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Allen
02-19-2011, 12:04 PM
Further to the epoxy pore filling demo's (http://www.ukuleleunderground.com/forum/showthread.php?41235-Pore-filling-demo) I posted a little while back, here is a video of the first spray session on a parlour guitar I'm building. Rather a difficult thing to film with my wife on the camera and trying to stay a good distance away while still getting the shot.

This was the first of 2 spray sessions that were 2 weeks apart. After 2 weeks the lacquer is really dry and I sand it back with P320 dry paper. Use dry so you can see if there are any low spots. They will still be shiny. Try and get them all out without cutting through. Then spray again as in this demo.


http://www.youtube.com/watch?v=rn9o9vi4DEE

Pete Howlett
02-19-2011, 03:06 PM
Thank you Allen for debunking the accepted spray mantras. When I built furniture in the 80's my finishers used the same technique....

Moore Bettah Ukuleles
02-19-2011, 04:34 PM
Nice video Allen. I'm spraying a couple of coats fewer than you but my mix is probably closer tho 60/40. Do you find you need to wait a full two weeks between sessions, especially since your pore shrink back is kept to a minimum with the epoxy filling? I usually find three days sufficient for what I'm doing. Then again I'm waiting a month before sanding and buffing.
BTW, what the maximum RH you need to keep under when spraying half outdoors? The only dependable way I've found to control blushing with my lacquer is by dehumidifying my spraying room, which is what I'm doing now. (My current lacquer, Mohawk, blushes very easily.) I've often wondered about the effects of too much retarder affecting the integrity of the lacquer and if it takes a proportionally longer time to cure.

Steve vanPelt
02-19-2011, 07:37 PM
Thanks so much, Allen. Great vid! My technique is similar, yet oh so different. I need a little practice. I think this tute will help a bunch on the next one.

Steve

Allen
02-19-2011, 08:56 PM
I like to leave a couple weeks in between spray sessions if I can. And 2 weeks after the last spray session before I buff out. So our spray schedules end up fairly similar Chuck.

One way or another the solvents need to get out of the finish before buffing or the final result is not going to end up as good as it could have been.

There are some things you can do to help speed up the process. If you abrade the surface with something like P320 after the first session, it greatly increases the surface area that can gas the solvents off, thus cutting the time required before the next session. Also placing the instrument in a very well ventilated area will help. You can get an envelope of solvent clinging to the surface if it's in an enclosed area. This air becomes saturated with solvent and will not allow any more to gas off.

Never add more than 10% retarder to a mix. At concentrations greater than this you are going to have detrimental effects. You are better off to get a slower solvent. This is something that gets a little confusing when talking about this stuff to people in different localities. BTW, what I call retarder might be called extra slow solvent by others. And all of this is brand specific. Always best to consult the professionals for the product in question. What some in the US market calls retarder I never use. I've never even seen it available here.

The product I use is about average in regards to sensitivity to blushing. If I didn't use the retarder (extra slow thinners) in the mix it would be almost unusable for most of the year here. I've actually not ever looked at the hygrometer for where the blushing point is. Just sprayed so many tens of thousands of litres of paint that I can tell by the feel of the air if it's good to go or not.

Timbuck
02-19-2011, 10:44 PM
You make it look so easy Alan..
I had a go at spraying..but the equipment I used was not very good ( I should have spent more money i think):(..the spraygun used to leak and laquer was running down my arm:confused:..then it would clog up:mad: ..I spent more time cleaning the nozzle than spraying...I would like to have another go one day...so if I did, what type of spray gun would you recomend?

Allen
02-19-2011, 11:23 PM
Should look easy. I started my panel beating / spray painting apprenticeship 32 years ago and am still at it.

Not sure what is available to you in the UK but there are some really good guns available without breaking the bank. The one I'm using I've had since 1984 and it's had 10's of thousands of litres of paint shot through it. Brand is Optima. Other name brand ones are Iwata, Sata, DeVilibis and Binks. They are all going to be at the pointy end of the price scale. There are lots of knock off's of these guns at a fraction of their cost. Certainly more than good enough for occasional use

I prefer gravity feed guns (like the one I'm using in the demo) as they are more efficient in spraying. You would be looking at one that has a fluid tip sized at 1.3 - 1.4 mm. A good place to go will be your local automotive paint supplier. They will be able to give advice on something suitable.

Moore Bettah Ukuleles
02-20-2011, 05:24 AM
I always wets sand with 400 the day after my first session. This not only opens the film up to allow for off-gassing as you mentioned Allen but it also removes some of the lacquer so there's simply less of it to dry. The retarder I use is a butyl cellosolve., about %5 added to the mix in my case. Nasty stuff for your health but then again it all is. I use a fresh air respirator thinking I'm avoiding most of the bad stuff. (I also shoot with an Fuji HVLP system which makes for a larger particle size, which is less risky on your health but harder to get a smooth finish.) My final coat is cut pretty thin with plenty of retarder in it. It's really worth the effort to get the finish laying nice and flat to avoid excessive sanding.

Kekani
02-20-2011, 09:27 AM
Its obvious that (as stated) you've been spraying a while, and made the disclaimer that distance should be adjusted for the less experienced. Its looks easy, and as a sprayer myself, I agree, it is easy, once the gun is setup - that's the hard part.

I agree with the gravity feed. Not unlike Chuck, I use an HVLP, but, mine's a Sata Minijet off the compressor. Oddly enough, I got mine from a wood finish supplier locally. Not sure if your's is an HVLP - looks like a lot of overspray, but I guess the waste is kept to a minimum with your speed.

For those that have sprayed before, this video is a bar. For those that haven't and want to try, this video is very deceiving in the skill necessary to do what Allen does.

Ken, Eastwood has a bunch of cheaper DevillBiss which I'd try if I didn't have the Sata, or the $$$. I have full size guns, but for `ukulele, the mini gun does well, especially since its and HVLP with very little overspray - unless you're doing a bunch at a time, then the full size may be better (don't have to keep refilling).

-Aaron

Allen
02-20-2011, 10:40 PM
Thanks Aaron. I think I will have to do another video or two of showing gun set up and basic technique. I spray without really thinking about it, but see others hold a gun like it's going to bite them.

This gun was made long before HVLP. But it's just about the best gun I've ever used. Cost me $850 back when I was only making $7 / hr. But it's been going without a hitch for over 25 years so I guess it's paid for itself by now.

There is a huge variation in the quality and capabilities of what is classed as HVLP. I used a Fuji for a while and it was probably the most economical system I've used with paint product, but the finish obtained with automotive paints was just so far below par that we could not justify the savings vs. quality. The Fuji is a true HVLP but as Chuck says it really doesn't atomise the paint well. That is because of the low pressure. You might get away with it for a clear coat on a uke because it's easy enough to level sand and buff, but when you are spraying anything like a metallic finish on a $150,000 Mercedes that rough, pebbly finish just isn't going to cut it.

Today the guns available from the main stream manufactures like Sata, Devilibis and Iwata all claim to be HVLP but are not in the truest sense. Yes they do offer efficiencies of product savings over other guns but all of this can be negated quite easily by the operator. What they have done is refined the air cap for better material atomisation, but the pressures required for proper use is still in the range of a non HVLP gun. In case you didn't know HVLP stands for High Volume Low Pressure.

When we were doing our tests of HVLP systems and material savings the Fuji system gave us a savings of between 15 - 18%. It's quite significant when you take into account that automotive paint is the most expensive stuff you'll ever come across in a can. The new breed of HVLP guns give us a material savings of 7 - 9%. This all by the same applicator over a reasonable time period in order to get good data as well as give the applicator time to adjust their technique.

Spraying the way I do with this gun, very fast and very close gives a material savings of 10 - 12% over other applicators. I know this stuff because ever single job that we do is tracked and has been done that way for the last 20 years. Bonus's are paid for material savings and time cost efficiency. All things that get your attention when pay day comes around.

Moore Bettah Ukuleles
02-21-2011, 06:40 AM
I wish I could use a conventional compressed air spraying system but when I was doing so I would have occasional problems with pin holing. Even with the inline filters I finally assumed the problem was contaminated air but it could've been a variety of factors including the pressures I was spraying or the gun itself. In any event, using the same lacquer and thinning ratios I've had no problems with the Fuji HVLP, including pin holing. As Allen pointed out, the main drawback is the coarseness of the finish but I'm having good results with using the smallest tip and thinning the lacquer properly. I also apply very wet coats and make sure I use enough retarder so that the the lacquer doesn't go off before it has a chance to flow out. Still, if I'm doing any shading, such as applying a sun burst finish, I'll use compressed air.

Pete Howlett
02-21-2011, 07:25 AM
I do not like the coarse finish from HVLP... I struggle with finishing. It's the one thing I have no training in so this stuff is great Allen.

Kekani
02-21-2011, 09:19 AM
Pete, as Allen stated, because the Sata Minijet is not a "true" HVLP - oddly enough, I use a larger compressor to run it - there's an atomization adjustment on it that works very well.

Allen, I think a setup video from you would be great. I know there's a lot of resources out there on how to setup spray patterns, etc, but to see how different reductions affect spray, air and material settings, as advanced as that is, will be great for all of us to see.

And now I know the underlying reason on your spray technique. . . bonuses. Good motivation.

Aaron