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Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Nitro vs Acrylic vs Alkyd Resin paints

Discussion in 'Finely Finished' started by TSG_Custom, Aug 25, 2017.

  1. TSG_Custom

    TSG_Custom NEW MEMBER!

    Age:
    67
    1
    Aug 25, 2017
    United Kingdom
    Hi folks, I'm a new member who joined the forum specifically to discuss paint finishes for guitars because over the years I have read so much mis-information on which paints are best for guitar finishing.

    This post goes on a bit and I won't blame you if you bale out before the end!

    First let's discuss terminology i.e. lacquer vs varnish.

    As all paint, be it clear or opaque, consist of solids mixed with an evaporative carrier, in that respect there is no distinction between a lacquer and a varnish, but varnishes usually have drying oils as a carrier where as lacquers tend to have fast evaporating thinners as a carrier.
    Also the term lacquer is usually applied to finishes where successive coats 'melt' into each other, that is a coat re-activates the underlying coat to become in effect a single thicker coat.
    Coats of varnish and all oil based paints just 'sit' on top of each other.

    Let's just get the term 'enamel' out of the way. It's a marketing term used to imply that the paint is harder than standard paint ........ but it's not! and bears no relation to the rock hard white enamel found on your tin bath, or the enamel used in jewelry making.

    So varnishes that use oil as a carrier dry much more slowly than lacquers that use thinners as a carrier.
    You can get oil based varnish to dry much more quickly by having a high content of 'drying' additive, Tru-Oil is a good example of this.

    Then there are unactivated finishes (e.g 1K acrylic, nitro and oil base paints) and activated or catalyzed finishes (e.g. 2K acrylic or catalyzed polyester). Although the latter are used in guitar factory finishing they are not suitable for spraying in your garage as they contain chemicals (isocyanates or isoacrylates) that are extremely harmful to health and require air fed breathing apparatus to be used. But the advantages of these paints are that they achieve almost instant high gloss with minimal buffing or polishing required and are extremely hard and durable when cured and in the case of clear finishes, are non yellowing.


    Here is a good time to mention the difference between a paint or lacquer drying and curing. A paint might be touch dry in 15 minutes but not fully dry until after 24 hours. Drying is where the carrier of the solids has fully evaporated. Curing on the other hand is a chemical reaction (hence the chemical catalyst in 2 pack paint which ensures full cure in hours rather than days or weeks.
    Single acrylic that you buy in a rattle cans (Rustoleum etc.) is touch dry in 10-15 minutes and fully dry in 24 hours but can take 2-4 weeks to fully cure, depending on temperature and moisture content of surrounding environment.

    So I will only discuss finishes that you can use at home or in your garage, assuming that you don't have access to air fed breathing apparatus. It goes without saying that you must always wear an appropriate mask when spraying paint, even water based paint.

    Acrylic

    Thinner based acrylic can be applied from a rattle can (Rustoleum, Minwax etc.) or spray gun. A good spray gun setup will always give superior results but with practice you can achieve good results from a rattle can for small jobs. Acrylic is classed as a 'plastic' and in my experience never cures as hard as nitro cellulose but is more flexible and therefore less prone to crazing or cracking.
    Water based acrylics are also available but they can take longer to dry and therefore more prone to running or 'curtaining' if care is not taken.
    I have used acrylic for small jobs (headstock fronts etc.) with success but wouldn't use it for a full body re-finish and definitely not for a neck, it just feels what it is ..... a 'plastic'.

    Alkyd Resin

    Alkyd resin paint is found mostly in rattle cans (Plasti-Kote etc.) it does 'gloss from the can' better than acrylic but takes longer to dry and even when fully cured is not has hard as acrylic or nitro.
    After various test sprays I have decided it's not suitable for guitars.

    Urethane or polyurethane

    This is usually an oil based paint of the type you would use to paint your house. Being oil based it is slow drying and can never achieve the hardness of nitro or acrylic. Yes, there are makers out there who make claim to producing 'diamond hard' polyurethane paints ............. BS!
    There are 'activated' urethane finishes which are super hard but again only available for finishing in a factory controlled environment for the health and safety issues already mentioned.

    Varnish

    Varnishes are almost always oil based, slow drying and in general not suitable for guitars except for natural wood finishes.
    They can vary in hardness, piano or violin varnish being the hardest. I have only ever used varnishes on bare wood, my favorite being Tru-Oil (yes it is a varnish! the clue is in the name, it is oil based); it is touch dry in 15-20 minutes for re-coating and after fully curing(up to 6 weeks) can be burnished to a high gloss using a water based burnishing paste. There's lots of good YouTube videos on applying Tru-Oil.

    French Polishing

    It's a common mis-conception that French polishing refers only to the application of a lacquer made from the secretion of the 'lac' beetle dissolved in spirit, but French polishing really refers to the method of building up numerous coats of finish that dissolve into one another; granted that over time it has become synonymous with the use of only that particular lacquer. It is a long and arduous process requiring time and patience, only used on high end classical guitars and fine furniture and not very durable; spill your Jack Daniels on a French polish finish and see what happens.

    Nitro Cellulose or just plain 'Nitro'

    Why have I left nitro to last? Because it's my finish of choice ...almost every time.
    You can buy it in rattle cans (very expensive compared to acrylic) or you can of course gun spray it.
    It uses a volatile thinner as a carrier for the cellulose solids so it dries and cures very quickly. I doesn't 'gloss from the gun' as well as some synthetic finishes, although 'rattle can' nitro may contain additives (retarders) to improve the gloss factor. The big plus with nitro is that after fully curing it can be buffed and polished to a mirror gloss finish that exceeds any acrylic finish.
    Nitro is not as flexible as acrylic which is why vintage guitars finished in nitro often display crazing and cracking ...... a look many consider desirable.
    Martin, Gibson, Fender and a host of independent guitar makers still use nitro.

    So what about compatibility between the various finishes? Here's a quick guide.

    You can spray single acrylic (Rustoleum) over old and fully cured nitro but not the reverse. Nitro will 'pull' single acrylic finishes.

    You can't spray anything over oil based finishes other than other oil based finishes or some water based finishes.

    If you want to re-finish a guitar with a catalyzed factory finish then just flat it off (takes for ever!) and use acrylic or nitro.

    What about polishing compounds and polishes? Avoid those designed for use on motor vehicles as they may contain chemicals that will attack single acrylic and nitro finishes. Use an additive free water based buffing or burnishing compound; and for that final polish? Carnuba wax every time!

    The end!
     

  2. Silverface

    Silverface Poster Extraordinaire Ad Free Member

    Age:
    65
    Mar 2, 2003
    Lawndale CA
    OK, this is pretty much an impossible thread to deal with as there are about 9 or 10 unique subjects.

    I suggest reading previous threads regarding each coating. There are dozens of practical application and problem-solving threads for every one. They ALL can't be handled in one thread.

    But to take care of one thing - there is not "plain nitro." Common lacquers on the market (both bulk and aerosol) and used in guitar finishing are *all* acrylic nitrocellulose lacquers - a blend of resins (and FWIW I worked in the technical part of the coatings industry for 35+ years). Lacquers have been that blend since the 1920's - it was done to improve flexibility of lacquers for use on automobile sheet metal. There are some minor differences (the exception is Deft brand which has major...slow...dry differences) but for the most part they apply the same and provide the same looks.


    There are a VERY few pure nitro lacquers in the professional market, but they are not suitable for guitar use. There are also a few uncommon "water based lacquers", which should NOT be confused with common acrylic nitrocellulose lacquers.

    And one simple point since you mentioned "garage use". If there's a gas water heater in it, NO solvent-based product should be sprayed ever; and many solvent-based brush/wipe products can't be safely applied unless it's far away from the water heater and the large door is open.

    Hope that gets you started.
     

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