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So frustrated with this, I have had good results in the past with these rattlecans (nitrocellulose) but getting horrible blushing now and the bracing is showing through the front !!!!!

Temperature is 15°C and humidity is around 60%, sprayed like this before and been fine. Any ideas?


Thanks

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Humidity.
I’ve had that issue.
In my case it disappeared on the next coat


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Did you sand the coat of first ?

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I just kept on w my schedule.
I’m sure someone will have more help than I can offer


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what brand? I don't use anything but Minwax anymore

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

what was your prep
sealer
filler
stain
water based
etc

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Water based stain, zpoxy fill, tried Nitrocellulose sanding sealer but it also blushed and I had to sand it off, then sprayed with nitrocellulose satin

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This stuff, highly recommended and used before with little to no problems

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Yes, humidity. I never sprayed when it was over 50%. With rattlecans, you can't add retarder or anything to compensate.

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"Act your age, not your shoe size" - Prince

Rub it with a soft t shirt type cloth. A little warming can go a long way. In a humid environment you need to apply lighter coats. And relax, there are ways to deal with blush. I’ve never had to sand it off.

Cool, never tried that

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Oh my.... So much going on here and unfortunately little to do about it since we are rattle cans... If we had a gun we could adjust things. But we don't so we are here.

Your spray pattern needs to be tighter, more overlap. Your coats are also very uneven with the blushing at the thicker areas. Most of this could have been avoided with better technique as your environmentals look fine for lacquer.

What to do now? well if you can find a spray can of retarder you can use that to re-wet and let the moisture out of the coating. That or sand it off and try again.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Humidity must be controlled . You may have a bad can , this stuff does spoil.

I stopped using most of the rattle cans , but I did find Minwax works well. I use it for touch ups for and I have done an few posts ok kgf
and showed my process. Unlike a sprayer you don't have a lot of adjustment so you have to work with the can. I lay the surface I want to spray flat so I can spray a nice coat. Blush usually comes out. I have used ever clear and noblush from big A auto.
Wipe this off with thinner or acetone. You also want sealer between your filler

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks guys, will sand off I think.
Can I use shellac as a sanding sealer under the nitrocellulose as had bad blushing with the nitro sealer as well

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yes I use Zinser transparent clear

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Spray another light coat, while the humidity is low, and the blushing will disappear.

Ah... The possibility exists that this is not all just typical moisture induced blush. And based on temp and RH given by the OP there should not have really been much blush. The possibility exists that what you are seeing is actually refractory paste used to make the finish satin that was not thoroughly mixed into suspension before spraying. These agents are thick and known to bve tough to mix in properly especially at lower gloss numbers. Rattle cans are even harder to mix up and if that can sat in inventory for a year it may take 40 minutes or more of shaking it to mix it properly.....

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

I think the fact that the blushing mirrors the bracing patterns on the top and back indicates that this is moisture related blushing. Stearate in the lacquer would not do that, but would make more random patterns.

I have used Mohawk & Behlens Blush Eraser for many years with great results. Just the lightest spray mist over the lacquer will completely remove the blush. It works best when the lacquer is fresh but also works when the lacquer is dry. I buy it from Stew Mac.

https://www.stewmac.com/Materials_and_S ... raser.html

Mike Franks
www.mjfranksguitars.com

Sometimes I just spray lacquer thinner on it. Light mist usually clears mine up. Normally another coat does the trick.

So the thinner sections of wood had more moisture in them? I doubt that. What I suspect is that the instrument was sanded with a RO sander and the spots over the braces were scuffed through the sealer which allowed the lacquer to absorb in those areas and that may have affected the flattening paste and how it aligned in the coating as it dried. The stuff behaves much like a fine metallic in suspension and though you cannot see it it flows around just like a metallic does as it dries.

That brace shadow is why I never sand an acoustic instrument with a RO sander.... guitars are designed to vibrate freely and trying to sand them while they vibrate at at 30-60hz..... You always sand thin over the braces because of this.

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

That's intriguing! Do you think the mechanism of injury is that the braced spots on the top provide more resistance to deflection, while the unbraced spots vibrate away from the sander? I am not disagreeing with you (I have no basis for disagreeing). I'm just trying to get a sense of how the problem happens.

This theory seems like a stretch. I have never seen this thinning issue from an RO sander and I use mine on guitars all the time.

Edit 1: The reflection of the braces is more likely due to the thermal mass of the bracing which slows down cooling and moisture condensation.

Edit 2: I added that last edit before I read Clay's post. You can see this thermal mass effect in windows and other areas where condensation occurs.

Edit 3: The overthinning of the top above braces can be minimized by using fresh sandpaper.

I have seen this effect from sanding. I was doing a WRC top and got epoxy on the top while I was doing the pore fill. I decided to try a wash coat of thinned epoxy on the top to even things out. That was another mistake since it came out blotchy. I decided to try to sand all of it off and risk over thinning the top. I didn't use a power sander just a rubber block and (in retrospect) too much pressure to try to speed up the process. It didn't' take long for me to notice that the top above the braces was sanded through and the open areas much less so. I suspect this has happened to me before but I never noticed because I usually don't sand once the finishing starts (french polish) but it really taught me a lesson.

The guitar ended up looking strange in certain light/angles but sounds good. It was for me so not a huge deal.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

When I have had that happen I assumed it was because there was a temperature difference between the air inside the box and the air outside the box ("spraying" also cools the air) causing some condensation. The thicker places where the braces are glued lessen the reaction to the dissimilar temperatures. I found immediately moving the guitar body to a warm environment and placing it under hot lights eliminated the blushing. Mohawk "no blush" (butyl cellosolve in a rattle can) would be a handy thing to have if you are doing rattle can finishes (Buying a small compressor and a cheap jamb gun would be a better option in the "short" long run).