Nitro & Humidity

[PoopSoupGuitars]

Soooo, I finally have my Tele guitar body ready for paint.

I'm going classic Blonde with some Amber overspray for a relic look and bought the nitro from Northwest Guitars (UK). Never sprayed nitro and want to get this right. All of the reading I'm doing is saying that humidity is the key factor (as well an no wind since I'll be doing this outdoors). Most people recommending below 55% humidity minimum.

Thing is, here in Ireland it NEVER gets below 55%. What are the dangers of spraying in say, 70%? Moisture in the finish? Presumably this can lead to sags and runs maybe?

Any advice is appreciated.

 

[Peegoo]

@PoopSoupGuitars

Elevated humidity causes nitro to "blush." This is an effect wherein moisture gets trapped in the finish (captured by the droplets of finish as they fly through the air) and makes a visible cloudiness in the finish. It can create a haziness in moderate humidity, and it can make darker finishes look washed out or even leave large white patches in higher humidity.

Blush cannot be polished out because it's not on the surface; it manifests throughout the thickness of the finish layer.

Best approach is to find a pal that has a heated garage, or even better, a paint booth where they do bodywork on automobiles.

If none of that is an option, then multiple very thin mist coats (not wet coats) with dry time between are the way to go. The thicker the coat you spray each time--the greater the chance of the finish blushing.

You're shooting blonde, which is white and makes it not so critical...but blushing in blonde can create a blotchy look.

 

[PoopSoupGuitars]

@PoopSoupGuitars

Elevated humidity causes nitro to "blush." This is an effect wherein moisture gets trapped in the finish (captured by the droplets of finish as they fly through the air) and makes a visible cloudiness in the finish. It can create a haziness in moderate humidity, and it can make darker finishes look washed out or even leave large white patches in higher humidity.

Blush cannot be polished out because it's not on the surface; it manifests throughout the thickness of the finish layer.

Best approach is to find a pal that has a heated garage, or even better, a paint booth where they do bodywork on automobiles.

If none of that is an option, then multiple very thin mist coats (not wet coats) with dry time between are the way to go. The thicker the coat you spray each time--the greater the chance of the finish blushing.

You're shooting blonde, which is white and makes it not so critical...but blushing in blonde can create a blotchy look.

Thanks Peegoo, as helpful as ever.

I will wait for the best conditions I can. I do have a mate with a large empty garage but it ain't heated, it ain't even watertight but might be the best option available to me. With a relic I guess some imperfections are ok, but I want her to be pretty too.

 

[Freeman Keller]

What Peegoo said. I have only had one instance of blushing with nitro and I very definitely pushed the humidity envelope. My rule of thumb is 60/60 - I want the temperature above 60F and the humidity below 60%. As long I as I follow that I've been fine.

 

[Nicko_Lps]

Any advice is appreciated.

Im not sure about Nitro but regarding the polyurethane 2 part finishes, there are special thinners for higher humidity conditions.

That should be the extremely slow curing ones.
Nitro is the fastest curing thinner, the brand i use then has P2 up to P4 the extremely slow one that is supposed to be used in humidity.

The downside is... These slow curing thinners cost like 3x of the normal price and they are a HUGE pain considering how slow they are. They are way better in making the varnish/paint not drip but for them to settle it takes HOURS.

Just for you to understand how slow it is, i know using the normal thinner a big surface wont make it to be completely wet until i finish spraying, adding a coca cola bottle cap of this P4 thinner gives me enough time to finish it and move it to where i store the curing items. Imagine using 100% of this thinner...

Just wait for a nice sunny day or add a dehumidifier in your shop to compensate

 

[LuxInterior]

See if you can get a can of Blush Remover (Retarder). Spray lighter coats of lacquer followed by a mist coat of Retarder and you’d be surprised what you can get away with

 

[BFcaster]

I make a paint booth from long sheets of clear plastic, suspended from my garage ceiling. I then use a shop work light on a stand with a halogen bulb and warm up/dry out the booth. No blushing when I've done this, but if I do, yes there are anti-blushing sprays, or wait a day then a thin layer of clear when there is low humidity sprayed over the guitar will fix it. Nitro melts into itself, and the thin clear coat over the blush releases it out.

 

[BFcaster]

Should also add-
Spraying from a aerosol can- make sure to warm the can in a pot of warm water.
Spraying from an air compressor- make sure to have a moisture trap between the hose and gun.
I get away with 70% humidity and below, btw.

 

[Cjteleforum]

IME blush has happened when the humidity was high AND I sprayed too heavy. Keep the coats as thin as possible, just wet enough to avoid pebbling.

 

[old wrench]

Unfortunately, it's just a characteristic of nc lacquer

When you are working with rattle-cans, you don't have the options to use a slower thinner or a retarding admixture either

Don't plan on using "Blush Eraser" as part of your finishing schedule - it's really something used as an emergency measure or as a last resort when everything else has failed - it's not the path to a superior finish



Even the land of Irish Mist must have days when the conditions will allow you to spray canned nc lacquer

You just have to pick your days -

It might even come down to a particular season - or portions of certain days

A couple of times when using rattle-cans, I was constrained to working within a space of a couple of hours during days when the humidity dropped to its lowest point in the afternoons - and then I was able to apply a few very light coats - it might take several days to finish a guitar this way, but it works

Don't rush it

.

 

[PoopSoupGuitars]

Unfortunately, it's just a characteristic of nc lacquer

When you are working with rattle-cans, you don't have the options to use a slower thinner or a retarding admixture either

Don't plan on using "Blush Eraser" as part of your finishing schedule - it's really something used as an emergency measure or as a last resort when everything else has failed - it's not the path to a superior finish



Even the land of Irish Mist must have days when the conditions will allow you to spray canned nc lacquer

You just have to pick your days -

It might even come down to a particular season - or portions of certain days

A couple of times when using rattle-cans, I was constrained to working within a space of a couple of hours during days when the humidity dropped to its lowest point in the afternoons - and then I was able to apply a few very light coats - it might take several days to finish a guitar this way, but it works

Don't rush it

.

ok, looks like I'm waiting for summer. Grateful I have my SG to noodle on til then

 

[old wrench]

ok, looks like I'm waiting for summer. Grateful I have my SG to noodle on til then

I love nc lacquer - mainly the way it looks and feels, but also the way it goes on as you build the finish

But, because of where I live and the high humidity we often have, I looked around for an alternative that would look similar, but be a little more forgiving humidity-wise

So, in addition to nc lacquer, I've also been using a Target product - EM6000 - a water-borne lacquer

EM6000 will still blush when the humidity is too high, but it's not as bad as nc lacquer in that regard


There are a lot of very good-looking guitars that are finished with thinner poly finishes - even wipe-on poly - and they really don't look whole lot different to me (I'm not an expert) than a nice nc lacquer finish


Some folks plan their building schedule to work with the weather in their part of world

Iirc, Freeman Keller said he does his building during the part of the year when the weather is not conducive to applying nc lacquer, and then he does his finishing when the weather finally dries up


I've got a couple of bodies and necks that are ready to be finished right now myself, but I'm waiting for some better weather to show up so I can finish them without complications

We don't have the same weather patterns that I remember from when I was a boy, or even a young man

The local weather this winter has been a real merry-go-round of really high winds and big swings of up-and-down temperatures and humidity levels

.

 

[eallen]

Already good input.

I spray above 50-60% quite often. I do use a spray gun so that allows me to mix a bit more accordingly. Humidity is not ideal but sometimes it is just what it is. As humidity goes up my coats get thinner with increased dry time between them. If you see even a hint of blush doing put any more on and it usually disappears on its own after a bit on light coats. If it doesn't after 10 minutes or so mist a light amount of blush remover on and let it set again to dissipate. In real humidity days I do keep my shop closed up if I am going to be spraying to help keep it lower inside.

 

[philosofriend]

In cold weather I shine a 300 watt halogen worklight on the guitar itself. These are sold as a cheap set on its own tripod. If you can't stand to hold your hands for a minute as close to the light as the guitar is, you are too close and this can cause the finish to bubble. For me, about three feet (1 meter) away from the light is good. You just want the guitar ten or twenty degrees warmer than the outside cold air. Also I put the guitar in a warm place inside for the half hour before going outside in the open doorway of the garage to spray.

These tricks let me spray on colder/more humid days than I could do otherwise.

One of the first laws of spraying is to keep on staring intently at what is happening to the finish right after it lands on the surface. If there is any problem (blush, runs, excessive orange-peel, etc.) you have to react immediately! If nothing else. stop spraying and think about it.

For only the cost of another can of paint you could practice you plan on a piece of scrap wood. You will be much more relaxed than you would be painting your beautiful valuable guitar. This could save you the long hard work of stripping a bad finish off the guitar. Or just dive in, pray and spray! Don't stop staring at the paint flowing out and flashing off the solvent!

Stradivarious made violins year round but only finished them in the summer.

 

[Silverface]

ok, looks like I'm waiting for summer. Grateful I have my SG to noodle on til then

Yes.

If you were using an HVLP and bulk lacquer, you can buy special lacquer blends that are made for low temperature and/or high humidity.

But with aerosols you are far more limited. I was in the coatings business for 40 years (tech support, applicator training, failure analysis) and in some parts of the world you are limited to better application equipment and special products (which take a lot of practice to use - o it gets expensive); waiting for an application/drying window of at least 2 days for 2 coats of most lacquers (which is not enough to even begin to cover or flow) - and that's after testing the wood with a moisture meter, and if it's over 11% - stop!

I can usually spray all but a couple of days/month, but we've had such rotten weather here I have a Tele body that(because of some unique effects the client wants) has been here 4 months - partially done, and no end in sight!

I tell DIY'ers in some regions that lacquer finishing just isn't practical for them. They try following other advice from amateurs after refusing to practice on scrap first, mess it up, and want to know how to "fix" it. My advice after that - ship it to a guitar refinisher.

Impatience is the single most common cause of coatings failures among DIY guitar finishers.