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A case for epoxy primer

Larry DeCamp

Well Known Member
I have been agonizing through prep for solvent borne base/clear paint. The problem is sanding over imperfect flush rivets and imperfect dimple perimeters . Sanding will strike through the primer back to bare metal, or expose the wash/etch primer which the paint maker says should be sealed prior to the finish coat.

Regardless of brand names, wash primer , etch primer etc. need to be covered with a barrier primer before finish coats. This requires a two step repair of each tiny flaw. I am joining the epoxy primer advocates so a “strike through” repair is a single puff of epoxy, awaiting another attempt to feather the edges without striking bare metal again.

Any wisdom you have to offer is welcome 😊
 
There are subtle and distinct differences between brands and products so I think in the first instance I would check the technical data sheet for the specific primers that you are using. One data sheet that I have seen for etch primer (Nason) states that it is not suitable for being overcoated with epoxy primer.

Another suggestion is to test a spot repair made using just the final primer sealer. Once it has dried properly (overnight) try an adhesion test with some strong self-adhesive tape and see if you can pull it off. Since the repair is such a small area of bare metal it could be OK.

Good luck!
 
So, are you sanding through the clear, base and primer? If so, suggest that you change your sanding method. Color sanding an airplane is hard for the reasons you mention, so the approach to sanding needs greater care. Not sure if that is what you are asking about or whether new primer needs to go over the areas broken through. To do it right, the paint maker is correct, a new barrier coat is required, though many roll the dice and skip it for small areas.

If sanding is going all the way through clear base and primer, whatever you are doing is being done too fast or too aggressive. Suggest using soft density sanding sponges - NO hard blocks. What grit are you using. Are you doing this with a power sander?

If you are sanding just the primer before base clear, please explain why and will give further pointers. Epoxy primer does not need sanding if top coated within open window. Are you taking out dust issues?

Larry
 
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Blow through

Agree with Larry.
Change your method. Less aggressive. Finer sandpaper. Wet sand. Checking often.
One trick is to tape areas where it happens. Rivet lines, screw lines, edges, corners. They all pose risk. I usually sand them last and only enough to accomplish the task. If I blow through, I have a favorite brush just for that purpose. I mix a teaspoon or two of whatever paint and apply a brushed repair. It's so small, I have trouble finding them.
 
Clarification

The base/clear instructions say the wash/etch primer SHALL BE 2K primed/sealed under the base coat. In the process of assuring this 2K sufacer is ready for base coat, it recommended to wet sand with 600 to assure optimum results. In that 600 sanding process, the 2K can be the removed over a high spot exposing wash/etch primer, or worse, exposing aluminum. Thus, you need to start over on those spots mixing, spraying both primers and again, attempting to feather the 2K surfacer without striking thgrough 😡

LR172, fwiw, I had a good talk with Barry at SPI. I will be using his epoxy hence forth. A strike-through will only require one coat with air brush and base can go directly onto it with no sanding within 3 days. Thanks !
 
Most epoxy primers can be mixed as a seal coat and sprayed, followed up by paint directly after without sanding. When doing cars, I would seal it, then paint about an hour or so after the final epoxy seal coat was applied.
 
The base/clear instructions say the wash/etch primer SHALL BE 2K primed/sealed under the base coat. In the process of assuring this 2K sufacer is ready for base coat, it recommended to wet sand with 600 to assure optimum results. In that 600 sanding process, the 2K can be the removed over a high spot exposing wash/etch primer, or worse, exposing aluminum. Thus, you need to start over on those spots mixing, spraying both primers and again, attempting to feather the 2K surfacer without striking thgrough 😡

LR172, fwiw, I had a good talk with Barry at SPI. I will be using his epoxy hence forth. A strike-through will only require one coat with air brush and base can go directly onto it with no sanding within 3 days. Thanks !

I am funding Airbrush can be pretty useful for fixinerrors
 
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