need a little guidance on block sanding

slammed57

Newbie
Well the media blaster warped my roof and so I put a new skin on. I used quantum 1 filler with slow activator and skmimed coated the roof( here in south florida filler kicks so quick is the reason for the slow activator). I used a 24" durablock with 80 grit to rough it in ,then 100 grit and this last shot was 120 grit. some areas I broke through the epoxy with metal showing and some areas, the epoxy just starting to show. also a few areas where Iam pointing to in the pic looks like I still need to continue to bring down.... so my question where route should I go, glazing putty the entire area, another skim coat of filler. I think its still to soon for high build primer... any advise is appreciated
 

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I feel your pain on the incompetent media blaster. You're still 1 coat away from being ready for primer. IMO. I see a lot of people prime too soon to get to the next step, but once the 2K primer is on it no more filler should be applied. Take the time to get the filler as perfect as you can, is my advice. That roof is a perfect candidate for polyester primer
 
3 coats, 2.3-2.5 tip, guide coat, initial block with 80-120, guide coat, then 150-180, guide coat, 220-320. Finish with 320, then 2 coats epoxy with a 1.4 is my procedure. Sand with 400-600 right before base or epoxy sealer. The initial blocking with 80-120 will tell you pretty quick if it is going to level or not. If you have some low spots like in your pictures, no need to go finer than 180 before spraying 2 more coats. One good thing about the poly is you can apply filler over it if absolutely necessary.
 
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Another thing to keep in mind is that it starts setting up as soon as you add the catalyst. Mix up only enough to shoot in 20-30 minutes or so. Essentially only enough for one coat. If it's going to take you sometime to put each coat on, mix less than that.
 
Thanks all I appreciate it. Can you put back to back coats on with polly, or need to let cure between coats. and once cured after a few days do I need to scuff up if I choose to put another coat or two on? Sorry for all the question , I just want to do it right.
 
Bought 2 gallons of G2 from autobodynow. off ebay. One was damaged and slightly leaking from shipping, and they sent me another one in 3 days. I didn't ask for a replacement, just told them what happened and they might need to reconsider the packing. Awesome communication and service from those guys.
 
Thanks all I appreciate it. Can you put back to back coats on with polly, or need to let cure between coats. and once cured after a few days do I need to scuff up if I choose to put another coat or two on? Sorry for all the question , I just want to do it right.
Following the TDS on any product, as Chris suggested, is always good practice. When using any polyester, filler or spray, always sand off any you don't need. In other words, keep blocking until you start seeing the epoxy or filler underneath start to show before applying more. Use the minimum amount required to do the job. The only part I question on the TDS is the sanding with 400-600 after it is dry. That is just nuts. No way would I consider anything finer than 180 to start. Once you break the skin it sands good, but I always start with 80-120 to do that. You need a coarse grit to start with to get it straight, also. Not going to happen with 400:)
 
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Here's a blog entry I did on Slick Sand after my first time using it about 9 years ago. I put some tips I figured out for myself as well as learning from others up to that point. It will be helpful to you for sure.

 
Some of my pointers... In a nutshell, use the longest block you can find. we used one that was too short and was sanding a low in the middle of the door because of it.. As seen here:

We had already done a couple sessions of priming/blocking the door across to the quarter and to the fender, all installed on the car. After this, more primer and put a perimeter of tape on the door skin. Now block separately, and the tape allows you to block the door and keep off the edge to prevent losing your match to the fender/quarter.

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I don't stick with 45* angles, if you want to keep a long direction flat, you need the long block to better follow that direction. So change up to some sharper angles, about 30* off the long direction every now and then. Work one end to the other, consistent spacing, consistent angle, end to end. Then alternate to passes in the opposite direction.

Once done, and the inner part is good and blocked, now remove the tape and GENTLY block to the edge, taking care to not pull down at the edge and round things back off again. Whatever hand is holding the block make sure it is minimal pressure and stays on the door skin. In other words, no pressure pulling down past the edge.

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One other point, to keep the inner end of the sanding block from sanding out all your hard work in the center of the door, put a wrap of tape around the end of the sanding block that is towards the center of the door. This helps that end to glide across the center of the door without cutting primer there.

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Now to show the importance of the long board..

We had done some blocking with the 27" AFS and seemed to have two high spots with a low in the middle of the door..
Note the high areas marked by the green tape...

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Now we can see that as the sander is moved to the left, the left portion of the AFS is over the high spot on the left, and a bit more movement and the right portion of the AFS will start dropping into the low void. Effectively, this is still cutting material out of the low, keeping it low.

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Looking at the next size up, a 36" AFS....

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Here we can see this one does a much better job of spanning the high spots and staying up on top, for a more effective job of knocking down the highs and leaving the low in the center alone...

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After a few horizontal passes at slight angles, like so with the 36".......

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We follow up with some vertical passes at slight angles with the 27".... all rods removed to better follow the contour. Then alternate back to the 36 and another horizontal session..
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Based on the above, IMO that 24" block is too short for a roof.
 
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