Im starting the process of cleaning up my frame and the underside of my 70. Unfortunately this is a body on job so I don't have the luxury of just blasting the frame, etc. Gonna be a pain in the neck (literally)

The underside and frame of my car is in pretty decent shape, just some surface rust, nothing to deep ... really no grime and gunk to deal with. I'm using a hand sander which is doing a good job and fairly quick. I plan on using POR-15 undercoating and the Chassis black top coat (overkill maybe?).

So my question is, since I'm using that product do I really need to sand down to bare metal or is my main goal to get it as smooth as possible? I realize the better the prep the better the paint but curious as to really how much sanding is enough?

FYI this will not be a trailor queen/show car. Just my weekend cruiser and local make shift shows. I am going for a "correct" restoration within reason of course but I do want a nice clean look.

Thoughts appreciated.

Dave

Dave, The Por-15 products are made to go over rust. I have heard good and bad with it's use. You might want to do a search and read up on it. Have you looked into using Eastwood Chassis black since you have it clean up? I have used both products and personally like the Eastwood line better, but have had good luck with the Por-15 product also. You don't want to get the Por-15 product on your skin from what I have read and you don't want to spray it without proper protection. As far as sanding it's what you feel is good and what look you are trying to achieve.
Ray

Thanks Ray. I'll do some research on Eastwood Chassis black. One reason I was leaning to the POR-15 is because I can brush it on while under the car and I figured trying to spray with rattle cans would be difficult for a smooth finish. Appreciate the info though, I'll do some more digging.

Think my next car I'll do it "right". Frame off to start and go from there. I know keeping the body on is alittle half-ass but realistically its all I can achieve at this point. My problem is I want it perfect in imperfect conditions :)

Why not separate the body/frame using small blocks to give you access to the top of the frame? This is what I did on my '66 and it worked great (Pics in my Signature link). Technically it is a frame off, since the body/frame were separated, but I didn't have the hassle by keeping them relatively close together still.

-b

You'll get very good results with the POR15 and a brush. It will probably be too shiny for your taste, so Chassis Coat Black is a good choice to tone it down. Again, good results with a foam brush.

I'd get some serious eye/head protection and head under there with a power wire brush and every other type of sanding tool you have and get the rust off. I just never felt comfortable leaving rust on. Good idea from Brandon on blocking it up....one side at a time possibly and install new body mounts while your at that point. Wipe it all down with lacquer thinner to get all the residue off and brush on your POR-15. Get the satin finish black instead of gloss. I don't think you'll need to top coat the POR-15 since it's outta the sun but it can't hurt either. Satin or chassis black not gloss.

Dave, I'm glad you asked for thoughts, because I have little experience in this, but need to do the same. I will do frame off, but our end expectation is the same. I have searched and read allot on here, and I have come to the conclusion that excessive frame prep is mostly for a correct restore or show cars. I plan on getting the grud and big rust off the frame, and using por or similar. For the most part, I feel everything I have read is mostly opinions on the product, and that a frame coated with it should outlive me and my kids.

I'll consider blocking the car up, that's not a bad idea. Currently I have on-hand: http://www.por15.com/POR15-CHASSISCOAT-BLACK/productinfo/S9G/

So you think I should just use the Chassiscoat Black and really not necessary to use the Rust preventative (red can)? I do want more of a stock look, not too shiny.

For the most part I will be able to get off just about all of the rust (maybe a smooth thin layer), its really not too bad under there

I believe if you read the POR 15 instructions, they want 2 coats of their products on (and BTW this has always worked best for me). And if I remember correctly they want you to put the chassis coat OVER there base (shiney) product.....so in this case I would do one coat of base product and then the second coat of chassis coat black.
Like they say...it'll out last you and your kids!

Exactly what I meant in post above. POR15 first, followed with top coat of chassis coat black to tone it down. You won't be disappointed. Also, this paint goes farther than anything I've ever used. Probably do whole thing with a quart each.

Gotcha .. thanks! Well gettin there lol Many layers of old paint to remove on the frame