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HOK Clear staying soft

13K views 25 replies 8 participants last post by  MARTINSR 
#1 ·
I'm painting some small plastic parts and was using the House of kolor kbc series of colors along with their usc01 show klear with ru311 reducer.

I'm noticing that even after 7 days I'm still able to make fingernail marks in the paint and peel off the clear/basecoat. The primer seems to be sticking to the plastic but almost is gummy. I also have noticed that the chipped area does still have a solvent smell after i pull with my fingernail.
From a previous post that 69 widetrack had responded to it seems like maybe I'm not letting my basecoat flash properly.

my ultimate question is that I need this clear coat to be rock hard and not get marks when say a coin is scratched across the surface.

Is the HOK klear a soft clear to begin with?

Here is my work process. Please let me know if you notice an area where you think I'm screwing up.
I'm at my wits end here.

Location : Houston TX
Temp/Humidity : 80-90 degree F/70-90 % Humidity

Material used
Primer : Duplicolor (rattlecan) auto sandable primer
Basecoat : House of Kolor Kandy base coat(brandywine)
Clear : House of Kolor show klear, KU152 hardner,

I'm using my airbrush because of the small amount I'm spraying
When I mix my clear I'm measuring using a syringe and measuring out 6ml of USC01, 2ml of KU152, 2ml of RU311 reducer.

Painting process
scrub plastic part with hot soapy water and rinse with hot water.
sand with 220 grit wet dry paper
rewash with hot soapy water and rinse
compressed air to dry
Light initial coat of primer with 10 minute wait, second light coat 10 minute wait, 3rd heavier coat and 30 minute wait per the can
I do not sand between primer and kbc
apply 3 coats of kbc looking for dull surface before respraying anywhere from 1-5 minutes.
wait 20-30 minutes after third coat
Mix up clear and apply a medium coat
flash for 15 minutes
2 more medium wet coats with 20 minute flash time

The finish is laying out beautiful and clear, no solvent pop or cloudiness or anything.
But for the life of me I can't get the clear to get hard.

What am I doing wrong oh gods of custom paints.?

Thanks for any and all help.
 
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#2 ·
A HUGE majority of paint failures are all do to the same thing, solvent entrapment. And it sounds like this is the case. It can be caused by many things, most often a combination of a few.

1. Over reducing.
2. Gun not set up and atomizing it properly.
3. Too slow of gun travel.
4. Too much overlap.
5. Too many coats.
6. Not enough flash time between coats.
7. Too slow of reducer or hardener
8. Too low surface temp

And probably a few more that I am forgetting. That and of course something like old hardener.

But it's most likely one or more of the ones mentioned above.

If this was a fender or something I would say color sand it like you were going to buff it and then let it "flash" more. With plastic parts, that isn't much of an option so just getting it out in the sun and where there is air movement, that may help.

It sounds as if what you did was all correct, but you could be off some on the time? Maybe it wasn't quite that long flash, maybe just a little less, with a little lower temp, maybe that and a little too slow of gun movement....that's all it takes!

Brian
 
#3 ·
Brian,
Thanks a lot for the possible causes. Let see if I can answer some of your points

1. Over reducing - Not likely as I'm following the formula on the HOK tech sheet to the T. Unless of course i need to lower the reducer because I'm mixing such small amounts at a time.

2. Gun not set up and atomizing it properly. - I'm using a Badger 105 gravity fed airbrush. I get good coverage with no splatter. I've asked some airbrush forums about settings and it seems that i'm task. Not sure though 100%

3. Too slow of gun travel. - I try to follow HOk video series on applying clear as well as the tech sheets. I use 50% overlap with fluid motion. I'm not getting any drips but the surface is noticeably wet.

4. Too much overlap. - See answer in Item 3

5. Too many coats. - HOK recommends 3 coats. one medium and 2 medium wet. I have stuck to that philosophy but using the airbrush i'm laying down such a seemingly light coat that I've thought of adding more coats for durability.
6. Not enough flash time between coats. - This could be my issue but more on the basecoats then the clear. I have some parts drying right now that I gave extra time on the basecoats to flash. We will see if that helps.
7. Too slow of reducer or hardener - HOK stated they thought the RU311 was perfectly fine in my environment.
8. Too low surface temp. Certainly not the issue in an 80-90 degree garage. But i know this wasn't aimed at me.

I guess a question that I should be asking is will a properly cured HOK clearcoat be soft enough to scratch with say a coin?

I have a commercially available plastic part that is painted with what seems like armor. I can take a coin, place it at an angle, press as firmly as possible against the surface and scrape back and forth and not even make a mark.

I would like to replicate that finish. Maybe I'm expecting to much?
My only experience is feeling the clearcoat on my vehicle which is harder then the HOK but I'm sure at this point i'm screwing something up.

How long should a typical HOK clear take to get hard enough to not leave nail marks? I know there are variables but i mean a week 48 hours? Whats your guys experience.
 
#5 ·
Understand that your answers to all the issues are only your opinion on what you thought you did.

Experienced painters would often think the same thing. And often it's a combination of a few.

On the temp, too high a temp can be just as bad! The top of the film flashes off too fast trapping solvents, So letting it flash longer means nothing.

Too slow of travel or overlap, that is really subjective and someone could think they aren't going too slow when they are. The answer is to apply it differently next time and see how you can vary it.

Your clear should not be soft now, leave it out in the sun with some air movement and see how that works for you.

Brian
 
#10 ·
Thanks TD. I'll try to setup my airbooth at a window and test a small piece as well. I wonder if going with the RU312 would be a better option?

Also would switching to an epoxy primer give me more durability? It seems like I'm not having issues of the primer not sticking but I was just curious.
 
#12 ·
Brian has done a great job explaining the problem solvent trap-age deep in the base coat.

I can't speak for HOC but will add, clear will not cure at a normal rate with trapped solvents coming out of the base, the clear is doing its job by staying soft to let the solvents out.

If this was my car, I will tell you, I could not get it out in the sun fast enough so the UV's can pull the solvents out, its the only way this will cure out and if you leave it inside you will increase the risk of de-lamination with either the solvents breaking adhesion of the base or the clear.

Brian and I may be all wet but here is how you can tell, put car in sun and in about 30 minutes your clear will get softer because the solvents are rushing out.
This car needs 7 full days in sun before anything is done and then long term we hope for the best.
 
#13 ·
i'm actually not painting anything on a vehicle guys these are plastic reel seats for custom fishing rods. But the same methods apply and I noticed in my searching that you guys were very knowledgeable and willing to help.

After all of the advice you all have given I do think that my underlying issue was that I was rushing the basecoat. I had watched a video about the KBC in which they spoke how fast they would flash and that they were almost able to be recoated immediately. They described waiting for the finish to go dull. I might have been rushing that portion. I've painted some test pieces again and given the base more time to flash between coats. we'll see if I still have a hardness issue.

Here are a couple I've painted thus far. The finish has come out great but the issues with softness won't due in something that will be abused like a fishing rod will be.
 

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#14 ·
Duplicolor primer? My bet is on that cheap crap being the problem. In a pinch, one weekend I bought some duplicolor wax and grease remover and it was the worst crap I ever used ,it caused more problems than if I hadn't used any at all. I threw the whole can away. Probably what you should do with the primer.
BTW, this is what happens when you spray a 2k paint over a 1k primer, solvents get trapped.
 
#16 ·
LOL, I read through that and glossed right over it! Good catch, that primer if not THE problem, it is certainly part of that "planets are aligned" we talk about. :evil:

Brian
 
#15 ·
Yep yep yep!

Hey Juice, you would be surprised how valuable tests are. I am big into spraying something and abusing it to see how far you can go. Spray some test panels VERY dry and VERY wet and see how they react.

I have to tell you, what you described with the amount of coats sprayed and over lap and all that, all that is OUT THE WINDOW when I see what you painted! OMG there is no way, no way you could have proper "overlap" when doing something like those pieces!

This is what I am talking about, Juice, I can tell you where the paint on the average car is going to fail first, you know where? It is going to fail at places like the where the windshield post meets the fender, where the rear roof pillar meets the quarter panel, you know why? Because that is where the quarter had three coats put on it and the roof had three coats put on it and where they meet got 6 coats! How about the center of the roof, the center of the hood and the center of the trunk. Watch for cars with failing clear, you will see that failure start in the center of those horizontal panels, why, because the painter came from one side starting out in the middle and ending on the side next to them, they then went over to the other side of the car and started at the center and out to the side next to them, thus putting twice as much material out in the center! This is why starting at the side and ending in the center, then going to the other side and starting in the center and ending at the side is the proper way to paint a roof or hood or trunk. But many painters don't do that, so they end up with twice the material on the center, twice the solvent, and that is where it fails first.

Painting those things is very difficult even for a seasoned painter, to keep it all wet you are going to apply too much, it's just human nature.

Scrap the junk primer, first off. But try to spray them drier, do some test panels you will see it's going to work better.

Brian
 
#17 ·
never waste quality products over that junk . duplicolor primer IS the problem . you can not mix cheap 1k products with 2k products. even good lacquer will not perform over that junk. sorry for your pain but i would trash the duplicolor and start over .
 
#18 ·
Thanks guys I had also sprayed some SEM auto primer but it was 1k as well. I recently picked up some epoxy primer that I'll lay down first then spray some drier coats of my KBC and top that with either the USC01 or a epoxy clearcoat I picked up to try. That'll keep everything in the 2k range or the world
 
#19 ·
Okay says so here was going to be my next process let me know if I'm screwing something up
Sand plastic part with 320 grit to remove mold lines etc.
Clean with hot soapy water
let dry
Spray mist coat of black 2 part epoxy primer. Let flash for a couple minutes
2nd cover coat of epoxy primer
let dry overnight
sand primer with 600 grit
wash with hot soapy water
dry
3 coats of kandy base coat. allowing time for flash
apply 3 coats of clear wait for tack but not strings.

How long should I expect to see full hardness on the USC01. I know it's a loaded question but with such a small part I wouldn't think as long as a car.

I'll do another panel with the epoxy clear coat as well.
 
#21 ·
That could certainly add to the issue. I had been putting the two parts into a small jello shot type cup, putting a lid on it and shaking the cup like it owes me money for a while.

On a side note I ran a test last night with two reel seats.
seat one was a seat I previously painted
seat two was the commercially avaialble painted seat that is hard as a rock.

I mixed the epoxy clearcoat and brushed it on various parts of both reel seats.
After 24 hours the reel seat I had painted and then put the extra epoxy clear coat on was harder but still able to leave a mark with my finger nail and i could pull the paint slightly.

The comercially painted seat that is hard as a rock was even freakin harder. The epoxy clear laid out nicely and I couldn't make a freakin mark on the epoxy until i got my paint can lid opener and forcefully scraped the test area.

Last night I sprayed a black epoxy primer over two test pieces after sanding with 220 grit sandpaper and cleaning the surface. I plan on painted them out tonight. 1 with kbc and usco1 clear coat and the other with kbc and the epoxy clearcoat. we'll see what happens.
 
#23 ·
I've got some more test panels on the drying rack right now boys. Both are painted with an epoxy tinted primer that was left to dry for almost 24 hours. Instructions state to topcoat within 1-24 hours. I sanded them down with 600 grit and then sprayed 3 coats of kandy base coat and 3 coats of clear. 1 clear was the epoxy clear i am testing and the other is the ucs01 clear.

We'll see if the primer helps hardness.
 
#26 ·
I've got some more test panels on the drying rack right now boys. Both are painted with an epoxy tinted primer that was left to dry for almost 24 hours. Instructions state to topcoat within 1-24 hours. I sanded them down with 600 grit and then sprayed 3 coats of kandy base coat and 3 coats of clear. 1 clear was the epoxy clear i am testing and the other is the ucs01 clear.

We'll see if the primer helps hardness.
That is a "re-coat window" where you can paint over it without even sanding. You can wait longer and just scuff it as you did without a problem, even months, as long as you scuff it well, it's not an issue.

Brian
 
#24 ·
That is really a strange problem. My experience with urethanes is they are super forgiving, almost impossible to screw up. And this is coming from the world's worst painter; use Harbor Freight guns, measure bye eye, pile on way too much paint at a time, use whatever rattle can stuff I can find on my old paint shelf for primer/color. Still get a great result most every time. I urethane clear just about everything including my wood carvings. My suggestion is the same as a couple above. Set the parts in the sun to cure. UV seems to be the key elixir to most modern miracle chemicals.
 
#25 ·
The clear that I sent you dries by temperature and humidity. A day or two after you apply it will seem soft and you won't be too impressed. By the time the seventh day comes along you will be impressed. Spray your color and brush clear over it. Hopefully it'll cure your problem
 
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