Workshop Humidity

Workshop humidity is a problem in that it can result in rust. Especially an issue on the surfaces of precision tools.

The humidity in the air comes from a number of sources: atmospheric, gas fire, blow torch, breathing and of course from some processes. Such as steaming wood, this will generate a lot of water vapour.

This means we have water vapour in the air in most workshops. There are a number of ways to control or limit the impact of this on tools.

Rust Prevention

You can spray tools with ACF-50. This works really well to stop rust. Not sure how often you need to treat surfaces, especially surfaces like lathe beds where they rub. Treating tools with ACF-50 is a great idea if you plan on leaving the workshop unattended for a period of time.


You can remove the moisture from the air in your workshop. This can be done using an electrically powered unit or using chemicals.

chemical de-humidifier

Chemical dehumidifiers are available in most household stores. They range from a simple bag of calcium chloride chips that you spread into a container to a scented compressed disc.

These products absorb the moisture from the air and collect it in a reservoir. The downside is you have to keep on renewing chemicals.

Electrical dehumidifiers are readily available in a number of sizes. Most of the small units once again collect the water in a container that will need emptying regularly. Larger units can be plumbed in.

You can buy 12V dehumidifiers and so it is possible to perhaps run these off-grid.

Dry Heating

Don’t add to the problem, use a dry heater such as an electric oil filled radiator or central heating. Avoid open gas fired radiators or space heaters. In a small workshop a small “greenhouse” frost protection heater (~150W) with a thermostat is a good way of reducing the condensation.

Controlled Heating

You can use a heater that is temperature controlled and so comes on when the temperature drops below say 7°C.

dewpoint monitor

Alan @ Woody’s Workshop has designed a control system based on dewpoint measurement: Dewpoint alarm monitor to help avoid rust issues in the workshop.

This uses the Magnus-Tetens formula and covers the temperature range -45°C to 60°C with an uncertainty of 0.35°C.

You can use this to switch on a heater, dehumidifier or both. Using a monitor like this will reduce running costs.

There are a few ideas here for coping with workshop humidity and you may find you need to use a combination of heat, de-humidifying and rust control with something like ACF-50.

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