question on roof repair

[AK-Z]

Whats the best way to body fill the roof?. Mine has all these dents and I'm tapping them out but its just not even. I've tried filling in trying to use the least amount that it possible, but it just isn't feeling right (by touch). I was thinking about just piling it on and just sanding down (out of frustration), but I've seen what can happen when you do that (after a couple of years).

 

My tools that I have been uing are:

 

high speed drill with sanding disk

sanding disk with grits 40, 80, and 120

 

Finishing sander with the same grits

 

block sander with the same.

[SSflyer]

My roof was also trashed, from hail damage. I tried spot filling all the dents, but the edges always showed through the primer. In the end I got some Plastik Honey and used it to 'thin' the bondo, and then spread a thin layer over the whole roof. Then I used an 18" sanding board to smooth it out. I rough sanded until the metal just showed, and then went to fiiner grits. When it was ready for primer the bondo was so thin it was almost translucent, so don't worry about having too much left behind.

[johnc]

Find another roof skin. It sounds like a buttload of work, but finding a good roof, drilling out the spot welds and cutting it off at the C pillar is a lot quicker then spending decades trying to get a dented roof straight.

[Sparks280zt]

My roof was also trashed, from hail damage. I tried spot filling all the dents, but the edges always showed through the primer. In the end I got some Plastik Honey and used it to 'thin' the bondo, and then spread a thin layer over the whole roof. Then I used an 18" sanding board to smooth it out. I rough sanded until the metal just showed, and then went to fiiner grits. When it was ready for primer the bondo was so thin it was almost translucent, so don't worry about having too much left behind.

 

This is the same method 240hoke used I think and his roof is so even its sick!

[rigez]

I can't remember where I saw it, but on one of the Z boards I read that one member used a blow torch to carefully heat up the problem areas on his roof and then used a damp cloth from the interior to cool it down. A heat shrink method. The damp cloth was used to snap the heated metal back to its original shape. I'll see if I can find the thread.

[Bartman]

I have the same problem, and this is great Information. My dents are more of the large surface area, but small depth. Some of them you can push out from the inside, but the metal is stretched so they come back.

 

I need to get the surface stable before I use any filler on it. Is this something I can fix by shrinking? I'm worried about shrinking it too much and losing the crown.

[Trevor]

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=012&item=220025138512&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1

[Bartman]

I hope this isn't a hijack AK-Z, and maybe this heat shrinking disk will work for you as well. I can see how this shrinking disk would work on a dent protruding out from a crowned area, but will it work for a depressed area in a crown as well. Here' a very simplistic drawing showing a crown and a crown with a depression.

Will attempting to shrink this dent actually pull the dent back up or just make it worse? In my case these "oilcan" dents cover a fairly large area, so if this method would work would I attempt to shrink the entire dent at once, or work on small areas at a time? Would you work from the center out, or from the edges in?

[jnjdragracing]

The way we fixed ours was to pop it out, take a punch and hammer and tap around the part we poped up, this will shrink the metal to be worked. Contiue doing this until it is rigid again. Then of course we air filed it, not getting it to hot. Then applied bondo with fiberglass resin so we could work a lot at a time and make it smooth as silk, then worked this with the air file and sanding block. The key thing is not to get it hot, this will cause it to warp. Then prime and paint it. It tooks us about three nights work to finish the job.

 

 

John

[Dayz]

Bartman,

In your case, I believe you have 2 high spot and one low spot. I would try my best to get that big low spot out by just pushing it. After you should still have 2 high and 1 low but a lot less difference between them.

 

Work your way from the outside with a mallet (not necessarily in metal, wood) with a flat backing plate in metal larger than the surface. Work your way from the outside gently, always pushing toward the center point wih a shrinking hammer.

 

You should be close to perfection at the end.

 

I have done a couple of leading edge of airplane wing without a backing plate, just by working my way from the outside.

 

It is fun, go slow, and when you get fustrated go get a scotch !!!

 

Dayz

[AK-Z]

I hope this isn't a hijack AK-Z' date=' and maybe this heat shrinking disk will work for you as well. I can see how this shrinking disk would work on a dent protruding out from a crowned area, but will it work for a depressed area in a crown as well. Here' a very simplistic drawing showing a crown and a crown with a depression.

[img']http://album.hybridz.org/data/500/dentInCrown.JPG[/img]

Will attempting to shrink this dent actually pull the dent back up or just make it worse? In my case these "oilcan" dents cover a fairly large area, so if this method would work would I attempt to shrink the entire dent at once, or work on small areas at a time? Would you work from the center out, or from the edges in?

 

Well I would assume that, that wouldn't work as it is. you would have to pop out the dent first and then use the "shrinking disc" on the portion was ceowned since thats the area where it was stretched.

 

Well I am "experimenting" on my other datsun that I'm going to trash after the one I'm wokring on is done (parts car, no title). I'm using a oxy torch with a NO 1 sized tip. Seems to be working pretty well. The parts car has a huge crown dent due to heavy snow last winter, popped it out and pounded out the crease and am using the torchand a wet rag, about 6" away from the metal and working in areas about a foot apart, so I don't have to go back and rework the metal too much. I found that whether you heat/cool from the outside or the inside also effects how the metal will shrink (not much but help in certain situations).

[AK-Z]

FYI' date='

 

Shrinking discs will not work very well - if at all - on a panel that was filed, used a grinder on, applied heat from a torch, because of memory loss.

 

Depending on your situation, you might consider the method of punch and hammer as JNJ mentioned!

 

RacerX[/quote'] Yeah I don't like the idea of using friction to produce heat on sheet metal. I might try that, but most of my dents are out along with the creases, so itits just a matter of shrinking in the right places at this point.

[Guest URSUS]

Did you try using a shrink hammer and dolly. You don't have to go crazy with it. Then use a body hammer to help smooth it out. The roof metal is very thin so it stretches easily. Also dont just work on one dent the whole time and move on the the next in the roof sometimes a dent won't properly smooth out unless another one is smoothed also.

[jmurphz33]

Oh no------

I feel your pain. The roof of my 280 looks sort of like a giant golf ball... it's not pretty at the moment.

But filling and using the long sanding block sounds like a good plan--- or that flexible sander that racerx posted. Looks like I've got some work to do.

Thanks for being so thorough and willing to help, fellow z guys.

I'm impressed with most threads I read on this site because it seems like everyone is really into helping eachother out. I dig!

-John

[MusPuppis]

On stubborn roofs I use an O/A torch to shrink the metal, if its being a pain.

 

In general, this is my method for filling and smoothing:

 

Back it to bare metal, do what metal work you can. Another thing to be cautious of here is when backing the panal to bare metal, go easy, grinders can build up enough heat to slightly warp panels on occasion. Once thats done, get your filler and fill the primary low spots, I cut it with 80 grit and leave it at that. When your satisfied the spots are decent (not perfect, just high or very close to correct) I go over the whole roof with a thin coat of the filler again. Cut the parafin(sp?) with 80, then take an air file with 180 and basidly rest it on the roof. Dont apply any real pressure, just the weight of the file and start filing. Direct it so it rides front to back, over and over and just let it keep going until you start seeing bare metal. Its a slow process but the file does the work, so you can kinda daydream, lol. Just let it go until your satisified with what you have and you think its very very nearly done. NOW! Apply another skim coat of POLYESTER METAL GLAZE (I LOVE that stuff) over everything and fnd yourself a semi ridgid sanding block. You can rebuild the crown now and make sure everything is completely smooth. (I use 180) This is the slow step because now it has to be perfect. Just be careful and maintain the contour.

 

Also, primer should ALWAYS be the bridge between your filler and the metal. Once the your done with the polyester coat and satisfied, prime the hell out of the roof and block her!

 

This is a technique we used on Rag's Z's roof and it came out pristine. Also used it on an S-10 and a Malibu, comes out slick and flat. It seems like its alot of material on the roof, but in the end it all sands mostly back out and you get this ultra thin, ultra smooth layer over everything.

 

Hope that helped, if I need to clarify any points please let me know.

 

Oh, Racer.. You use those blocks? I have been SO wanting to get a set but wasnt sure if they were really as good as they claim to be. Your opinions?

[Ferd/289]

can you tell me what are you thinning the materials with?

[DemonZ]

Find another roof skin. It sounds like a buttload of work, but finding a good roof, drilling out the spot welds and cutting it off at the C pillar is a lot quicker then spending decades trying to get a dented roof straight.

 

 

Words of wisdom.

 

 

Getting a wavy roof straight with bondo is a lot of work. An expert body man recommended that option to me years ago. I foolishly did not fully research that option, and forged ahead with bondo. I got close quickly, but lost myself in the bondo maze later. Bondo work doesn't come much harder than this. But this tool makes a difference, http://www.nationaldetroit.com/tools/tooldetail.aspx?model=900 200 bucks and well worth it. The knock off is about $100, and I think IR makes one. Use plenty of alternating guide coat/spray paint so you can see what's going on.

[MusPuppis]

Sup Racer,

 

Yeah, everything is going well, about to fly to Tampa for 10 days to help a friend out for a little bit, hehe.

 

I think I just might pick up a set of those blocks when finances permit. I noticed that about the paper, I had wondered.. Normal paper crimps if you give it a little too much bend. Found that out the hard way a couple days ago, lol.