Sanding primer - can it be too smooth?

[Matthew Barnes]

In the long process of shooting epoxy primer on a bare metal resto.

Sanding procedure as follows:
- 180 blocked
- 360 / 400 blocked.
- 800 wet
- 1200 wet.

The 800 wet leaves a smooth finish. The 1200 / 1500 makes it shine.

Is the 1200 / 1500 a waste of time?
And more importantly, will the smooth shiny 1200 grit surface effect topcoat adhesion?

Thanks.
Matthew

[KevinP73]

Anything beyond 600 is a waste. Your paint requires a certain amout of mechanical bonding to adhere properly.

[962porsche]

when it comes to epoxy primer just what type are you referring to ?
there are medium build epoxy primers and low build epoxy primer that Is used for things like getting a filler primer to bond to a substrate and to replace say the galvanized coating that may have been removed in stripping a panel to bare .

with most all E-primers (low build ) you would not want to sand the surface it's going over/on with less then a P grit 800 wet . or P grit 500 dry .
in the States we use the P-grit sand paper system .
if you look at the sand paper were the grit number is you will see on most there is a P in front of the grit # .
if your over seas a wet grit 600 would be our P grit 800 or close to .
so if you look at your TDS most of the time it will have the two different grits to use listed .

when they give a grit of say P800 that does not mean you have to take the hole area your applying product to down to P800 .
that is what is called the grit you want your blend area AKA BACK SANDING to be for the over spray to land on and stick to .

because most low build epoxy primers only require one to two medium coats (more is not better) then going finer with your sand grit is pointless .

say you get your panel / panels or car back from the blaster .
you would want to prep it for a e-primer your case epoxy .
you 1st would want to sand with 180 or 220 grit to give a uniform substrate for the primer to go over .
you could go down to a 320 to 400 P- grit but there is no need if your using a build primer over the E-primer .

to sand the bare metal so it looks like chrome is pointless !
many E-primers you can not just top coat you have to 1st seal with a sealer or use a filler primer.
because with many E-primers you have to use a mid undercoat product there is no reason to sand with suck a fine grit . it's a lot of money in product and a lot of time for no reason .

if you are using a epoxy primer that you can top coat with out having to use a sealer or filler primer over 1st then stopping at a 400 to 500 wet or 320 to 400 dry is more then fine .
a low build primer will bite into the substrate with out sanding marks coming back later .
when ever you buy a product always get a TDS with and about the product your using .

[Matthew Barnes]

Thanks for the input gents.
Appreciate it.
M.