Cloudy patches in clear gloss nitro coat

[7thstring]

Hello!

So I've been chipping (actually, mostly sanding) away at my first ever build - an SH-1 build - and I've applied a clear gloss nitro coat today and found I've ended up with cloudy patches, primarily at the edges of the guitar. This the second time this has happened to me, first time I assumed user error/dust got caught under the coat and I ended up sanding down and giving it another go, but now it's happened again I'm questioning that - any ideas what I'm doing wrong?

Rough timeline is that I sprayed a few coats of a blue nitro yesterday, ended up leaving this overnight then sprayed the first gloss coat this afternoon - when I came back to it the cloudiness was already apparent.

Have (hopefully) managed to attach some pictures

Thanks, Dan.

[Sonic Mountain]

This is usually caused by moisture being trapped in the paint. If it's too humid when spraying, water will condense on the spray as it's leaving the can and get trapped in the finish, it can sometimes happen when it's too cold to spray as well, perhaps the drop in temp overnight led to some condensation?

If you notice it when you are spraying you can sometimes rescue it by hitting it with a hairdryer while it's still wet. It wouldn't hurt to try this now, just be gentle and keep the heat spot moving.

Nitro in particular does seem to be more prone to going cloudy, but it seems to be more of an age thing usually. There are some products available to help remove it, so that might be worth a google. Otherwise you are probably up for sanding back and re-spraying in better conditions.

[Simon Barden]

I've suffered from similar issues this year when using aerosols, a couple of cans in particular gave me much grief. Not so much on wide areas, which is normally down to it being too cold or too humid, but on smaller areas. Previous clear gloss nitro aerosols just went on fine, but these two from the same fill batch, were thicker, and very spluttery. Some of my issues were down to poor technique making this worse. Despite knowing better, I often failed to start with the spray off to to the side of the guitar and then move it on to the guitar. So the first second or so when the spray was often most lumpy, went on to the body at the edge. This often resulted in a thick layer with trapped solvent and propellent in it making bubbles. This was made worse in my case by it often really being too hot to spray, so the surface of the nitro dries very quickly, trapping moisture and gasses underneath that will normally escape over a few seconds when cooler, but get trapped when it's all too hot.

You can get a general haze if you spray when it's too cold or too humid, due to trapped moisture droplets from the air forming within the lacquer.

When using a can, always shake well, to mix the nitro, solvent and propellant together. Some can nozzles can start out partially blocked and not spray well, so it's worth investing in some replacement nozzles and swapping over if you feel that the can isn't spraying well. That's helped me in the past. Warming up the can first by leaving it in warm water will also help the liquid/gas mix flow better within the can. And don't spray on to a hot or cold object. Try and keep the guitar body/neck at a reasonable temperature, don't leave it sitting outside in hot sun for ages before you spray it. Too hot and the paint surface dries quicker and the temperature encourages solvent gas bubbles to form which get trapped by the dried surface skin.

Around 20°C/68°F is an ideal ambient spray temperature. Below 15°C and above 25°C, the more problems you are likely to encounter. And any time the relative humidity is high.

If spraying with a gun as I normally do, you can get anti-bloom thinners, which help when spraying in cooler temperatures or more humid conditions. You can also get retardant thinners which slow the drying rate of the lacquer, which also allow any trapped gasses more time to escape and also give a smoother paint finish.

But once you've got those little bubbles trapped in the finish, you've either got to sand them back or else remove them by getting some cellulose thinners on a brush (I use a flat artist's paintbrush with fairly short and quite stiff bristles), and working that in to the finish on the misty areas. This will re-melt the nitro and allow any trapped gas to escape. Just keep working the thinner in until the mistiness has gone, then that's it. You'll get a rough finish, but at least you can continue spraying over it to build up enough depth until you have enough to sand back flat.

You can fool yourself and by continuing to spray over the cloudy areas, it can look like the cloudiness has gone. But take the guitar into bright sunlight and you'll still see it. Or it will look fine until you sand back to level the finish for polishing, and the mistiness suddenly reappears. So you really do need to deal with it each time it happens.

[7thstring]

Ah brilliant advice both, sounds like moisture is the cause, both attempts have been on cooler, rainy days so would explain it.

Sonic mountain - tried the hairdryer to no avail (although was a little wary as the misses has one the worlds most overpowered hairdryer and I didn't want to overdo it and cause a blister)

Simon - I'm in the UK in Peterborough, sounds like I've probably missed the window for the ideal temperature and humidity given the last week or two! I've been spraying in the garage primarily as I can hang the guitar in there in a faux spray booth made out of an old box, some wood and a wire hangar, so probably is getting a touch too cool for it, and the rain isnt going to be helping. I have a dehumidifier I could potentially stick in the garage as well, not that I think its going to handle a room that size - but wont hurt me to try I suppose.

Have sanded down and have begun the process of applying some more blue again to bring the surface to be more consistent - although I think I might need another can at this point...

I also have a tin of the clear gloss as well as a spray - do you think it would be possible to apply using a cloth/brush and potentially get around the issue I'm having with the spray, or am I likely to run into other issues doing it that way and best waiting for a warmer/dryer day?