Moisture in workshop

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Established Member
28 Sep 2015
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south Wales
I noticed a small amount of rust on one of my hand places over Christmas, my workshop is concrete block construction with a pitched slate roof. The outside is also rendered with waterproofer in the render then painted with a good quality masonry paint.

I have set up a dehumidifier in the workshop and am staggered by how much water it is collecting. Every morning, the machine has switched off and there is 2 litres in the drum.

Cannot get to the bottom of where this is all coming from.
The air is moist. At this time of the year it often has 90% or more relative humidity. At these levels it will readily condense on any cold surface. Planes are cold.

Oh, and waterproofing is a bad plan on the outside of a wall. Typically, inside a building is damper than outside, so a waterproof layer on the outside of a wall simply traps moisture within the fabric.
Same issue here. Spent some time this year doing french cleats so I could get more kit onto the walls. A few weeks before xmas I went into the workshop and found planes wet with condenstation. The hand tools quickly went back into their boxes with big bags of silica gel and I bought a couple of those thermostatted tubular greenhouse heaters to stick in the bottom of my most vulnerable machines with some insulation over the top.
I'm not working in there for my living so cost of running a dehumidifier isn't viable for me but I'm not surprised at the amount of water you're pulling out of the air.
I have a similar issue. It isn't dripping off tools or anything, but sheets of paper and books are damp to the touch. Was wondering if running a dehumidifier for 1/2 days would be an idea

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If you are open to the outside air then a dehumidifier is trying to dry out the whole of the world's atmosphere. It's an endlessly losing battle. You have to sort out the insulation and get some ventilation going, or you have to sort out the insulation and get some background heat in there.

I've never had any condensation issues in any of my home-built workshops.
There are a few ways to deal with this;

Heat the shop beyond the dew point.

All three will require adequate insulation and relevant sealing to some degree. My own approach is to insulate where ever possible and run a dehumidifier. I also have background thermostatic heating to assist (although this is more comfort than anything).

If you go the dehumidifier route, use the desiccant version, not the compressor units. Desiccant dehumidifiers will work down to low temperatures whereas compressor units will not usually function under 10 degrees which is often the temperature of the workshop it is operated within in this circumstance. Desiccant's will also help to heat the air itself.
If possible warm your machine surfaces 1-2 deg above ambient , likewise hand tools inside tool cabinets, not just wall racks, small vivarium heaters, low wattage light bulbs etc. running 24/7 they only need to be just above dew point. One low wattage long life bulb keeps all my chucks and associated lathe tooling rust free.

Thanks, I can see how this is happening. I have a suspended timber floor with plenty of ventilation below to stop any rot. I also have vents in the facials allowing air to travel through the roof space and over the rafters. It’s such a large space, heating would not really be a viable option. The dehumidifier is 300w so running this is possibly a more costly option. I could always modify the water container and connect a hose which could go through the wall and drain outside. But as MikeG said, I am also drying out the rest of Wales.
Woodworking in a damp, unheated workspace can be a pretty miserable occupation. It'll never be ideal, but there are steps you can take to make the experience a little bit better.

Don't leave your tools out, when you finish work pack them away in a traditional wooden tool chest. That really helps, I've been there and I'm speaking from experience. Hanging tools on walls is fatal unless you have a warm, dry workshop.


Don't have too many tools. Stick to a small, basic kit that will fit in your chest and keep them wrapped up and oiled. The fewer tools you own the more you use them, and therefore the quicker you spot any small patches of rust.

Cover any machines with dust sheets.


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When I was an apprentice the workshop was made of t.n.g flooring walls, the roof was slate that use to ice on the underside in winter. Sheesh we were hard in them days!! Our tools were always ok because they were used six days a week. My workshop/cave on the other hand has a dehumidifier working most of the time. The walls are six inch hollow concrete block, the roof Marley type tiles with insulation and 1/4" ply. I do have a thermostatic greenhouse heater on low.

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