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MG MG Y Type - IS YOUR GARAGE DAMP? ARE YOU SURE?

I opened my garage earlier this month to check the tyres on YA7207, on a dry day but cold, and I found that my hub caps had beads of moisture on the top edge, so I assume that other less obvious parts are likely to be wet as well.
I remember my Morris Traveller lying unused in a modern garage, but with an MOT. Three years later, the floor was rusted to pieces beyond economical repair.
So I bought a humidity meter from the garden centre and after calibration it registered over 80% relative humidity which the scale calls “damp”. Normal is between 40 and 70 % apparently.
I can’t be the only one with this problem
The cause seems to be lack of heat to stop condensation, , a cold uninsulated metal door, and the two walls not attached to the house being single skin brick and therefore not damp proof.
Plan A has been completed and comprises a dehumidifier (Ex John Lewis’s - £99) and an electric greenhouse heater which is set to come on at about 5 degrees, at which temperature dehumidifiers tend to stop work apparently. This results in about a litre of water every day, and humidity hovering around 60 %.
I’m not looking forward to the electric bills, but they will be better than the cost of repairs I guess.
Plan B is to insulate the door and damp proof the walls. Is there an expert on damp proofing walls out there or anyone else with experience of the problem?
Michael Nicholson

Yes, my garage is damp and I'm going to do something about it this year.
I do find it helps a lot to open the door a little bit and put a large desk-ventilator in the garage so that the air circulates. The water beads disappear.
Willem van der Veer

I discovered why I had this problem (still have) - the central heating outlet is near the garage roof and was exiting into the roof space causing lots of condensation - only cure is leaving the door open. I wil have to fit a larger flue.
David Mullen

I would bet that laying down an inexpensive, ordinary indoor/outdoor carpet would do wonders for lowering condensation and preventing surface rust. The carpet will collect some moisture during the night and dry it during the day. Plus it will keep the car off that cold, damp concrete floor. This is all in theory of course.
Steve Simmons

With regard to the comments on ventilation, and drying out during the day, this only works if the humidity outside is lower. I checked it recently on a dry, cold but sunny day and still recorded 80% outside. And before you ask, yes, I have checked that the hygrometer is set accurately, at least at maximum humidity.
Michael Nicholson

Michael, FWIW I've got a single precast concrete garage not attached to the house. I bought some dampproof membrane(green polythene) and laid that on the concrete floor, then put an old carpet pile downwards in top, going about 4-6" up the walls. I've then got v.cheap carpet tiles where the car runs and at the front (back?) where my bench is. The walls I did by fixing wooden battens and then plasterboard to them. I didn't insulate behind the board, but you could easily do that. Painting the boards white increases the light enormously, too.
I have a simple draught excluder on the main door and the side door, and in the winter I stick bubble plastic over the windows. Like you I run a dehumidifier and a fan heater, and I find that I can maintain 50-55%Rh with no problem. I've never had any condensation and it costs me about £1/week for the power.
It's also a helluva more pleasant place to work!
John Marr

Damp is a normal thing in a garage in wintertime. Therefore you should remove the humidity before it damages your car. The right humidity for a car is about 55%. Below this the leather and other materials are starting to dry out, above that the metal starts to rust. You can lower the relative humidity, as written before, either through a dehumidifier or with a heater. A heater is the cheapest to by, but the most expensive to run and do not remove the water from the garage, but only raises the temperature of the air. Warmer air can carry more water then colder air and because of that the relative humidity is falling. If you want to run a heater in your garage you should not run it with a thermostat, but with a hygrostat, because you should get the relative humidity right and not the temperature. Many people thing 15°C or even 20°C in the garage is the best temperature for a car in wintertime, but at these temperatures the relative humidity will fall under 50%.
The best way to do it is a dehumidifier, which is much more expensive but running costs are much lower (about the same as your refrigerator). There are to types of dehumidifiers on the market. The absorption type and the cooling dehumidifier. The absorption type is a very good dehumidifier, which is still running at –10°C, but it is normally much to expensive. If you still are interested try the company Munters that is a worldwide Swedish company. The second type, the cooling dehumidifier is the right thing to by. But do not buy the cheapest on!! These are only good for temperatures above 15°C, even if the brochure tells you different. The first thing you have to ask the dealer is, if the unit has an active de-icing system. If he does not know, leaf the shop and try a better on!! A cooling dehumidifier has an evaporator, which will build up ice at room temperature under 18°C. To get rid of the ice you have to de ice the evaporator and this can be done passive or active. Passive means that just the compressor stops running and the ice is melted by the room temperature (takes a long time at 5°C and you can forget about it). The more expensive units have the active de icing system (hot gas is injected into the evaporator) and this are the units, which also will run at 3°C. Try for example Dantherm or Ebac, but there are much more.
When you run a dehumidifier in the garage the most important thing is that the garage is totally sealed to the outside, so you do not dehumidify your garden too.
Hope this has clarified some things.
Frank Neumann

This thread was discussed between 27/01/2004 and 17/02/2004

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