Overthinking

5

50Shep

Promoted Users
I’m sure I’m overthinking all this……I get a panel acceptably straight at 180 grit with body filler, epoxy, and slick sand. I apply another 2 coats of epoxy then I start at it with 320. Invariably I will hit metal or a lower coat of epoxy usually at at edge ( my first coat is usually black). At this point for some strange reason I usually keep sanding. God only knows why…. But eventually I hit metal. At this point, can I just respray that general area with more epoxy? Or do I need to sand that area with a lower grit (80, or 180) before respraying any more primer?

After I respray that area, can I keep on trucking with 320? Or do I need to start back with a lower grit?

If my epoxy seems to be getting thin (seeing outlines of filler or metal) and I spray another coat of epoxy do I start my sanding at 320 or do I need to go back down in grit?

Thank you
Jason
 
Restorations, high end stuff, I like to get it straight in a grit no higher than 180. Once you know it's straight, then spray 1-2 more coats of epoxy and go 320 dry, then 600 wet. Or you could go 220, then 320, then 600 wet. Others may do it slightly differently but that always works well for me. One thing I think we all agree on is that you shouldn't go any finer than 180 until you know it's straight. The finer grits are for refining your scratches.

Sand evenly across a panel. Never concentrate on one spot or area. You gotta be religious about that. And if you hit metal you stop. Figure out why and then proceed.

Small bare metal spots it's ok to recoat with epoxy, but like I said above get it straight in 180, if you do you shouldn't be hitting metal in the finer grits.
 
Last edited:
I would add to Chris's advice the following:

Block sanding to get a panel straight requires a coarser grit and remember to sand diagonally. Also, do not apply a lot of pressure to the sanding block, firm consistent pressure that doesn't flex the panel is all you need. Change the sandpaper as soon as it stops cutting so you don't press harder on the block.

Guide coat is your friend when it comes to block sanding, especially if you have a tendency to over sand.
 
Thank you. I’ve read a lot of your posts and I have definitely been trying to stay in the lower grits to reduce the up and down in grits crazy cycle. But I still think I tend to go up in grit too soon and I do push hard. I use the mirka vacuum sanding blocks and the paper is expensive so I’m probably not changing as often as I should.

I think for me, Since I’m doing this in my garage, spraying is a pain so the alternative is to just keep sanding when I should stop and spray some more slick sand or epoxy. It sounds psychotic I know.

When you do 220,320,600, do you usually have enough build to get through all three grits without respraying? Or are you putting another coat on in between there?
 
50Shep said:
But I still think I tend to go up in grit too soon and I do push hard.
Click to expand...

I don't ever push very hard. It is not necessary to put a lot of pressure on a panel when sanding. Most of the time you do more harm than good doing so. Especially if your panel is flexing when you are sanding. Now "hard" is probably a relative term to folks, but ideally you want to let the paper do the work. I would say light to a most medium pressure. Another way to describe it is you want your fingers to be doing the work, not pressing down with your palms.

The key to when to change grits is reading the panel and doing what it tells you. That's where guide coat helps as well. As you progress you are sanding off the guide. Where it remains is low. If you hit metal before getting all the lows out, you need to determine if that area is high, or if you have reached "level" and need to add more filler or primer. You should be using your hand too. Running it across the panel trying to feel where it's high and low.

Put any grit higher than 180 away for the time being. Act like you don't have it. Before you sand anymore run your hand (fully on the panel including your palm)over the panel(s) with your eyes closed. Back and forth horizontally. Use a paper towel between your hand and the panel if you are having trouble feeling. Observe what your hand tells you. If there are highs, try to understand why it's high there. Could be several reasons.

Sometimes(often) a dent will cause the area around it to go high. Novices don't always understand that or get the highs out when working a dent. Same with the lows. Correct any high spots and evenly cross hatch the panel again with 180. If you start hitting metal in multiple areas this is a sign you are at level and if you have lows still then you need more material. Then run your hand over it again. Do what the panel tells you. That is the key to all of this.
50Shep said:
do you usually have enough build to get through all three grits without respraying?
Click to expand...
220 would only be necessary if you hosed it on. At this point if it's straight you are not doing any correcting, only scratch refinement. Guide coat it and sand the guide coat off with 320 dry. Do that and the primer should be completly sanded no texture or lows. Then 600 wet is simply scratch refinement of the 320 scratches.
 
Great write up, Thank you. I’m using a long block and have started using 3m dry guide coat. I noticed the first few small pieces that I painted still showed sanding scratches, I’m hoping the dry guide coat will help with that. I was greatly underestimating the amount of sanding it takes to get rid of all previous scratches. I’ve painted the running boards and a few small pieces on my truck but this is the first fender I’m working on so I want to up my quality of work. I really don’t want this to look like a first paint job, even though it is.
 
I filled a few lows and put two more coats of gray epoxy. The fenders look really good. I was planning on blocking one more time with 180 but if they look really good can I try with 320 and see if I missed any lows? If I start see lows, I can switch back to 180. Or is 320 just too fine and won't show any lows? Is 320 purely for scratch correction? Thank you for all the help.
 
It sounds like you are rushing to the epoxy from the previous steps. If your Slick Sand step is sufficiently completed, then you should have no breakthrough anywhere because the panel is leveled. On your final epoxy application then it is just smooth sailing and if you have guidecoat, it will all sand off easily.

Graduate to your epoxy step too soon and you're doing two things: 1) playing whack a mole with chasing bare metal high spots, or 2). decide it's good enough and live with it.

I keep on black sanding (with reapplication of guide coat) high build or slick sand until I can see it just start to break through to the previous layer in some areas. In doing so I've removed most of the mil build on the panel which is undesirable and have enough build in lower areas. With Slick Sand especially, there is a lot of the material on the panel. Once all the guide coat is sanded off, I will spray more guide coat and block again and you'd be surprised how much this reveals errors in your sanding technique or low spots that didn't quite get sanded out the first time.

Once the final pass of blocking has been done and it's all sanding off evenly, I go over the entire panel/car with one medium coat of high build and then sand that with 400. This is a great trick I learned from Barry years ago. The high build fills in your sanding scratches from 180/220 and eliminates having to move through multiple grits and you end up with only 400. Saves a LOT of time because I can spray an entire panel faster with 2k much faster than I can correctly block it with several grits.

Then I do a final coat of unreduced epoxy and wet sand that with 600. That provides a perfectly smooth substrate for base. Uniform color of seal coat, no peel, no trash, or nibs.
 
Thank you Chris, I will hit it again with 180. I think I’m close.

Lizer, I am playing wack a mole for sure. I’m trying to stick with all epoxy. So trying to do some build with epoxy.

I did have some SS but I think I’ve sanded it all off.

Here’s my crazy cycle: I find a low, I add some filler, I sand it too much, not really sure what the guide coat is telling me so I spray epoxy and block it, find the area is still too low and add more filler….. I’m spraying in a home made booth in my garage so I was trying to keep things simple (not too many different isocyanate products that have to be sprayed). I think I just needed to mainly work on my leveling techniques. I feel like I should be able to get filler perfectly level before spraying primer but I just haven’t figured it out yet.

I may not have used guide coat with the slick sand so that may explain why the slick sand didn’t level things out as much as I was hoping…. Having said that, I absolutely hate the smell of slick sand, not sure why but I hate sanding even weeks later so I’d rather just not use it anymore.

Thank you
Jason
 
Last edited:
I use the regular 2k (I only use SPI products if it's in their product offering), and have used Slick Sand before but only for really extreme cases. I don't like using epoxy to build. It builds much slower than 2k and the entire process is slower. The nanoparticle used for the solid in the 2k results in less shrinkage vs others (at least it did at one point unless Barry has changed it).

You need to be using your hands to feel your panels, especially when you don't know what the guide coat is telling you. Lay hand flat against the panel and just go over the panel feeling for imperfections. You can put a shop towel flat underneath your hand. (PS--wash your hands first!!!)

Also sounds like you're sanding too hard. There should be almost no pressure on sanding block besides its own weight. Let the paper do the cutting. I use Indasa rolls for blocking. They last a long time and are inexpensive compared to 3M.

And then learn when to stop.
 
I don’t pretend to be a bodyman by any stretch of the imagination but I learned a number of years ago from my nephew who is. When sanding do not go in horizontal or vertical directions. Diagonally is the way to do it. I like SS and I use the powdered guide coat material which helps me a lot...

But you probably know this already!
 
dhutton01 said:
If you are not using guide coat and a long sanding block you are not going to be successful imho.

Don
Click to expand...
What is considered "Long" when dealing with a very curvy car like a Karmann Ghia? What composition would be best, hard, soft, Plexiglas?

-----
Emil
 
Evil_Fiz said:
What is considered "Long" when dealing with a very curvy car like a Karmann Ghia? What composition would be best, hard, soft, Plexiglas?

-----
Emil
Click to expand...
You are going to get a lot of varying opinions. :) I would get a set of Durablocks and maybe 18” and 24” Hutchins sanders. And a lot of dry guidecoat.

The Durablocks came in handy doing the 63 Corvette which is also a curvy car.

Don
 
dhutton01 said:
You are going to get a lot of varying opinions. :) I would get a set of Durablocks and maybe 18” and 24” Hutchins sanders. And a lot of dry guidecoat.

The Durablocks came in handy doing the 63 Corvette which is also a curvy car.

Don
Click to expand...

Durablock makes an 11" round sanding block that works very for curved panels. They also have a Teardrop shaped block https://www.dura-block.com/11-Tear-Drop-Dura-Block--1-Piece--AF4406_p_26.html that I like as well for getting into those tight spots.
 
You can get a car straight with nothing more than a paint stick or two taped together. But not the best choice. Durablocks will work well. Acrylic in varying thicknesses would probably be the most foolproof method as they conform to a panel without deformation of the block itself.

Just as important would be technique. When you are blocking to correct you want to cross hatch. Meaning draw an imaginary horizontal line through the panel and sand 45 degrees to that line across the panel. Then go back across the panel at the opposite 45 degree angle. You have to sand the entire panel even if you are just trying to remove one low spot. That is the key to this.
You only sand in one direction in limited situations like color sanding or your final wet sand.
 
You must log in or register to reply here.
Back
Top