Nitro vs. Poly?

[bleujazz3]

Over the past few decades, there has been some debate as to what is more production-friendly; the use of nitrocellulose finishes or polyurethane finishes.

Not being totally aware of what the volatility of either compounds are, I'm asking more qualified individuals to enlighten me so I may hear their opinions.

If possible, it isn't necessary to quote actual numbers in terms of volatility constants, just a relative overview that stands to reason. Extra points for efficient use of terminology that can be expressed in laymen's terms.

Further, being aware of the less durable nature of nitro over time, how does the different uses of finishes affect desirability of instruments, relative to aging?

And from what tone quality point-of-view do the different finishes play? Vintage vs. Recent?

[redmax61]

They're both pretty brutal. Honestly.

I hope I'm not overstating what you already know. I'm just piping in from my experience in using the stuff.

Most states have outlawed the use of Nitro. I don't remember the exact reason for it - harms the ozone layer, causes cancer or both.

Nitro flashes off very quickly which is both good and bad. It's good because that makes it less likely to run, but it's bad because it can lock in moisture and "blush". It also chemically binds with previous layers which makes sanding between coats unnecessary for anything but levelling the surface. Nitro is much more capable of mirror like finishes than Poly, but it also extremely susceptible to fisheyeing and other imperfections. It usually cleans out of paint guns by running thinner through them.

Poly is much less caustic than Nitro but it's basically a plastic coating, so you have to wear a mask that'll keep the stuff out of your lungs. It has better protective properties. It seals the surface better, dries harder and doesn't yellow. Because it flashes off more slowly, is almost impervious to blushing. However, poly is more likely to permanently clog paint guns and needs to be sanded between every coat for adhesion.

[bleujazz3]

I can also surmise that because of recent developments in technology, there are more poly finishes that are driving down the cost of the lacquers. With more availability, this has allowed finishers to choose more wisely between what particular finish works with regards to drying and providing an even spray coat without the usual pitting.

Nitro was the original idea that allowed for quick drying, but at the risk of volatility (fumes given off that were biohazardous to sprayfinishers).

Likewise, any spray finish must be used with caution, using a respiration protection device.

Much like a firewall on a computer protects against unwanted entry, a finished dried coat protects the guitar from the elements.
Thanks Robin. I might just try and find that Kohl's shirt.

[Big Mike]

nitro is generally faster and more forgiving,
Poly more environmentally friendly, and more durable.

I know not which is better, I appreciate each guitar for what it is. I have both.

[mr.flash]

Nitro looks better, thats for sure. But i heared it wares out more easily.

[PRSPlayer]

Nitro yellows and cracks over time.
I've been using acrylic urethane with pretty good results.

[Czar Of Zonk]

Hi, my intuition hints to me that the sound quality is better a la nitro than poly?

[PRSPlayer]

Hi, my intuition hints to me that the sound quality is better a la nitro than poly?
I think most people have the same "intuition" which isn't a bad thing, but may be a little biased based on the fact that nitro has been used to finish instruments since what seems like the beginning of time.

My personal experience has been that nitro yellows and cracks over a period of time.
That's not to say I wouldn't buy a guitar because it was painted with nitro, but if I'm going to spend time finishing an instrument, I'm not going to want it to turn yellow and crack.

As far as tone ... I think a big factor would be the number of coats used to finish the instrument, not necessarily the type of paint, but that's just my opinion.

I've read the same arguement (nitro vs. poly) on other forums a million times and from what I've read it really is all a matter of opinion.

For those who swear by nitro, I ask ... if nitro is so great, why does PRS use acrylic urethane? ;)

[bleujazz3]

I think most people have the same "intuition" which isn't a bad thing, but may be a little biased based on the fact that nitro has been used to finish instruments since what seems like the beginning of time.

My personal experience has been that nitro yellows and cracks over a period of time.
That's not to say I wouldn't buy a guitar because it was painted with nitro, but if I'm going to spend time finishing an instrument, I'm not going to want it to turn yellow and crack.

As far as tone ... I think a big factor would be the number of coats used to finish the instrument, not necessarily the type of paint, but that's just my opinion.

I've read the same arguement (nitro vs. poly) on other forums a million times and from what I've read it really is all a matter of opinion.

For those who swear by nitro, I ask ... if nitro is so great, why does PRS use acrylic urethane? ;)
I believe it's because of the application and volatility factors. Also, nitro is more biohazardous than poly, but both must be applied with respiration masks.

PRS also wants their guitars to last longer (look better) over time, and a poly finish only gets absorbed into the wood (correct me if I'm wrong) that adds to the tone of the instrument over time. A correctly applied poly finish, (applied, sanded, applied, sanded, etc.) makes for a better sounding guitar.

Nitro has the same qualities (absorption/tone) but cracks and chips, being a more brittle finish. Poly endures more (holds up better) than nitro.

[redmax61]

You are correct on all of the above.

[PRSPlayer]

That's odd ... I posted a separate thread asking what type of paint PRS uses and the reply was Acrylic Urethane, not "poly". :confused:

[Bill McDowell]

That's odd ... I posted a separate thread asking what type of paint PRS uses and the reply was Acrylic Urethane, not "poly". :confused:
I've dived headlong into this topic a number of times - the answer seems in motion - I'll try again here.

If you are talking about a (let's say pre 95 just for argument's sake) custom - they use polyesther.

If you are talking about a pre 95 CE - its polyesther body, nitro on the neck.

If you are talking a post 95 (or so) custom - its polyesther base coat, with polyeurethane top coat.

If you are talking about a post 95 CE - its polyesther base coat, with plyeurethane top coat, then nitro on the neck.

I believe the satin models and MEs are nitro, excepting the ME is a 'porefiller' base coat of (something) then nitro top coat (which the satins don't). The ME necks have no coating (raw braz baby).

I think that's what I've been able to piece together.

[bleujazz3]

That's odd ... I posted a separate thread asking what type of paint PRS uses and the reply was Acrylic Urethane, not "poly". :confused:
Sorry, poly is a generic term to denote acrylic urethanes among others. Poly is the most recognizeable term used among non-builders, therefore I used poly to collectively describe this as opposed to nitro.

[RRRcustom]

The finish PRS as well as most modern guitar manufacturers use is termed "poly" but really it consists of a polyurethane base coat(used to seal the wood pores, and level the surface, and then an acrylic urethane top coat for the clear and color. The polyurethane base actually has a pink tint to it.


I worked for Carvin for some time, and build my own guitars, so I can speak to this. The reason the modern manufacturers use the "poly" finishes is because the finish builds quickly, resulting in less total time needed to apply. One coat of the polyester base, one coat of each color applied to the guitar itself, and one coat of clear. There is no sanding between the color and clear coats. The paint system each company uses is designed to be compatible in this way.

The real reason nitrocellulose is thought to sound better, is because the poly finishes tend to be thicker. Depending on how much is required to level the surface, the polyester base can be quite thick(1/8" is common on cheaper guitars.) The higher end manufacturers take greater care in the prep and application of their finishes, so they are ususally almost as thin as nitro.

Nitro requires multiple coats to build. That's why it's so much more expensive to apply. Nitro doesn't build as quick, and is softer than the acrylic urethanes, so when you level the surface of a nitro sprayed guitar, you remove more material each time. I sprayed as many as 30 coats of nitro to build a finish(I don't use pore filler, rather, I apply more lacquer and let it fill the pores.) I spray 2 coats a day, so that works out to be about 2 weeks of spray time.

Now, remember, you must also allow the nitro time to dry and harden before it can be buffed to where it will give a mirror like shine. Too early, and you won't get the scratches out. Because the nitro is so soft, it just keeps scratching during buffing. I usually wait a month before I can buff a guitar. Even if I used pore filler, I would have to wait approximately 2 weeks. I have to wait longer to allow for the shrinkage that will occur in the nitro that has sunk in the pores. It is possible to get the completely flat, but it takes much more effort this way. I just hate the way pore filler looks. On opaque guitars, I don't mind it. As you can probably figure out, no manufacturer wants to wait that long for a finish to cure.

Another reason nitro sprayed guitars are thought to sound better is because the nitro finishes "breathe". They expand and contract with moisture, so generally, the older the guitar is, the older the wood is, thus the dryer the wood has become. This is why the old Les Pauls that everyone covets are lighter. The wood has dried out considerably. The drier the wood, the more it resonates. Guitars with a "poly" finish are, as someone else put it "sealed in plastic". They won't absorb moisture, except through the face of the fingerboard, or damage in the finish. Whatever moisture content was in the wood had when it was new, will remain in the guitar.....for the most part. The wood will dry some as finish damage occurs, and through areas like the pickup cavities, and control cavities where the wood isn't sealed as completely.

Nitro is an old product. The only reason it sounds better, is because of the deficiencies of it's actual nature. If properly seasoned, and applied, a poly finish can actually sound better than a nitro finish. Guitar companies won't dry wood out that far because it becomes less stable. The percentages they like to be at(6%? I believe), are what they find to be a good compromise between tone a stability.

[paintguy]

Nice post and well said RRRcustom.:dude:

Nitro or poly????

Hmmmm......


I'll take acrylic urethane myself.:D At least that's my choice for refinish material.

Oh yeah, it's pretty much poly sealer and acrylic urethane topcoat/clearcoat for Prs. There are a few models that differ.

[bleujazz3]

The finish PRS as well as most modern guitar manufacturers use is termed "poly" but really it consists of a polyurethane base coat(used to seal the wood pores, and level the surface, and then an acrylic urethane top coat for the clear and color. The polyurethane base actually has a pink tint to it.


I worked for Carvin for some time, and build my own guitars, so I can speak to this...
So, from a production point-of-view and the timeframe required to produce a said number of guitars, it is just more feasible to use poly and acrylic, seeing that nitro takes so darn long to dry.

Poly and acrylic take much less time to dry, and as a result, factories are much more able to produce higher quantities of guitars to meet demand.

Now it makes sense.

With the higher demand for guitars, factories needed alternative finishing coats to meet that demand.

Methinks big business scores again. :rolleyes:

[RRRcustom]

Nitro dries very quickly. It's the number of coats need to build up the finish to a thickness that can be sanded and buffed, and still have a barrier left when you're done.

Nitro coats are very thin. The acrylic urethane isn't necessarily thick, but the polyurethane base they use is. It's heavy, that way it can be sanded and leveled. Usually, a great deal of it is sanded back off, but depending on how well (or how bad) the guitar was sanded prior to paint, the polyester base may be thick in some places to make the surface of the guitar level.


Remember, the polyester base is used specifically for filling pores, and leveling the surfaces of the guitar.

Once the guitar is level, the finish only needs a color coat(if any), and the clear coat. That's where the time is saved. Remember you need anywhere from 15-30 coats on a nitro guitar to get the finish thick enough to buff out. You're looking at only 3-5 on most poly guitars.

[bleujazz3]

I stand corrected. Nitro needs additional coats being so thin to cover imperfections, while thicker-based poly and acrylic goes on and requires little or no sanding to finish the coat. Drying time is almost a moot point here, but sanding and recoating with nitro takes longer than working with poly. 3-5 coats compared with 30 for Nitro. From a production standpoint, it is much more cost and production-friendly to use Poly and Acrylic.

[PRSPlayer]

Thanks RRRCustom ...
You've answered alot of my questions without me even having to ask. ;)

[RRRcustom]

RSgilbert- that is corect. Basically, it's easier and quicker to use poly/acrylic urethane, while at the same time being more durable. That's why the guitar manufacturers use it

[Mike Dresch]

I believe it's because of the application and volatility factors. Also, nitro is more biohazardous than poly, but both must be applied with respiration masks.

PRS also wants their guitars to last longer (look better) over time, and a poly finish only gets absorbed into the wood (correct me if I'm wrong) that adds to the tone of the instrument over time. A correctly applied poly finish, (applied, sanded, applied, sanded, etc.) makes for a better sounding guitar.

Nitro has the same qualities (absorption/tone) but cracks and chips, being a more brittle finish. Poly endures more (holds up better) than nitro.
I've noticed the cracks and chips thing quite a bit on my own guitars that I've finished in nitro vs. the guitars I either own currently or have owned in the past that are finished in poly or acrylic urethane. Nitro is WAY less forgiving to damage than polys and chips off much easier.