How to apply body filler- Fix, Fill, and repair body damage Correctly.

How to Apply Body Filler – Mixing, Spreading, Sanding & Tips
From a YouTube Livestream with Kevin Tetz

Eastwood with its videos, tech library and online forums want to help you become a better body man. Kevin Tetz is already a pro, turning out show quality paint and body work, and teaching you how to do it yourself on his Paintucation series of DVDs. Together they have teamed up for a series of live streamed how to sessions, and the new Hands on Cars web series, both aimed at showing you the correct way and maybe teach you some time saving pro tips from years of experience. This body filler demo first streamed on April 11th, 2014, and the full video is up on YouTube on the Eastwood channel in 3 parts.

How to Body Filler

In this how-to session Kevin goes over the various Eastwood Contour polyester body fillers and surfacers, as well as other Eastwood products. He talks about which to use where, how much to use, how to apply it, how to shape and sand it, and how to get it ready for primer and paint.

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Up until the 1950s the standard way to smooth panels after dent repair was with lead body solder. Even up into the early 80s the factories still used lead solder on bodies, like this 1978 Chevy Camaro Z28. Some old school traditionalists still prefer metal solder based body fillers, and that is why Eastwood sells lead free body solder. There is really no reason to use lead now with the polyester fillers being as good as they are, and if you try to apply the same techniques you have used for lead to modern filler your repairs aren’t going to come out too good.

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For instance, this dent is over a 1/2 inch deep where the hammer hit it. Sure you could just slather on the filler, sand it smooth and paint over it, but it would be a low quality repair, the would not last a particularly long time. That much filler will shrink with time, and a wad of it that thick won’t be flexible enough to move with the fender, so it will eventually crack.

What to Use Where

Flexible Filler – This Evercoat Poly-Flex Polyester Flexible Glazing Putty is great for filling in gouges and imperfections in flexible parts like urethane bumper covers. When you use it be sure to also add a flex agent to your primer/surfacer and paints, otherwise you can still get a cracking issue eventually.

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Fiberglass Short Strand Filler – The Contour Short Strand Filler impregnates the normal polyester filler with strands of fiberglass for extra added strength. It is particularly good for use on fiberglass body panels, such as Corvettes. Because the stands also add stiffness it is not good for places like the leaded sail panel seam on the 70s Camaro because the body flexes there, and the filler will crack. The strength does make it particularly good for use on the edges of panels and straightening out gaps.

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Aluminum-Filled Compound – The Contour Aluminum-Filled Compound is great for use where back in the day you would have filled in with lead. This is what will eventually be used to fill in the Camaro sail panel where GM applied lead. The reason for this is that it remains more flexible than the other fillers, so it will move with the flex of the roof and car over the years.

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Body Filler – The Contour Premium Body Filler is going to be your go to filler for the majority of jobs. Unless you need to use one of the other products, this is the one to use. It’s great and has thousands of uses.

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Glazing Putty – Contour Polyester Glazing Putty is the step between the filler and the primer surfacer. Like it says right on it, it’s great for filling sanding scratches and pinholes. Shape your filler with 36 and then 80 grit sandpaper, then do a coat of glazing putty to smooth it and sand with 180.

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Polyester Primer-Surfacer – The Contour Polyester Primer-Surfacer is like a cross between a high build primer and a body filler thinned down enough to be sprayed like paint. It was originally developed as a way to smooth larger surfaces with lots of small imperfections, like hail damage. It is easy to apply, will tolerate massive film thickness, and doesn’t ever shrink.

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Shaping and Blocking

There are lots of different opinions on how to shape and block and what grits to use, but here is what Kevin recommends: Shape and smooth the filler with 36 grit. When its smooth and feathered properly (this may take more than one application) use 80 grit and glazing putty to get rid of the sanding scratches. Finally smooth the whole area with 180 grit before applying primer-surfacer.

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Now blocking is a whole other subject that Kevin did a whole other video about, which can be found here. But there are tons of different sizes, shapes and techniques to be used in shaping an blocking filler.

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Filling the Dent
1) Once you have sufficiently hammered and dollied out the dent you are working on, you can check with a straight edge. It is more important to get any lumps level with the surface than it is to get the low spots up. Look along the straight edge for daylight to see how far off you are. You don’t want to have to apply any more filler than is necessary. Any spots lower than 1/8 inch could use some more work.

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2) It’s already been done here, but you should strip the paint off the area to be filled, and a large portion of the surround area to give you room to feather the filler into the existing surface.

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3) Mix up the filler in the can and make sure it is uniformly mixed with its resin. Knead the hardener in its tube too, to make sure it is uniformly mixed. Spread a dollop of filler on you board, and mix in your hardener.

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4) Start applying the filler to the dent. Just gently spread it on the surface with the spreader. No need to use a lot of force, or try to apply a lot of filler. The first coat can even be just like a primer to establish the bond between the metal and the filler, and the next layer will just stick filler to filler.

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5) Once it starts to kick off and harden, is time to leave it alone, clean off your stirrers and spreaders with a little PRE painting prep and a rag. Feel the surface of your filler and see if it is tacky still, or as Kevin say “smuckin”, because that is the sound the glove makes pulling away from it. Spray a little Chassis Clean or Aerosol Injected Cleaner on a rag, and use it to wipe the resin off the top layer which will help it flash quicker so you can get to sanding.

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6) Once the tackiness has gone, and the filler has started to powder you can proceed. Now, with the filler just barely hardened you can shape it with a sanding block much, much faster than if you were to wait an hour, or several hours until it is fully hard. Doing it this way you can do 20 minutes worth of work in just 2 minutes.

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7) Spread, spray or scribble (with a magic marker) a guide coat on to see where any low/high spots are, and continue shaping. The guide coat is also great for seeing the 36 grit sanding scratches you need to get out before primer. Now block and shape with 80 grit and a block big enough to bridge most of the repair.

guidecoat

8) Next mix up some glazing putty and repeat the same process you used with the filler. Glazing putty is thinner, and goes on finer for filling in minute scratches and such.

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9) Once the glazing putty is not tacky anymore and started to harden, wipe it down with the cleaner and start blocking with the 80 grit until smooth. Once it is shaped and feathered with 80, move onto 180 grit and feather and smooth it some more.

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Other useful Products

Here’s a few other Eastwood products that are useful for this stage of a project. The pad of Quick Sheets are great for mixing body fillers, then tearing off the old page when you are done for easy clean up. The various plastic spreaders make it easy to get filler smooth when working in tight bends, cracks and crevices of the body work, so you have less shaping to do. Next to the spreaders are a spray guide coat, and a rub on powder guide coat for finding the high and low spots while shaping and blocking.

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Blue nitrile gloves are great if you don’t want to be picking filler out from under your nails for the next week, and they keep your skin oils off the surface for a better repair.

The Aerosol Injected Cleaner is made for cleaning out spray guns, old fuel and brake lines and other hard to reach little places, and it will wipe the resin off the filler allowing it to harden faster. PRE painting prep has thousands of uses, and one of them is to clean the filler off your spreaders so you can reuse them. It also will wipe still soft filler off body work if you happen to get some somewhere it shouldn’t be.

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Conclusion

So there you have it, hopefully Kevin gave you some good tips that will take away some of the work aspects of body work. If you want to see more of Kevin’s tips and how-tos just take a look at Eastwood’s YouTube channel for his other projects including the “Jaded” Mustang. Be sure to watch Hands on Cars too, as Kevin takes a tired broken down 1978 Camaro Z/28 and rebuilds it into a budget pro-touring car.

Questions and Answers

What is better body filler over bare metal, or body filler over epoxy primer? – Epoxy creates an excellent bond over bare metal, and the filler will create a chemical bond with the epoxy with is stronger than a mechanical bond. But, you can apply it direct to metal, or DTM. If you have a late model car with galvanized body panels however, you must spray the metal with an epoxy because the layer of zinc put on in galvanizing is not a strong enough bond for the filler. If you have the whole car media blasted, it’s a great idea to have it sprayed in epoxy afterwards, because then you don’t have to worry about rust happening before you can get to the body work on the whole body.

What is the application window on epoxy? – You can spread filler, or spray paint over epoxy for up to 5 days without sanding it and get a chemical cross link bond.

If you have a body seam that you would like to fill and hide on a custom car, which was exposed from the factory, what would you use? – What you don’t want to use is just a layer of body filler and hope. The seam was there to allow flex and make assembly easier at the factory. If you just fill it in the flex will eventually destroy your filler. The best thing to do is sand it down, TIG or MIG weld the pieces together to eliminate the potential for flex, and then finish it with filler.

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Do you need to re-sand the metal after media blasting in order to make paint or filler stick? – The answer to that is it depends on the media. With heavier media that leaves a rough surface you can paint right over. But if you use soda blasting or something that is very gentle you will need to re-abrade the metal to establish a tooth for the paint or filler to stick too.

What is the maximum thickness of filler you can use and have a good repair? – You want to keep it to an 1/8 inch of thinner, 1/4 inch at the most if there is no way to get the metal any smoother than that. Think of the filler as polyester surface enhancer, and not dent filler.
Are there any tips for keeping body lines crisp when filling around them? – Yes. The best thing to do is use some masking tape. Apply the masking tape along one edge of the line and do your filling, then peel is off while the filler is still wet for a crisp line. After blocking out that filler apply the tape to the other side of the line and do the same thing again. This is a great thing to do when blocking the primer-surfacer too.

Are there any tips for keeping body lines crisp when filling around them? – Yes. The best thing to do is use some masking tape. Apply the masking tape along one edge of the line and do your filling, then peel is off while the filler is still wet for a crisp line. After blocking out that filler apply the tape to the other side of the line and do the same thing again. This is a great thing to do when blocking the primer-surfacer too.

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2 thoughts on How to apply body filler- Fix, Fill, and repair body damage Correctly.

  • I actually have a question, I have done body work but it has been several year since doing, I have a 1995 Ford F150 XLT which I have babied since buying it new! It has 91,000 actual miles on it. I have noticed that the wheel well [arches] exterior is just beginning to have some small rust spots show up and I would like to address this situation before it becomes a major issue and I would prefer not to do body replacement panel if possible. What or how would you all suggest that I go about repairing this problem?

    Looking forward to hearing back from you in the near future as I would like to get started on this project as soon as possible.

    Thank you and may you all have a ‘splendid’ and ‘blessed’ week!

    In His Service,

    Dave E. <
    Saint Joseph, MO

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