hey guys,
its now time to start filling in some dents and rust spots on the doors.
if you could give me one good pointer on this subject even down to the littlest thing i may not know, it would help me out alot.
i have layed on bondo/sanded repeated about 50 times and still can feel a bump or imperfection. i just cant seem to get it perfect.
so if you had to give me a tip big or small what would you tell me to do?
thanks
Mitch

 

Try using a sanding block. If you're just sanding by hand then you're not getting an even wear.

 

the best way , as said is a block ,, I do all my finising with a hand board sander ,in a cross hatch pattern, make sure the paper isn't loaded up ,, . this is where I spare no expense , as in stop using paper even when it looks to be still good . I begin with 80 end up with 180 ..A guide coat may help if you are a beginner...

When you get it close to straight ,, use primer surfacer to finish getting it straight..

I have found that if the early layers of filler get too hard compared to the final layers,the harder ones will tend to make bumps, do to they are harder to sand (thats where the sharp sand paper comes into play the most).. Try to do each area , from start to finish , on the same day

 

Well I'll throw this out there... Maybe your problem is not the filler work but in the sheetmetal preperation. Did you bang (or pull) out the dent completely and correctly? Or did you just fill in? That makes a world of difference... A little metaloligy:
as metal dents inwards it stresses outwards usually following the path of least resistance. for instance if the dent were in the center of a flat pannel then there would be a dent inward and surrounding the entire dent would be a "ridge" outward. Filling the dent will cover the dent but do nothing for the ridge which you will see very clearly when painted!
If the dent is in a body line then the "ridge" will go where ever it is easiest to bend outward, usually in the flat areas...
As metal bends it also stretches so it actually becomes larger than it was therefore will not want to just go back into shape. In order to fix this you must reshape the metal with dollies and body hammer effectivly shrinking the metal back and even smaller than original shape so it will stay there and not want to "pop" inward and outward when pushed on.
I hope this makes some sense to someone, you must understand what the metal is telling you so you can put it back. Only then can you apply filler to smoothe out imperfections from beating.

As for filler the largest mistake people make is to just "bondo" the size of the dent... After working the metal surrounding the dent a 2" dent usually ends up filling a 10" area with filler (keep in mind the filler will only be paper thin) if the metal is reshaped correctly. Use the largest block possible that will fit in your work area (body lines, end of pannels, bumpers, ect use smaller block)

 

Yes if the metal has oil canning at all that must be fixed first. You should grind aways pas the actual area that needs fill and featheredge the paint at the edge for a gradual transition from the metal to paint so you can't easily feel it when you run your hand over it. You should also apply your filler a little ways past the area you are filling and the edge should feather when you are sanding. Many beginners end up taking too much filler back off. Like action said sand in an x patterns in different directions (except where trying to make a straight bodyline). Use the longest block you can comfortably work with, and if its possible block sand across the entire filler area until the edges of the filler begin to feather in, and it should start to be getting straight other then what low areas are there that still need fill, or you are breaking though because of high areas. A guide coat may help you see where areas are still low, and high areas will break through. You still need some feel (holding your hand and finger tips flat and running them over the spot)which experience helps to tell you what areas may still need somework and when your feeling a highspot or a low spot. I still use 36 grit if its a larger area and have a bit of fill. If its a smaller dent and I am using a finishing filler, I'll normally start with 80. 80 just cuts too slow for me roughing larger areas out, and think its easier to get things straight with a courser grit. I'll either leave some room in the filler to go over with 80 well, or run over with 80 when straight, and skim coat the whole thing again with filler and block that with a finer grit. You should have all your scratches to a minimum of 80, even better 180 before priming. 36 is too course for primer (except possibly poly primer) and even 80 if you don't put the first coat of primer on somewhat wet, its possible you can just bridge over the scratch and the primer not really fill them. If you stir your filler or mix overly hot, or apply thick coats, you will have more pinholes, I usually stir in the harderner a little at first, but filller is best mixed using a spreader and folding it over on to itself to avoid introducing air and to squeeze out the air pockets if that makes sense, which is what I do for final mixing of filler. Little hard to explain.

 

....Not always....

Depends on the size of the dent & what caused it...The area around the dent , will be raised up...need to tap it back in....

Then remove the dent....

 

I add a little honey ,to make the final coat "flow out".....& less work to sand.....

 

Yes, you need to see that there is no metal that is slightly too high.

You also need to make sure that once the edges get milky, you quit sanding or you will dig a hole aroung the edge.

Once you get that high spot out, use a skim coat for the final filler coat. To do this add fiberglass resin at a rate of about 25% of the filler volume. This will let the last coat flow on better.

Good luck,

 

I did not read all of the replied above...but I can echo what has been said so far...you may not be using enough material in your repair....Too, the bondo will not work over paint....you must bondo over the bare metal....I really do not know if this was covered inthe above replies, but putting bondo over rusted areas is really just procratination....sooner or later the real problem of RUST had to be addressed. The answer it to cut out the rusted areas, apply sheet metal and then tap it down and use the bondo.
My understanding is that there are new products on the market that work just as well, but I have never used them. I am a garage bodyman, so you should basically pay attention to the replies above....Many of them sound very PROFESSIONAL to me...

 

**** body filler needs to be at about 68 deg or warmer- same with the metal - I like them both as close to the minimum as possible and even 65 or so....gives you more time to play before it stiffens. might have to wait another 5-10 min before forming but don't care as that 5-10 minutes or more is spent removing stuff that i don't have to when i have more time to apply it.

**** I've tried a lot of different brands and really like evercoat ...especially their polyester metal glaze as a finisher...comes in a thick plastic tube you squeeze it out.

****used a lot of the metal to metal which is silver and comes with an amber liquid hardner...does not make a 3rd color when mixing and it's hard to tell if it's all mixed in with the hardner...it clogs the sandpaper as well but it smoothes out real nice and seems to be stronger than even the fiber filled fiberglass filler....?? still need to experiment more...and have tons of projects.

**** I use 80 grit or rougher under filler even if it's going over filler...rough it up and give plenty of area to stick!!! and keep using cleaner before applying...I use the ppg stuff.

 

wow fellas, thanks for all the help and replys! i think im starting to get the hang of it! but still cannot get to my satisfation.
i dont know if im being to picky or if im just feeling things that are not there.

and i forgot to mention im working on 2 doors and 2 fenders that i have sand blasted. so its all nice bare steel.

and when my edges start getting milky and its still not perfect what do i do stop and put on more bondo?

and i try to tap down all my high spots with one of those hammers to get them a little lower. and there all little dents that im trying to fill in, maybe the size of a bottom of a can. and they are not deep either so i dont know why i cant get it?

and i have been starting off with 80 grit and work my way up to 220 as a finnal. is this smooth enough or do i need to go to the 300's?
and im using one of those hand sized sanding blocks.

sorry it took so long to reply but my comperter had some trouble, my damn brother and his naughty web sites, LOL!

any ways thanks alot guys!
couldnt do it without your help!!!!!
Mitch

 

when using a "hammer" on the high spots you need to use a shrinking head...ie one that pulls the metal in a little while moving it...other wise you stretch the metal even more and it moves somewhere else to accomodate the stretching. If bare metal i'd use a bit of spray can primer and a 10" or longer block....sanding at an angle the high spots become obviouse quickly...then a pick hammer and lighly work over the high spots...even use a hammer and metal punch to get the smaller areas as i am not that good at controlling the pick yet....then respray and you will begin to see significant changes. the sharp poke that the pic and punch make...though barely noticable pulls metal towads it rather than pushing out....makes a big difference.

Do everything that you can to move the metal before you use filler and i have grown to really dislike "bondo". There are other products that imo are much better, stronger and easier to work with.

hope your having fun. I'm getting ready to epoxy my 72 torino and go after the body again. i've screwed up a lot but have learned much doing so...I also read and there is a video on one of the ebay stores that looks really good for reasonable.

my homemade paint booth is almost ready as well...timeto break out the iwata and do some damage!!!!