I've done some searching and couldn't find anything real conclusive. I was going to Por my floor boards which are just surfaced rusted but I wanted to make them look good for when I sell the car with no interior, also to protect it from future rust. The floorboards right now have a mixture of old paint and rust, should i take them down to bare metal then apply the Por or just paint it on as is. Because Por 15 adheres to rust correct? So if it adheres to rust then I should be able to paint it diectly on with any metal prep.

Probably better to take it to bare metal. It will look neater when you paint. Especially if you are not covering them.

I've painted metal I've ground down to bare, and also minor rusted panels with POR. It does a remarkably good job over rust. I wouldn't spend all the time to take it to bare metal. Just treat the rust with their metal ready and paint over the treated surface. In fact I recall POR over rust holding up better than POR over bare.

I have been using the rust treatment spray from NAPA on some spots on my floorboard and on my undercarriage and it works just as well in my opinion and is alot cheaper.

I would just knock off any loose rust or paint and POR right over it. In my opinion, POR is for areas that can't be sandblasted/stripped properly, and if I recall correctly they say that it doesn't adhere as well to clean bare steel.

Originally posted by snydes:
and if I recall correctly they say that it doesn't adhere as well to clean bare steel. They do say that, but I put some POR15 over a small patch panel that was competely bare and it stuck ok. It wanted to run if it was too thick, but it took a nice coat.

For clean bare metal, you need to etch it first with Metal Ready, which is also sold by Por.

I've used it on rust and bare metal and it sticks fine if you use the metal ready to prep it. It will look rusted when you are done anyway and white powder all over. It will stick to this just fine as por15 states in there instructions.

i have had great success with POR by removing the loose, scaly rust so that there is just a tight layer of oxide left on the surface. then i clean it really well with lacquer thinner, let that dry off and then brush on the POR. i have areas that were done 8 or 9 years ago that remain unchanged. it does not form a good bond on shiny metal but works great on unrusted metal that has been grit blasted or wire brushed.

However, do not use Metal Ready on cast iron parts. It will adhere to cast iron just fine as long as it's good and clean. I suspect this may be one of the reasons why some people can't get good results. They're using it on cast iron parts like rear end housings and brake drums and they're soaking those parts with Metal Ready which gets down into the pores and causes problems. For cast iron, just degrease it, dry it thoroughly, and apply the coating.