Blocking – How to and when
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I am refinishing a 67 Chevelle and most of the body work came out well. After painting however I noticed small imperfections in the panels such as small waves. Nothing major but the panels are just not exactly straight. I realize without seeing what I am talking about it is hard to address the issue properly but can someone comment on the importance of blocking an entire panel. What technique works best? How many time should you block? Prime? What grades of sandpaper, etc?
This is how I do it, but I am sure one of the experts will chime in more professionally. If the body panel has had body work and filler, I mechanically sand the filler with a DA or inline sander until the shape is right and it is almost straight with 36 grit, then I block sand it mechanically or by hand with 80 grit. Then I final block it with 180 grit. Then I prime it, block it, reprime and seal, then block that 180 grit. Last, guide coat it and block it with 320, then shoot paint.
Doc has a pretty good procedure for doing bodywork,everyone also has there own way of doing things to get the result they want.I treat restos a little different than a collision job.I always strip to bare metal so there are no paint edges to deal with.Using a machine to rough in your mud work is fine as long as you finish by hand with a block.I usually prime a resto twice so I’m not concerned with finishing my mudwork to 180 for the first prime.I will finish filler to 100grit,the finer you go the more wavy it gets,so use sharp paper and cut it flat.When you are applying primer put on a good 3-4 coats and it won’t hurt to let it dry for a couple of days,primer can shrink on you.For my first round of blocking I will start with 150-180 with the longest board I can by hand,no machine.Using a guide coat is a good idea but you also need to use your hand to check things.When it is ready for more primer I will apply 2-3 more coats,let it dry a few more days then wet sand with 400 if I’m going to seal or 600 if no sealer.Post some pics of the chevelle,they are my favorite musclecar HTH :cheers
just a tip that i recently discovered is that 3m’s purple paper makes blocking primer so much easier. dont forget to use a guide coat and i like jaysons idea of priming twice.
just another tip…
Jayson is right that blocking with too fine of paper(or worn out paper) may make it less straight. I usually finish body work with 80 (filler) or 120 (putty). When I think I am done, I will run a few passes over it with 220…not to get it straighter, but just enough to make it feel smoother. This will make it easier to feel the panel. When feeling the panel, don’t look at it, if you can feel any transitions from paint to metal to filler, you are not done. Feel it at a medium speed, not too slow, not too fast…
there are a lot of tricks to getting the panel straight, but if you can’t master feeling the panel, they won’t do you any good.
This is a good tip,do not put filler over paint,you should have a nice transition from filler/putty an inch or two of bare metal then your feathered paint if you did not strip the panel.Really old school and picky but it makes a difference,it will save you from shrinkage and sand scratch swelling.It makes me cringe when I see mud over paint and nice 40grit scratches all over the paint and guys just trying to cover it up with primer :sick: :sick:
so how heavily do you pros use air longboards? inline or orbital? In my small area of expertise I have had just as many issues with using power tools as they have solved, until I learned exactly how long to use the air tool before switching to hand tools. However, I know some guys that literally never sand by hand and manage to crank out some very nice work….
Hi guys
Im just an apprentice and the guy who is teach me told me never to use a D.A. on large panels to cut the filler because he said that you can make waves. :unsure:
the only thing that i can add is that repairs done correctly will come with experience, its not something that your going to learn overnight. you have to master to feel the repair with your hand and you will have no issue. and there will be no need for guide coats. its the same as everything, practice makes perfect. 😉
thanx alot smooth :clappy
I have hand blocks that separate the boys from the men. These wave you see could have been caused mostly by one of two things, or both. First, a large flat primer surface should be blocked with a long flat block getting as far across the panel as you can while keeping contact with the surface as close to 100% of the blocks area. From there your sanding pattern should resemble an x. Depending on the primer, and coats, (I prefer 3 coats then sand), and how straight the panel is, you might go down to 180, but if that’s the case you need to just redo your body work. In theory one would use a block larger then the panel, but that’s not practical.
If you do not have experience, don’t use a power sander. You can make waves all to easy picking up a DA and sanding your car. Most likely you won’t see it till it’s painted.
I sanded new parts for a year at my first job, I had to prove myself to finally use the DA. Now I wet sand new panels, it’s cleaner, safer, and just as fast as a DA.
Well I am 😆 unless were talking a 350 hood or bed side, but I still wet sand it by hand. Any grit over 280 works better wet.
thanx adam for the info :pcorn:
No problem :cheer:
Are you gonna sand it again, and re shoot it?
[quote=”bodymanhelper” post=21478]Hi guys
Im just an apprentice and the guy who is teach me told me never to use a D.A. on large panels to cut the filler because he said that you can make waves. :unsure:[/quote]
Sounds like you have a good teacher, it is in the utmost importance to learn how to do things the right way in this industry. Hacks area dime a dozen, talent is rare.
hat about air longboards?
I have a big, and growing, collection of sanding blocks and longboards. It seems there’s always just a perfect tool for the job.
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