What to do with primed areas that sand down thin?

[Cpt Custom]

Currently tidying up the underside of Lily's bonnet before fitting a new soundproffing kit.

I've previously rubbed the dodgy areas back to bear metal, treated with rust eater and applied several coats of primer. All going well until this afternoon when I went at it with wet and dry to get it ready for applying the final layer of primer. I used 400 and 600 grade, which I think is perfectly okay and was extremely gentle flatting back, but some bits have gone a bit thin. I'm not back to bare metal, but the primed areas look a bit grey if you know what I mean.

My question is should I give these 'thin' areas extra attention in any way or should I just apply a single final coat everywhere as I was planning to do and hope that when I then get top coat onto it everything looks okay?

Ideally, I'm hoping to do it tonight so any quick advice from anyone who happens to be online would be really appreciated.

[DT1]

...and hope that when I then get top coat onto it everything looks okay?

This is from the man who shot me down for suggesting that the finish on the front valance didn't have to be perfect because it was hidden by the bodykit.

If you are applying another coat of primer before the topcoat it shouldn't be a problem.

By the way I find that scotchbrite pads are quite a good alternative for preparing primer for the final coat if you don't have any overruns or other major blemishes that you need to remove.

[Cpt Custom]

Thanks Colin!

[Cpt Custom]

Really getting hacked off with this rattle-canning malarkey now. No matter how gently I go at the final flatting back before attempting to put on the top coat some bits just keep going back through. There are so many high spots under the bonnet it's unbelievable. I even went as far as taking a photo of where they all were, then applied a few more coats of primer and let that rest for several days before gently trying to smooth it off for top coating ... and I'm still finding some bits wearing through.

I'm using lots of water and working with 1200 grade wet and dry so I'm at a loss as to what to do next. At this rate I'll still be priming and flatting back come Christmas! Has anyone got any suggestions as to how to get beyond this problem?

[DT1]

What high spots are you talking about? Runs? Some of those pictures would help.

The top coat of paint itself will create the smooth finish so there is no need to go overboard with sanding the primer down.

[Cpt Custom]

Not runs Colin, just on some of the curved sections that run around the soundproofing pads and other bits like the bonnet edge and what looks like small spot welds. Nothing major, it's just that there seem to be an awful lot of them that it's almost impossible to flat the overall areas back without rubbing through the primer. Like I say I'm being as gentle as I can, but it seems an uphill struggle.

Wasn't aware that the top coat would be so forgiving ... do you think it would cover the 'thin' areas okay? I mean it's not like I'm going back to shiny metal, but the areas look grey as opposed to white (using white primer as you'd expect).

[DT1]

Not runs Colin, just on some of the curved sections that run around the soundproofing pads and other bits like the bonnet edge and what looks like small spot welds.

Mmm, I know where you mean but without pictures it hard to say what the problem is, maybe the metal isn't as flat as you think it is. You really only need to remove any burring on the surface of the primer and feather the edges where you overlap where it hits the paint that's already there.

Wasn't aware that the top coat would be so forgiving...

You'd be surprised, I only go to 600-800 grade for prepping, as long as there is no heavy gouging the top coat will smooth out any fine lines from sanding (after all that's how keying works). I only use the higher grades for for feathering and finishing.

do you think it would cover the 'thin' areas okay? I mean it's not like I'm going back to shiny metal, but the areas look grey as opposed to white (using white primer as you'd expect).

Along the bonnet edge you really want it white.

[Cpt Custom]

Really struggling to get any decent shots Colin … even my Nikon is struggling with the white.

Took a few though which I hope will come across okay, so here goes …

First, to give an idea of the area I’m now working on …



Now some examples of what I’m talking about. Even if you can’t see too well how bad the problem is at least they’ll maybe help give a better idea of the bits I’m having problems with …







And on the top …





At least there are fewer problem areas this time around so I am making some progress.

I might have one last go at putting some more primer down on just the areas that have worn through. Then if they still come back through when I flat them back I might just put on top coat and hope for the best. What do you reckon? And don't worry there'll be no repercussions if it goes wrong! My call at the end of the day, just curious what you think.

Anyone else wants to chip in feel free.

[DT1]

It's all edges...makes sense now.

Are there imperfections in those areas? If not you just need to be a bit less vigorous, edges can be a pain.

Just think you're on a learning curve. I think you are improving your technique as you're getting less of those bits.

Watch out for, 'Just one more to finish', if it looks OK just leave it alone.

[Nate]

try putting 2 or 3 coats on before you flat it off, so there is more paint there to sand thru

[Cpt Custom]

Job done ...