primer compatibility (dupont 131s fill 'n sand)

[Tscott38]

The first car I painted, I used Dupont varathane acid etch primer with Dupont 131S fill 'n sand as a primer surfacer.  Years later later, I primed my '68 Charger with a PPG epoxy primer instead - I used DP40 or 50 I think.  I proceeded to use the Dupont fill 'n sand 131S over it just like before as a primer-surfacer.  I put one coat - it went well and then stopped.  For 16 years.  Ran out of time to work on it.  The car has been garaged the entire time and is showing no signs of rust anywhere. 

The project has restarted and I am considering 1)sanding it all off again and starting over with DP50LF and K36 or 38 as a primer surfacer; or 2), just shooting a few more coats of the PPG K38 over the Dupont fill 'n sand 131S prior to me startign my block sanding.  A few years ago a painter told me that the fill n sand is old technology and its best to get it off of there.  I dont know enough to disagree.  Since its in decent shape, what's the harm in leaving it?  Is it in any way incompatible with the K36 or K38 PPG product?   

My plan is to do the primer and primer surfacer myself.  Lots of block sanding/leveling I think I can do.  The sealer/color/clear
final painting will be done by a pro with the proper equipment.  Anyone have any thoughts or suggestions that could help me out?

[bill440rt]

Your painter friend gave you some good advice. 
It was a step back to use Fill-n-Sand over the PPG epoxy.
DuPont Fill-n-Sand is old school, lacquer-based primer. Can you still buy this stuff? 
It was OK back in the day, but advancements in paint/primer technology have left this stuff in the dust. Since it is lacquer based, it will be prone to cracking over time.

The DP epoxy is the best of what you mentioned to use over clean bare metal. Great primer. You can sand it & do your body filler work directly on top of it. Then, a 2K filler primer can be used over that.
Leave the Fill-n-Sand for small parts, spot repairs, etc.

I would either sand the FnS stuff off & re-coat with DP, or strip it again down to bare metal & re-prime with DP. 

[Tscott38]

Thats what I needed to hear.  I'll get the Fill n sand out of there.  I am sure I am going to sand thru the old epoxy though in the process, but I'll use the DP50 again.  Thanks..

[Dino]

Look at it as an opportunity to block sand your car again!   

Don't try to preserve the epoxy or you will be sanding with that goal in mind and that's not a good thing.  Sand it with the intent to start over and block it until it is ready for primer.  You will have spots of bare metal, primer and filler and that's fine.  In the end it is worth doing all the extra sanding.  I have seen way too many people rush into painting their cars only to be disappointed when it looks like wavy gravy.

Put in the time and get the best products you can afford.  Do it once and do it right.   

[bill440rt]

Look at it as an opportunity to block sand your car again!   

GREAT idea, Dino!

Just make sure you block the FnS stuff completely off. Think of it as a pre-existing guide coat.