sanding bumper

contagious18 · Post by **contagious18** » Mon Feb 16, 2009 7:19 pm

wats size grit is the best to sand down for paint

FAC3L3SS · Post by **FAC3L3SS** » Mon Feb 16, 2009 9:19 pm

i started with 80/100. then eventually was using close to 400 once i got the gist of it off. my painter told me it was plenty good enough...

srtgtr34 · Post by **srtgtr34** » Mon Feb 16, 2009 10:48 pm

FAC3L3SS wrote:i started with 80/100. then eventually was using close to 400 once i got the gist of it off. my painter told me it was plenty good enough...

I wouldn't use sandpaper that course, its makes to many deep scratches.

I would use 180 grit to lightly sand over the base and clear coat. Preferably by hand if you have never done this before.

You said you bought a sander, I'm assuming you mean a DA?, which is air powered or did you buy an eletric sander?

Once the surface is sanded down get it primed,then get yourself a can of guide coat and lightly spray it over the dried primed surface, its will show you the high and low spots and wetsand with 400 grit to get the imperfections off. If you did a bad job sanding with the 180 and made high and low spots you may need to reprime. Then ifd your happy with your results use some wax and grease remover and wipe the bumper down a couple times and your good for paint..

Good luck, if you have any questions just pm me..

benzsxt · Post by **benzsxt** » Mon Feb 16, 2009 11:07 pm

Are you painting bare plastic or repainting a painted bumper? Never use 80 grit paper on a bumper cover.

jetas · Post by **jetas** » Tue Feb 17, 2009 12:38 am

280 is wat i used wen i repainted my car all 3 times. 80 is really coarse unless ur using a DA.

contagious18 · Post by **contagious18** » Tue Feb 17, 2009 4:28 pm

bumper cover and sideskirts thanx srtgtr

FAC3L3SS · Post by **FAC3L3SS** » Tue Feb 17, 2009 9:36 pm

lol geez. my bumper was wack though. had almost three layers of rattle canned paint on it....it was AWEFUL. i did end up doing srtgtr's strategy and priming/wetsanding until smooth.

srtgtr34 · Post by **srtgtr34** » Tue Feb 17, 2009 10:56 pm

FAC3L3SS wrote:lol geez. my bumper was wack though. had almost three layers of rattle canned paint on it....it was AWEFUL. i did end up doing srtgtr's strategy and priming/wetsanding until smooth.

Its not the strategy, its the "book way" of doing it.

LilSparkPlug · Post by **LilSparkPlug** » Wed Feb 18, 2009 9:24 am

You guys are ALL giving HORRIBLE advice. Holy shit. Sanding TPO with 180 or 280 grit...are you INSANE?!!!! The book way of doing it? You're reading the wrong book.

The coarsest you should ever go to prep for paint is 400 grit, and even that can be too coarse if you don't use the proper primer. 600 grit....PLEASE!!! I painted my entire car this way over 2 years ago....Its 400 to 600 grit, that's it. You only sand with coarser paper if you are sanding body filler or repairs.

benzsxt · Post by **benzsxt** » Wed Feb 18, 2009 12:52 pm

^^ That is why I asked if it was bare plastic or painted.

FAC3L3SS · Post by **FAC3L3SS** » Wed Feb 18, 2009 1:07 pm

^^ must not have seen my bumper.

srtgtr34 · Post by **srtgtr34** » Wed Feb 18, 2009 3:18 pm

LilSparkPlug wrote:You guys are ALL giving HORRIBLE advice. Holy shit. Sanding TPO with 180 or 280 grit...are you INSANE?!!!! The book way of doing it? You're reading the wrong book.

The coarsest you should ever go to prep for paint is 400 grit, and even that can be too coarse if you don't use the proper primer. 600 grit....PLEASE!!! I painted my entire car this way over 2 years ago....Its 400 to 600 grit, that's it. You only sand with coarser paper if you are sanding body filler or repairs.

I know my information is correct.

First of all, you use the 180 to to get all the clear coat off, you don't have to go down to bare plastic. If you use 400, you will be sitting there for a while and since its so fine it will not allow the primer to bite into the plastic/ base coated surface. This will result in your paint lifting, it may not be now but in 1/2 to 2 years you'll see it. Primer is most oftenly gets sanded with 400 wet but when cheap primer is bought 600 is the best route like you said.

I have painted several cars and components this way and so have my professors at school, even the shops in my area use this method.....

LilSparkPlug · Post by **LilSparkPlug** » Wed Feb 18, 2009 5:23 pm

Sorry, I'm certified by PPG. I was taught 400 grit at the coarsest if no body work is needed. There is NO reason to sand ALL of the paint off down to the plastic. Nor is there a reason to sand all of the clear coat off. The purpose of wetsanding a part is to simply get rid of the orange peel and make a nice surface for the paint to adhere to.

I've seen things painted over 180 grit....and it looks horrendous. You choose who you want to listen to. Take a look at my car, wetsanded with 400 grit then 600 grit (my car has NEVER been wetsanded or buffed after paint) and make your decision.

Your final paper should be 600 grit before basecoat I don't care what anyone says. Any coarser and you will see sandpaper marks through the paint. I've been painting since 2005....and haven't ever had any complaints, even when I worked for Mercedes and sprayed Sikkens.

FAC3L3SS · Post by **FAC3L3SS** » Wed Feb 18, 2009 6:36 pm

^ good point. i did A LOT of excess sanding.

and i went to bare plastic....so idk

LilSparkPlug · Post by **LilSparkPlug** » Wed Feb 18, 2009 6:54 pm

There is absolutely no need for that unless the paint is so beyond repair that you need to. In which case there are stripping agents used to get rid of the paint so you don't waste hours upon hours sanding. Even still down to bare plastic a 3M gray scuff pad with some PPG scuffing solution, done wet, will take care of the surface prep for you.

benzsxt · Post by **benzsxt** » Wed Feb 18, 2009 8:34 pm

All you need is a gray 3M scuff pad. You want to keep scuffing till the shine is gone.

contagious18 · Post by **contagious18** » Fri Feb 20, 2009 2:26 am

ok so wat i want to do is get the paint off my sideskirts so i can repaint them to match da car, so 400 fine grit to 600 fine grit should do the job like crystal said

hybrid-Srt2001 · Post by **hybrid-Srt2001** » Fri Feb 20, 2009 6:10 am

for the side skirts yes. I assume they are in good shape and you just want to re paint over a good surface. Then yes 400-600 wetsanding is what you want. As far as the bumper, i know that you are doing fiberglass/bondo work. For that i suggest 80 grit for the fiberglass portion, then 180 grit for the final shaping/smoothing, then down to like 220. Then you are going to want to spray on a high build primer surfacer. wet sand that down with a sanding block, or flexible backing board till smooth. next mist on a light guide coat of a light color, and sand again with 320-400 to be sure all the spots are smooth and even. You can do one more layer of primer surfacer if you like and wet sand with 400-600. then you should be ready for primer/paint.

Mopar65 · Post by **Mopar65** » Fri Feb 20, 2009 9:40 am

I think we need another how-to from LSP for us first time painters

Im painting my lip black over spring break, but I reall have no idea how to do it well

InfinityAudio · Post by **InfinityAudio** » Fri Feb 20, 2009 9:52 am

do it just as LilSparkPlug said it it's the best way to get a super wet finish like I call it. If you use under than 400 you'll see after paint that you had sand before paint. I did on my front bumper las summer and it's going to paint again with sanding it to wet 400 because I want to be as best as possible

DoubtedNeon · Post by **DoubtedNeon** » Fri Feb 20, 2009 10:20 am

There is a guy I live close to thats helped me repaint 2 cars ive had so far, hes been painting old corvettes for the last 15 years, he uses crystals method, it takes longer, but if you do something right its not going to be easy or fast, 400 to 600 is the way to go, way to be LSP!

contagious18 · Post by **contagious18** » Fri Feb 20, 2009 12:30 pm

hybrid-Srt2001 wrote:for the side skirts yes. I assume they are in good shape and you just want to re paint over a good surface. Then yes 400-600 wetsanding is what you want. As far as the bumper, i know that you are doing fiberglass/bondo work. For that i suggest 80 grit for the fiberglass portion, then 180 grit for the final shaping/smoothing, then down to like 220. Then you are going to want to spray on a high build primer surfacer. wet sand that down with a sanding block, or flexible backing board till smooth. next mist on a light guide coat of a light color, and sand again with 320-400 to be sure all the spots are smooth and even. You can do one more layer of primer surfacer if you like and wet sand with 400-600. then you should be ready for primer/paint.

so i would have to 400-600 to get the paint off and then start the bondo work

benzsxt · Post by **benzsxt** » Fri Feb 20, 2009 8:17 pm

Do not use Bondo on your bumper. I will come back off. For any damage on a flexible bumper you will want to use a flexible filler or a 2 part plastic repair by 3M or Lord Fusor. If you are adding a lip to your cover I recomend a 2 part epoxy.

srtgtr34 · Post by **srtgtr34** » Fri Feb 20, 2009 9:02 pm

To each their own, thats all I have to say, I am not a person who likes arguing. So I'll leave it at that...

LilSparkPlug · Post by **LilSparkPlug** » Fri Feb 20, 2009 9:54 pm

Yeah you'll need to do the plastics repair first. You don't need to strip all of the paint down except in the area that you are working. Follow hybrids instructions for that. 80 grit for repairs. Then 180, 220, 320...etc.

benzsxt · Post by **benzsxt** » Fri Feb 20, 2009 10:58 pm

BTW I am a bodyman with 10+ years exp in collision, custom and paint work. LSP has a lot of experiance and built a beautiful car to prove it. Watch where you get your info from. Try not to take advice from someone that may have 6 months exp in a auto tech class.

contagious18 · Post by **contagious18** » Sat Feb 21, 2009 2:50 am

benzsxt wrote:Do not use Bondo on your bumper. I will come back off. For any damage on a flexible bumper you will want to use a flexible filler or a 2 part plastic repair by 3M or Lord Fusor. If you are adding a lip to your cover I recomend a 2 part epoxy.

not really need to repair the bumper but modify it

Fuzzyneon · Post by **Fuzzyneon** » Sat Feb 21, 2009 3:08 am

LilSparkPlug wrote:You guys are ALL giving HORRIBLE advice. Holy shit. Sanding TPO with 180 or 280 grit...are you INSANE?!!!! The book way of doing it? You're reading the wrong book.

The coarsest you should ever go to prep for paint is 400 grit, and even that can be too coarse if you don't use the proper primer. 600 grit....PLEASE!!! I painted my entire car this way over 2 years ago....Its 400 to 600 grit, that's it. You only sand with coarser paper if you are sanding body filler or repairs.

LSP <3 much love but i loled so hard good advice just funny how you presented it!:-p

DoubtedNeon · Post by **DoubtedNeon** » Sat Feb 21, 2009 11:38 am

benzsxt wrote:BTW I am a bodyman with 10+ years exp in collision, custom and paint work. LSP has a lot of experiance and built a beautiful car to prove it. Watch where you get your info from. Try not to take advice from someone that may have 6 months exp in a auto tech class.

???

benzsxt · Post by **benzsxt** » Sat Feb 21, 2009 2:06 pm

not really need to repair the bumper but modify it

What are you doing to your bumper?