Prepping roof for rust prevention before headliner install.

POR products work well.  I did my engine bay with it.  It is used on frames as well.  It is a tough material.  Check the mfg for use in this application.

Any of the rust removers or rust neutralizers will help (Loctite, Navy Jelly, or phosphoric acid aka concrete etch).  In this case it is difficult because it is a roof and the liquids tend to fall to the floor.  You can also sand it with coarse grit which might be easier.  If treated with a liquid it will still need sanding.  Once the rust is knocked off then it needs paint.  Spray is easy but brushed on POR works well as Jimmy suggested although it can leave brush marks.

Thanks guys. I ordered some POR15 brush on.

There was a past thread where they used foam core board. Glued the head line to that. It gave a nice smooth finish with out needing to sand the POR 15. Less of a mess.

I just ran across this thread, suggesting to use magnetic sign material and glue the headliner to that. Seems kinda brilliant!
https://pantera.infopop.cc/topic/headliner-2

After obtaining a solid and clean mounting surface I covered the entire cabin roof with a single layer of Dynamat.

I used a heat gun to preheat the roof to enhance adhesion and covered all seams with 2 inch HVAC aluminum foil tape. Lots of roller rubbing to remove air bubbles and maximize adhesion

for headliner I chose a commercial foam backed headliner material in black and aerosol 3M headliner adhesive.

I successfully did a minimal amount of masking, as I always used a cardboard edge guard to confine the spray as I proceeded gluing the entire piece, starting at the center of the windshield.

I used a heavy steel straight edge to hold the rear of the headliner on a suspended plywood shelf. Followed adhesive instructions carefully working section by section down the center and to the sides

Cut the excess fabric from the purposely oversized headliner and did a lot of firm but gentle pressure rubbing to maximize adhesion.

car now has about 1500 miles on her, about half of that in 90°-105° California sun. No sagging or smell from the Dynamat

Larry

+1 on the phosphoric acid. If you live in an area where there is any dairy farming you can also use milkstone remover, used for cleaning out milking machines. Can be bought from farming supply shop, and is around £12 per gallon in the UK , so probably half the price in the US. Water it down about 50/50 then spray it on with a squirty bottle.

Thanks Phil. Good tip. We do have dairies around here. I went with the much more expensive POR15 option though but this is good info for next time.