VCCA Home Forums TECHNICAL - GENERAL Body - Sheet Metal, Paint & Wood Flash Rusting

I'm in Michigan so humidity levels are not those of the South, but last spring and summer we had a lot more rain and humidity. For the first time since I built my garage in 2003 I had flash rusting on my cars, parts and even my large bench vise. Most days when the temperature is above 75 I might even run a window air conditioner so I don't think of my shop as being damp! I also do not wash cars in the garage. How are others dealing with this problem? Should I be coating my metal parts with oil or grease? Is there something that is easy to apply to reverse the process and coat things?

Thanks, Mike

Mike,
Some of us in the DEEP South give a quick coat of a metal prep. I personally brush or wipe on Ospho and before it dries wipe it off. That way I don't get the white residue. It will keep bare metal parts from rusting for a while. Also helps roughen the surface for future painting. If I want longer lasting coating I use self etching primer. For nearly infinite protection thinned epoxy or urethane primer. Most primers become sealers when thinned a bit to give a less porous coat.

You can run a dehumidifier just for periods when it's unusually humid and the temp is >70F. Colder than that and you need a cold climate dehumidifier as they will freeze up. If if dips cooler than than 70F you can use desiccant pellet or chemical dryers that are sold at RV dealers but you need to add some air movement for them to work. Often bumping up the heat a bit will reduce the relative humidity enough to make a difference as well as running AC in the summer as you have.

We have very low humidity here (30% today) so usually not an issue compared to where I grew up in Ontario. I know a few people with car bodies they blasted bare several years ago and have no rust sitting in an unconditioned garage that entire time.

I'm working with bare metal presently so have 2 dehumidifiers running and heat set to 70F. My hygrometers are showing 15-25% (they are always so accurate lol) . It is almost uncomfortably dry when working in my garage.

My experience is the opposite to Chippers though I must admit the time frame may well be different, I sanded my 38 to bare metal and applied a heavy primer/surfacer within a couple of days. About 2 years later I noticed rust was showing through the primer, when I spoke to a proffessional painter he informed me that the only paint that wasnt porous was the actual finish coat. If a scratch goes through the color the rust will happen.
Tony

I'm thinking more of parts that are not painted like gears steering box or transmission cases, oil pumps, distributor shafts, nothing related to painted areas.

Thanks, Mike

Mike,
Can do the same with parts that are not to be painted. The metal prep will put down a molecular layer of iron phosphate which will retard moisture reaching the surface. When I rebuild carburetors I coat the unpainted surfaces with Ospho and wipe it off. It protects from flash rusting for a long time. I don't put it on highly polished bearing surfaces but even there it might be okay. The slightly irregular surface will provide nooks and crannies to better hold lubricant.

Tony,
Primer/surfacer is intended to cover a surface and provide an irregular profile to allow sanding and improved paint adhesion. What you need to protect the surface is a "sealer". Many primer/surfacers will give a surface relatively free from holes and voids when thinned. Check on the can to see if the product of choice has that option. If not there are "sealers" specifically sold to maybe not as good as the top coat but a close second. On surfaces to be painted I use a metal prep (wiped off), self-etching primer, sealer and then primer/surfacer. If I intend to apply the top coat in a short time I sometimes don't apply a separate sealer.

Chipper that is exactly what I have been told after the rust came through. Since then I have taken it all back to metal again but this time I have put a light coat of color to seal it.
Tony

The Ospho and other Metal Prep products that leave a phosphate coating as Chipper has suggested are ideal for Mike's concerns. It still looks like bare metal when treated. Tools, equipment, etc you could just wipe with a light coat of oil as needed as they are easily accessible.

Raw, unpainted car parts like the transmission case being restored correctly are tricky. Ideally they need to be finish painted to LOOK like bare metal as they will all rust in any environment over time if left raw. Since you are past that point of restoration, I'd be tempted to treat like Chipper suggests and then oil lightly. Here where they use salt based chemicals on the roads for deicing, many of us spray our daily driver bodies with undercoating oils. Many can be purchased in a spray can like Rust Check or Krown. They are thin enough to migrate but foam up when first applied so it all doesn't drip right off. No effect on paints. On a fair weather car this oil should last and stay clean for years.

Maybe look at a dehumidifier for the worst humidity periods as it sounds like this is an abnormal condition for you right now.

Tony, use an epoxy primer. It gets pretty humid here in South Carolina, USA, and I use it on everything. I even use it on nuts and bolts. Epoxy and etch primers are not made to provide fill or to be sanded. They're designed simply for protection and adhesion. Primer surfacers (build primers) are made to fill and level as well as sand easily. They are not designed to provide adhesion and protection to bare metal...

I have the moisture issue two times a year in my garage. Spring and end of summer when the weather starts getting cold. The moisture in the air( I live less than two miles from the ocean) along with the concrete in my floor working against the temperature causes the inside of my garage to get wet. I bought some big fans and keep them going lightly to help stop the sweating. Putting your cars and machinery on some sort of matting will also help immensely. I’ve been looking into the interlocking garage flooring which will help stop the problem. I’m willing to bet it’s the concrete in your garage causing your problems more than anything. Many of the parts on my 32’ Olds that probably were left raw from the factory, I cannot leave that way. Plain and simple, the NE environment will not allow me to as rust will start simply from the salt in the air that gets blown in with our very frequent SW winds. I have to paint those parts or see them surface rust pretty quickly. I’ve even tried clear lacquer to no avail. I can say the fans in combination with keeping a barrier between my stuff and the concrete has made a huge difference.

Ted,
Most people think the moisture that appears on the concrete floor come from the ground beneath. It actually comes from condensation when the concrete surface is lower than the dew point as you well know. Same a dew on grass or droplets on tree leaves. Putting junk carpet on the floor will dramatically reduce the problem. Will not help the tools in the tool box or metal parts on shelves. Plastic bags, doors on cabinets will help those items. I wish I only had two times per year. Being about twice the distance from the Gulf of Mexico as you are from the ocean and our higher average temperatures mean we have two full seasons, Spring & Fall, to humidify my shop.

I know this thread started about protecting metal, and then into concrete.....and as already mentioned, dehumidifiers are neat. My father in law used one just a few miles from the beach at North Myrtle and never had a problem...and sealers, on metal or concrete all help.
I know your talking about concrete floors inside but we also need to remember .... that many concrete slabs were poured years ago and no barrier were ever put down. I have built houses for many years and poured many yards of concrete. The proof is in the pudding....I will admit this is outside my shop and not inside. When building my shop 2004, I poured a nice "run off" pad before coming into my shop. One side was not poured level and the concrete guys had to re-do, at their expense. Well, I wasn't here when re-poured but found out they did NOT put down a barrier on the half redone. Needless to say, its interesting to watch the side with the barrier vs the side that doesn't have it. No comparison. My shop inside has no problem winter or summer but I do have an epoxy floor paint.

If you ever spent much time at an oval dirt track you will find that the moisture will rise at night. Much like Chipper says about the dew point. Same thing happens with concrete. When the moisture rises it will soak through concrete...... it (rain) even soaked into a granite marker that I was having engraved last week to the point it could not be engraved until it dried out as there was no barrier.
Depending on what part of the country you live will definitely make a difference.

Food for thought: You ever notice the bottom of a washing machine sitting on a concrete floor will start to rust and the paint peel off after a while. The same thing will happen to floor pans of our cars....unless, as mentioned above, there is some type barrier....and I say the "barrier" starts before the concrete is poured, and additional precautions afterwards.....but I guess it is different in different places.

Lucky you're not in Southeast Florida.....unless you have AC or dehumidifier it's horrible....can't leave virgin metal out for a few days without rusting.....supposed to go in the 40's tomorrow....that should fix the humidity!!! Can't wait! Billu38

Totally agree Chipper. Those big pedestal fans I have help keep the air moving and will dry a lot of the sweating going on. Machines like my lathe and vertical miller get “deep” cold overnight and then when the day warms, humid air will make them sweat very easily. I spray fogging oil on the ways and beds plus cover them with dunnage bags which help keep the machines at a more even temp during the course of the day by making an air barrier insulation. Running the big shop hot air furnace I have in the fall has also stopped a lot of my rusting issues as it does basically the same thing as the fans by blowing a lot of warm, dry air around when the season first starts. Later in the year as the air is much dryer but a ton colder, it doesn’t cause the problems. I run the heat when I’m in the garage and things don’t sweat up but again, it’s a huge hot air furnace with two big squirrel cage blowers so there’s a large amount of air circulating. It can warm my 30x60 concrete block shop from 25d to 70d in about 15minutes. It’s flat roofed with insulation in the roof only. Bare concrete blocks and non-insulated overhead doors. Of course it uses about 1gal of heating oil per hour but since I’ve had it and used it, my cold late summer-early fall and winter rusting issues have gone away.

I had my garage built in 2013. It has radiant heat in the floor and below it is sand, a plastic vapor barrier, then 2"s of styrofoam. The foundation's 4' walls also have 2" of styrofoam on the inside. I am very heat sensitive so I run an air conditioner when I am working in the garage. I used to be able to open the windows at night and the door to my loft for night cooling, then close everything up during the day. I think I will try a ceiling fan and see if it helps. I am trying the metal prep.

Thanks, Mike