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What grit sandpaper do you guys recommend using on the primer before the first top coat goes on?

400 or 600

600

Thanks Blacky

The reason I asked is I wasn't sure if the 600 grit would be too smooth for the topcoat to 'bite' into.
But, also wasn't sure if scratch marks would show using the 400 grit.

My painter mate told me you want to use the roughest grade you can but still get all the scratches out - when we painted the Chev we used 320 over the guide coat , then 500. The 500 wouldnt get all the marks out so we had to go over it again with 600 so I figure that if 500 wont get it right then 400 has no chance.

Depends on what paint your using. For acrylic you don't need to use as fine a grit as you do for 2 pack. Acrylic 600, 2 pack 800.

This is how I did mine:

I used 320 for the first rub, then checked it for any imperfections before reguide coating.

Checking for straightness can be done by drying off the panel (air dry with compressed air) after the first rub, then using a prepsol soaked rag wipe over the complete panel section at a time, looking along the panel. Make sure when doing this your looking towards the light as this will show up any imperfections better, and look from different angles.

If there is any imperfections after the first rub, reguide coat it and rub it again with 320. If you use a fine paper on the first rub you tend not to straighten the panel , all you do is sand the surface and run over any highs and lows.

Make sure when doing big panels like doors and guards ect, that you use a long block as this will also help straighten the panels.

If after the first rub, you've checked it and are happy with how straight it looks, reguide coat and rub with a small block with 600.
After doing this recheck again with prepsol.

I then reguide coated and did a final rub by hand, using the palm of your hand not fingers (no block) with 800.

Once finished dry off panel and recheck.
Make sure panel is completely dry prior to painting. Give it a good blow down with air.

Hope this helps

cheers

malcom out of curiosity why the final rub useing yor hand and not a block, personal preference or is there a reason

When using any block no matter how fine the paper is, you will always get block edge marks. This is caused from the sides of the block digging into the surface your sanding. When I say digging in its very fine, and is more a problem when spraying 2 pack clear over base (metallic or pearl).

When using your hand for the final rub this eliminates any change of getting block edge marks and depending on your spraying conditions you have more of a chance of getting a perfect of the gun finish (no buffing) when using 2 pack.

On acrylic is not as critical because 99% of the time you will cut and buff the paint to get that deep gloss, but still, the better the base the better the finish.

Great advice Malcom
there is nothing like experience when it comes to prep
and paint
jay

thanks malcom
EKjay, and lots and lots of patianance

Thanks Malcolm

When you say "guide coat again" do you mean prime again then guide coat?

Just guide coat, not reprime unless you don't have enough primer on and you end up with a shit load of rub throughs after the first 320 rub.

Make sure when you guide coat, that its only a very light mist coat, as you don't want to be spending time and paper rubbing down a thick coat of guide coat before you even get to the primer.

What type of primer are you using
What parts are you painting

If your using acrylic primer its best not to rely just on primer to try and get things straight. You will need some sort of high build primer filler or a spray putty to alough for any low spots in the panel.

I've found in the past, when doing acrylic jobs its better to use a 2 pack primer as this tends to have better build and hold out (no sinkage) and it holds its gloss longer.

And yes RB is right, plenty of patianance. Rubbing down is not something you don't want to rush through.

Keep in mind what your doing hear is going to reflect what sort of job it looks like in the end.

Thanks again Malcolm

At the moment I'm on the engine bay, the rest is waiting till the weather warms up a bit.

I'm using spray putty till straight then I put a final coat of normal primer before the top coat.

I have done a couple of quick spray jobs ages ago, but I want to do this one properly Plenty of patience to be used up here