Your roof will be leaking nearly all of the heat and have the biggest temperature differential. Insulate the underside of that and your rusting problems will be severely diminished.

asbestos roof. Any insulation will improve matters.

small heater How small and what is the energy source? Any fuel-burning heaters would produce some water.

losing all the heat You are not alone. Every building loses exactly all the heat put into it – sooner or later. The trick is to slow down that heat loss.

Insulation, draught-proofing, dehumidifying and some warmth is necessary to.avoid the condensation which is causing the rusting. Consider the value of your machines and decide whether you wish to ‘lose’ them when deciding on how much to invest in preserving them. My capital costs were quite high, but the running costs are acceptable and low. The running costs would already have cost more if the insulation and draught-proofing were not indtalled.🙂

My heavily insulated, draught-proofed workshop now has a Chinese Diesel air Heater to help keep the contents, as well as the space, warm. The desiccant dehumidifier is currently only running one hour (on the low setting of 375W) during the E7 period and the CDH is run for while I am in residence, or for a little longer (I set it to run for as long as I think necessary when I vacate the workshop).

The insulation was all secondhand (as were the non-working dehumidifiers I bought and repaired) and the oil I am burning was purchased some time ago. The CDH runs from an old battery which is permanently connected to a float charger.

If you block the ventilation gaps with spray foam the roof will run with condensation.

If the slab extends outside the walls the rain will come under the walls.

8 x 4 sheets of foam are not expensive, Wikes sell it for £11 a sheet 25mm thick, sealing the roof off with it will not be pointless. However, most of the damp comes from the floor so applying a big sheet of membrane and then screeding over it will be needed.

There have been quite a few threads in the past on this subject. Try the search option on the hme page, not the one on this page.
The condensation dripping off the roof will soak into fiberglass type insulation so bear that in mind. Ideally you want inside>waterproof layer>insulation>drip catcher>ventilated air gap for condensation to leave> roof sheets. therefore it may be better to put in the insulation as a continuous layer below the rafters rather than between. Any gap in the waterproof layer allows moist air to pass either from inside or outside depending on season. It is important not to let the insulation get damp or it just sits there absorbing your heat to evaporate the water.

As a stop gap cover all machines with a cotton not synthetic sheet (jumble sale) and if available a blanket over that. Not plastic sheet which sweats. This catches the dew which does actually form even inside a building.
Make a box or shed within a shed for all small tools, or a cabinet or shelves to gather things into a smaller space, insulated if possible, and heat just that.
If you can spare the headroom, at least for this winter, a few pieces or 8x4ft OSB will make a 'room' leaving say1 ft clearance above. This will give you space to put an insulating layer on top and in this case I would put a plastic sheet over that insulation to catch the drips off the roof.
Apply diluted clear Waxoyle to all stock material and tools thinned with white spirit so it dries to a slightly tacky wax. It is much nicer to handle than oil. You can treat the whole lathe too as ail will wash it off bits that need oil.

As many will know i built a fully insulated fridge panel type garage /workshop. I still have the dehumidifier running through the winter months. I get about a litre of water out every 3 or 4 days. Probably coming through the concrete base.

At my previous house i insulated the garage door with polystyrene panels , which helped. A friend had a company in who fully spray lined the garage with insulation. That was toasty warm, but probably very expensive.

Brother in law had a concrete garage with wriggly asbestos roof. He bought large sheets of poly insulation from the.. builders merchants. He did all the roof & the concrete walls. The walls he then oversheeted with ply . It worked well.

Edit… I still spray coat some cutters & other tools with the shield stuff but i guess these days it is banned. 

Steve.

Edited By Steviegtr on 04/12/2022 20:59:31

Edited By Steviegtr on 04/12/2022 21:00:27

Edited By Steviegtr on 04/12/2022 21:01:16

Wooden shed. Roof, walls and door all completely covered with roofing felt to keep rain off wooden structure, so waterproof. 3 ply sheets on interior walls. Void stuffed with loft insulation. Roof lined with polystyrene panels glued in place with overlapping joints. Tubular heater +thermostat + timer on lathe. Timed off during the daylight hours. Lathe covered with thin plastic sheet. Mill 1 covered with thick plastic sheet and home made low wattage heater on drip tray. Heater is 4 old style bulbs wired in series on protective box. On 24/7 except when mill in use. Mill 2 covered with thick plastic sheet, no heater. Tools and work left on bench with thin plastic sheet cover, no heater. Tools on open shelves around mill and lathe, no cover or heater. It's that tubular heater that warms the whole workshop with its heat gradually escaping from under the plastic cover. Comfortably warm upon unlocking anytime next day. Concrete floor sealed with black sealant jollop, covered with scrap sheets of hardboard with old redundant car mats. Wooden walled shed stands on brick walls, 3 courses. Felt overlaps brick wall base. Windows boarded up. Small wooden frame around inside of door, to which 3 ply glued and screwed and voids stuffed with loft insulation. System works well, just a bugger getting from house to workshop and back in wet/freezing cold. Yes, it does get cold down 'sarf' in Brighton! Shed size, 10 x 8ft, so fairly small volume. Max/min thermometer to keep check on temperature variation.  Humidity gauge to  get some idea of air condition. Got dehumidifier to remove moisture but never use it. Others have said plastic sweats but not if low heating keeps the dew point high enough.

Edited By DMB on 04/12/2022 22:47:39

Edited By DMB on 04/12/2022 22:52:11

Edited By DMB on 04/12/2022 22:55:19

There is something call ‘controlled ventilation’. Much better than uncontrolled draughts.

I sorted that problem (mainly) by screeding the garage floor.

I’m like Pete, there is no ventilation (so no draughts). Humidity is kept under control by use of a dehumidifier.

I wouldn’t consider anything less than 50mm of insulation – mine is now all 100mm or more – although there are some 25mm sheets amongst the mix.

But any insulation helps – it is a balance of cost and effort versus energy requirement reduction in the longer term.

I was wondering if the concrete itself make things worse from a chemical point of view. I'm no chemist so maybe someone with a little more knowledge may like to comment. What I have found is that concrete carbonates by reaction with CO2 in the presence of moisture and produces Sodium biCarbonate which is described as an acid salt so maybe the dampness and the moisture in an enclosed concrete building is better at promoting corrosion due to it's chemical nature than neutral pH dampness. If that is the case then a coating of paint to seal the surface of the concrete walls and floor could help. We need a tame chemist really.

regards Martin

Martin
Sodium Bicarbonate forms an alkaline solution.
Keith

I should have said Calcium Bicarbonate which ranges from 6.3 to 10.25 according to the carbonate species (so I’m told by looking it up) so it seems at least possible to generate a mildly acidic vapour. Carbonation of concrete certainly reduces it’s pH to the extent that reinforcing steel work begins to corrode according to the literature.
regards Martin

Edited By Martin Kyte on 05/12/2022 20:04:44

Well, Calcium Bicarbonate is alkaline and not very soluble so unlikely to create a vapour in this case. Alkalis and acids are both capable of attacking metals, for instance Aluminium reacts violently with Sodium Hydroxide (Caustic Soda), evolving lots of Hydrogen. Sodium Chloride is almost neutral, neither acid or alkaline, and it causes horrible rust.

However, the Oxygen and Carbon Dioxide in air make water vapour and condensate highly oxygenated, slightly acidic, and able to invade tiny cracks and pores in metal like a first class penetrating oil. Condensation murders tools, so reduce the water by keeping it out of the building, ventilating or dehumidifying what's left, avoiding temperature swings, and protecting with grease etc.

A big part of the problem with single skinned workshops, is the temperature rises during the day and falls during the night, making it likely that wet air warming up in the morning sun will be in contact with lots of cold tools, wallop. It explains why experiences vary so much: a shed tucked away in a cold, shady, north facing sheltered garden will have much less trouble than exactly the same shed in a warm, exposed, south facing garden. The location matters. Lots of insulation helps.

Dave

Sorry, but a long way off re cement/concrete chemistry. Cement is calcium silicate based (with a few other necessary constituents) and concrete typically only contains about 15% cement. Perhaps 20% in precast thin sections.

My workshop is in a sectional concrete garage and is insulated, so definitely possible!