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Switching To A Poly U Finish...any Tips?


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The last four guitars I've refinished /finished have been done with Nitro lacquer, and I've had pretty good results. I used behlen nitro and sprayed through a DeVillbis Finishline III gun with a medium sized compressor. My latest project is almost finished - a flat top Dean Cadillac copy (slightly larger than a Dean) with a neck made for me by Doug Darling at Soulmate Guitars. A little final polishing on the lacquer and wiring left before I call it done. It looks pretty good so far. My biggest mistake was not grain filling the Black Limba body back before staining and finishing; so it took a LOT of nitro to get it level. I did not even lift the grain with water and sand back before staining either (Colortone w/alcohol), so that could have been part of the problem. Anyway, its almost a done deal. Live and learn!

However, I've been tempted to go for a polyurethane finish on my current project; an Eric Clapton cut Explorer - one piece mahogany back from Kalamazoo (1980) with a 1/4" curly maple flat top and black Limba neck with a couple of hard maple stripes for stiffness. I've read Jeremy's (LGM) tutorial and I'm convinced that I would probably really like a Poyurethane finish because of its ease in working, durability, stability and lack of shrinking, and still giving a deep gloss. I used to be afraid of poly u because I thought it made guitars sound "dull". But I've read enough now that I think the key with any finish is simply not to get it too thick, and then it will sound fine.

First, Jeremy said that he prefers to use a "gravity feed" gun, and not a HVLP. I am confused by this because I believe my DeVillbis Finishline III is both!...gravity feed and HVLP. What am I missing here?

Secondly, I plan to use a two part automotive type poly u, as he and others recommend. What type of prep, if any, should I use between the transparant dye and spraying the poly u clear finish?

Thirdly, Jeremy recommends multiple coats, then sanding to 800 grit, then spraying 3 more wet coats within 36 hours, then sanding up to about 3600 micro mesh, then two more wet soats, then micro mesh to 12,000, then buffing! Dave at McNaught Guitars told me that when he uses poly u, he just sprays on about 6 coats, waits until the next day, then sprays about 6 more coats, waits 24 to 36 hours, then sands to about 1000 to 1200 grit, and then polishes with a buffer. Noticing a pretty big difference between these two methods, I'm wondering what MY method should be. Any thoughts on this?

Last question: I've never used a respirator mask when spraying nitro in my garage or outdoor storage closet, and have only experienced minimal permanent brain da...dam...dam...dammmmage. :D Jeremy says that poly u is DEADLY and that you MUST use one. So; how much will I have to spend on one that will be adequate and where is the best place to get one?

Thanks for any comments.

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The last four guitars I've refinished /finished have been done with Nitro lacquer, and I've had pretty good results. I used behlen nitro and sprayed through a DeVillbis Finishline III gun with a medium sized compressor. My latest project is almost finished - a flat top Dean Cadillac copy (slightly larger than a Dean) with a neck made for me by Doug Darling at Soulmate Guitars. A little final polishing on the lacquer and wiring left before I call it done. It looks pretty good so far. My biggest mistake was not grain filling the Black Limba body back before staining and finishing; so it took a LOT of nitro to get it level. I did not even lift the grain with water and sand back before staining either (Colortone w/alcohol), so that could have been part of the problem. Anyway, its almost a done deal. Live and learn!

However, I've been tempted to go for a polyurethane finish on my current project; an Eric Clapton cut Explorer - one piece mahogany back from Kalamazoo (1980) with a 1/4" curly maple flat top and black Limba neck with a couple of hard maple stripes for stiffness. I've read Jeremy's (LGM) tutorial and I'm convinced that I would probably really like a Poyurethane finish because of its ease in working, durability, stability and lack of shrinking, and still giving a deep gloss. I used to be afraid of poly u because I thought it made guitars sound "dull". But I've read enough now that I think the key with any finish is simply not to get it too thick, and then it will sound fine.

First, Jeremy said that he prefers to use a "gravity feed" gun, and not a HVLP. I am confused by this because I believe my DeVillbis Finishline III is both!...gravity feed and HVLP. What am I missing here?

Secondly, I plan to use a two part automotive type poly u, as he and others recommend. What type of prep, if any, should I use between the transparant dye and spraying the poly u clear finish?

Thirdly, Jeremy recommends multiple coats, then sanding to 800 grit, then spraying 3 more wet coats within 36 hours, then sanding up to about 3600 micro mesh, then two more wet soats, then micro mesh to 12,000, then buffing! Dave at McNaught Guitars told me that when he uses poly u, he just sprays on about 6 coats, waits until the next day, then sprays about 6 more coats, waits 24 to 36 hours, then sands to about 1000 to 1200 grit, and then polishes with a buffer. Noticing a pretty big difference between these two methods, I'm wondering what MY method should be. Any thoughts on this?

Last question: I've never used a respirator mask when spraying nitro in my garage or outdoor storage closet, and have only experienced minimal permanent brain da...dam...dam...dammmmage. :D Jeremy says that poly u is DEADLY and that you MUST use one. So; how much will I have to spend on one that will be adequate and where is the best place to get one?

Thanks for any comments.

Interesting reading this. The strangest thing about almost everyone who use poly finishes is that they nearly all have their own opinions and methods about how it should be done. Trouble is, someone else may try and use the exact same method and it won't always work for them quite the same. Likewise having tried various different methods along the way with varying degrees of success (and disaster), I ended up finding a method that works for me. But crucially - and this I think is the main point - a method that works for me with the particular kit that I've got, used where I use it.

When I'm applying poly I apply a really light 'misting' of finish to the surface of the guitar first with a 0.8 or 1mm nozzle, applied with the least pressure possible through the gun that will still atomise the finish for an even, very light 'misting' coat (basically just a quick sweep of the gun over the whole surface of the guitar body). I leave this for a couple of minutes, maybe five at most (I'm using a fast acting hardner), then apply a second slightly heavier - but still comparatively light - coat of finish. This I then leave for fifteen to twenty minutes and then apply another coat of lacquer, this time applying it in what I'd call a normal coat, heavy enough to cover evenly, but not so heavy as to risk runs or pooling. As this coat goes onto the guitar it doesn't generally go on looking perfectly shiney and smooth, it has a very slightly grainy looking effect when first applied. If you try and get it to look shiney straight out of the gun at this stage chances are you've applied too much. But leave this coat for another twenty to thirty minutes (leave the 'normal coats' slightly longer to flash dry before re-coating),and when you go back to apply the next coat it will have leveled out and should be starting to look fairly smooth and even. Once I've repeated this process until I've got three or four proper coats (and the original light misting coat), I then leave it for 24 - 48 hours to cure out.

Then I generally rub the finish back with 1000 grade wet until it's perfectly smooth and there's no shiney spots anywhere on the surface and then repeat the clearcoating process again. The second time through the process the finish should go on really nicely and unless you have major issues with the application, will often be good enough for a really nice finish when rubbed down and finish polished. It all depends on how the coats go on as to whether third session of finishing coat needs to be applied or not.

Rubbing back for polishing is another one where everyone has their own method that works for them. After my finish is to a standard that I'm happy with it, it'll at most need rubbing down with 1200 grade wet and dry, if it's gone on really well I'll sometimes just start straight in with 2000 grade wet and dry - but it's usually 1200! B)

I do have electric polishers and the various recommended cutting compounds, but again here, I'm not terribly trusting of electric polishers - far too easy to go through a finish and make a mess of my work - so I always polish my guitars totally by hand. Takes longer and it's a pain in the butt of a job, but the end results are worth it for me...........and it's safe!

Once I've got the whole body perfectly smooth and flaw free with 2000 wet and dry, I then normally just use T Cut, on a duster, by hand to finish my guitars. I know there will be people out there howling now that T Cut is far too aggressive a compound to be finishing a guitar with - but on a soft cloth with lot's of elbow grease it works for me. I too read LGM's tutorial and very informative it was too, in fact so much so that I ordered a full selection of Micro Mesh - and tried them out on the Guardian Guitar I'm polishing up now - it didn't work out for me though (obviously the way I was doing it), so I re-sanded with 2000 grade wet and dry and spent two days polishing with T Cut as I normally do. I do now have a finish that I'd challenge anybody to find a flaw in though. Basically, it's really all just down to personal preference and what works best for you with the kit and the knowledge that you've got.

A good quality mask is absolutely essential when spraying poly's, along with good ventilation, preferably filtered in and out of your spraying area - and no ignition sources from either electrical fittings or any other open flame around the spraying area (it's highly flammable as well as deadly on the lungs). Ideally it's recommended to use a positive pressure mask when spraying poly's, but the very least you need is a really good quality vapour filtering mask (merely dust filtering simply isn't enough!), I use a 'Gerson' mask most of the time.

HVLP stands for 'High Volume Low Pressure' as I'm sure you'll know. This means in very simple terms that the paint or finish used through the gun is atomised at the nozzle to give an even coat at the lowest pressure possible. This is a common advantage of gravity fed type guns, where because of the gravity feed, extra high pressure airflow isn't then necessary to create the low pressure area (via venturi effect) inside the gun, which in turn effectively sucks the paint or finish up to the nozzle from a bottom or side mounted resevoir. This means there is less air pressure being exhausted out of the nozzle along with the paint or finish, which greatly reduces overspray and wasted paint, but also reduces the risks of applying too much finish at too higher pressures - and the associated problems that can then arise.

Anyway, I'm rambling on and no doubt sending folks to sleep so I'm going to go do some work. But hope this helps rather than confuses the issue even further.

Jim :D

Edited by Foggy
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Thanks for the time and info you put into your comments Jim. Just hearing from someone in Orkney gets the Scottish/Viking part of my blood excited! (Ancestry from the Outer Hebrides[Morrison] and Sutherland[Mackay] amoung many others to the south).

I think I will try your method of "misting" and building gradually with the Poly Urethane. It also sounds like your method does not involve applying a lot of Poly overall, which appeals to me. I want to keep the finish thin, while having enough to get a good depth in the gloss.

I will reread your comments on the mask several times, and hopefully get some comments from others as well before I make a respirator mask purchase.

Thanks again, Robert

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Thanks for the time and info you put into your comments Jim. Just hearing from someone in Orkney gets the Scottish/Viking part of my blood excited! (Ancestry from the Outer Hebrides[Morrison] and Sutherland[Mackay] amoung many others to the south).

I think I will try your method of "misting" and building gradually with the Poly Urethane. It also sounds like your method does not involve applying a lot of Poly overall, which appeals to me. I want to keep the finish thin, while having enough to get a good depth in the gloss.

I will reread your comments on the mask several times, and hopefully get some comments from others as well before I make a respirator mask purchase.

Thanks again, Robert

No problem at all - we fellow Celts have to stick together after all :D

Regarding the mask, positive pressure masks are the 'ideal' recomended form of mask, but then again, unless you have an industrial sized compressor it's unlikely that it would run a positive pressure mask and your spraygun too............mine certainly won't. So many people (and professional sprayshops too) often use a good quality filtered mask like the Gerson mask, 3M also do a slightly cheaper to buy, but still very good mask that works perfectly well. The beauty of the Gerson though, is that it has a two filter sytem (a pre filter and secondary filter), the pre filter being replaceable (unlike the filter on the 3M mask), so that by replacing the filters the mask can last a long time and reduce the overall cost. But I'm sure there are others who will chip in here with other possible alternatives.

Jim :D

Edited by Foggy
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