filling the sinker marks correctly

[minkos]

Hello, i am having trouble mastering the most elementary of body filling tasks, that of filling the sinker marks on the trunk lid. The photo is of a '64 Pontiac Bonneville convertible, with the sinker marks circled. I used bondo over a thin guide coat of lacquer primer, sanded it to what i thought was smooth (didn't feel anything when running my finger over them), then hit it again a couple of times with the primer, sanded that with 600 and 1000, then shot the lacquer color. i could have sworn that i'd filled the sinker marks correctly but obviously i didn't. the bondo looks like it's too low.

any suggestions on how to do this properly? thanks very much.

[southpier]

is there a depression on the underside which needs to be filled?

when you sand, are you sanding with something (piece of anything with paper wrapped around it) to distribute the grit over the entire area, or with your finger concentrating the pressure in the immediate area over the depression? in effect just making a smooth depression.

[SterlingStang13]

Are you using a one part or two part bondo? Also make sure you're sanding with a block, and sanding in a cross pattern like an "X" so that you get an even contour.

[Foxer]

That looks like a pretty flat surface, so a sanding block should work. If there's a slight curve to the surface you have to "roll" the block as you go to maintain the shape.

Worst case you can grind the sink mark deeper which will be easier to fill. You want to use a 2-part putty for sure on a thick fill.

[Cato]

You need to shoot a real guide coat. On top of a coat of regular primer, MIST a coat of contrasting color primer or flat black. Do not make it a solid spray color - just sprinkle a fine mist you can see through. Then sand in cross pattern. The low spots will show the top primer and be sanded off the flat areas. Re-fill with Bondo, slightly raised above surface and repeat until all flat.

Edited January 21, 2015 by Cato

[jbwelda]

in other words: its more difficult than it looks. stupid putty shrinks with time and especially contact with the next coat of paint or primer, and come right back. very frustrating. like foxer says, sometimes you have to grind the problem deeper and then fill that, as backassward as that might sound. also the part about using a firm sanding block; don't know how long it took me to realize that's the problem with my prior technique, not using a firm block, even a coffee stick for close areas.

jb

[minkos]

excellent suggestions all, i will try them out. thanks very much.

[Krazy Rick]

Carefully enlarge & roughen the sink mark area, use Miliput ( Red box ) 2 part putty. slightly dampen the area, mix a small amount of putty, fill the depression and smooth using a damp finger & applicator ( piece of a credit card. let set & sand with 600 wet/dry sandpaper on a sanding block ( clothes peg, hard wood block, etc. ) .... and bit of warm water; this should take about 30 seconds if you filled the area fairly even, before letting dry ) .... Grey Primer coat, super light black mist/guide coat lightly 600 wet sand to check area for high/low spots...... ( chances are good it will be perfect at this point though ) - now paint 1! - good luck

[SterlingStang13]

  On 1/21/2015 at 6:11 AM, minkos said:

excellent suggestions all, i will try them out. thanks very much.

Let us know how they work out for you!

[Snake45]

All of the above techniques will work. But I've found the easiest/quickest/surest way to fill depressions of this kind is to rough up the area a little with a Scotchbrite pad, steel wool, or maybe #400-600 sandpaper, then lay a coat or two of superglue over the dent. When it dries, block-sand it (start with #320, then #400 or #600 to smooth), then prime and paint as normal. When sanding cured superglue, a sanding block is ESSENTIAL.