Underhood Black – 2 Questions

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    Hi, I’m new to the forum, signed up to hopefully get some quick help with a problem I ran across over the weekend.

    My first question is about using the Underhood black (rattle can) in conjunction with primer. I have used this paint a handful of times in the past but only on small things and I never bothered to use a primer. Over this past weekend my project was to paint my power brake booster and some brake hard lines. Since these were all bare metal and I wanted a durable result I figured it would be wise to prime before painting. Once I started applying the Underhood Black after the primer 2 things were quickly evident:
    – I was going to need a LOT more paint than I was used to using w/o primer
    – The finish was not going on smooth

    The finish was very rough in the beginning so I started putting on heavier coats of Underhood black and this helped but I was not able to achieve the finish I’m used to with this product. Previously I’d always been able to achieve a perfectly smooth finish – no orange peel. But yesterday my booster turned out like this:

    It’s a little hard to tell in this pic but here are two brake lines I painted with the underhood black. The black one in the middle was a test I did over the original brake line finish (simply to see how I liked the look of this color for the brake lines). The black one on the very top is a line that I stripped, cleaned, primed and then painted. It’s significantly more rough than the line which had ZERO prep.

    So, did I just use an incompatible primer? (Rustoleum automotive primer) Does the primer need to be sanded before top coating? I’m not sure how best to proceed to get the best durability and best finish. I already wasted about $30 in paint yesterday as well as many hours in the garage, plus now I need to strip all these parts and start all over. Hopefully someone will have some suggestions to point me in the right direction.

    My second question is about using the paint that comes in the quarts opposed to rattle can. Is that stuff easy to work with? I have a cheap HVLP gun that I’ve been practicing with, I’m not good enough to spray quality automotive clear coats yet but wondering if spraying the underhood black from an HVLP is as easy as the rattle can and maybe it’d be more economical?

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