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Article: Fixing the Holes in
Last updated: 10/27/01
Symptom: Your feet get wet when you drive through a puddle, you can see the road going past when you look down, the battery just fell out of you car and was demolished by a Kenworth rig behind you.
NOTE: Before you get into this you should
read "General: Dealing with rust".
Basics, choose your approach....
Probably the most often required body repair on the Beetle and also the seed for some of the most creative solutions. My first advice: Metal. Forget fiberglass, plywood, plastic, newspaper, cardboard, carpet, etc. The fiberglass replacement pans may seem like a good idea at first, but the problem is in getting a good fiberglass to metal bond. The effort and expense it would take to do the job properly, sealed and watertight, far outweighs the simple metal repair. This is a somewhat controversial opinion, but it's my story and I'm stickin' to it.
And spend some time with your battery too.
Used to be that battery acid started all of these problems. Now sealed
batteries are commonplace and eliminate this problem. Consider replacing
you battery if you don't have a sealed one. Also, place a piece of low
cut carpet or rubber mat under your battery. If you use carpet, put it
upside down, pile side facing the floor pan (you are protecting the floor,
not the battery). The battery case can chafe the floor and expose
metal to rusting (Oh, and it's always a good idea to have something over
the top of the battery so if a really heavy person sits on the battery
side of the rear seat the springs don't short out the battery terminals.
Trust me, I know).
The most important thing when you replace metal in the floor pan is to remember your "Rust Basics". Water on bare metal causes rust. Water trapped between layers of metal and/or tar causes more rust (faster). Water on metal coated with cheap and/or improperly adhered paint will eventually rust. The idea is to keep the water on the outside of the car and seal up any exposed metal on the top AND bottom of the pan. This may sound obvious, but I have seen many a brilliant solution dragging the ground a year later because the job wasn't finished right.
If you read the "Dealing with rust: General" text you know that I outlined 4 methods of dealing with rust. Well, when it comes to your floorpans, #1 and #2 are not options. Because if you let the rust continue, or even just stop it you will still eventually fall out of your car without opening the doors, get hurt bad and cause all of our insurance rates to go up. Don't fool around with this. You must maintain the structural integrity of your floors.
So that leaves you with options #3 and #4. Remember #4 is about replacing the metal with the absolute correct replacement pan and having all of the tools and welders and heavy equipment in the world at your disposal. I have personally never done a front to back floor pan replacement, but it can be done without removing the body. Hot VWs magazine did a good tech article on this a few years back, I'm sure you can get a back issue from them. You must weld these panels in though. After you've done a #4 on your pans, you can paint murals on them so you can put mirrors on the grass at the VW shows and so the small animals that you run over can have an esthetically pleasing experience. But we're not discussing #4 here so that just leaves #3.
Method #3 was about stopping and/or removing
rust and restoring the structural integrity of the car. The appearance
of the repair is secondary. Unless you have an absolutely pristine Beetle,
I'm sure that you can find parts of your car that you would rather spend
time to paint, buff and shine than the underside. The top of the floor
is going to be covered with carpet anyway, so no one cares what that looks
like. So lets just get the job done. Waterproofing is what it is all about.
I recommend cutting out the rusted metal and replacing it with a similar thickness sheet metal about 1/4"-1/2" larger than the hole you have all the way around. A sabre saw with a metal cutting blade works very well, a set of pneumatic nibblers even better. You want to avoid having large areas of "overlap" because it is almost impossible to keep the metal from rusting in between. Treating the facing edges with a paint like "Corroless" (See the "Rust" article) is an excellent idea. If you will be welding the new piece in, about an 1/8" overlap is best, but you don't want to leave holes. (If you happen to be welding, you want to use a "weld through", zinc based primer on the facing edges. Any good auto paint supply will have this) You may be figuring out by now that the part you need to replace isn't exactly flat, so the piece that you use to replace it won't be either. You're probably right. You need to cut out the smallest piece of the floor out that you can that 1) removes all of the rusted metal and 2) provides an opening of a shape and contour that you can replicate. I purchased a 22 gauge 2x3 ft sheet of metal from an autoparts store for about $10. Using tin snips, vice grips and a hammer I was able to shape a piece that matched the "well" contour of the area under the battery. "Rear" sections of the floor, already stamped to the correct shape are available pretty cheap, I would recommend using them where you can.
My "I'll modify anything" brother replaced
the rear half of his '68 right side pan with a flat piece of 10 gauge steel.
Doing this eliminated the "well" on the floor and the seat rails but since
he bolted Honda seats to the floor anyway, it really caused no problems.
It also made this part of the floor impermeable to armor piercing aircraft
fire. But if you do this, make sure you cut away enough of the old floor
so that there is not a huge overlap underneath. Whatever you do, BE PATIENT.
Cut a little, fit, trim a little, fit, bend a little, fit. If you do this
right, you won't have to do it again; at least until you sell or wreck
that car and get another one. Always place the new panel on TOP of the
existing floor. This is the safest approach.
I strongly recommend welding the new metal in. Now before you go shutting me off because welding is like nuclear fusion to you, hear me out. There are tons of welding shops out there. So many in fact, that in most places there is not enough customers to keep them as busy as they would like. If you do all of the prep work to fit a new panel, and bring them your car (if you can still drive it) with shiny metal-agaist-metal panels ready for welding, chances are you can get the job done for cheap. The trick here is never go to a shop and say "how much?". Go to a shop and show them or completely describe what you are doing and say "will you do that for $30?" or whatever you think is the right price. Figure about a $40/hr shop rate. You are the one holding the money. If they say no, ask them if they can tell you how to get to "Ted's Welding and Metalworking" or whatever the welding services listing is directly under theirs in the phone book.
And, I have been fooling around with MIG welders for about a year now and I am convinced if you can brush your teeth all by yourself, you can MIG weld. Really. If you can borrow or rent one, you may want to give it a try. Practice a lot until you get the results you want on scrap (perhaps some good metal you cut out of your floor). You will need a gas MIG welder that can use the .024" wire. I have a gasless (flux core wire) unit as well a gassed MIG. The problem is that the smallest flux cored wire you can get, at least today, is .030" and it generates too much heat to do floor thickness metal (although the ad for the welder said "down to 22 gauge"; yeah, right). You will just burn a bigger hole. Don't buy one thinking you will be able to do sheet metal work with it. In addition to being too hot, the welds are pretty crappy.
The trick with MIG welding sheet metal is
to never sustain an arc for more than a second or two. This allows too
much heat to build up and warps or burns through the metal. Another trick
is to make sure that both pieces of metal are touching each other tightly;
this optimizes heat dissipation. It is best to "stitch" (ie.: dotted-line
weld) then go back and fill in the spaces in between. You can get an inexpensive
gas/MIG for around $300.
I used to do a lot of brazing, and it is OK if you are careful about "cleaning up the weld". Brass gets a bad rap because of the flux on the rod (the white coating). It melts down, gets impregnated in the surface of the brass and will begin to expand and corrode anything that is covering it in a few months. So if you use brass, be sure to use lots of rod and then grind the welds down good so they are clean before sealing the repair. Also, you would never want to try to braze up a hole in the middle of a door panel for example (I did, that is why I am recommending that you not). The torch generates a lot of heat and flat panels will warp. But for floors, it is ok with a small torch tip.
In either case, when you are done, you should try have a continuous weld, not a tack or stitch. Sealing out the elements with metal is the best. Ideally you want a "butt" weld (no overlap), but this requires you to cut the new panel to exactly fit the hole and some "more than beginner" welding skills.
If you absolutely can't get it welded, my next recommendation would be aluminum rivets. (For small "patch" panels, NOT for whole pan replacements!) Buy or borrow a rivet gun and rivet from underneath, with the panel on top. Get rivets with about a 1/8" or 3/32" grip length and 1/8" diameter. Space them every 2" or so, they're cheap.
As a last resort: #8 sheetmetal screws, from the top. Get them as short as you can, pre-drill the new panel with a hole big enough for the screw to freely slip through, then pilot drill the old floor with a smaller bit about 1/2 the core diameter of the screw. Space them every 2" or so. Now from underneath, grind off the screws to within 1/8" of the old floor.
Don't assume that you have to do the
whole repair with just one piece of metal. If the rust is dispersed, smaller
metal patches work well and are much easier to work with than one mammoth
sheet. On the other hand, don't rule out replacing the entire floor. Pan
halves are available for around $70. They weld to the front firewall and
tunnel on the inside, and bolt to the body on the outside edge and under
the back seat. They come with seat rails already on them and you can paint
murals on them before you put them on, eliminating unnecessary back and
Finish the job...
DON'T SKIP THIS PART. No matter what you
did, you must seal the repair from the top AND bottom. Clean the surfaces
with solvent and use roof tar (see the "General:
Dealing with rust" article about using tar). Make sure that all cracks
and crevices, especially if you didn't get a continuous weld, are sealed.
Large overlaps between the existing and new panel are bad. No matter what
you do, this metal will eventually start to rust in between, so eliminate
this as much as possible. If you used rivets or screws, make sure that
they are sealed well. Seal the top too. If you really want to make the
car weather proof (and able to survive a "Big Gulp" spill from above),
I would apply a thin coat of roof tar to the top of the repair and then
put some grocery bag paper over it before putting the carpet back. But
the longer you can let the tar "air dry" before you put the interior back
in, the better. The tar will stink for a week or so though, so be warned.
If you live in a nice warm, dry, salt free climate and only drive your
car on nice days, clean the metal with solvent and use a quality spray
paint that can adhere to bare metal over the panel. In any case, inspect
the underside of your repair after a few rainy months. Poke around and
try to find any areas that are not sealed well and fix them. Also look
for water inside your car after you have driven in the rain.
Copyright© 2001; John S. Henry
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