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How much time do you spend 400/600 sanding?

6K views 36 replies 9 participants last post by  John long 
#1 ·
I'm just curious how much time you guys spend when you're final sanding before sealer or base. I'm sanding 400, then 600. My final block was with 220. I'm dry sanding because my panels were sprayed with Slick Sand and I don't want to get water on that. I'm using 3M paper. I'll be putting lightly reduced epoxy on as a sealer, and my basecoat is a metallic blue.

However, it's taking me HOURS per panel. So far I've done a fender and I've now spent half a day on my hood already, plus some time on previous days. Granted the fenders on my 67 Mustang have several body lines, and I have a scoop on my hood which takes more time as well. But I'm sanding with 400 until every last detectable scratch I can see is gone.

I'm just trying to figure out if I"m doing something wrong, being too anal, or this is just how it goes. The last time I prepped something was a fender years ago and I don't recall how long it took me.
 
#2 ·
Well yeah the fussier you are the longer it will take. Dry sanding will also wipe out and clog up your paper faster than if you wet sanded. Don't think you are really doing anything wrong, and yes the more contours and body lines a panel has the longer it will take to sand for sure. Are you going over the 220 scratch with a dry guide coat? If you are going to seal I don't really see the need to go all the way with up to 600 grit, 400 should be fine enough before a seal coat. Now if you were going straight to a metallic basecoat then I would go to 600 grit.
 
#5 ·
Why are you dry sanding? As another said, the paper clogs - and I've found almost instantaneously. Also, when it does clog, it will usually form a bunch of globs on the paper that are digging furrows in your poly primer, 2K or even the epoxy if using a sandable like SPI. If you are worried that it will cause rust if you wet sand - it will only if you cut through the substrate then leave it for an extended time. Soak the torn, not cut paper pieces a half hour in a bucket of luke warm water with a couple drops of Dawn or similar dish soap, then alternating between several pieces, resoaking and cleaning in the bucket, go to work with whatever sanding blocks and pads blocks you have along with a constant water source(you aren't doing it without blocks are you?). You might not save a lot of time, but you will save the cost of lots of paper plus really have a 600 finished panel (I finished my last car with 1000 before paint:eek:).

Now, how long does it take? As long as it takes to get a perfectly prepped surface ready for paint and often that's dependent on how slick you put the undercoat down and to cut the 'nubbies' down smooth :sweat::sweat:
 
#8 ·
I went out and started the other fender with this (it's one of the few panels with 2k and not poly) and it was SO much faster needless to say. The paper cuts better, faster, longer. The problem is I can't see the scratches very well when doing it wet.
 
#6 ·
Josh, I am not a professional painter so maybe I should not contribute here but...... If you are going to seal I agree that 400 should be fine enough and also believe that you should be fine to wet sand it. I am sure you started out with Epoxy on your bare metal so you have protection from rust there.

Hopefully Ray, Henry, Brian or one of the true experts will join in. You could also check with Barry K at SPI. He would be more than happy to give you sound advice if you are in a hurry.

John L
 
#7 · (Edited)
Why am I dry sanding? Because most of the panels--except the fenders--have poly primer on them. I'm not real crazy about wet sanding polyester 'filler,' essentially. I have spoken to Barry on that issue before and he also wouldn't do it in a million years. Evercoat says the Slick Sand is dry or wet sandable but I just can't get brave enough.

I am constantly blowing the paper off with air. I sand a little bit, blow off the paper and panel, sand a few more strokes, and blow off some more. This avoids sanding with the paper completely clogged.

I am using blocks. On a tricky contoured spot that my round blocks can't do I'll cheat and use a piece of paper folded over several times and scuff out the area by hand.

I am not using guidecoat for the 400 sand. Someone here once (it was a professional) told me it wasn't necessary and I don't think we did it in some tech school classes I took a long time ago either. But I am sanding it outside in the sun and the light dances off the scratches well, so they have high visibility. That is if you were referring to guidecoat for scratch visibility as opposed to panel straightness.

I've visited with Barry about this in depth already which is why I've been doing what I've been doing, but was starting to really wonder on the amount of time it's taking me.

I'll seal a panel after just 400 and see how I make out.
 
#12 ·
Why am I dry sanding? Because most of the panels--except the fenders--have poly primer on them. I'm not real crazy about wet sanding polyester 'filler,' essentially. I have spoken to Barry on that issue before and he also wouldn't do it in a million years. Evercoat says the Slick Sand is dry or wet sandable but I just can't get brave enough.

I am constantly blowing the paper off with air. I sand a little bit, blow off the paper and panel, sand a few more strokes, and blow off some more. This avoids sanding with the paper completely clogged.

I am using blocks. On a tricky contoured spot that my round blocks can't do I'll cheat and use a piece of paper folded over several times and scuff out the area by hand.

I am not using guidecoat for the 400 sand. Someone here once (it was a professional) told me it wasn't necessary and I don't think we did it in some tech school classes I took a long time ago either. But I am sanding it outside in the sun and the light dances off the scratches well, so they have high visibility. That is if you were referring to guidecoat for scratch visibility as opposed to panel straightness.

I've visited with Barry about this in depth already which is why I've been doing what I've been doing, but was starting to really wonder on the amount of time it's taking me.

I'll seal a panel after just 400 and see how I make out.
On the rounded areas that a block won't work try the small 3M sqeegee they work great for those tight curved spots, there just flexible enough yet stay flat to the surface your sanding, I use them all the time in those complex curves. If you are using guide coat after the 220 grit the powdered version works much better for showing ANY imperfections or sand scratches.
 
#10 ·
guide coat also worked awesome. I did this fender in a fraction of the time and used a fraction of the paper! :thumbup: And it's so much cleaner. I thought I hate wet sanding but I have clearly forgotten how the experience actually was.
 
#11 ·
Why did Barry say not to wet sand a poly primer? I don't misunderstand. I am not arguing just trying to learn something here. As long as it is given plenty of time to dry and breath I don't understand what the liability is as long as it is not over bare metal.

John
 
#13 · (Edited)
Would you wet sand body filler? My answer to that question is 'No,' which is why I elected not too. Apparently it's the same answer as Barry's. My fear is the poly primer absorbing too much water and not getting out. I think deadbodyman has actually discussed situations where it lifted when wet sanded. This clearly needs googled. I'd consider spraying 2k over it, blocking and wet sanding that but a concern of Barry's was having too many different substrates on there.

How long is long enough to breathe? After sanding these I'll be sealing in good time and I think it would be devastating to have that moisture trapped in there.
 
#24 ·
If this is just a base primer you are trying to sand, why go with such a fine grit? For a full / big job - do your bodywork, ruff it in down to 80, prime it, block it straight with 80, prime it, block once more with 180, final prime and sand it with 400. Then seal it and paint (wet on wet).
 
#25 ·
the 600 was only because I was doing metallic, but was not considering that it is a moot point when I'm putting sealer over it anyways.

What I'm going to end up doing is final block with 220 as I've done, two coats epoxy, then wet sand with 600. I won't be able to put paint on wet on wet.
 
#28 ·
Does that mean you cant learn anything else???? I learned the HARD way about these primers and blocking also..8 yrs is nothing..As much as you gonna hate hearing this: This is what I would do at this point...get a long stiff block and 80 grit and block all that poly off leaving it in the waves but nothing left where it isnt needed...spray two coats of SPI epoxy and block that with 180 dry then two more coats blocked out with a long rubber block 400 wet....then 600 ...
something else that poly primer does well is chip real easy...so be extra sure theres none at the edges like your jambs and wheel openings...
Since your not a pro I'll asume that your doing this for fun and enjoyment not to mention a love of old cars..Theres nothing fun about blocking so why make it harder than it needs to be you can block that off of there in no time and make things much more enjoyable using SPI and it'll last....
 
#29 ·
I've been spraying SPI for the last 3 years, and it's the only thing I've ever sprayed (besides the Slick Sand). The Slick Sand is already blocked nearly off with 220. I think it sands like butter once I break through the crust with 120. Your suggestion isn't really any different than what's already been talked about here or what I've discussed with Barry, and it's what I'll be doing. Two coats of epoxy, wet sand to 600. I get little to no peel when I spray the epoxy so it will be easy sanding smooth. This is actually more convenient for me because I can just shoot the panels outside and if I get trash on them it will be sanded out.
 
#32 ·
Professionally, I would use the dry stuff, but being an amateur, use SEM guide coat, and purchased really cheap at a swap meet from a guy that always has a bunch. I dislike giving 3m any more of my hard earned dollars then necessary - even for their $$$ tape which doesn't seem as good as it was:pain:.
 
#33 ·
I am with you, I LOATH big corporations and chains believe me, I VERY rarely go into any chain when I have a local store or restaurant to give my money to.

But this 3m guide coat is SOOOOOOOO good, it is SOOOOO much better than spray paint you can't believe it. It covers EVERY square inch you want it, with a very fine dust going in very small scratches, it is well worth the money if you ask me.

There are alternatives, just yesterday at a swap meet I was having a long chat with one of my mentors from 35 years ago, one of my very valued mentors (and I tell him every time I see him) and he told me how he had begun to use soot from the torch for guide coat! He fires it up with just the acy on low and waves the torch on the panel putting soot all over it. He then wipes it all over with a rag and it goes in all the scratches and it's his guide coat. He told me how he found it by mistake after he welded a missed crack and then while sanding the area WHAM there were all the scratches. :D Never done it but it may be an alternative to the 3M stuff.

I am stubborn as heck when it comes to giving money to someone I don't like, I really respect your opinion on not giving money to 3m, believe me I do, but damn it if it's going to make my job easier and better sometimes I will just bite my lip and do it.

Brian
 
#36 ·
Yes - or at least the can's I've had did. Ya gotta remember, if the corporate finance guy can save a penny a case, things change

Brian - I've seen that acetylene trick used, but have never tried it - remember with some of us being overly mature, CRS goes hand in hand, so had forgotten.
 
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