Does Anyone Know why paint wont to stick to an AR Receiver!?

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Forcesbeyondcontrol
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Does Anyone Know why paint wont to stick to an AR Receiver!?

Post by Forcesbeyondcontrol » Thu Jan 15, 2015 6:12 pm

I decided to build my son an AR-15 for Christmas and his is a die hard Red & Black fan. So I decided to step out of the box with the finish on his upper and lower. Both are Billet Aluminum and were finished from the factory with the normal Black coating. I cleaned them with Brownell TCE degreaser and made sure they were dry. I then sanded the coating down using a 400 and 600 grit paper, keeping it smooth but having something for the paint to adhere too. I then spray a light coat of aluminum color dupli-color 500 degree engine paint and allowed them to dry for several days. I then sanded them down with the 400 grit paper and made sure to blow off any dust, etc.

The next coat was dupli-color Metalcast engine paint which gives them a Red anodized look. This stuff dries pretty quick so I gave them several light coats over a 30min time frame. I then allowed them to air dry for approximately 3hrs and then baked them at 250 degrees for an hour. Once it cooled I allowed them to sit for 7days until I began to install the parts into the upper and lower. They both came out looking awesome, you can see where I sanded through the silver and exposed the black. It gave it a distressed look and my son couldn't be happier.

Here is the problem!!!!! When I started to install parts I applied some blue painter's tape to the majority of the lower to keep from scratching it when I was installing the parts. When I began to remove the tape it pealed the paint in several areas!! #-o

Does anyone know why? Can you not paint over the black coating that comes from the factory? I know that his will not be as durable as some finishes and I am not worried about some scratches happening as I can touch them up, but when it peals off that just aint gonna work. Any help would be appreciated as I want to complete this for him the way he wants it.

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draggindakota
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Re: Does Anyone Know why paint wont to stick to an AR Receiv

Post by draggindakota » Thu Jan 15, 2015 9:27 pm

Those are hard coat anodized. Supposed to be smooth and hard for good wear resistance. To get the best finish you would need to get down to the bare aluminum and then prime and paint. You may be able to scuff it up enough to get a good bite with some self etching primer. Hit that with a coat of high build primer and sand smooth then top coat it. I see you didn't use any primer so that played a big part.
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ipscscott
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Re: Does Anyone Know why paint wont to stick to an AR Receiv

Post by ipscscott » Fri Jan 16, 2015 2:09 am

Ryan, the easy button is call me. ;-)

Anodizing actually makes a good base for paint as-is and is better than bare aluminum for adhesion. A little more texture is a good thing so a light hit in the blast cabinet, just to rough it up a touch is my usual process. Your sanding to 600 grit did the opposite of what you wanted and made the surface too smooth for good adhesion. I follow up the blasting with a thorough degreasing and then a light coat of epoxy primer.
The lack of primer is also big factor. Secondary to that would be something called "intercoat adhesion". It sounds like you pulled the silver off as well and not just the red but if that's not the case and just the red came off then you likely let the silver cure too long before the next coat (red) and it became too hard for the subsequent coat to adhere well to. Read the can and it will tell you the recoat widow.
Lastly, that can be a reasonably durable finish IF you do your prep work properly and if you top coat it with a 2 - stage urethane it'll actually hold up surprisingly well.

BTW, skip the high - build primer on most gun stuff. You don't want to fill in engraving and such and you also typically want to keep your coating as thin as possible to avoid tolerance issues.

If any of that doesn't make sense call me tomorrow and I can try to explain.

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Forcesbeyondcontrol
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Re: Does Anyone Know why paint wont to stick to an AR Receiv

Post by Forcesbeyondcontrol » Fri Jan 16, 2015 9:09 pm

I appreciate the information from you both. [smilie=cheers1.gif] ipscscott I will send you a pm you a question 2 - stage urethane.

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