My primer (Color Horizons ML011) says that it can be used as a primer or sealer w/ add of 1part Red. What is the difference between sealer and primer? When and where would I want to use this as sealer? Butt Dumb about this stuff. My last job was 15 yr's ago new, aluminum 2part paint w/lots of sanding on the clear coat saved it.All help appreciated. (PS-this is a high fill/sandable that can be sprayed over paint and/or bare metal. Perfect for my needs!)

A sealer is a product that (allegedly) separates the new paint from the old substrate, preventing the solvents in the paint from lifting or wrinkling old paint especially on the edges of repairs. A true sealer is sprayed on right before paint, usually 10-15 minutes dry time before paint. Primer bonds to metal (sort of) and filler is just that, it fills the deep scratches and minor low spots from the repairs and sands easily to a fine finish (400-600 grit) for paint prep.
The nice thing about sealer is that you can spray on $20.00 of sealer and most problems that may develop will develop at that point rather than right after you catalyze and begin spraying $500.00 worth of paint.

Thanks Steve. I know a little more now. Should I be gathering lots of sand paper for the eventual?

What color? Bright or light solid colors 400 wet is fine, dark or metallic go with 600 wet at the end.
Remember, get it flat, then smooth. No point in worrying about smooth when it's all wavy or the wrong shape.

I'm going original L80e white. Probably the most forgiving color for a novice like me. Good info for the final sanding (color sanding?). I wouldn't have known that. Thx again, Steve. I'll post pic's when painted; probably late Aug. I'll do the spoilers and valances next week, then build the temp paint booth the week after, then..........

is that white ?(L80e)