hey yall, i filled in holes on the door panel, got it lookin good and stuff, well i go to put on the filler u know, i had bondo at the time and that **poopoo** really does suck ass, idk if i get it on to thick but ive used it a few times now and i can usually not get it real thick on there, i sanded it down with 60grit but got it smooth in some areas other areas still u can tell and has an edge on it and stuff like that, do i just need to keep sanding or what? thanks for any tips and help

Its hard to get the edge to disapear on bondo sometimes. usually I sand the edges smooth first, then go back and level & smooth the rest out. Just make sure you put the bondo in a big enuff area to go beyond the area you want it. That way once you sand the edges smooth..you dont end up sanding all the bondo off where you need it.

thanks man, yea i spread it out pretty good on there, just glad this is a practice door, i hate dealing with bondo. also when u get warpage what does the metal usualy look like. i dont have gas yet just used the flux core, and probably did get the metal hot, but coudlnt really tell if it looked out of shapre or anything

paging martinsr's filler basics thread..........

:) Below text should be of some help. The feathering of the filler should literally be "transparent" as it feathers off. If you see a sharp METAL/BONDO line, it is likely it can be felt as well, and WILL be seen after primering.


"Basics of Basics" Plastic filler
By Brian Martin

What ever tools you use the trick is to not add the last "skim coat' till you KNOW that it is all you need. Don't try to block out that first coat, just use it as a base for the LAST skim coat.

I was taught this procedure after doing bodywork for a number of years and it really works well:

Just apply a nice coat of filler (what ever brand, whatever style, we will put that aside right now). Cut that coat NOT to make it perfect, but to get the basic shape and filling you need as a base for the skim coat. You can cut it with 36 40 or 80 depending on how big the area you are working is. In other words, if you can cut it fast with only 80 then do it. But I would say that this would be limited to an application that is no larger than about 8 inches.

If you happen to have a few high spots, see if you can tap them down.
If you have a few low spots add a bit more filler to ONLY those spots.

Re-cut these last low spots you have just filled with the same grit you have been using (most likely 36).

If you now have a surface that ONE skim coat will fill, then apply it. If you don't work with it a bit more, but NEVER add a little here or there and think you will finish it without a skim coat.

If you have a surface that is very close with only a few VERY MINOR low spots like poor feathering onto the metal, poor transitions from one application of filler to another, or from the metal that is "poking" up here and there you can do the LAST skim coat.

This skim coat is very important, you want it to extend over the COMPLETE area, this is well past the damage you have been working. Maybe as much as 3 inches past the plastic that you have applied to "rough" it out.

This skim coat can be regular filler or a polyester glaze like "Icing" or "Polyester glazing putty", that is your choice, I use both depending on the size of the area being worked. Do not use anything that doesn’t mix with a hardener. NO, “Spot putty” in a tube, only polyester putties or fillers. If it uses a hardener, it cures to a hard film. The “spot putties” stay soft and can become even softer when the solvent from the primer coats it.

You now run a block, long board, or hog even over this skim coat with a little bit coarser paper than you plan on finishing with to cut off the resin that has surfaced in the filler. I usually just use the 36 or 40 or whatever I have been on the "rough" work. BUT take CAUTION not to cut much off, you want to JUST take the very top, don't really sand AT ALL.

Now finish sanding with your longboard or block or hog or whatever using the finer paper like 80 on a large area or 120 on that small 8" sized area. Block it out to perfection with a nice feather edge to the surrounding metal.

I can't stress enough, the trick is to know when just ONE LAST skim coat will do the job. And apply it COMPLETELY over the surface. If you only one little low spot in the middle, DON'T just do it, skim the ENTIRE thing. You HAVE to have one LAST skim coat over the ENTIRE thing every time. If you get in the habit of this you will do it over and over on every dent you repair and find that you can do just about any dent with just
two applications.

As you sand the filler let the board or block you are using run over the surrounding metal. If you only work on the filler you will sand it too low. You need to keep it as high as the surrounding metal, so use the metal as sort of a straight edge that you run the block or board off of.

Don’t worry if you cut through this skim coat here and there. In fact, you WILL most likely cut through. The point of that "LAST SKIM COAT" is that after you add it, you don't add ANY MORE filler. That "LAST SKIM COAT" is just that the LAST filler you add. If you hit a little filler below, or metal, that is normal and fine. The only thing you are looking for at that point is if the panel is FLAT. The filler skim coat is serving no other purpose than to finish you filler work, it is not a "sealer" or anything like that.

You can add fiberglass resin (“A” coat if you have a choice) adding the resin was exactly how I learned from the great Emery Robinson (my personal hero in the auto body world). But remember there was no products like polyester putties back then. When you add resin, that resin comes to the top of the film of filler. It is then something you have to deal with. The whole purpose of the SKIM COAT is to put a layer of filler over the top that is easy to block out with as little effort as possible. You want to be able to concentrate on making the panel FLAT not fighting with gummy resin, sand scratches and the like.

So the polyester putty though expensive is what I use.

How is this for an idea, a co-worker of mine showed me this very obvious tip. :)

Add pour-able polyester putty to the regular filler! What an idea! LOL A little pour-able squirted into the "bondo" really thins it out nicely.

The "LAST SKIM COAT" should be left to cure a good long time. Where you may jump on filler and sand it as soon as it is hard, the skim coat should be GOOD AND CURED for an hour or more. If you can of course, in the production shop you may not be able to wait that long. The benefits of the procedure will not be diminished.

A little added note, I have found that I don’t use 36 or 40 grit at all anymore. I went to work at a shop that didn’t use the coarser grits so I had to learn not to also. I have found that using just the 80 and then finishing the Skim coat in 120 or 180 works great, even on large panels.

At this shop it was the first time that I wasn’t doing my own primer work. This meant that I couldn’t “cheat” with a lot of primer and blocking the body work “one more time”. I found that I had to get the work PERFECT, then give it to the painter. I did this in an interesting way, I look at the last skim coat as even a more “final” step. I now look it as “primer”. You see I have used polyester primer, which is like spraying “bondo”. They are both polyester resin based and act and sand very much the same. So, I figured why not just “spread out my primer” as the skim coat! It has worked GREAT, the painter jokingly says, “do you think I’ll need to prime this or just paint it?” I tell him, “Just clear it, it’s a shame to hide that work under primer”.

This method has worked great for me, it’s more of a state of mind than a procedure.

And don’t be afraid to buy the best sand paper and use a lot of it, the cost of the paper will be nothing next to the time and muscles saved. Find the paint store in town that services the PROS the Body shops in town, that is were you will get the right stuff and the right info.

thanks man that helps alot and really explains it to me, guess ill be gettin some more materials pretty soon and give it another try! thanks alot people :metal:

DEFINATELY buy the best paper. the cheap stuff will just piss you off. the brown 3m 80 stickit on the roll isnt even comparable to the longboard stickit green corps. for the 36 and 80 grit i use 3m green corps stickit or the comparable carborumdum or norton( i recenty tried the blue stickey norton and i like i better than the 3m, it seems like it has less grit so it doesnt clog and lasts longer.) after you block out the filler, use a high pressure air blower to blow the filler out of the paper. if you do this 36 on a block will last forever.

thanks man, ive just started doing body work like shaving tailgate handles and weld in roll pans. and that write up has helped a lot. its the same basic for of the way i taught myself how but its good to see that it does actually work!! thanks agian

You need to finish off your filler with 180 grit atleast 80, but 180 will be much better. Priming over 36 grit WILL just cause you problems later down the road like sand scratch swelling, meaning you WILL SEE every single mark left by that 36 grit paper. Same can go with 80 grit if you abuse your primer,but with 180 its darn near impossible to get swelling.

Sand your filler with 80 grit but then switch to 180 right before you get it straight with the panel.