Blush - Yeccchhh

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old_picker
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Blush - Yeccchhh

Post by old_picker » Fri Sep 07, 2018 10:07 am

Never had blushing before and I've sprayed in pretty awful conditions. Yesterday afternoon and this morning however, spraying black acrylic coats has blushed like crazy. It is 79% humidity and 11degC here :(

Wondering which is the most efficient way to deal with this.

Will blocking it back with 600 grit make it disappear permanently?
Should I just wait for better conditions and respray over the top of the blush?

As I understand it moisture trapped in the finish causes blushing

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kiwigeo
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Re: Blush - Yeccchhh

Post by kiwigeo » Fri Sep 07, 2018 10:32 am

Too much blush...you see this a lot. One of our finishing experts will be along shortly to provide advice.
blush-mistakes.jpg
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Martin

simso
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Re: Blush - Yeccchhh

Post by simso » Fri Sep 07, 2018 1:33 pm

Spray a mist coat of thinners over the surface, it will hopefully soften it long enough for the moisture to escape

Steve
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old_picker
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Re: Blush - Yeccchhh

Post by old_picker » Fri Sep 07, 2018 5:25 pm

give that a try and it did knock it back quite a bit but with black it's gotta be 100%.
I'll block it on Monday, shoot clear over that and see how she looks

blackalex1952
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Re: Blush - Yeccchhh

Post by blackalex1952 » Fri Sep 07, 2018 7:12 pm

It is 79% humidity and 11degC here
You answered your own question here, in a way. Was the guitar fresh out of a lower RH environment? That might have helped. Also, I have had good results in low temperature by making sure the guitar timbers are at low RH, using a heat gun to keep the guitar a little warmer, or better still, heat lamps, (particularly with volatile finishes like nitro which could explode with a heat gun if any lacquer fumes are about), and warming the gun pot in hot water to raise the temp of the paint in question. This also has the effect of thinning the lacquer which means it can be sprayed using thinner coats. It will also flash off faster. My thinking is to get the surface temp and the lacquer to be the same when the spray hits the surface, and the wood has very low moisture content so that water doesn't migrate out and cause the blushing. I also think that, given the thinner coat, it is like sealing the wood with a flash coat first. Alan will probably chime in and he is the expert with spray finishes. Get the data sheet for the finish in question and look at the minimum spray temp they specify. And allow longer at 11 degrees for the finish to fully harden prior to polishing and buffing.
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Blackstar1099
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Re: Blush - Yeccchhh

Post by Blackstar1099 » Fri Sep 07, 2018 9:38 pm

I've managed to get blushing out by spraying a light mist coat in lower RH conditions a couple of times. It does work. It was with clear though.

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WJ Guitars
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Re: Blush - Yeccchhh

Post by WJ Guitars » Sat Sep 08, 2018 11:26 am

Very helpful advice. Will keep this in mind when planning spraying.

Wayne

simso
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Re: Blush - Yeccchhh

Post by simso » Sat Sep 08, 2018 11:34 am

Very good, sometimes it’s too late, had one guitar that I couldn’t resurrect, man that drove me nuts that one. Back to wood finish, and it was gorgeous at that point mi us the white haze everywhere.

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Allen
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Re: Blush - Yeccchhh

Post by Allen » Sun Sep 09, 2018 6:39 pm

There is absolutely no time whatsoever that you should not add 5-10% of extra slow or retarder to your mix. It helps with flow and leveling. Allows you to spray thin coats. And if you ever get blushing with that mix, then you shouldn't have been spraying then.
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Woodsy23
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Re: Blush - Yeccchhh

Post by Woodsy23 » Mon Sep 10, 2018 1:02 pm

Speaking of retarders, I once had a problem with blushing of a nitrocellulose finish. I googled for help and found some advice from a "finishing expert" (which I am not) to spray lightly with retarder. I did that and the blush disappeared instantly and completely (as far as I could tell). I have no idea if that always works or if I was just lucky. I'm also not sure if it works with acrylic but it's worth thinking about.
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Re: Blush - Yeccchhh

Post by WJ Guitars » Mon Sep 10, 2018 2:08 pm

I also am not an expect on spraying, however, on one occasion I had an blushing problem when spraying with Nitro Lacquer and eventually discover that the air hole in the HVLP spray gun canister lid has partially become clogged. This had constrained the Nitro Lacquer flow in the spray gun and i ended up with a blushing problem.

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Re: Blush - Yeccchhh

Post by old_picker » Tue Sep 11, 2018 3:13 pm

I blocked it today and conditions good this arvo - so a couple more coats of black and I'll start in on the clear. BTW first job in the brand new workshop whoo hoo - builder isn't out yet but not back here again for a few days - while the cats away :)

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