi-gloss finish - how far up in sanding do I have to go? 600/800/1000 or will I need to go into buffing compound?

For reference I’ve been using the solowoodworker.com blog as my guide through this process.

[John TenEyck]

I've never looked at solowoodworker, but wound be surprised anyone recommends sanding the finish with 180 grit, or even 220 grit. Those are far too coarse to use even on primer and are more appropriate of the grit you might stop sanding at prior to applying your sealer or first finish coat. 320 grit is the coarsest I use after I start applying primer or finish, and I often use 400 or 600 grit for denibbing.

OK, now about oak. You are never going to get a glass like finish on oak unless you fill the grain beforehand.

Are your surface nibs coming from dust or could it be air bleeding back out of the pores and causing the finish to form little volcanos? If it's dust then your work environment isn't clean enough or your makeup air has dust in it. If it's little volcanos then it could be the EM6000 doesn't like oak. I had a similar problem with EM-9300 on white oak and ended up having to switch to another product to resolve it.

Assuming a clean environment where you don't get nibs in the sprayed surface you should expect to be able to get an off the gun finish that is essenitally flawless, good for anything except something like a Steinway piano or maybe a high gloss dining table top. But if you want to finish the finish, 0000 steel wool will give you a beautiful satin sheen, and automotive polishing compounds or Micromesh or Trizact pads can produce anything up to high gloss.

John

[Ben Grefe]

Thanks John,

To not disparage the blog I linked, he doesn't say 180 grit or 220, just 'sand after the sanding sealer' so that's what I did. Guess I need to go higher (though I will say this oak really raised the grain after the first coat of sanding sealer).

I didn't fill the grain on the oak and I understand the valleys of the grain won't fill but I still think there are nits (nibs?) in the finish. I'll have to take a much closer look to understand if these are volcano's or nibs.

I think my spraying room is about as clean as it gets (separate room with plastic on all the walls / doors. However my 'fresh air' is from outside and now that I think about it, I was doing this project during the 'historic' rainfall that Seattle got last weekend. 6 inches in 2 days. The air was probably about as humid as it gets. Could that be it?

Next time I go about this I guess I'll go:

Sand up to ~320 -> Sanding Sealer -> 220 (if needed) -> 320 -> 4 coats of EM6000 with 400 -> 600 in between the last coats? I'll also pick a drier set of days.

[John TenEyck]

Oak loves to give nasty raised grain with WB products. Because of that I often start out with a coat of Sealcoat shellac. It greatly reduces the amount of grain raising. Also, with oak it's rarely necessary to sand finer than 180 grit unless your first finishing step is coloring with a waterbased dye. In that case I go all the way to 320 grit before applying the dye. But now that I think about it more, if I were using WB sealer like you are I would go to 320 grit first.

A magnifying glass or glasses will help identify if you have nibs or volcanos.

John

[Denis Kenzior]

I've sprayed several gallons of EM1000/EM6000, here are some things you might try:

- Try applying some water (distilled if you're paranoid) with a bottle sprayer or a rag prior to the sanding with the final grit. This will help with grain raise quite a bit and will also help identify any areas that might need a bit more attention.
- em1000 shouldn't raise grain excessively if you're spraying it. Try using a diluted coat (I think Target recommends thinning 50/50 with water) and spray on the thin side first. Then a full strength coat shortly after (not necessary to sand between these). Sanding with 320 should be enough to produce a smooth surface.
- For 'finishing the finish', since you're starting with semi-gloss, buffing compound isn't needed. Try sanding with some 600 grit abranet, followed by synthetic steel wool, something like 3M 07523. I cut the synthetic wool to size for my orbital sander, and use it like a sanding disc. A sander on the more powerful side is useful here, like a Festool rotex or a buffer/polisher if you have one. Use a Mirka pad protector since the wool has a tendency to shed.

That said, I was never happy with how EM6000 performed with a turbine. I tried extensively with a Fuji Q4 and an Apollo 5 stage turbine setups. No amount of playing with settings helped. I attribute it to the hot dry air coming out of the turbine and messing with EM6000. I've had better luck with General Finishes PreCat Lacquer and High Performance. One day I tried a compressor based system with EM6000 and ended up selling my turbine setup shortly thereafter.

[Ben Grefe]

I have a pet peeve of people who never follow up on threads that get good advice, so here I am.

First off, I’ve now sprayed a half dozen projects and I’ve learned a lot. The most recent project (bathroom drawer boxes) was smooth enough right off the gun to warrant no additional work. Some of the other projects have benefitted from some post-spraying smoothing with 600 sand paper and synthetic steel wool. Here are the lessons & tricks I’ve picked up that have really helped out:

1) I wasn’t sanding high enough before sanding sealer and then again before finish coats. I guess the wipe on finishes I had been using in the past were much more forgiving to intermediate sanding steps.

2) I was ignoring overspray. This came in 2 ways, first my ‘drying rack’ was too close to the spraying turn table I built and my exhaust fan setup just wasn’t clearing enough overspray from the room. Moving the drying rack was easy. I haven’t fully figured out the fan yet, but my temp solution was to take the furnace filter off the front and just put some cloth over the fan. I know this isn’t perfect, but I’m only spraying water based finishes. The furnace filter was blocking too much airflow from my box fan.

3) Using a headlamp. I was having trouble getting a full coat of spray which didn’t end up as a sagging mess in place. Using a headlamp really lets me reflect light off the surface as I’m spray and get a nice thin consistent coat.

4) Practice with the gun. Seems obvious, but the more time I get with it, the better it seems to work for me.

Thanks again for the advice, really enjoying how much this has cut down my project finishing time.

[John TenEyck]

Thanks for the follow-up Ben.

John

[Tom M King]

That's all great advice, Ben. I don't use a headlamp, but do try to use a strong, raking light when possible.

Denis, I agree. One thing they don't tell you about a turbine is that it heats the air.

I don't know about waterbourne finishes, but when spraying gelcoat, any moisture in the air will leave those pinhole craters. I know that guys spraying automotive finishes, like waterbourne clearcoat, say that it's much more sensitive to having dry air than solvent based. I never bothered to try to figure out why that is, but have no reason not to believe them. I have no idea how that applies to woodworking finishes, but would be surprised if it's different.

To get a perfect finish off of the gun, every step, and factor of the process needs to be perfect. There are no shortcuts.

[Matthew Curtis]

Any other info would be appreciated

[Tom M King]

https://generalfinishes.com/faq/trou...based-finishes

https://www.bodyshopbusiness.com/com...-need-to-know/

https://www.woodworkersjournal.com/s...lip-ups-avoid/

http://www.ronbryze.com/waterborne/A...terborne_C.pdf

https://www.popularwoodworking.com/a...ying-problems/

https://www.eurofinishes.com/euro-fi...based-finishes

Those were the top of the list off a google search.

This next one may appear to be advertising, but I've never heard of this company before, much less have any dealings with them. I just added this one for the comparison between HVLP, and conversion guns. I'm not impressed with what they think is a good compressor.
http://www.spraygunworld.com/Informa...ompressor.html

[Tom Bender]

Tom
Moisture in the air slows drying of waterborne finish just like it slows drying of wet clothes hung out to dry.