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Spraying lacquer - repairing blush

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Forum topic by unclearthur posted 09-23-2020 01:01 AM 412 views 0 times favorited 16 replies Add to Favorites Watch
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unclearthur

375 posts in 2671 days


09-23-2020 01:01 AM

I’m a novice sprayer and I think I’ve run into my first problem with “blushing” after spraying a tabletop with nitrocellulose lacquer. The cloudy / milky areas are most easily seen on the dark parts (walnut):

The bottom side of the table is or course perfect, lol. (The top is on hinges and opens). The base was OK too.

I didn’t realize what was going on at the time, and I think a sprayed a couple of coats on top of the one that produced the blushing. The underlying problem was probably humidity (which was around 78%); I did not thin the lacquer or use any retarder.

Anyways, I am looking for some advice on how best to fix this? I have lacquer thinner and something called “No Blush (Butyl Cellosolve) from Mohawk, which I think is a retarder.

Do I just sand down to wood and start again? Or use the chemicals somehow?

And if I am sanding down all the way down to wood or just so I can’t see the blush? Can I just do the regions with blush and leave the table edges (which look fine) alone …. ie will a new layer of lacquer mix in or do I have to remove everything? Never refinished anything before.

Also if I strip and respray ….how much lacquer thinner and retarder to use? (HVLP sprayer).

Thanks for any tips.


16 replies so far

View CWWoodworking's profile

CWWoodworking

1092 posts in 1063 days


#1 posted 09-23-2020 01:21 AM

You can try-

https://www.mohawkproducts.com/MOHAWK-SUPER-BLUSH-RETARDER-p/m103-0476.htm?gclid=CjwKCAjwwab7BRBAEiwAapqpTMJhhRFpXDanQkPLJtToYo7BYih95OYF9WRtY9IZnrrPT-arNw9GABoCurcQAvD_BwE

You could also sand it with some 320 and hit it again with a thinned out coat with a little retarder in it.

If you don’t already have the aerosol, just try the thinned coat. Lacquer is very forgiving.

View Rich's profile

Rich

5987 posts in 1473 days


#2 posted 09-23-2020 01:58 AM

Try the No Blush first. You can spray it directly from your sprayer, full strength. Be careful not to get puddles on the surface, because it’ll leave an edge when it evaporates. Just multiple light dustings until the blush is gone.

Regarding the No Blush for mixing with lacquer before spraying, I use it or Sherwin Williams K27, depending on what I have around. I add about 4 to 6 ounces to a half-gallon (which is how much my pressure pot holds). Using it up front will probably save you from getting blush in the first place.

Since you’re getting into lacquer, I highly recommend a de-nibber. When you get an uneven surface from drips, runs or whatever, it’s better to shave it flush than to sand it. Sanding removes the finish from around the defect as well, which is not what you want. Also, even without runs, you often will feel nibs when you run your hand over the surface. The de-nibber will knock those off without marring the area around it, often so smoothly that you don’t need to spray back over it.

Finally, I keep plenty of the Mohawk No Blush in aerosol cans around. It’s much easier than loading up your sprayer, and it often can save you from needing a new coat of lacquer. It’s a life-saver in many different situations. Try some and you’ll see.

Anyway, here's a de-nibber:

Don’t worry that they refer to it as a file. It will glide over a smooth lacquered surface without scratching, but will knock off any protrusions in the finish.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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unclearthur

375 posts in 2671 days


#3 posted 09-23-2020 03:41 AM

Thanks Rich & CWW. Much obliged.

View Planeman40's profile

Planeman40

1519 posts in 3645 days


#4 posted 09-23-2020 05:24 PM

Lets define what “blushing” really is. When lacquer “blushes”, It is the rapid evaporation of the lacquer solvent that chills the surface causing moisture in the air to condense on the surface. This is why it usually is a humid summer problem. Using a “retarder” to slow the evaporation usually cures the problem.

-- Always remember: It is a mathematical certainty that half the people in this country are below average in intelligence!

View pintodeluxe's profile

pintodeluxe

6210 posts in 3697 days


#5 posted 09-23-2020 05:33 PM

I wouldn’t sand back to bare wood. Just scuff sand and topcoat the one problem area with one more coat. Spray on a day with less humidity.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View typing's profile

typing

46 posts in 469 days


#6 posted 09-24-2020 05:54 PM

I often have to redo the finish sometimes multiple times, either because I make a mistake or I do not like the results.
Sander is your best friend when it comes to finishing.

View Rich's profile

Rich

5987 posts in 1473 days


#7 posted 09-24-2020 06:37 PM

Actually, your best friend when it comes to finishing is knowledge and practice, which will allow you to get a good finish first time every time.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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LeeRoyMan

1422 posts in 611 days


#8 posted 09-24-2020 07:06 PM



Actually, your best friend when it comes to finishing is knowledge and practice, which will allow you to get a good finish first time every time.

- Rich


LOL, yeah,
that sander is like your teacher standing over you giving you a lecture while you sand out your mistakes.

View unclearthur's profile

unclearthur

375 posts in 2671 days


#9 posted 09-25-2020 02:26 AM

So I bought a tin of the No Blush aerosol that was recommended above and tried that. A few seconds of spraying and boom, problem solved. Stuff is magic! Thanks all.

View woodbutcherbynight's profile

woodbutcherbynight

6302 posts in 3293 days


#10 posted 09-26-2020 12:20 AM



Actually, your best friend when it comes to finishing is knowledge and practice, which will allow you to get a good finish first time every time.

- Rich

Exactly

LOL, yeah,
that sander is like your teacher standing over you giving you a lecture while you sand out your mistakes.

- LeeRoyMan

Had to bring the teacher thing up? LOL

-- Live to tell the stories, they sound better that way.

View CWWoodworking's profile

CWWoodworking

1092 posts in 1063 days


#11 posted 09-26-2020 02:02 AM

Rich, can the retarder effect the sheen when sprayed too heavy? It’s been a long time since I used it, but I remember dead flat production lacquer looking slightly glossier? Maybe I just dreamed this.

View Rich's profile

Rich

5987 posts in 1473 days


#12 posted 09-26-2020 03:49 AM


Rich, can the retarder effect the sheen when sprayed too heavy? It’s been a long time since I used it, but I remember dead flat production lacquer looking slightly glossier? Maybe I just dreamed this.

- CWWoodworking

Yes, that’s what I was referring to above when I said to do multiple light mists, not a heavy spray. Once you see it look wet, you’ve gone too far, and it can affect the sheen and leave a visible edge around the puddle once it evaporates. It does that because you’ve completely liquefied the lacquer finish and the flatteners that make it, say satin, move from the surface, leaving a higher sheen. If you’ve ever floated concrete to bring the cream to the top—it’s the same concept. The edge results from surface tension.

Generally it’s no big deal since you can do a touch-up with aerosol of the correct sheen. Even with that though, light passes are needed.

Since retarders are such slow evaporating solvents, even a light mist doesn’t flash off like acetone would and continues to do its job much longer. It also means when you leave a puddle, it will stay there long enough to completely melt the lacquer below it and allow the flatteners to float below the surface.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View Rich's profile

Rich

5987 posts in 1473 days


#13 posted 09-26-2020 03:51 AM


So I bought a tin of the No Blush aerosol that was recommended above and tried that. A few seconds of spraying and boom, problem solved. Stuff is magic! Thanks all.

- unclearthur

I’m glad it did the job. That stuff truly is magic. It can cure so many little issues.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View unclearthur's profile

unclearthur

375 posts in 2671 days


#14 posted 09-26-2020 07:42 PM


Rich, can the retarder effect the sheen when sprayed too heavy? It’s been a long time since I used it, but I remember dead flat production lacquer looking slightly glossier? Maybe I just dreamed this.

- CWWoodworking

Yes, that s what I was referring to above when I said to do multiple light mists, not a heavy spray. Once you see it look wet, you ve gone too far, and it can affect the sheen and leave a visible edge around the puddle once it evaporates. It does that because you ve completely liquefied the lacquer finish and the flatteners that make it, say satin, move from the surface, leaving a higher sheen. If you ve ever floated concrete to bring the cream to the top—it s the same concept. The edge results from surface tension.

Generally it s no big deal since you can do a touch-up with aerosol of the correct sheen. Even with that though, light passes are needed.

Since retarders are such slow evaporating solvents, even a light mist doesn t flash off like acetone would and continues to do its job much longer. It also means when you leave a puddle, it will stay there long enough to completely melt the lacquer below it and allow the flatteners to float below the surface.

- Rich


On my repair, which overall I’m happy with, there was one spot where I did exactly what Rich said not to do (too much blush spray to it looked wet) and the end result is exactly what Rich describes – the area that was too wet has an increased sheen. So now I understand why that happens. So I guess I’ll try to topcoat with a little more lacquer spray.

View unclearthur's profile

unclearthur

375 posts in 2671 days


#15 posted 09-26-2020 07:46 PM

Question though. The original finish was nitro-celluslose lacquer from an hvlp sprayer. I’d rather do the touch up with an aersol can, but all I have is precatalyzed lacquer (both Mohawk, both satin sheen). Any issue with using the pre-cat on top of the nitro-cellulose?

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