Joined: Mon Oct 10 2005, 08:43PM
Location: Calgary, Alberta
Posts: 978
After looking at rustholes pictures, and that super looking finish, I am now wondering what is the best size block !bbb to use - the longer the better or ????? !stars !stars I will be starting this process soon, and any advice (good and on topic that is !crazy ) is appreciated. What grit paper should I start with and what should the final grit be?
Joined: Sun Feb 05 2006, 11:51PM
Location: Pa
Posts: 3064
If you are talking about bondo work, I sand the filler with longboard 40 grit Norton or 3M paper in large diagonal strokes across large surfaces. For smaller areas a standard sanding block works. For curved areas I use a hunk of radiator hose again with long strokes to keep things straight. When the surface is sanded, go back with some more bondo and fill in any low areas and heavy sanding scratches. This gets sanded with 80 grit, 100 grit, and finish with no finer than 180. Otherwise, the primer-surfacer won't adhere well. That gets sanded with 180, 220, and finish with 320 before final sealing and painting. The sealer should be scuffed with grey Scotchbrite pads (red pads are good for scuffing before sealing) but do not break through the coating.
The new paint systems may have different methods, so ask your dealer or check with the paint mfg. for specific details....
<span class='smallblacktext'>[ Edited Sun May 27 2007, 08:48PM ]</span>
Joined: Sun Feb 05 2006, 11:51PM
Location: Pa
Posts: 3064
Then skip to the 100 grit and up sandpapers. I use a DA to sand the paint back to a featheredge first.....keeps those pesky sandscratches from showing up later once the solvents get into them
Joined: Sat Sep 23 2006, 04:30AM
Location: Sharpsburg, GA
Posts: 924
It's a dual action sander for feathering the paint around a repair. Are you making spot repairs or painting the whole car? Stripping all the paint or painting over the old paint job?
If you are doing the whole car, you will need an assortment of sanding blocks- check out a supplier like this one.....
Joined: Mon Oct 10 2005, 08:43PM
Location: Calgary, Alberta
Posts: 978
Just checked out their site - lots of stuff there. I'll be painting the whole car, and painting over the old, except the hood and trunk lid which are being bead blasted - it's just too much of a pain in the @ss to deal with all the bracing underneath. So this is going to take more than an afternoon to do, is it???
Joined: Sun Feb 05 2006, 11:51PM
Location: Pa
Posts: 3064
Make sure whoever is doing the blasting on those parts takes care not to blast too hard...I gave a 63 T-bird trunklid to a new kid at our shop to blast and when he was done, you could see the outline of all that structure on the top surfaces of the lid ....threw it away and had to find another lid
While it is usually ok to sand original paint and paint over it, you have to make sure the old paint is tightly adhering and free of cracks and surface checks. We used a product called "Rust Defender" which was a yellow primer-surfacer that had a small bottle of hardener like fiberglass uses. It keeps everything down under a new paint job...no problems on the Little Red Express truck we did for over 6 years, before it was sold (probably still nice...it went to MI ) !thumb
Joined: Sat Sep 23 2006, 04:30AM
Location: Sharpsburg, GA
Posts: 924
You may also have several paint jobs one on top of another on such an old car. Mine had three. That is too much paint to leave on there. You can use a DA sander to cut through several layers until you get to undamagd paint with no checks or cracks. It will create a massive dust cloud, so wear a mask and have good ventilation. Then you can fill those dings with a little bondo or some glazing putty if they are very minor..
You will need a long, flexable board (longer the better) to get the large open areas smooth enough for a wet sanded finish. a mirrorlike finish magnifies the slightest errors. Things that you can't even feel by rubbing your finger over will be visible. Your car has lots of very curved areas where you will need something like Stitcherbob's rubber hose. I use small flex pads from Eastwood.
Plan on a long, frustrating project with lots of do overs. It will be worth it in the end, though.
When block sanding your primer use a guide coat (light mist of darker colored paint) to see where the highs and lows are. Dont chase after the lows too much, if you get down to metal and you still have low spots, then you need to reprime or fill with glaze coat. The most common mistake I see is someone who will dig into a low spot to get that last bit of guide coat cleaned up, when all their really doing is making a bigger low spot. Use light pressure and long even strokes at about a 30 degree angle, then turn around and do the opposite angle. Always sand the direction you will be looking at a panel (ie dont go up and down on a quarter or door, or side to side on a hood) that will help hide any waves in the panel. Use the longest block you can fit on a panel, and dont use hard blocks on round corners or you'll have flat spots. I start with 180 grit, then reprime and sand with 320 grit. Depending on how straight it is after the 180, you may have to prime and 180 again. After the 320 grit I go over the car with 5-600grit by hand without guide coat to knock down any 320 marks. If your painting a dark color or metallic you can spray on some guide coat and do the 5-600 grit wet with a soft block. Remember that any chip or scratch you miss is going to show up in your paint job, make sure to get door, hood and fender edges cleaned up good, there will be a lot of chips in those areas that you will miss while trying to get the flat parts straight. I use Dura-Block sanding blocks, you can pick up a set for about $35-50. I could lecture for hours about block sanding, its what makes or breaks a killer paint job and its easy to do wrong. I'm so anal about it I dont even let my employees do it. Take your time is the last piece of advice, it should take days of block sanding to get it good, a week or more to get it perfect.