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loosing adhesion between primer and basecoat

#1
Let me start by saying I spoke with Barry on the phone earlier this week and could not have been more impressed with the level of knowledge and the willingness to share as we spoke. With that being said even though I was taking down notes I failed to fully capture exactly what I might have been doing wrong so here goes.

I have just recently started painting some smaller objects and have noticed that I'm not getting great adhesion between my primer and basecoat. I am able to chip the basecoat off of the primer and with my fingernail chip more and more off.
If I remember Berry correctly I think i was screwing up the process so I'll outline it below.
I'm using all HOK products at the moment(don't hate I hadn't found SPI yet). I'm also applying with an airbrush but am able to get a wet coat through it.
After sanding the part to 600 grit.
1.I apply my KD3000 hybrid epoxy primer at a 4:1:1 ratio medium builder surfacer/sealer.
2. After an hour I wetsand any imperfections, wash with soap and water, and let air dry for 30 minutes or so.
3. Apply BC25 or BC26 basecoat depending on what midcoat requires(KBC)
4. Allow proper flash times
5. Clear

If I remember correctly I think Berry had mentioned a couple areas.
1. I wasn't applying a sealer before the basecoat so there wasn't a chemical bite happening
2. applying the kd3000 as a sealer but then wetsanding it and washing it was defeating its ability to do its job
3. setting the part out in the sun will help cure everything up faster.

I had been wetsanding because I was getting some dryspray when applying the primer. This was more my fault and ignorance in not slowing down enough. Think I still had rattlecan application on my brain.

I do have a small detail gun with a 1.2 tip that I could apply the sealer with if you guys think that it would be better then the airbrush.

The parts I'm spraying are small roughly 3-4" and about 1" in diameter. You can see what I mean about a detail gun being overkill.
Maybe something like an Iwata lph80 would do good.
 
#3
Since the KD3000 open time is just 4 hours maximum, you are better off putting a coat of base or SG100 on it first, then sanding the nibs out.
 

Barry

Paint Fanatic
Staff member
#4
I remember the call and this is really a tough one as, you are not doing a normal area (car).

Its has to be one. of the three:
Solvent trapped in first coat of base, breaking adhesion.
Dry spraying and not creating adhesion due to gun??
Or parts wet-sanded and not allowed to set long enough to get cleaner or water out of sand scratches.
I would lean to the painting to soon than waiting to long idea, especially the epoxy being wetsaned in an hour, Id never thought possible.

This is a tough one.
 
K

keith_y

#5
IMHO, kd3000 is garbage. It says it's an epoxy/urethane hybrid. It dries and sands like cheap urethane. Throw it away and use SPI epoxy reduced as sealer. It's unbelievable how nice it is. Never seen its equal.
 
#7
Thanks guys for the responses. What I'm painting is small and as a new painter i tried to stick within a system. I have actually been happy with how well the KD3000 adheres to the graphite reel seats I'm painting and how easily it sands. I am only using the primer/sealer as a way to get better adhesion and smooth out the surface before basecoat.
In all honesty if I could spray it as a primer let it sit overnight, wet sand it then go straight to color then that would be best for me. I need minimal build.
 
#8
i actually paint fishing rods for a custom rod company. couple few thousand a year. if you want minimal build the best thing you can do is shoot a very thin coat of spi epoxy primer down then go right to base.
 
#9
It does seem like something with a longer open time would be better. I'm not familiar enough with the HoK primer lines to say, but they must have a more conventional epoxy if you don't want to use SPI.
 
#10
It is not that don't want to use SPI at all I simply have a quart of KD3000 that will last roughly 300 parts. I'm only really using the KD3000 for adhesion of basecoat. The part is pretty smooth to begin with.
 
#11
Juicegoose;n85405 said:
It is not that don't want to use SPI at all I simply have a quart of KD3000 that will last roughly 300 parts. I'm only really using the KD3000 for adhesion of basecoat. The part is pretty smooth to begin with.
Sometimes we answer our own questions. You are only using this product for adhesion of basecoat and you have bad adhesion of the base coat. Also, if it is smooth to begin with, why are you wet sanding again?
 
#12
The parts are a nylon/graphite composite mix so there are mold lines that have to be removed and small itty bitty fibers sticking out. Spraying the kd3000 gives me good adhesion to the substrate and then I can sand it back to create a smooth surface for metallics etc. The adhesion issue I was having I think was less about the product and more that I am a new painter and was wetsanding the primer/sealer. I think that alone was killing some of the chemical bonding that needed to occur. i never had an issue where the paint of clear would flake off and certainly haven't had an issue where the primer/sealer is coming off. Out of pure newness to painting I would take a painted part and hit it with something. If it chipped it would chip the clear and basecoat off but the sealer wouldn't break free from the part. So i went searching. Maybe that is normal. I have no idea. I'm just trying to make it as best as I can. Barry helped a lot when I spoke with him and in the future I will be looking in to SPI but for now I've got to learn and work with what I have.
 
#13
the kd3000 since its not a true epoxy will never have the adhesion of a real epoxy primer/sealer. the only advantage to the kd is that is fast. your doing your dtm primer and surfacer in one step. what you have is a product that's not as good as a real epoxy and not as good as a urethane 2k primer because its neither. not saying its a crap product but it is what it is. its a compromise all for the sake of speed. if that's what your looking for then super.
 
#15
ITs also a tough substrate, Graphite and Nylon both have self lubricating properties so part of their job is not allowing anything to stick to it.Maybe its just dry sanding instead of wet now. I know we had plenty of discussions about cutting and buffing and some prefer wet and some dry.
 
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