Reading an email this morning from a friend working on his TT cab, and he mentioned that he filled some voids with foam. Guys, PLEASE DON'T USE construction foam in your body! The kind that is sold at home improvement joints to keep air out of your house...you know what I'm talking about. It is not designed for use against steel, and I can just about guarantee you it will eat your car's body up. The automotive foam is a totally different animal, and formulated to be compatible with steel as well as form a bond to the steel and prevent migration of moisture.
This isn't a T, but the whole concept is the exact same thing! This 48 Ford I've been working on, and in process of finishing an article for webrodder.com, was near ruined because of that household foam. The owner thought it a good idea to fill the voids in the lower body with the stuff as a sound deadener and to hold off condensation by preventing moist air from contacting the steel. It was much cheaper than the automotive foam too. Personally, before I saw this car I would have thought it was maybe not a bad idea. The email this morning prompted me to warn you guys, just in case you might try to save a buck and think filling a void is a good thing.
The car was finished and painted, and even featured in a magazine, but in a year's time it all started to go bad. The previously unrusted body was full of holes and getting worse fast. He brought the car to me and I was amazed at what I saw when I started cutting into it. Everything that foam had touched was rusting away at an accelerated rate. It had allowed moisture to migrate into places, then kept it there. All along the top edge of the foam was a line of holes, like the moisture would lay on the foam and in contact with (painted) metal and oxygen it started eating away the metal. I can't say for sure since I'm no chemist, but there must be something in this stuff that promotes corrosion.
There is one more twist to this. There is no solvent that will cut that foam once it has cured. In other words, it has to be dug out and scraped off. I had over 10 hours in this body just digging and scraping the foam out after I had cut out the rusted panels.
I'm not trying to tell you fellas what to do, but I just wanted to show you what can happen. Automotive foam is expensive, yes...but it won't do this to your car!
By the way, the gray epoxy was sprayed on the car in an attempt to slow the rust until he could find someone who would tackle the project. Lucky me
I have to admit I have done the same. Years back when "restoring" a Fiat Spider I did use the expando form to provide a base to apply the ton of bondo I had too. For that use it was great if your going to cheat the buyer. But you are correct, it just causes the body to rot from the inside from the moisture not being allowed air to dry out. Tyrone Thomas
AKA smilebigtt I'm really sorry about that guys
You don't owe me an apology Ty. A lot of good conversation came with that thread you started!
I can see how that might happen. Take some of that great house foam and spray it into a plastic bag. It won't cure without air. So, maybe the outside cures on the car, but the stuff touching the metal does not? Wet+metal=rust? Maybe the two part expanding foam would work better, as it chemically cures? What "automotive foam" do you recommend?
Tim, I use 3M Duramix 04350 Semi-Rigid and 04320 Flexible Foam. It is very similar to what is used by GM and other manufacturers. It stays pliable, and also seals out moisture. it is more of a rubber type foam that adheres to the body like paint. There are other brands sold by auto body supply stores and I'm not pitching any particular one. I think SEM also makes a body foam but I've not used it. THe brand isn't as much the factor as is that the foam be specifically for steel car bodies. If Lowes, ACE, Home Depot, etc. sells it, it ain't for cars. I think a can of hardware store foam is maybe $5? The car body foam is $35-40 a can. That is the main reason he chose to put the house foam in the car, to save few bucks. It cost him about $1500 to fix what was damaged (the pictures I posted wasn't all, and since I was doing some more custom metalwork on the car and the repaint, I gave him a break on the rust repair), not counting what was lost in the first restoration as far as the bodywork, paintwork, and labor assembling the car. Believe me, I don't think he will ever let a can of that stuff near one of his cars again
How will you ever get all the rust out of those body cavitys? Wow,what a mess,and that is the very type thing I woulda thought about doing on a car to make it queiter.Thank you for the heads up sir.
Actually, it doesn't take air to cure expanding foam. Beleave it or not, it takes moisture. On my last project (building a hovercraft) we laminated layers of 2" blue dowl foam board together using expanding foam as the adheasive. You spray it on, allow it to expand, then quickly squeege it out onto the surface. Both surfaces are misted with water before applying the foam. When sandwiched together, the foam doesn't allow air in. If you don't mist the foam with water, the expanding foam won't cure. Under "normal use" the foam gets its moisture to cure out of the air.
Yep, leave that home-center expanding foam for sealing around your home. I think the reason it causes rust is that it's not air tight and it doesn't allow both sides of the metal to change temperature at the same rate. When that happens you get condensation which leads to rust.
Nice work on the rust Ray. Glad to see it done right!
Filler? Bondo? What's that?
New steel, Ken! That's what I think is right anyway, and I'm willing to bet you do too. I like to metal finish stuff for the challenge more than anything, but he liked the price to get it close and a thin skin of filler, so this one went that direction. Speaking of condensation, the rusty streaks on the quarter in the following pictures are the result of a cold night followed by a warm humid day here in the West Ky rainforest.
Mack, that car is almost finished now. It is sitting in the building, waiting for paint. I cut everything out that was necessary to get to all the rust and sandblast, then coated everything with 3M Weld-thru coating. That's what looks like running silver paint in the following pictures. I would have liked to go deeper in the body and remove more panels, but it wasn't the owner's preference to spend the extra money. You gotta find a stopping point, and he had his.
What is 3M Weld-thru coating?
dave, it is a coating for lap joints and any other weld where you cannot access the areas once the weld is done. The heat of the weld melts the compound and it flows around the spot or MIG welds and seals them off from moisture. Google "3m weld-thru coating". Lots of discussion on boards about it. About $28 for a spray bomb, but I won't weld two pieces together without it. Especially in rockers and lower parts of a body wher you are welding up a cavity that can't be painted inside after it is welded up.
I noticed in the last "Vintage" magazine on page 40 that Joe used a plastic sheet and caulking rope to seal his car against moisture. That may work in Arizona but I live in Northeast Ohio. I was thinking about doing that but with all the temprature changes and after seeing this... should I just leave it open like Henry did or protect the interior somehow? What would you suggest?
Here in west Ky we have the same problem you do, drastic temp changes that cause condensation to form on cold metal and drip off the outside. When the glass sweats on the outside it also is going to sweat on the inside. That water drips somewhere...right down into the bottom of the doors and quarters. Either leave it with plenty of routes for water to get out, or seal it up tight, but whatever you choose make sure that everything has a very good coating of paint. The pinchwelds are the worst area, where the water can migrate in between two pieces of steel that were not coated when assembled. It don't dry fast so it helps along the rust that started 80 years ago. Most important, if you seal only one side of a seam, you are making matters worse by closing off a potential exit for moisture. If it isn't going to be 100% sealed off, leave it 100% open. One problem I've seen a lot is plastic filler covering a hole and the backside of the panel left uncoated. Moisture can (and will) through capillary action move into the filler and corrosion will slowly work behind the filler. That's why you see blistered filler where it has been put over pinholes or thin metal that develops a pinhole later. Moisture is like a mouse; if it can find a hole it's head will fit through, its in.
I poured oil in the bottom of my TT doors and along the seams in the floor so any water that got there can't get into the welded seams before it evaporates, because they are saturated with the oil. The cab is open at all the original locations and it can breathe. I don't recommend the oil on a show car, my TT is unrestored and will remain that way. Dust accumulates on the think film of oil that is constantly making its way out along the bottom of the body, but its a small price to pay for keeping water out of the seams.
I would imagine Ken Kopsky could interject other solutions, although he being in Texas I guess he has a bit less humidity and regular drastic temp changes to deal with. What say you, Ken? How do you deal with these problems?