Dealing with Blush

[Mike Griffin]

I live in New Orleans and we have lots of heat and lots of humidity.  I do not have extensive experience in applying butyrate colored dope but I do know that blushing in this heat and humidity is going to be a problem.  I cannot spray indoors where the temperature is controlled so all shooting of color with be in this heat and humidity.

Here are my questions?

I have tried retarder but it doesnt seem to work well.

Is there anyway to prevent the blush?
If blush does occur, is it permanent or is there a way to get rid of it.
Does clear coating over the blush in the color make it go away?

In general I am asking how to prevent blush but if it does occur, how can you get rid of it.

Thanks much

Mike

[Paul Taylor]

Mike,
Thanks for posting this... I have some of the same concerns with my build that will need to get some dope on very soon.
Being in about the same weather conditions as you.

I will be watching this thread.

[Mike Griffin]

Hey Paul

Glad I am not the only one wanting to know this.  I feel assured there are some guys out there that know the answer to this.  I am hesitant to do it until I get some advice from experienced finishers...thanks for your input.

Mike

[Neville Legg]

I haven't had the "blushing" problem since I purchased some very high quality thinners (expensive) from an auto paint store, and kept the dope thin, 70% thinner!

Cheers

[Tom Rounds]

Neville,
Please give us some product names ands numbers of the thinners that you have had such good luck with.
Thanks,
Tom

[FLOYD CARTER]

No one has yet answered the questions.  Blushing is a pain, but retarder will help some.  Also, try for a "slow" thinner, if you can find it.  If the humidity is too great, some blushing will still occur.  The best remedy for a dried blushed finish is to wet sand with 600 and try again.  Usually, subsequent coats, including clear, will cause previous blush to go away.  FLOYD

[Neville Legg]

Blushing is caused when the dope dries too quickly trapping moisture underneath. You can usually get rid of it by spraying or brushing (spraying will be better) a coat of neat thinner (quality thinner) over the dope! I had a can of gun wash, (cheapest of the cheap thinner, purely used for cleaning up spray equipment) where the bottom of the can rusted and fell off, can only imagine that it absorbed water?
The thinner I use is SWS Quality thinner product code  S120 High Gloss, It cost me about £25.00 about $40.00 at todays rate, I have seen it cheaper on the net but then you have postage, if they will post it? By the way this is a British product.

Cheers

[Mike Griffin]

No one has yet answered the questions.  Blushing is a pain, but retarder will help some.  Also, try for a "slow" thinner, if you can find it.  If the humidity is too great, some blushing will still occur.  The best remedy for a dried blushed finish is to wet sand with 600 and try again.  Usually, subsequent coats, including clear, will cause previous blush to go away.  FLOYD

Floyd can you tell me what ratio of color to thinner you use and then how much retarder to add to that mixture.  For example if a good mix is 30% color butyrate and 70% butyrate thinner (and I dont know if this is the right ratio or not and if not please advise what is)how much retarder should you add? 

Thanks Mike

[Mike Griffin]

Blushing is caused when the dope dries to quickly trapping moisture underneath. You can usually get rid of it by spraying or brushing (spraying will be better) a coat of neat thinner (quality thinner) over the dope! I had a can of gun wash, (cheapest of the cheap thinner, purely used for cleaning up spray equipment) where the bottom of the can rusted and fell off, can only imagine that it absorbed water?
The thinner I use is SWS Quality thinner product code  S120 High Gloss, I cost me about £25.00 about $40.00 at todays rate, I have seen it cheaper on the net but then you have postage, if they will post it? By the way this is a British product.

Cheers

Thank you Neville

[EddyR]

Mike go to the search engine at the top of the page and type in" Dope blushing"
Also go to the finishing section and ask the question
Ed

[Jim Thomerson]

As far as I can tell, you cannot have too much retarder.  I once doped a free flight wing outside in misting rain and got no blush with lots of retarder in the dope.  Brushed on retarder will take out blush.  I have not tried spraying it. 

[wwwarbird]

 Mike,

 I recently finished dealing with some blushing issues on a smaller plane. While fighting through it I made this post asking some questions in the "Painting and Finishing" section here. You may find some info in it that will help, or not.

 http://stunthanger.com/smf/index.php?topic=22098.0

 

[Chuck Feldman]

Hello Mike,

The dope has to dry slowly to avoid blushing. I have found that the more thinner you use the worse it is. I have also found that retarder doesn't do much either. So all that aside I would find a real aircraft re builder who works with dope in the area and go visit him. He will know the answer you need.  If you do that I would like you to let me know the result.

Chuck

[Chucky]

Unless you live in the deep swampy south where humidity is simply crushing during the summer rainy season, you can't imagine what a horrible problem bushing is for any lacquer finish.  When I moved to Orlando, I ran into the same problems Mike is facing and after many attempts at using various products, came to the conclusion that I simply could not successfully apply a glossy dope finish at any time during the 6 month long summer season.  Then I discovered dope retarder and the problem became manageable.  I use at least 10% retarder in all dope and up to 40% during the summer wet.  I only spray final clear coats on sunny days in direct sunlight regardless of season.  This alone makes a significant difference since this is the least humid time of day.  I have also found that there are conditions under which using 100% retarder for thinner will not fully prohibit blushing.  During those times when humidity reaches saturation levels, one simply needs to wait for drier weather.  The alternative is, of course, an air conditioned shop with air handling system -- a luxury that I don't currently enjoy.

[stunt1]

Hello Mike, Stunt Supply.,

A thinner that will help with your problem is Dupont 3696S Acrylic Lacquer High Performance Thinner. Around here in NY at the Auto Supply Guys that I go to this is $58 a gallon but definitely worth it. They originally turned me on to this when I queried about spraying a repair and you usually wind up with a haze where the spray stops. This will totally eliminate that because it takes longer to dry and loosens the paint it is sprayed on. It is high gloss, flow out and Blush Resistance Holdout.

It does the trick and I recommend it.

Cheers and Good Luck,

Bob "Champione" Lampione

[Allan Perret]

  I only spray final clear coats on sunny days in direct sunlight regardless of season.  This alone makes a significant difference since this is the least humid time of day. 

Why the direct sunlight ?  I would think that would speed up the drying and work against you.

[wwwarbird]

Hello Mike, Stunt Supply.,

A thinner that will help with your problem is Dupont 3696S Acrylic Lacquer High Performance Thinner. Around here in NY at the Auto Supply Guys that I go to this is $58 a gallon but definitely worth it. They originally turned me on to this when I queried about spraying a repair and you usually wind up with a haze where the spray stops. This will totally eliminate that because it takes longer to dry and loosens the paint it is sprayed on. It is high gloss, flow out and Blush Resistance Holdout.

It does the trick and I recommend it.

Cheers and Good Luck,

Bob "Champione" Lampione

 Thanks Bob, good to know about the 3696S. Man is that spendy though!

[Neville Legg]

Unfortunately good thinners does cost a fortune, but you don't use it to wash your brushes and spray equipment, for that, you use the very cheap stuff. So it should last? I've just bought a gallon of SWS S120 high gloss thinner from Ebay (Nu-Agane auto finishes) for £18.74 approx. $30.00 incl. postage, that's what I call a bargain 

Cheers

[Bryan Higgins]

Well my wife uses that stuff "Blush" but i never really asked her how it works.

[larry borden]

Thanks Bob, good to know about the 3696S. Man is that spendy though!

I had never heard of that thinner. I buy Dupont 3608S from Finishmasters and use it for everything. I'll get a gallon of 3696S and only use it for the clear coat.

[Mike Griffin]

I want to thank everyone for all the great input on this thread.  Lots of good information here.

Mike

[GGeezer]

Hi Mike,

At high humidity when the dew point temp. is very close to the air temp., the evaporating thinners cause the paint to cool off and if the paint temp. goes below the dew point, moisture from the air condenses on and in the paint to cause the blushing. What we need to do is prevent the paint temp. from going below the dew point temp. This is difficult when the two temps. are only a degree or two apart but there are several approaches that you can use in combination:
1. Slow down the evaporation (cooling) rate by using slow thinners and/or retarder.
2. Raise the temp of the painted surface. This is why painting in the sun often works.
3. Warm the paint.

What we want to do is get the greatest temp. difference possible between the painted surface, paint and the dew point.

This is how I do it:
Using my B&D hot air gun in my left hand and set at the 500 deg. setting, I first warm the surface I'm painting. Then, with the gun bathing the surface in warm air, I spray on the paint which I have also heated somewhat and thinned with some retarder. The warm air from the air gun will both keep the paint and the painted surface above the dew point while the paint flashes off. Use only as much heat as is needed to keep the temp above the dew point.
If you get a patch of blush, concentrating the hot air on that area will usually remove the blush.

Again, the trick is to get the paint, and the painted surface temp. as high as is practical above the air temp.
The hot air gun trick works but takes some practice so it is a good idea to try to paint something not important to get the hang of it.

Orv.

[Chucky]

Hi Allan.  As to the benefit of direct sunlight, I'd have to agree with Orv that warming the surface of the model works the treat.  It's just easier to let mother nature do the warming and here in sunny FL she's more than willing. 

[Chuck Feldman]

The process of using heat as above seems like a reasonable way to cure the situation. I concure with it and the science being used to get a good  finish.

Chuck

[Ward Van Duzer]

Hummel's right, DuPont 3602 S from the ground up when using dope. Learned that real quick when I moved from Jersey to Georgia! Junk thinners a definate no-no.


W.

[Steve Helmick]

Why not just use the same (slowest you can get) thinner all the time, and never bother with retarder? It might be a little pokey to dry under some circumstances, but would it be all that bad on average?  Steve

[wwwarbird]

Hummel's right, DuPont 3602 S from the ground up when using dope. Learned that real quick when I moved from Jersey to Georgia! Junk thinners a definate no-no.


W.

 So Ward-O, a person could do their normal complete dope prep finish and paint job (Brodak dope) and then do the final clearcoats thinned with 3602 S, correct?

[Chucky]

It shouldn't matter much how one attacks the blush problem -- add retarder to fast-drying thinner, or use a slow drying thinner that has retarders in it like 3602 S.  The big difference, for me, is cost and who's in control of the amount of retarder in the paint mix.