Ok, read the previous post a number of times, take two asprin and call me in the morning. Over sanding the filler is with out a doubt the most common mistake of a beginer. Not giving it the respect it deserves and filling too little is the second most common mistake.
The secret, are you ready for this, I am telling you how the water torture trick works, how the lady disapears. Let me say, I can tell if plastic filler work is straight by looking at it, JUST looking at it before it is primed. That's right, not even touching it, just by how it looks from across the room, I can tell if it is right or not.
The dead give away is how the transition from filler to the surrounding metal LOOKS. It should have a transparent edge, sometimes an inch or more of this literally transparent look. The color of the filler should change from the filler to this transparent area. This color change is the filler going from full thickness of 1/8" or even down to 1/16" which is the same color as if it were an inch thick. But in the inches up to the bare metal it is going to be so thin that it will change colors, up until that magical transparent look right before the metal.
To achieve this you sand with fine paper (we are talking the "Skim coat") very slowly at the begining. Until you get a feel for it, take your time, slowly block it taking time between a few strokes to feel and look at your work. Try to run the block off the filler onto the metal with a fluid motion. When you start seeing that transparent look, really slow down pay attention.
As far as the epoxy, first off, you could apply that first then put the filler over it. If you are not familer with this procedure let me tell you it is a standard of the industry. I know you have heard do not apply filler over paint, or primer. HOWEVER, that is not epoxy primer, it is a recommended procedure by most every manufacture.
The k36 will fill some imperfections and waves. If you follow the guide lines I have writen you will not need more than four coats or so of the primer to take care of it.
Remember, give it the respect it deserves. It is VERY common to have many, many small dings all over the back of that cab. If you guide coat it by spraying a light, VERY LIGHT, mist of primer (a rattle can is fine being you are sanding it off) and using a block,sand it off. The dings will show up very fast because the primer will remain in the low spot after you block.
It is VERY common to end up with a skim coat over a large area taking care of many small dings. Trying to fix a number of small dings in close proximity is much harder than just coating the whole area with a THIN coat and sanding the majority of it "transparent".
Have fun and post with any questions.
Brian
