When you begin your classic auto or classic truck restoration, without a doubt, you will run into rust. On this page I will show you how to remove and repair rust holes without using a welder, and this repair should last for years. There are several steps to this procedure. Learn them and you will be on your way to getting great results. You don’t have to be a pro to do basic auto body repair at your home. So, if you have never done any, you’ve come to the right website.
As like with most any project, you will need some basic tools, but you probably already have most of them. At the bare minimum you will need a hammer, a flat tipped screwdriver, a scissors, an electric drill, a palm sander, an electric grinder, safety goggles, a small bucket, a pair of leather gloves, a small rubber sanding block, a small pliers, a wire brush and a stool to sit on (I turn a small wash tub over and sit on it). Here are some photos of some of the basic tools that I used at my daughter’s house because they are what she had that can be used to repair dents, remove rust and old paint.
What can you expect to pay for tools? The electric drill, and the electric grinder together will cost about $100.00 for brand new. Palm sanders are about $30.00. Once you “get the feel “ for the palm sander you can do a good job with it. A double action (DA) sander is the preferred sander, however, it can cost anywhere from $40.00 to more than $100.00. These tools will save you a lot of hard, hand labor and time, and they will help you produce better results.
Did you notice in the above photo that the electric drill has a round, wire brush attachment? It’s inexpensive and often times it can be used instead of the wire brush.
Did you also notice the large sheet of sandpaper next to the palm sander? I prefer to buy large sheets (9″ x 11″) of sandpaper because they can cut into four smaller sheets which will fit the palm sander just fine. Also, if you cut a sheet lengthwise into strips, they will then fit the block sander. Of course you can spend more money for an already cut to size package of the smaller pieces of sandpaper which fit palm and block sanders.
OK, you already know that you are going to need some sandpaper, but that isn’t all. Here is a list of the materials that you will need:
Sandpaper – 60 or 80 grit, 150 to 220 grit, 320 grit, and 400 grit. The 400 grit should be able to be used wet. You start with the rougher 60 to 80 grit and work your way up to the super fine, 400. Later you will see this in some photos. The sandpaper, and most all materials needed, are readily available at Ace Hardware stores or you can shop online at Capital Supply. You can buy it by the sheet or in packages. For a small repair just get a couple of sheets of each grit to start. Expect to spend about $15.00.
A quart size can of Bondo Body Filler. This costs about $10.00. See photo below.
A quart size can of Bondo Glass. This costs about $17.00 because it has fiberglass hair in it.
A tube of Bondo Glazing & Spot Putty. It’s about $5.00.
Bondo Body Filler Spreaders. They come three to a package (small, medium and large) and cost about $3.50.
A smooth, non-porous piece of plastic, to mix the body filler on. I sometimes use the large spreader to mix it on. Once it’s hard the Bondo easily peels right off the spreader and makes cleanup a snap.
A small package of 4″ x 11″, Drywall, Sanding Screen. This comes in handy for repairing holes when using the Bondo Glass and it costs about $3.50. See photo below.
A small wood putty knife. This is used to scoop out the Bondo that from the quart containers. Costs about $1.00.
A couple cans of automotive paint primer. Costs about $4.00 a can.
A couple cans of color matching, spray paint. Costs about $5.00 a can. I prefer to use Rust-Oleum because it has rust inhibitor in it.
A bottle of white vinegar. It’s used to treat rust spots and is under $2.00 a bottle.
A spray bottle. Used for the vinegar. About a buck.
A roll of paper shop towels. Under $2.00.
A container of painter’s wipes. I use Goof Off and it costs about $3.50.
A small bottle of liquid dish detergent. Used to clean the area to be worked on. This also is only about $1.00.
Some clean soft rags.
A roll of half inch masking tape. About $1.50.
Some old, but clean, newspapers.
I recommend having all these materials on hand BEFORE you start working on the repair.
So, now that you have the tools and materials, let’s get started. Here is a photo of rust holes in my classic 1962 Ford F100 Pickup truck that need repair.
The first thing to do is to put some water in the small bucket along with the dish detergent. Get a rag and clean the area all around the rust hole. Clean well beyond the hole. If you see something that refuses to come off, like maybe some road tar, then get a painter’s wipe and see if that works. If it still won’t come off and it’s close to the hole, don’t worry about it. The grinder will do the job.
Ok, now that the area has been cleaned, it’s time to get busy. Put on the goggles. Take the grinder, or if you prefer, the electric drill with the wire brush attachment, and get rid of all the paint and primer and old Bondo that may be near the rust hole. WARNING, power tools can hurt you if you aren’t careful. Try to get down to the bare metal all around the hole. You need a good couple of inches of bare metal all around the hole. Sometimes you will run into a previous repair area. Try not to to ruin it as you can use the old repair to your advantage. Just get rid of the paint and primer. Here is a photo of me running into a previous repair.
Now that you have done that, you might need to use the hammer to remove any high places around the hole. It’s better to have low spots, that can be filled in with Bondo, than to have high spots. Just tap them down until it looks ok. Next, put on the leather gloves and carefully use your fingers to bend away any rusted, jagged pieces of metal. Sometimes a small pliers can be used instead. Also, use the flat tipped screwdriver to dig out as much rust as you can. If you can get to the back side of the hole, use the wire brush or the electric drill with the wire brush attachment to clean it as best as you can. Keep the goggles and the leather gloves on and be careful. If you have a shop vac or a portable vacuum cleaner you can use it too.
It’s now time to go get the vinegar and fill up the spray bottle. Spray the hole inside and out generously. The vinegar acts as a future rust preventer. You could also use a more expensive rust treatment called Ospho. It’s about $20.00 a quart. The vinegar needs some time to work, at least an hour, so take a break or start working on another rust hole. I am repairing one on a fender (above photo) and on a nearby door. See photo below.
While the vinegar is doing its thing, look to see if there is an area that needs to be protected from unintentional grinding or sanding. If there is you can use duct tape or masking tape. Put it on in several layers. Here is a photo showing how I protected the edge of my door while I was working on my fender.
You will need to remove the tape before you spray paint.
It’s now time to fill in the hole. One of the best ways to do this is to cut a patch out of some steel stock and then weld it in; however, you may not own a welder or don’t know how to weld, or maybe right now you can’t afford one, or maybe you don’t even want to learn how, so as I said at the beginning, I am going to show you a less expensive option that doesn’t require a welder and if done properly will last for years. Go get the drywall screen, the scissors and some string. Also you are going to need the Bondo Glass and the cream hardener (It’s in a small tube under the white plastic cover of the Bondo.) You will also need a spreader and the non-porous piece of plastic and the small plastic putty knife. Use the scissors to cut the screen so that it’s just a little larger than the hole. The screen will act as a back support when you apply the Bondo Glass. On the fender I am fixing, I can not physically get to the back side of the hole. So what I do when this happens is to cut a couple short pieces of string and slip it through the screen. Then I’ll tie a couple of knots towards the end of the string. Now you can put the drywall screen in the hole and use the string to pull it tight against the metal when you are applying the Bondo Glass. Here’s a couple photos.
Now that your screen is ready, open the Bondo Glass by first removing the white plastic cover. Set the cream hardener to the side for now. Use the flat tipped screwdriver to pry open the metal lid. Use the putty knife to scoop out enough material so that it will cover the hole and the bare metal and put it on the non-porous piece of plastic. (Don’t worry. If you didn’t scoop out enough you can always mix up some more later.) Get the cream hardener and squeeze out about a half inch right on top of the Bondo Glass. Now use the spreader to quickly and thoroughly mix it and the glass together. The mixture will start hardening immediately. Depending on temperature and humidity, you may only have a few minutes to work. Once it hardens it can not be applied. (Perhaps you would like to mix a little now to gain some experience with it?) OK, now use the spreader to get some of the mixture and quickly spread it over the screen and the bare metal. Remember to pull on the strings to help with the back support. (If you can reach the back of the screen then there is no need for the strings. Mix a little Bondo Glass and put some on the edge of the screen to help hold it in place. Then use one hand to press against the screen when you apply the fiberglass with the spreader.) Keep applying the mixture until you have completely covered the screen and the bare metal. If you do this correctly, you will not see either the screen nor the bare metal. Once this is done it’s time for a break. Taking into consideration the temperature and humidity, the mixture will harden and be sandable in 15 to 30 minutes. If you didn’t mix up enough the first time, then go ahead and mix up some more right now and apply it as there is no need to wait. Of course, instead of taking a break, you can always continue working on another rust hole. Here’s a photo of fiberglass covering the repair area.
OK, the fiberglass has hardened and is now ready to be worked. Go get the palm sander and put some 60 or 80 grit sandpaper on it. The palm sander only sands back and forth. You will get better results by working the sander in a circular motion. It might take you a minute to get the hang of it, but you can do it. Now, turn it on and sand the fiberglass so that it is even with the surrounding paint. Try not to sand too much. If you start seeing bare metal or the drywall screen stop sanding there. You don’t want to make a hole in the screen or weaken the fiberglass too much. Here’s a photo of roughed in fiberglass.
Now that you’ve got the fiberglass roughed in, it’s time for Bondo body filler. Bondo likes a good scratch and the 60 or 80 scratch is perfect. So, just as you did with the fiberglass, mix up some filler. Then spread it on thinly over the fiberglass. You may have to do this several times until you can see that all low spots have evened out. It’s better to apply the Bondo in several thin coats than to apply it thick once. As with the glass, Bondo filler also needs between 15 and 30 minutes to be workable. You need to cover all of the fiberglass. While it is drying, if you see that you obviously used too much or that there are high globs of it, you can rub it with your fingers to remove the excess. This will save you some sanding later. For large areas use a rasp to knock down the excess. Here’s another photo.
While the Bondo is setting up, put either 180 or 220 grit sandpaper on the palm sander. Then, once the Bondo has hardened, sand it so that you can just start to see the fiberglass or you can see that it is nice and even with the surrounding area. When you are done doing that take a shop towel or a paper towel and wipe off the dust. You could also use the shop vac, or an air compressor, to just blow the dust away. If you notice air pockets or pits or low spots, then you will need to mix and spread some more Bondo. Repeat this as necessary. Once you are happy with the way things look then you are ready to sand it with 320 grit. By now you should really have the hang of sanding in a circular fashion and now is when this becomes really important. You need to sand the edges of the Bondo so that it feathers into the paint. You don’t want any sharp edges or streaky looking things. Feather it so that it looks rounded. It’s alright if you are removing some of the old paint. Once you are done sanding, feel your work. If you can feel any difference between the paint and the Bondo, then you need to sand some more. Here’s are some photos.
Once you are happy with the 320 sanding, look to see if there are any pinholes or other minute imperfections. If there are then get the Bondo Glazing and Spot Putty and use a small spreader to fill them in. Once it’s hard gently sand with the 320.
Now that you have finished sanding with the 320, it’s time to prepare for the primer. Use a shop towel, a paper towel, or a rag, your shop vac, etc., and clean off all the sanding dust. Then use a painter’s wipe to thoroughly clean the entire repaired area and the surrounding paint. Clean at least a foot beyond the repaired area. After everything is clean and dry, you may need to use the masking tape and some newspaper to mask off any chrome or glass or anything else that might accidentally get sprayed with primer.
Get the can of primer and shake it rapidly for at least a minute. The first time you spray primer you might make a mess. You might want to practice spraying it on a piece of cardboard or whatever you have handy that you can throw away. Hold it about 6 to 10 inches away from the surface and then spray back and forth, just overlapping where you sprayed before. Once you are ready, spray the repaired area until you can no longer see any Bondo. Don’t worry if it runs. Later you will be sanding it with 400 grit. If it runs onto paint just quickly clean it off with a painter’s wipe. At this point it’s time for a break and your work should look like this photo.
Let the primer cure overnight. Some people get in a hurry only to regret it later. If you don’t let the primer cure, it will cause the fresh paint to spider web. Trust me, you don’t want that. If that happens you will need to sand off all the new paint and probably have to apply primer again and then give it time to cure and then repaint. Just do it right the first time and that won’t happen.
Now that the primer has cured, get the bucket and put about 3 or 4 inches of water in it. Then put some 400 grit sandpaper on the rubber sanding block. Also put a 4”x4” piece of the 400 in the water. Soak the sanding block in the bucket for a little while. Next, splash some water on the primer and then use the sanding block to sand the repaired area. Be sure to sand wherever the primer is. Try to sand in a criss cross, first one way and then the other. Be gentle. You don’t want to hurt your repair job by scratching into the bondo. If you have some runs, now is the time to sand them away. Then, once again, feather the edges until you can’t feel any difference between the paint and the primer. If you feel something then when you paint you will see what you felt and you won’t be happy. Use the 400 that’s been soaking instead of the block if you have a tricky spot where you just can’t use the block. All the primer should look the same. If some looks too new then you missed that spot and it needs to be sanded to look like the rest and also be smooth to the touch. Here’s a photo of what it should look like.
While the sanded primer is drying, dump out the bucket and refill it with clean water and put a clean rag in it. Then, after the sanded primer has dried, clean it and the entire surrounding area with a shop towel and a painter’s wipe. You are now ready to spray paint. Get a can of your color matching spray paint and shake it for at least a minute and also during breaks in spraying. If you have one, use a spray can attachment. It makes spraying with a can much nicer.
Using the same back and forth method, spray the entire repaired area. If it runs, stop and quickly wipe it off with a clean wet rag. Then continue spraying until you can no longer see any primer. Take a break. In about 15 minutes spray it again. Usually two coats of paint will suffice. Here are some photos of my painted repairs.