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Good Old British Weather?

Humidity issues.

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Ian B.16/12/2020 08:41:27
163 forum posts
5 photos

Hello All,

Is anyone else having particular humidity problems this year in the workshop? This year seems really bad. This workshop is relatively new and this is my second winter. Not had real rust problems before. Close watch on dew point and as soon as condense appears off with heating I know paraffin heating and all that. The ventilation is the same .

No real issues until a couple of weeks back. I have quite a bit of plastic/resin work to do so did the usual, plenty of oil and maintenance spray on the machines, threw old dry yes very dry old towels over them and got on. Took a look two days ago and everything is rusty. Yesterday it had spread like a very infectious disease. A lot of work now to clean up. There was just one session with polyester resin and of course the associated styrene fumes on some ply bases for outside. The rest is all polyurethane with little or no fumes when casting.

Is it the covers? Is it me? Or is it more general a being so wet this year, the humidity in the background is so high? I would like to find solution to reduce the effort now. Parafin heating costs 7.12 pence per hour. Any equivalent electric heating will cost 32.8 pence per hour.

Any thoughts please?

Martin Connelly16/12/2020 08:49:15
2007 forum posts
214 photos

Don't heat, de-humidify. Uses a lot less power with much better efficiency. The power needed to raise the temperature enough to reduce relative humidity to the point where it is not an issue is much greater than the power needed to reduce the humidity to the point where it is not an issue. When heating you have to heat everything which in a workshop can mean a lot of mass in machines. When dehumidifying you are just taking out a small amount of water in the atmosphere. It is also useful to note that, like a lot of chemical processes, rusting proceeds faster at higher temperatures.

Martin C

Dave Wootton16/12/2020 08:49:40
228 forum posts
56 photos

Don't know if it would help with the styrene fumes, but I live very close to the sea and everything rusts if it can, costs me a fortune in brake discs and pads. in the workshop I have a cheap B&Q dehumidifier that does keep rust at bay from the machines and materials, which are kept well oiled ,I also use ACF50 on the machines, about four applications a year seem to do the trick.

The dehumidifier cuts in and out on it's humidity sensor and doesn't seem to make much difference to the electricity bill.


Martin is much quicker at typing than me!

Edited By Dave Wootton on 16/12/2020 08:51:05

DiogenesII16/12/2020 09:06:33
431 forum posts
181 photos

The weather-pattern of the last few weeks has been particularly bad for condensation - cold dry northerly air has been displaced by warn wet southerly air in repeated sequences of fronts passing through.. Last Sunday, in my unheated & draughty shed, everything was dry in the morning, but by lunchtime was quite literally running with condensation.

It's vitally important not to let any fabric coverings lie directly on the bed / shears / table / any machined surface, because they absorb moisture from the atmosphere and then hold it in direct contact with the metal as it evaporates, causing corrosion.

I keep everything oiled, throw a light sheet loosely over the machines to keep the dust and animal-poop off, and try to twiddle the handles / rack the saddle / raise and lower the head, etc. as & when I'm in the shed for any purpose..

Oh yes, and of course any freshly cut surfaces develop surface rust, and all my free-cutting steel gains a patina.. ..c'est la vie..

Edited By DiogenesII on 16/12/2020 09:09:08

SillyOldDuffer16/12/2020 09:54:38
7904 forum posts
1725 photos

Chief suspect is the paraffin heating! Does it have a chimney? If not, the heater is a potent source of warm wet air, slightly acid because of Carbon Dioxide.

Condensation occurs whenever damp air meets a colder surface. Heat alone is unlikely to fix it, and applying warmth at the wrong time and in the wrong place will cause rather than prevent condensation.

For example consider a cold workshop with high winter humidity. No problem because metal tools are at the same temperature as the air. Then the moist owner arrives and lights up a paraffin heater which dumps water into the air and quickly lifts the air temperature. Meanwhile the lathe stays cold because it's a large lump of metal insulated with towels. Water condenses on the machine because towelling doesn't stop wet air getting through the fabric. In this example, towels are a mistake, plastic sheet is better.

Be aware the causes of condensation are local : what works for me may not do for you. General principles: stop water getting in and encourage damp air to leave. Dehumidify. Avoid temperature changes or slow them down as much as possible. Insulate! As warm wet air is more corrosive than cold wet air, cool damp air is better than warm and wet - put on a jumper!

If heat is applied, aim to maintain a continuous steady temperature all the time. Don't switch heat on and off, and don't make wet heat by burning. Usually cheaper to keep machines just above air temperature with black heaters than to heat the whole workshop,

If money is no object, apply professional methods. Double-skinned workshop with well insulated watertight roof and fully effective DPC and membrane. Air-conditioning left running continually, providing dehumidified air kept on the cool side at 17 or 18°C. Much harder for condensation to form when workshop and contents are all at the same temperature.


not done it yet16/12/2020 10:19:21
6514 forum posts
20 photos

If you dehumidify, draughts are your enemy, as you will be trying to dehumidify the whole world!

If you use a compressor dehumidifier, efficiency will decrease rapidly below 20 Celsius and not a lot of good at all below 10 Celsius. Desiccator types are far preferred at these lower temperatures, but running costs are higher than compressor types (although that extra energy used might help to warm the workshop - it does with mine).

Those using paraffin have the worst situation as the heaters produce lots of extra water and need good ventilation. The truck/caravan heaters are good as the exhaust is carried outside the workshop - but they need about 120W while operating, I believe.

I’ve recently extended my workshop and am still boarding it out. Some door insulation needs to be refitted and there are still a few leaks. It has recorded a low 6 Celsius this last month (just briefly) but with good humidity levels - apart from this morning, as the humidifier didn’t run last night and I had taken in a full sheet of wet ply. After an hour and a half run the temp is up to11-12 Celsius and humidity is below 70% this morning. That 1 1/2h cost me nearly as much as a 3h run during the night.🙁

Frank Gorse16/12/2020 10:35:21
65 forum posts

According to Wikipedia-yes, I know- burning 1 gallon of kerosene produces 10 pints of water. Even if the figures are not exact surely that tells us all we need to know.

Steviegtr16/12/2020 14:01:56
2311 forum posts
317 photos

I used to use a propane type matrix heater. Too much condensation, so now only Electric heating.


Clive Hartland16/12/2020 15:10:12
2757 forum posts
40 photos

This is more than likely caused by the Dew point. When I go to bed the cement path is dry, no rain, but in the motning it is all wet. The path is colder than the air and the dew condenses on the paths so the air must be full of moisture.This no doubt also gets into your workshop to condense on the cold machinery.

Luckily, I have a spur radiator in the garage and it keeps the garage dry, It was in tere when I bought the house and have never had any rust problems. It comes on with the central heating each year.

Henry Brown16/12/2020 15:28:33
509 forum posts
106 photos

I was having problems with damp causing rusting but a bit of attention to the drafts and a dessicant dehumifier has sorted it. I put the dehumifier on for an hour when I go in first thing and it gives a bit of heat too, I keep a eye on the humidity level display on a cheap led display, if it starts creeping up then the dehumifier goes on for another hour. The machined surfaces on the lathe and mill always always have a wipe over with an oily rag.

Dave Halford16/12/2020 16:18:21
1884 forum posts
22 photos

Having seen how soldering with gas and small amounts of a non acid flux still promotes rusting within 4" of the joint after a day and noticeable rust 2ft away on bare steel after 2 days (steel out of range stayed clean) I would suspect the fumes. More so if you had the paraffin stove on at the same time.

Bazyle16/12/2020 19:26:39
6174 forum posts
222 photos

You haven't mentioned where you are. It has been a wet year in the west since about the first of July. there is a huge difference bwtween the west country or up norht and say London.

Richard S216/12/2020 19:51:03
227 forum posts
131 photos

I suppose I'm lucky, as my workshop is the ground floor integral garage. Unheated, it never suffers from condensation, or the rusting of machines. I presume it is because of very slow temperature variation and quite well sealed. It does get cold in there, so I don't stay down there for long.

I have had the challenge trying to complete the etch priming stage of my models with the high humidity and lower temperatures over the last 3 months down here in S/East England., but nearly finished that part now.

Ian B.16/12/2020 21:04:57
163 forum posts
5 photos

Thanks all for the replies. There is much to mull over. Whilst the parafin heater is held up as a significant problem IT DID NOT HAPPEN LAST WINTER. Now as to workshop construction. It is a sectional wooden building. It is 12ft x 10ft. Framing is 3in x 2in. Outer cladding i 3/4in thick shiplap. Then the whole frame is covered with double layer bitumen between building paper. Each bay of the framing is fitted with 1 1/2in roofing batten blocks. Butted tight against these blocks giving 1 1/2in still air is tightly fitted Kingspan/Celotex insulation Foil layer inboard. Any flaws in fitting are sealed with alloy tape. The specialist stuff. The whole thing is then lined out with 1/4in WBP ply. There are two opening lights open when paraffin stove is lit. Its an end door lined and constructed the same as the rest. It is as tight a fit as decent sheds allow.

One thing that may contribute is the wick in the heater. It is worn and needs careful adjusting to remove all yellowness from the flame. I have spares to fit and a dry heater now. Gas heaters are even worse. I wanted to try the catalytic versions but they seem.not readily available currently. In my previous workshop a concrete sectional building I went from gas to pot bellied wood burner. Best thing since sliced bread and became spoiled with no rust at all.

So I think I will buy a dehumidifier. Seal up the shop and pump away. Just have to watch fumes from paints and resins. According to the charts I probably need a 20litre version for the size and conditions.

Oh and sorry I am Staffordshire based near Stafford. Rainfall is heavy.


Edited By Ian B. on 16/12/2020 21:10:59

Ian B.17/12/2020 07:59:33
163 forum posts
5 photos

Just for completeness. The floor is 3/4 in thick tongue and groove framed on 1 1/2in x 1 1/2in timber. The whole is raised on 4 in x 4in bearers. The floor is lined inside with 2 grades up double bitumen building paper covered with fitted 1/2 in thick WBP ply.

Managed to clean up 3 main items yesterday. All now fully lubed and oiled. All sprayed with 151 maintenance spray. Uncovered. Just some smaller items to finish. However this has shown how differing grades of steel and cast iron react. On the WM 180 lathe , the cross slide, top slide, the chuck and bed were plastered. The exposed parts of the mandrel were untouched. Similar for the mini lathe except the collett chuck was untouched. The bed where I had removed casting flash during the massive works on it was badly affected but the exposed casting surfaces on the old Clarke tailstock heavily modified to lever operation were completely untouched. Even the base casting which is completely now paint free, yet the main bed casting had rusted right up to it.

not done it yet17/12/2020 08:02:29
6514 forum posts
20 photos

So I think I will buy a dehumidifier. Seal up the shop and pump away. Just have to watch fumes from paints and resins. According to the charts I probably need a 20litre version for the size and conditions.

I have bought meaco 8dl (or something like that) which are rated at 8l per day @~750W setting. All second hand basket cases or not running. They are generally easy to fix and cheaper to buy several than one new one. I have three (out of four purchased) which are serviceable.

I am currently running one for three hours each night on the lower power setting. Although they may well be more efficient running at full power/speed running them for longer may help during very cold periods. Humidity (likely still from the sheet of ply) was still high at 72% this am.

As they only hold 2 litres in the collector, I run two - each for a shorter time each day - if we go away in the winter. That avoids one filling (and switching off) or the possibility of one stopping working (they are not the most reliable machines.🙂 Now my workshop is about 30 cubic metres, I may find I need a bit more heat/drying time in the depths of winter. A small price to pay to protect several thousands of pounds of machines, tooling and equipment.

I have previously collected only about 2l per week, but I expect a little more - but not much more, once I get it sealed to my satisfaction.

Edited By not done it yet on 17/12/2020 08:03:21

Ian B.17/12/2020 08:24:42
163 forum posts
5 photos

Thank you not done it yet. That is really useful information. I am much convinced by the help here that dehumidifiers are the way to go. Like I said earlier I probably spoiled. Fitting the woodburner to my previous workshop was the solution absolute in a concrete building. Even that dark damp looking patch that appears in concrete sections slowly disappeared as well. Sadly no longer have access to the timber or the facilities. Plus round here they really frown on burning scrap timber.

It is what it is.

SillyOldDuffer17/12/2020 09:29:02
7904 forum posts
1725 photos
Posted by Ian B. on 16/12/2020 21:04:57:

Thanks all for the replies. There is much to mull over. Whilst the parafin heater is held up as a significant problem IT DID NOT HAPPEN LAST WINTER. ...

Don't draw any conclusions from that! Without measuring what goes on in Ian's workshop we can only guess, but I suggest last winter was luck. Condensation mainly depends on how combinations of temperature and humidity change over time. Air pressure is involved too, but the effect is smaller. Common sense doesn't apply - you have to draw graphs.

One simple principle stands - dry air can't cause condensation. Removing water is good, anything that adds it is bad.

An ordinary paraffin heater is a device for covering cold tools in hot acidic water droplets! At minimum, fit a chimney. My advice - get rid of it.

I couldn't find anything linking Styrene to rust. Possibly some of the other resins being used release acid fumes? Consult product Safety Datasheet. If they do, the paraffin heater may be making them worse too, the flame isn't hot enough to destroy, but it will warm acid air, and might convert fumes into something corrosive.


Adrian R217/12/2020 09:44:24
134 forum posts
5 photos

Has anyone tried a heat pump? In theory 4x output for a given electrical input, they don't make a lot of heat hence all the discussions around problems retrofitting houses but for a workshop might be OK? I've toyed with the idea but as they are still £££ to buy then thinking is as far as it has got.

Air conditioning was mentioned earlier, I have seen bidirectional units that will both heat and cool, but again, I've not tried it.

Ramon Wilson17/12/2020 10:02:40
1239 forum posts
330 photos

Hello Ian B,

I have a 14 x 14ft wooden workshop that is insulated much as your own. It has a 14 x 8 ft extension on one side with access from the main workshop. Although there is an air gap below I did not insulate the floor - something I wish I had done. Originally I had two 3ft long tubular greenhouse heaters permanently on but these had no thermostat. These would be boosted by secondary heating used as and when. I accepted the cost as part of my hobby.

I experienced no rusting on machine surfaces over this time but the odd piece of stock would sometimes acquire a slight patina.

I replaced all with a seven fin oil filled 3Kilowatt radiator in each side set on the one kilowatt setting. The two or three Kw settings have never been used. Save for the very warmest months these are also on permanently but of course thermostatically controlled. My wife, who keeps a wary eye on such things - assured me that the extra cost of not having to reheat the workshop on each use was hardly noticeable so it has worked like that for years now.

None of my equipment is covered other than when I am taking a break from machining - lathe has its original Myford cover and one mill a cover made from an old sheet. The other mill and all other tooling is left uncovered. It is a permanently warm place to walk into but ready for instant use without having to wait until things warm up. FWIW I have no rust issues whatsoever with this set up.

I spend a lot of time in there so the cost, as said, is considered part of the hobby - we've just this last week had a smart meter fitted. Last night as we retired my wife remarked we were spending 4p per hour at that point - not bad she said for two 1Kw heaters and two fish tanks plus an outside pond pump as well as the lighting.

Never ever having had to deal with condensation in the workshop I can't comment on de-humidifying but if you can prevent the temperature deviation in the first place (and do away with that paraffin heater) I'm you'd find you soon make a huge improvement given the insulation you have installed already.

Regards - Ramon (Tug)

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