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12/13/2018 7:56 AM

What tip or nozzle size are you using for the Mohawk lacquer? I'm wondering if the 1.4 I'm using is a bit too heavy.

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12/13/2018 10:25 AM
Edited Date/Time: 12/13/2018 10:26 AM

borg wrote:

What tip or nozzle size are you using for the Mohawk lacquer? I'm wondering if the 1.4 I'm using is a bit too heavy.

I'll double check my gun when I get home. I'm running a Sata Mini-jet 4.

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12/13/2018 4:20 PM

I'm running a 1.4 tip on my gun. 6 to 8 coats at can strength for the Mohawk sprayed an hour or so apart. Wait 2 or 3 days then flat sand. Then shoot a wet coat with the lacquer diluted with Mohawk thinner at about 20% thinner. Then I let it hang for 3 to 4 weeks before final wet sanding and buffing.

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12/13/2018 5:11 PM

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12/14/2018 12:06 PM

Foghorn wrote:

I'm running a 1.4 tip on my gun. 6 to 8 coats at can strength for the Mohawk sprayed an hour or so apart. Wait 2 or 3 days ...more

I cant spray right out of the can. I'm using something a little different than you are though. I have to thin or I get weak volume. I'm using the 1.4 also. I'm using their Piano Lacquer with just plain lacquer thinner. It's designed for higher build. Still getting some tiny tiny pinholes that don't show up until final buff out. You also have to see it in the right light but they are there. Added a filter and a desiccant dryer thinking it was moisture. The smart guy at Mohawk, Phillip Pritchard, is layed up after back surgery. His backup seems to think I'm trapping solvent in previous coats. Could be. I'll wait for Pritchard.

I have one that's been on the hook for about 4 weeks. It was all done with the filter and dryer. Will start fishing process in a couple of days. I guess I'll find out.

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12/14/2018 3:38 PM
Edited Date/Time: 12/14/2018 3:39 PM

borg wrote:

I cant spray right out of the can. I'm using something a little different than you are though. I have to thin or I get weak ...more

Ahh. I haven't tried that lacquer. I've always had good luck with the instrument lacquer so haven't changed. As you know, nitro is very forgiving but when there's an issue like you're having, it can be hard to figure out. Fish eyes, bubbling, silicone contamination and other things can be a real pain at times. If there's not too many, you could do drop fills.

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12/14/2018 5:25 PM

Foghorn wrote:

I'm running a 1.4 tip on my gun. 6 to 8 coats at can strength for the Mohawk sprayed an hour or so apart. Wait 2 or 3 days ...more

borg wrote:

I cant spray right out of the can. I'm using something a little different than you are though. I have to thin or I get weak ...more

Foghorn wrote:

Ahh. I haven't tried that lacquer. I've always had good luck with the instrument lacquer so haven't changed. As you know, ...more

There would be no reason why you would would change. The lacquer you're using is designed exactly for what you're doing. It allows a high enough build but is a little less brittle. Perfect for hollow bodies. It would actually work just fine for me too. I switched because I was having issues that turned out to be unrelated. I may go back to it so that I wont have to thin.

When I get the pinholes there are hundreds. Only solution is to sand em out. Problem is that they only show up on final buff. It's a huge backwards step that adds another month to the process. I need to get to the bottom of it.

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12/14/2018 5:26 PM

Okay, Guy B had canned me for some trivial bullshit(tongue ) in the past when a paint question had come up and I couldn’t participate in the thread . What exactly are you guys spraying start to finish? Mini jets with 1.4 needle and fluid tips?? That’s big.

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12/14/2018 7:05 PM

newmann wrote:

Okay, Guy B had canned me for some trivial bullshit(tongue ) in the past when a paint question had come up and I couldn’t ...more

I actually tried paging you way back with similar questions and never got a response. Didn't know you were on time out.
Anyway we build guitars. Foghorn builds hollow body acoustics and I build solid body electrics. We both use nitro cellulose lacquer for finishing. Mohawk to be precise. Foghorn has been at it much longer than me so he is my go to guy when I have questions or issues. I use a cheap Husky HVLP he uses a nice Sata minijet.
That's pretty much it.

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12/14/2018 7:22 PM

How porous is the wood? Are you seeing pinholes developing in the clear or is it just from soaking into the wood and opening up? Are the lacquers you guys use some of this new catalyzed stuff I heard a furniture refinisher speak of? He did my old mahogany desk and is currently working on another project for me. I could quiz him if you have specific questions???

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12/14/2018 7:24 PM

Also have a fellow body shop owner here locally that builds guitars and he is over the top OCD about everything he does.

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12/14/2018 7:44 PM

The problem I am having is in the last few finish coats. Bear in mind that guitars can have as many as 10 or 12 coats with sanding and such in between. We are not using a catalyzed lacquer. It's part of the reason we have to wait 4 weeks to level sand and buff out. It's just an old school nitro lacquer with some mods specific to musical instruments.
I would be curious to know how much you do to keep moisture out of the compressed air that you use for painting cars. Not sure if that is the culprit but I'm clueless at this point. The guru at Mohawk is mia right now but should be back in Jan.

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12/14/2018 8:10 PM

I have a refrigerated unit of sorts that I rent from a guy out of Louisiana, Dry Air Service for about $120.00 per month. It's a sealed unit and he never really lets me peak inside when he comes around and services it and checks for moisture. It however does not remove any oil and my main compressor is a 15hp screw. It has a electric tank drain that bleeds about every 30 minutes between the compressor and the air dryer. After the dryer, all the air lines run up high and drop down the walls to a drain valve. I tee off above those to go to the air hoses. At the paint booths I have a huge desiccant filter to catch any possible oil or moisture that makes it that far. One drop of water spitting into a hood can easily be a 500 plus dollar re-do not to mention not getting paid for the next one in line while you are redoing a fugg up for free...wink

How do you guys have your compressors and air lines set up? Compressor size? Anything to cool the air? Air line sizing and layout?

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12/15/2018 6:49 AM
Edited Date/Time: 12/15/2018 6:56 AM

newmann wrote:

I have a refrigerated unit of sorts that I rent from a guy out of Louisiana, Dry Air Service for about $120.00 per month. It's ...more

Spraying old school nitro lacquer like they used for cars in the 50s. I use a portable Makita 10 gallon compressor with two water/oil filters at the compressor and one at the gun. I spray at 19 psi and the gun gives great atomization. If a guy were spraying high volumes, then a pro set-up like yours would make sense. For one at a time like for a guitar, it only takes 30 to 60 seconds for a coat and then wait an hour. I also leave the drain valve open every time I shut the unit off when I'm done spraying. I believe the lacquer I'm using has about 20% solids which is over twice what a spray bomb of nitro would hold. Very low humidity here most of the time so never any issues with blushing etc. I use a shed lined with cardboard for spraying and hanging and a good mask. It wouldn't pass the sniff test literally if I were spraying more than a couple of guitars a year but works fine for what I do.

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12/15/2018 11:17 AM

Small portable comp for me. 4.5 cfm with what looks like about 10gal tank, I spray at about 25 to 30psi. I don't spray if the humidity is above 60%. I have a regular filter and a desiccant at the comp end of the hose.

I saw a video of a guy that took the tube coming from the compressor pump and routed it through a water tank and back to the compressor tank. He dumped a bunch of ice in the water tank when he sprayed. It's just not that humid here to go to those extremes.

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12/15/2018 1:47 PM

My compressor is 6 or 8 CFM at 100 psi if I recall correctly.

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12/15/2018 2:23 PM

Your HVLP guns need a good bit of air volume. Correct size air hose (3/8 ID) with high flow fittings and couplers all the way from the tank to the gun will get you what you need. Next, make sure the air compressor is actually putting out enough cfm's at the pressures you are spraying at.

When we would spray any automotive acrylic lacquers, they were thinned a minimum of 150% up to 300% to make sprayable. That was pre HVLP with higher pressures (35-40 psi at the gun) and a poor transfer efficiency of about 35%. Lots of overspray and in flight loss of solvents. HVLP is getting you 65-70 % to the surface. Make sure your pressure is correct at te gun, not 50 foot away at the other end of a 1/4 inch diameter air hose. Huge pressure drops over 50 foot in a 1/4 hose, very little in a 3/8.

And although you have low humidity, you have hot air from the compressor go through your filters to cool down in your air hose laying on the ground which may be introducing some moisture into your finish. You need your air dryers and filters at least 25 feet away from your compressor.

If you are spraying it too thick, it could be skinning over and trapping solvents in the finish. Your micro pinholes you are describing??? Do you have different temperature range thinners to use? I would always use a slow thinner for hot weather to allow it to stay open and flash off slower. Was quite common to see old lacquer base primers shrink up and have porosity in the primer when you started sanding. People always used fast dry thinners and hosed the primer on trying to get a high build out of a low build product. The stuff would skin over and trap solvents and never dry. It would eventually soak down to the substrate and cause the finish underneath to react.

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12/15/2018 5:43 PM

newmann wrote:

Your HVLP guns need a good bit of air volume. Correct size air hose (3/8 ID) with high flow fittings and couplers all the way ...more

A lot of what you said there rings a bell. I'm using 50' of 1/4" hose. I will soon go to 25' of 3/8". I'm in contact with Mohawk on the thinner. What you said about trapping solvent is exactly what the rep from Mohawk said. A slow thinner should help and longer times between coats too.
Great info newmann.

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12/15/2018 5:58 PM

newmann wrote:

Your HVLP guns need a good bit of air volume. Correct size air hose (3/8 ID) with high flow fittings and couplers all the way ...more

Some good advice Newmann. My Sata only needs about 4 CFM at 19 psi so plenty with the compressor I have. I also have a digital regulator at the gun. Many guys use cheap jamb guns with great success however. Nitro also sprays very thin compared to acrylic or catalyzed or even water based although I've never tried any of those as nitro works so good. It really is one of the most forgiving finishes ever but small things can give you problems unfortunately. Hopefully you can figure out what's giving you grief Borg.

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