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A Couple More Nitro Questions
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Author:  Joe Beaver [ Mon Mar 23, 2015 8:50 pm ]
Post subject:  A Couple More Nitro Questions
I an getting ready to try nitro for the first time. I am using cardinal luthierlac.

Questions are:
1 Should I stir the lacquer before using?

2 From what I have read it says spray 3-5 coats a day. Since it calls for recoating every 15-30 minutes, can I spray more coats in a day? Say 10-12 ?
Author:  Kelby [ Mon Mar 23, 2015 9:04 pm ]
Post subject:  Re: A Couple More Nitro Questions
Lacquer is pretty forgiving.

I usually stir, but I don't know whether it is necessary.

As for coats per day, I think you can get away with a lot, depending on humidity. A certain amount of moisture gets trapped under each coat, and if you don't let it breath a bit between coats you can get blushing (a white cloudy finish).
Author:  kencierp [ Mon Mar 23, 2015 9:41 pm ]
Post subject:  Re: A Couple More Nitro Questions
Instructions state very clearly max of six coats a day and that it takes three days to get sufficient build of film thickness. I believe the concern is allowing time for gassing off of the solvents. I've speeded up lacquer dry time with heat Lamps and hot air --- but I'd check with Cardinal tech before doing that with their product.
Author:  Joe Beaver [ Mon Mar 23, 2015 11:12 pm ]
Post subject:  Re: A Couple More Nitro Questions
Based on this info I guess I would be wise to limit it to 5 or 6 coats. I was thinking I might get a better burn in with more coats per day.
Author:  Jim Watts [ Mon Mar 23, 2015 11:22 pm ]
Post subject:  Re: A Couple More Nitro Questions
Joe, stirring is not necessary. I spray 3 coats a day with a with a day off between sessions as I think this allows a little better gassing off as the finish is thinner than if I were to spay 5-6 coats a day. That last bit is just an opinion of mine, but it seems to work well.
No need to worry about better burn in with nitro, it burn in no problem.
Author:  Rod True [ Tue Mar 24, 2015 1:00 am ]
Post subject:  Re: A Couple More Nitro Questions
I'm with Jim. I spray 4 coats a day waiting an hour between coats. Then I'll let it off gas for a day the spray another 4 coats the following day, wait again then 4 more coats.

I'll build the 12 coats, wait a couple more days, drop fill then wait at least 2-3 weeks, level sand, wait another week then do the final sanding and buff if all is good to go.

You can leave nitro for several months then spray more coats and it will burn in just the same as if you had sprayed the next day...
Author:  Joe Beaver [ Tue Mar 24, 2015 1:14 am ]
Post subject:  Re: A Couple More Nitro Questions
Jim and Rod,

Good info. I'm glad to hear no cross link problems. That can be bad, hate those witness lines.

When I read the cardinal write-up it says they recommend five to seven .5 to 1 dry mil coats, They don't say anything about how many sessions that should take. I suspect you could do 7 coats a day if conditions were just right, (warm and dry), but I think the 3 coats a day schedule will avoid problems. I'm all for that.
Author:  Clay S. [ Tue Mar 24, 2015 3:55 am ]
Post subject:  Re: A Couple More Nitro Questions
I always stir (not shake) the lacquer. This is especially needed if it has flatting agents in it.
Author:  Hesh [ Tue Mar 24, 2015 6:45 am ]
Post subject:  Re: A Couple More Nitro Questions
I spray 3 coats a day with a day off in-between sessions for the same reasons as mentioned above. We all know that we also have to wait 3 - 4 weeks for the stuff to cure enough to have a pleasurable buffing experience with no unwanted burn throughs... My take on it is that not doing too many coats in a day also helps it gas off the solvents (also as mentioned) and cure faster also contributing to that future day when you can buff with reckless abandon. Not really, just always wanted to write the term reckless abandon.... ;)
Author:  kencierp [ Tue Mar 24, 2015 7:02 am ]
Post subject:  Re: A Couple More Nitro Questions
Unless you have added chemicals to the lacquer there's no need to mix it -- but shake or stir matters not if its going to be sprayed on -- it gets atomized anyhow. Now for brushing that's different, it is necessary to take great care in mixing to prevent bubbles which are a PITA.

Here's some application instruction for Cardinal

http://www.lmii.com/cardinal-lacquer-mu ... t-coatings
Author:  B. Howard [ Tue Mar 24, 2015 7:10 am ]
Post subject:  Re: A Couple More Nitro Questions
I always stir my products before spraying. I usually run out all my coats of nitro in one day but I am using a different product. Mine is a high solids product so I only need 5-7 coats overall. The coating will outgas the same whether you wait a day between coats or not. The reason most manufacturers want you to wait a day here and there is to reduce the risk of solvent pop and other problems that can occur when the wet film surface dries before the rest of the film and another coat gets shot on. Wait time between coats will depend on environment but usually somewhere 15-30 minutes for nitro with that time increasing slightly as you add coats.

To figure how much material you are putting down requires a mil card and some math. Spray out on a test piece with your normal pattern and then measure the wet film thickness with the card. Take this measurement times the percentage of solids in your ready to spray mix and you have your dry film thickness. You must use your RTS mix percentage to account for reducers. Example, I spray a nitro with 28% solids. While I do not reduce for sake of this example lets say I add 7% reducer to make my RTS. So my RTS would be 26%. I am spraying about 3.5 mils wet per coat. That is .91 dry mils per coat.I am targeting 5 mils with my nitro so in this case I would run out 6 coats and after I cut and buff I should be right at my 5 mil target.
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Author:  Ben-Had [ Tue Mar 24, 2015 8:27 am ]
Post subject:  Re: A Couple More Nitro Questions
B. Howard wrote:
The reason most manufacturers want you to wait a day here and there is to reduce the risk of solvent pop and other problems that can occur when the wet film surface dries before the rest of the film and another coat gets shot on. - I got a couple small areas of this on my last 2 builds. What is the best way to prevent this?

I am targeting 5 mils with my nitro so in this case I would run out 6 coats and after I cut and buff I should be right at my 5 mil target. - So basically you're saying you only take off about .5 mil leveling and buffing?



I added a couple questions to the quotes above.
Author:  James Orr [ Tue Mar 24, 2015 11:00 am ]
Post subject:  Re: A Couple More Nitro Questions
Does anyone have a link to a mil card? Whenever I try googling, nothing comes up. I may need different search terms. I've been wanting one.
Author:  Alex Kleon [ Tue Mar 24, 2015 11:23 am ]
Post subject:  Re: A Couple More Nitro Questions
James Orr wrote:
Does anyone have a link to a mil card? Whenever I try googling, nothing comes up. I may need different search terms. I've been wanting one.


You should be able to get one at any good paint store, James. Where ever you get your nitro from will probably throw one in, if you ask.

Alex
Author:  kencierp [ Tue Mar 24, 2015 12:06 pm ]
Post subject:  Re: A Couple More Nitro Questions
I see we are drifting a little here --- perfection is great try to hit those "numbers" if you will. But the new comer be warned, there are far more headaches coming your way if you "do not apply enough coating material" (wet coats!) the nature of the beast is that you can remove a little extra during leveling and even final polish. If too little material you can waste several days gas of time, even the ten days of shrink time. Not to mention inevitable sanding cut through and that sucky feeling. Actually I think John Hall and some others say it right "its not what you put on but rather what you leave on." $.02
Author:  John Killin [ Tue Mar 24, 2015 12:55 pm ]
Post subject:  Re: A Couple More Nitro Questions
Ken,

That is a very good point. I'm working through my first use of nitro now. This is a "touch up" project where I needed to rebuild the finish over some scraped back binding and repairing some damaged areas on the guitar.

Over all in my original attempts I hadn't applied enough to level it out with the existing finish. I had sand through in some areas. Every time I had a sand through I needed to reapply a full thickness and wait for it to cure. If I had just applied it on thick and sanded it back from the start I would have been done. Instead I've spent a few months babying it up to level.

For the original poster, I found that if I applied to many coats in one day that I build up blush underneath. I could get rid of it, but I noticed it on days where I was laying on quite a few coats. I'm in Florida so the humidity is high here.
Author:  Joe Beaver [ Tue Mar 24, 2015 1:53 pm ]
Post subject:  Re: A Couple More Nitro Questions
There is some great info here!!! Thanks guys.

One more silly question, with water based I found if I brushed the spray gun tip between applications, (about 6 coats an hour and a half apart), I could leave the jar full, only cleaning the whole gun at the end of the day. When do you clean your guns?
Author:  Alex Kleon [ Tue Mar 24, 2015 2:52 pm ]
Post subject:  Re: A Couple More Nitro Questions
Joe Beaver wrote:
There is some great info here!!! Thanks guys.

One more silly question, with water based I found if I brushed the spray gun tip between applications, (about 6 coats an hour and a half apart), I could leave the jar full, only cleaning the whole gun at the end of the day. When do you clean your guns?


I spray water based on cabinetry with an hvlp, and often leave the jar full overnight, and spray again in the morning. I clean the tip every few minutes, while spraying, and if left over night, I empty the jar, and remix the finish in the morning. I think you'll be fine leaving finish in the gun for the day, Joe.

Alex
Author:  Ken Lewis [ Tue Mar 24, 2015 3:47 pm ]
Post subject:  Re: A Couple More Nitro Questions
Joe Beaver wrote:
There is some great info here!!! Thanks guys.

One more silly question, with water based I found if I brushed the spray gun tip between applications, (about 6 coats an hour and a half apart), I could leave the jar full, only cleaning the whole gun at the end of the day. When do you clean your guns?


Joe, if you've sprayed waterborne finish of any type previously you'll find everything about
nitro to be much easier and less finnicky IMO. As for cleaning the gun, end of day or even next day is fine. [:Y:] The smell is another story.
Ken
Author:  Joe Beaver [ Tue Mar 24, 2015 5:16 pm ]
Post subject:  Re: A Couple More Nitro Questions
I sure like the idea of cleaning the gun once a day. I may just like nitro. Except for the smell [xx(] I did a brush on application on my test panel. One whiff and I moved it outside and put my respirator on.
Author:  John Killin [ Tue Mar 24, 2015 5:37 pm ]
Post subject:  Re: A Couple More Nitro Questions
You do need a respirator. But once you have that it isn't so bad. Not really something you want to bring back in the house right away though.

What I was doing for cleaning was to spray some thinner through the gun. Then I'd pour the remainder of my mixture back into the Jar (on the gun) and seal the gun back up. The next day I'd undo and spray some thinner again. It was that easy. I got lazy and it worked. I used both a jam gun and an air brush. I don't think a full on HVLP spray gun would be much different, but I got away with very little cleanup.

Much better than with EM6000.
Author:  Jim Watts [ Tue Mar 24, 2015 9:52 pm ]
Post subject:  Re: A Couple More Nitro Questions
As far as measuring finish thickness goes I just use a micrometer at the sound hole being careful to measure in the same spot each time after the finish dries for a day or two. Much like Brian above I've learned I spray on about .0007-.0008" of dry film thickness per coat.
I'm not sure I would know how to use a wet film gauge if I had one. How do you not mess up the finish?
Author:  Joe Beaver [ Wed Mar 25, 2015 12:35 am ]
Post subject:  Re: A Couple More Nitro Questions
The mil gauge looks pretty cool, but I would have do some learning on it. I check thickness after all the spraying is done.

I like you way of doing a clean up. Sounds easy.
I use an old school Devilboss JGA gun. It is a workhorse. Never did get the desire to go HVLP
Author:  B. Howard [ Wed Mar 25, 2015 7:20 am ]
Post subject:  Re: A Couple More Nitro Questions
Ben-Had wrote:
B. Howard wrote:
The reason most manufacturers want you to wait a day here and there is to reduce the risk of solvent pop and other problems that can occur when the wet film surface dries before the rest of the film and another coat gets shot on. - I got a couple small areas of this on my last 2 builds. What is the best way to prevent this?

I am targeting 5 mils with my nitro so in this case I would run out 6 coats and after I cut and buff I should be right at my 5 mil target. - So basically you're saying you only take off about .5 mil leveling and buffing?



I added a couple questions to the quotes above.


Solvent pops can be caused by drafts in the drying area or water in the air supply but often they occur when the wet film is applied too thick for conditions and the surface dries but the underlying coating has not. This can be prevented of course by applying less material but other solutions include making sure the reducer you are using has the proper evaporation rate for the ambient conditions or adding a touch of retarder to the RTS. If you find you are having a solvent pop issue in the same areas on successive jobs you should consider rethinking your spray out pattern that you are using. For instance when i first started finishing acoustic guitars I found I would get a bit of pop or sag on the rims at the shoulders. Once I stopped spraying around the rims and started to spray across them I no longer had that issue.



The amount you loose cutting and buffing will directly relate to how much surface texture (orange peel) is left after you spray. I get a great surface right off the gun and I find I lose just under a mil on average in my cut and buff. Buffing removes hardly any material if done properly so the loss is mainly in the level sanding.
Author:  B. Howard [ Wed Mar 25, 2015 7:24 am ]
Post subject:  Re: A Couple More Nitro Questions
Jim Watts wrote:
As far as measuring finish thickness goes I just use a micrometer at the sound hole being careful to measure in the same spot each time after the finish dries for a day or two. Much like Brian above I've learned I spray on about .0007-.0008" of dry film thickness per coat.
I'm not sure I would know how to use a wet film gauge if I had one. How do you not mess up the finish?



The mill gauge is typically not used on the object you are spraying. You spray a test panel with the same pattern you use on the guitar and measure that.
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