Humidity And Your Classic Car


Rust will form where the surface of the steel has air and water. The first step is to stop the elements reaching the steel, paint does the job pretty well, but even better is wax or similar coatings, or Waxoyl etc. Chrome is surprisingly porous and normally underneath the chrome plate is steel so it needs protecting. A covering of wax, ordinary car wax or Gibbs, will do the trick, it looks invisible, adds shine and protection. Don’t forget that a chrome cleaner is generally abrasive and removes any wax coating, by all means use it to clean, but it doesn’t protect the chrome.

Don’t get to hung up about the temperature vs humidity, as it’s often being mentioned to keeping humidity below 50% to stop rust, but it’s a bit more complicated than that and one of the keys is understanding about “dew” points. All air contains water and as the temperature drops that water tries to change back from a vapour to a liquid, that’s what causes rain, warm moist air pushed up by the weather cools and the water in that cloud becomes a liquid which is heavy and falls out of the cloud – rain. In your own home you see it as condensation around bedroom windows on cold mornings. It is around the window because that is normally the coldest part of the room.

There are 3 ways to fix condensation:

  1. Heat the room so the air inside can hold more water.
  2. Open the window (ventilate) in the hope that air coming in from outside will be dryer and therefore hold more water.
  3. Use a dehumidifier to reduce the percentage of water in the air.

The theory of condensation effect is to take a can of cold drink from the fridge and put it on the table or work top. Even in a warm house you immediately see condensation on the can as the water in the air rushes to the can and condenses back into a liquid. This is the same principle as how a dehumidifier works, you present a cold surface to the air, the air in turn gives up its water which is then collected in a container. The fan in the dehumidifier keeps an airflow over the cold chilled surface so as much air as possible reaches the cold surface.

Back to my Garage; heating the space to about 20c works well (in fact any heat helps) because the higher the temperature the less the water has a chance to condense back to a liquid. This is why I fitted a radiator in my garage, much to the bemusement of my wife! unfortunately it’s not the complete answer though. Another example of the condensation is that you get condensation in a bathroom after a long hot shower even if the air temperature is 25 or even 30c. You could indeed heat a normal garage to 20c, the car would sit in there and not deteriorate, but even with insulation that is expensive way of doing it. Hence why the US “dry State” cars are so popular in UK as there is not much chance of the rust taking hold in the past.

I have done all the usual things; The heating and water boiler is in my garage and gives of heat to the room as the hot water passes through the pipes. I have insulated as much as possible, the walls are cavity filled, the ceiling has plenty of insulation up there and the all important plastic floor to stop the cold coming up through the concrete. The up and over door has brushes to keep the draft out and the back of the door has heat insulating sheets. That way I should then be able to keep the space at least 9c throughout the winter with no additional heating and that is obviously a big help.

On the other hand, when you open the garage door the same thing can happen on a warm moist day, the air rushes in and condensation forms on whatever is coldest part in there, that is mostly going to be your prized possession, your car. I found this rather good chart to show the relative ranges of humidity and what I am trying to explain:

So I have bought myself a dehumidifier. I have reviewed it here and is also under the accessory menu on the main bar. I wanted two things from the non-negotiable options. An option for constant draining and the low-cost of running it over 24/7 scenario. The options were a little limited for my modest budget. I managed to pick up a well rated PureMate PM412 for a modest cost of £120 reduced by sixty pounds from the recommended retail price. I also purchased a digital humidity gauge and left it in the garage for a couple of days to get a reading. There is a max and min scale for both the temperature and the humidity. The gauge is on top of the car in the middle of the garage.

The unit is compact and neat looking with a capacity of twelve litres a day. There is a digital read out and super simple to work and set up. The gauge above shows the first night was 45rh to a max of 50rh which I was super happy with.

The unit has a castor wheels and a recessed handle which is so easy to move around. There is a one meter length of tubing they even supply for the constant drain should you need it which I will of course. The ease of movement makes it ideal to shove out-of-the-way in the corner of the garage when working on the car.

The collection tray can hold one and half litres of water, and over night I think it was up to about a little under a litre. So I am having to empty it morning and evening now until I plumb it in. But, that is the unit settling the environment down then they should reduce considerably after a few days. It doesn’t matter if I forget to empty it as the unit will shut down when the tray is full.

The power consumption os a max of 245w on full power, but as I only ran mine on a low setting it should work out quite economical to run especially as it will be on all the time. Has anybody else got any tips or tricks they would like to share storing their car over the winter? Please post a reply and we can all share the knowledge.