Hello, need to ask a question on sandpaper . I am working on a small panel repair got my first coat of bondo on, need to sand down , possible a second coat for a level finish. I was told to hand sand down using #40 grit paper as the 80 work loaded up too fast and also you want a finish on the bondo that primer and paint will stick too. Is this correct?
What do you recommend I use between coats all the way to the final prime and paint and what should it feel like? Sorry for the questions , new to this like to do this once. Thanks

There was a discussion about this on another board a short time ago. It seems the current trend is to use nothing coarser than 80 grit for your initial shaping on a bondo job. I've got some 40 grit to use up,so I think I will continue to use it until I run out.I am no expert,just a backyard body man.

ive always used 40 gritfor initial shaping because it cuts it alot faster and dont load up nearly as fast as 80 does. after it cut down to were i need to be then i do use 80

:agree:

I too have always used 36 to 40 grit on the initial shaping. Once I get the form I want, I switch to 80.

Mike

Thanks guys for the help much appericated. Is #80 grit okay to use for the final sanding before prime and paint, or should I use a finer grit for a smoother finish? Picked up a assortment of pieces so I would have, just wanted know what is best for final sanding. Thanks alot

IF you really want your bodywork to look good and get a good feel for what it is, good or bad, finish with 180.

yeah most filler primers will fill in 80 grit scratches, but 180 grit scratches fil a lot better. sand with the 80 first and then with the 180 and run your hand across the material and you will feel the big difference.

Use the 40 grit to shape not 36 cause primer fillers can fill 40 grit scatches not 36 (I know it does not seem like much between 36 and 40 but its a world of difference in the finish) Also it's always best to work your surface when your bondo is semi hard and to cut it quickly while it is still soft either with a cheese grater or 36 grit sand paper. Have a small wire brush to keep your sanding block clean as you make passes cutting your bondo down. If you wait for bondo to get hard (especially if you wait a couple of days) then its hell to get off and it also has a tendecy to warp cause you generate a lot of heat when you sand a fully hardend surface

Spend more time and effort getting the metal closer to the right shape and practice spreading your filler smoother in the first place.
There should be no need for anything nearly as crude as the old cheese grater thing. You shouldn't be building the truck with plastic, just filling minor imperfections. Proper metal finishing and spreading techniques will save you quite a bit in materails and sanding time/effort.

if you get high quality wet/dry sandpaper and wetsand with it you will have no problem with clogging up and the only time you would have to replace paper would be when it wears out. just my .02

I may be wrong here, but I don't think you want to wet sand your filler. OK for final stages of surfacer sanding though.

I was told to never wet sand plastic filler as it will abosorb water and cause rust and eventually blister into the final topcoat.

:agree:

I too have always used 36 to 40 grit on the initial shaping. Once I get the form I want, I switch to 80.

Mike


I agree works great