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Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Body - Exterior> Scratches in the primer filler after blocking
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Topic Review (Newest First)
11-20-2005 09:05 PM
JLarson69 I 've always started blocking with 180 wet, reprime, block with 220 wet, and then DA with 320 and then 400 dry.
It seems to me blocking with anything finer, you'll just be chasing the waves instead of making them straight. It doesn't take long with 180 to block it straight.
11-10-2005 03:14 PM
Scode68 The guide coat is applied like a fog, just enough to give it an off color look and when sanded you can see the difference in color. Seems to be a difference between the 1104 applied with the conventional gun and the 1107 applied with a HVLP. I have to add that it seems like I get the polished look after wet sanding with the 400. All of the guide coat disappears though and I canít see or feel any low spots.

While dry sanding I brush the paper off to keep the dust down (or blown when sanding outside) but would often replace the paper when a difference is felt between it and a new piece.

Iíve been pretty busy at work lately so Iím beet when I get home. Needless to say nothing has continued but then again the weekend is almost here.
11-10-2005 12:48 PM
Bee4Me My thinking is this for your problem.
IF it's taking THIS long to sand out something of this size,
Your paper is clogging and your NOT sanding,just rubbing,your "polished" look.
Your spraying the lacquer guide too heavy and clogging your paper with IT.

Fact is, Wet or dry,it should not take this long.

When I do dry sand,I keep my paper blown off with air.
11-10-2005 06:46 AM
Scode68
Quote:
Originally Posted by Lost in NJ
I also have an older Dupont technical book from a class and they recommend URO at 4:1:3 for a sealer. I put on two coats as a sealer and did a light sanding with 600 wet (hey I have a lot of it). It sands out real nice and no scratches show through.

How old is that Tech sheet? The most resent one shows the sealer being mixed at 3:1:2.

I donít know why there are a lot of people beating me with the guide coat since I said that Iíve been using a light colored lacquer for that. And it also looks to me that I was done with that part as far as using it to block out the high ands low spots. Other than the scratches and the concerns about the URO, I didnít have a problem.
11-10-2005 05:29 AM
jcclark I tried dry sanding 2k primer once with 400 and had scratches
showing up, I never got them when wet sanding with the same paper.
If I dry sand I have to go to 600.
Different papers and primers behave differently, for me 400 is to course
when dry sanding but fine for wet.
11-10-2005 04:04 AM
adtkart I personally don't use anything finer than 320 when sanding dry. The finer grits do clog up more, as there is no way for the dust to escape. If it has to be blocked with finer, use water. It does help with the clogging and also lubricates. Using a brush to clean the paper, in my opinion, reduces the cutting of the paper. You can blow it off with air and get better results. Just make sure that you wear a face mask. You don't want to breathe in all of that dust.
11-09-2005 08:51 PM
Mark'zinger70
primer

respray 2-3 wet coats/ block with 240 blow off gidecoat sand with 500 da softpad and your ready for paint....
11-09-2005 12:13 PM
Lost in NJ
URO and sanding

I am not pro, but I have been playing.

First of use a guide coat before beating yourself to death chasing problems.

I recently got some hookit II 320 (real cheap) and was using it dry on the URO. That is the ticket. It sands fast and is high enough grit for final sanding on solid colors if you need to do that. The hookit II 320 lasts forever without buildup. I had been using some open cut 320 sheets for my primer.

I also have an older Dupont technical book from a class and they recommend URO at 4:1:3 for a sealer. I put on two coats as a sealer and did a light sanding with 600 wet (hey I have a lot of it). It sands out real nice and no scratches show through.

I also have been using the hookit II finishing film for color sanding and that is wonderful.
11-09-2005 06:41 AM
Scode68 Here are two quotes from the thread

Quote:
Originally Posted by Bee4Me
I prefer 600 wet followed by a double stack gray scotch pad dry.
Quote:
Originally Posted by baddbob
Since then we've had to change to finer grits for prep especially on metalics. My preferred grit is 600 followed by a rubdown with a grey scotchbrite but sometimes I use 800 depending on the mood I guess because I really don't see much of any difference in results. If you're spraying a sealer 400 dry (hand sanding)would be about the coarsest grade I would consider using especially with metalics, 400 wet may be too aggresive IMO, 400 on a DA is usually alright. Bob
Link to Thread
11-08-2005 10:58 PM
Scode68 I didnít get a chance to do anything tonight but maybe tomorrow. I think I remember reading someone saying that they will sand with 400 and then run a gray scotch pad to eliminate any of the 400 scratches. Maybe Iíll try that.
11-08-2005 06:59 PM
roger1
Quote:
Originally Posted by chadsbodyshop49119
I feel the same way with 400 and sanding, it clogs to fast.. i don't know how you guys do all your sanding dry... I did one today and it sucked.. although, it's getting painted right now, that's the plus side. no sloppy water everywhere
I have good luck sanding dry with the 400 3M stikit roll paper. I do use a brush on the paper to knock off any loading of dust occasionally.
I think maybe it does make a difference which kind of paper you use. Give that paper a try. I always keep a roll of 180, 320 and 400 on hand. I also have the 3M board that is meant for use on their stikit paper but, it should work with any board.

I agree about the 600. That has to be wet sanded.
11-08-2005 05:53 PM
chadsbodyshop49119 I feel the same way with 400 and sanding, it clogs to fast.. i don't know how you guys do all your sanding dry... I did one today and it sucked.. although, it's getting painted right now, that's the plus side. no sloppy water everywhere
11-08-2005 04:38 PM
mrcleanr6 600 dry in my opinion is a losing battle. a couple swipes and its clogged with dust and doesn't work anymore. there is really no reason you cant do 400 dry with a block. you can then lightly go over with 600 wet if you want. if it was me i would get it flat with the 400 and a block then very quickly run over it with a da and a soft pad with 400 to smooth out any uneven scratches and your ready to go. if you spend more than 3 min with the da your overdoing it. da scratches are much smoother than when blocked and if you put a soft pad on it, it will smooth it evenly.
11-08-2005 05:39 AM
Scode68
what about the paper?

Ok, I sprayed it with a further reduced filler primer mix of 4:1:2 (primer:activator:reducer) and there is defiantly less build but it looks like the scratches were filled. I will know better hopefully this afternoon if I get a chance to sand it. Since the primer is dark gray I have been using a light colored lacquer guide coat and that is how I knew that I had a flat surface.

Now for the paper! I was going to start again with 400 dry and then hit it with 600 dry but I think I am going to see how the 600 works first. As far as wet and dry paper goes, is there a difference in the grit? I thought 400 would be 400 regardless. Thought the only difference between the two was that the wet type could handle the water and not lose the aggregate.
11-07-2005 07:55 PM
chadsbodyshop49119
Quote:
Originally Posted by scrot
That white plastic Hutchins sanding board is a Bad Mamma Jamma!
I really like it for final sanding. It's light and has a Pistol Grip handle and knob that's easy to hold onto.
It's bad, bad, and bad!

I'm with this guy..
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