Sanding body filler. Newbie question.

Heres how I like to do it, get it to the metal, dp 90 it, then where the bondo will be , rough up the surface. I like to use Rage bondo, I use 40 to get the rough off , 80 grit to get it almost there leaving enough material behind to finish off with 180. I roll the 180 grit around a straight paint stick or yardstick. I wrap the 40, 80 grit too. I can sand faster with sticks. A sanding block covers up what your sanding and a stick will not, that comes in handy . Once I.m at the 80 grit blocking stage, I cover the bondo up with flat black spray bomb, then proceed to block with 80 grit until the black is gone. This is a good time to fill imperfections and pinholes with more BONDO. Make sure there is no bondo dust in your pinholes etc. before you put more on. I go over my bondo with a air hose and a pick to get out the dust and to pop any bondo zits, where dust may have been trapped earlier. Then I spray it again, and block with 180 until the black is gone. When I'm at the 180 stage of blocking I dont want to add any more bondo because that will **** up the surface you got going with the 180. Make sure you have enough bondo on at the 80 grit stage. Once I achieve perfection at the 180 grit stage , I start laying on Ditzler K36. I try to put at least 4 to 5 heavy coats on. I'll do the whole car like this and then go back to the first thing I primed and cover it with black spray bomb. ! wrap a stick with 180 and I star blocking until the black is gone. I usuall can get stuff straight with those first primer coats, but if not,3 or 4 more will finish it off. Then I move on to 360 grit wrapped on a stick and stop there. During final sanding I find a place in the shop where the light is right, wipe down my sanded panel and it will shine like its wet in the right light and you can see if there are still waves or whatever. You don't have to wet sand , Im supersticious, I dont wet sand any primer with the metal directly under it, that comes from the old lacquer primer era. I cant see what I'm doing wet sanding anyway and you cant properly feel the panel when its wet. Everything feels slick when its wet, it will fool you. Everything needs to stay dry until your wet sanding the final paint before buffing. I don't use glazing putty becauce you shouldn't need it if the bondo was right before you primed. The stuff drys in down the road. Its for insurance work that has to be done yesterday. Practice, practice, patience.

 

My technique, using modern B/C. Start with 80 grit, get it real close, then finish with 180. Prime and spritz a marker coat. 400 wet block, reprime/re block if neccesary, then a light p*** with 1000 grit wet. Adhesion promoter, then shoot it.

 

120-180 dependet upon whatgrade primer, polyeseter is good with 120 and 180. if eurethane....180 fo sure. if you have bare metal anywhere....the metal needs enough etch to bond with the primer. at the same token....if you have a large area of metal showing....some primers will not stick to the metal for very long. which brand of primer?

 

Barry, it really depends on what your next step is going to be. Once the primer is sanded in your 400, are you going to seal or go right to your basecoat? If you were to seal it, I have no problem leaving a few small bare spots. By small I mean no bigger than a half dollar. If not, I would dust some primer back in on the spots that are bare. The bare filler is going to soak up whatever goes on top and that can cause coverage nightmares if you're trying to base over it.

 

Thanks Bill - I was going to shoot another round of primer and hit that with 600 before basecoat. My big concern is about any moisture that may have been absorbed by the filler coming back to haunt (or hurt) me later. Will leaving it to dry out be enough?

Also learnt about the benefits of quality abrasives (again!) Was out of sandpaper on the weekend and picked up some cheap no-name at our equivalent of Lowes/Home Depot. Damn 220 grit was disintergrating and leaving scratches almost as bad as 80. Would have had less work to do if I'd have just waited till Monday

Barry

 

I'm not sure if you know this but filler goes under primer, not on top.

 

That really depends on the materials you're using, its not black and white.

Barry, the moisture that the filler ****ed up shouldnt be a problem provided you give it some time to dry out before recoating it.

 

Im a firm believer in 120, prime 2 or 3 times. Finish it all in 400. SHOOT DA PAINT

 

Thanks again Bill!

Langy, that is how most people over here seem to do it too. I got to wondering why every panel that I dug old bondo out of would have rust under it and chatted to a respected local restorer. His recommendation was to give the metal some protection before the mud went on - seemed to be saying that bondo may actually be hygroscopic and trap atmospheric moisture(don't think this is neccesarily true?)
Anyways the bondo seems to stick equally well to any surface (primer or raw metal) as long as it has some key - I lightly scuff the primer with 36 grit in the areas I'm adding it to. To my mind even going onto clean metal you should run over it lightly with a grinder to give some bite.

Barry

 

I should of been a bit more specific, I never put filler on bare metal, bare metal gets 2 coats of epoxy primer first, then i key the epoxy wth 120 then do my filler work, once filler work done I lay on 1 coat of epoxy and leave for an hour and then go wet on wet with my 2 pack hi build.

Although i'm not a trained painter i do all my own cars and was taught by a friend that has 2 best paint pots from Pebble Beach, This is how he does his work.

Barry in my humble opinion i think your absolutely correct that filler will **** up moisture, Did you know that Epoxy primer is anti corrosive and moisture resistant, Its used on Oil rigs.

 

Cleaning out my "old thread" closet..............giving the old girl a bump back to the top.
up-dates anyone??.......

 

The finer your prep work the finer your paint job will be and this goes for every stage of the work.

You can primer over 80 grit marks and get away with it, if you use enough primer. It will look nice long enough for the customer's check to clear the bank. But sooner or later it will shrink, low spots and sanding scratches will start to show, and the car will look like hell.

With the old lacquer primer if you did sloppy work it would show up in a week because the primer dried and shrank. Today you can get away with it longer because of epoxy primer but it will show up eventually. It might take a year but it will show. Paint does not completely dry for months. You may have noticed a smell of fresh paint around a car on a hot day, even though you knew it was painted months earlier. The paint was still drying and throwing off enough volatile matter that you could smell it.

I used to know a bodyman named Wavy Dave. He was just a whiz, all the shop owners loved him because he could take some beat up old wreck and knock it out in 2 or 3 days. He never picked up a torch or a hammer, everything was done with fibregl***, bondo, primer, spot putty and an orbital sander.

When one of his cars left the shop it looked great, from 20 feet away. But a few months later you could see how he got his name.

Forget all that apcray about bridging over gaps and ****. Paint, and primer shrink when they dry and there is no getting around it. Leaving a car in the sun for a few weeks in primer will get most of the shrinkage over with but the best idea is not to depend on primer and filler to do your job for you.