Thread: Filling Grinder Scratches

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3m is always coming out with new abrasives. their new scotch btide discs are getting better. they leave a really nice clean suface to work on. i use them on surface rust. for the first time in my life removing old paint or sanding old paint will not be a problem. one day in the blasting booth and they'll be picked clean. plasti grit is the way to go.

one thing to keep in mind usin the newer style urethanes is that even tho they are high buidl, do NOT spray it heavy, as in 'fill in scratches"!! , if sprayed properly it wil build on its own, even if scrathec are stil seen afterward they will sand out, leavi na smooth surface, hammering the primer on will cause em to swell ater, ijust spent the entire morning redoing a repair one of our new guys did thurs, finishing plastic work with 80 then decidnin glazeing andrepriming would make him stay late so he"filled "em with Nason 2k.....looked good til the bakecycle, then every block an DA scratch in there showed right back up under the shiny cadillac red...

yes i don t like thick primer or filler less is better. and if the sub strait is soft like plastic is can be bad .but if you try to fill scratches or grinder marks and sand it the thinner in the top coats will make the repaired edges move.and so will the deep scratches in steel this make it a pain. on bumpers i did all work to220 or 320 plastic the thninner dry much diffrent on fillers and plastic i did all my work as good as i could so that this did not happen and not try to hide bad work . when i could i would strip it down to one sub strait this keeps the thinners from swiming around and finding edges to pull up old paint work or poor body work and i guide coated all my work and block it to 220 to 320 before primer went on

I've been stripping paint with 36 grit for about 15 years, shooting 3-4 wet coats of two part urethane primer, then guide coating and blocking with 360, and painting base coat clear coat on top. I've never had one come back for sandscratch swelling.

yes but you know when to stop? some new guy with 36 on a grinder ?? i strip cars and trucks down to this way for over25. years but i take off the top coat not to the steel and if you are grinding on steel with36 why??would you let some new guy work on a car with 36 grit on doors or truck lid hood?? the frist time you slam the door the skin would fall off

Tell him not to grind the edges, and stop ginding when the paint is gone.

My approach is as simple as I can make it. Find a way to do things that doesn't use a lot of extra hours, and it works every single time.

I can't make a living if my work keeps coming back. Do it that same way every time without changing anything.

Guarantee my work as long as he owns it.

If someone wants advice, tell them what is working for me.

There are a thousand ways to do anything, and each person you ask will have their own methods. I don't care if someone chooses my method or not, I'm just offering it.

36... to 60 to 120... to 180 to 240... then 320 if you like the look stop at 180 or 240. There is no short cut to prep. You'll always see it if you do.

Absolutely more is not better. Proper prep to the surface is very important. The question originaly was he had a surface that looked like it had grinder marks or had been stripped with a grinder. You can spend hours, if not days sanding with 80,180, 220. The final outcome is a lot of money spent on sand paper that really is not needed. A metal surface sanded with 80 grit throughly is fine enough for surfacing with any of your quality 2K primer surfacers. Allowing the primer to cure for a period of time will allow it to shrink and do what it will. I personally prime and let sit for 72hours or more before continuing .

be sure to get your disc from a welding supply. big difference in auto body paper and metal working. the better your surface is before you start the better your finished product. i agree with most that 80 grit is a good start.

you should use mar hid sprayable body filler with the biggest tip you have it will go on like oat meal you might think to yourself what have you done but it sand easy with 80 grit its a hevy builder fills in ding and uneven spot if you use a long board or air fill

K36 is good stuff but it will never fill like k38 does also omni’s 232 works well to if your on a budget.

But like they said DON’T just fill the scratches sand um or you might as well save yourself some $ and rattle can it because if just fill um it’s going to bight yu anyways.

Rick.

even with smoothing the metal out before primer, how much was it grinded on before that there are that deep of scratches in it? The metal might already be pretty thin, and using a d.a. might make it even worse, and if you're new at it, possibly even warp a lot of the sheet metal. It was already said, but you can never do enough prep work, but you might have to be really careful in your situation. If you do end up using the high build primer, make sure it sits for a while, and if you can, let it bake in the sun for a few days, the u.v. rays will help evaporate all the solvents. To help minimize the shrinking, you could spray your high build primer, wet sand it, and then let it bake in the sun. By wetsanding it first, that will break the skin open on the primer and let the solvents evaporate more. But before the primer, try to get the metal as smooth as possible, without making things worse!
Good Luck!!

You know clean94ranger maked a GOOD POINT, I’ve known a couple Boneheads that told me they level the metal by grinding out some high spots! So always "be careful" because you never know if those boneheads ground on it, lol. you could find doneheaded tinfoil spots.

Rick.

If I have a vehicle that get's a lot of body work/metal work,, and the customer is willing to pay for a extra step,,, i'll spray 3-4 coats of z-chrome, this shit is awesome,, you'll need a big tip to spray it though... the reason i like it is that i've never ever seen this stuff shrink on me.. If i use this i'll block it down with 120 then 180, and then i re-prime with NCP-270 or NCP-271, plus the extra step of blocking primer makes things that much straighter.. just a idea..

this is a very good point on the d.a i have help may here. running the d.a to dam fast the sandpaper lose it grit and makes heat and if you pay for the paper you try to make it last . i fixed a 64 gto hood that was a geat hood till some shi$t head fixed it by d.a it look like he was standing on it when he strip it with a d.a. grinding d.a and disc sander 36 grit and griders should be band from some . this suff in the wrong hands can make it hard to do a good job and griding hi spot thats a big NO NO i did all my metal work with a hammer and dolly and a slap file then i guide coat it and work it till it look good it is better to take off the guide coat and work the metal more than grinding the crap out off it and when it is rigth as you can get it before i use filler