Stopping everything from rusting.

I've studded mine out, 4 to 6" of glass wool all round, door clad over with cellotex, ancient (free!) Upvc side door added, vapour barrier and Stirling board inside, I have no issues with rust or damp, it's sudden changes in temperature that cause the dew to form on your stuff.

I have a fan heater for really cold days, the florescent lights do quite a good job of heating it too!

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

I have a concrete sectional garage with an asbestos roof...

I erected stud walls 3" deep, 1" in from the walls themselves, then put 75mm Acoustic Rockwool into the studwork followed by a vapour barrier over the top, and OSB to cap that.

the 1" air gap around the insulation is ventilated to ensure that any condensation on the walls is removed, and the vapour barrier keeps any internal moisture from getting to the cold surfaces.

I use a combination of trace heating and dehumidification to absolutely minimise the risk of rust, but in practice the temperature stablising effects of insulation would probably be OK on their own for this purpose.

From a thermal perspectve, having the air-gap which makes a major difference to the overall insulation of the wall design, without requiring additional material... When I did the calculations there's an optimal gap size before the space becomes becomes big enough that it's liable to convective heat transfer predominating, and the insulating properties drop off to less than a much thinner air-gap.

What's particularly awkward about that is that the optimal air-gap is determined in part by the temperature differential you want to maintain.

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!

Yes I know but what I'm talking about is the reaction of CO2 with concrete in the presence of moisture as described here.

**LINK**

and the following :-

Calcium bicarbonate, also called calcium hydrogen carbonate, is an unstable inorganic chemical compound with the chemical formula Ca(HCO₃)₂.

The compound cannot be isolated in solid form as it decomposes to calcium carbonate and carbon dioxide upon removal of water via either boiling or vacuum drying. It exists only in aqueous solution containing the calcium (Ca²⁺), bicarbonate (HCO−
3), and carbonate (CO2−
3) ions, together with dissolved carbon dioxide (CO₂). The relative concentrations of these carbon-containing species depend on the pH: bicarbonate predominates within the range 6.36–10.25 in fresh water.

came from here

**LINK**

regards Martin

All I can say is in an integral garage where rusting is not an issue, painted 3 draw cabinets rust where they touch the bare 1980's concrete. A piece of old carpet stops it.

Yes same here, I had one. I started keeping a lot of my tooling in clip lock boxes to stop them going rusty. Oil or grease on some of the big stuff if I wasn’t going to use it for a while.

Martin
I think that you are confusing what happens to steel reinforcing in concrete with rusting away from the concrete. The water in the air will be mildly acidic due to dissolved CO2 forming a weak solution of carbonic acid.. The acidity is caused by hydrogen ions not the bicarbonate. The pH you quote is referring to the disasiciation of the calcium bicarb, not its pH per se.
As others have said rust formation needs oxygen and water, removal of either prevents rust. My asbestos garage is lined with a timber lining plus a bit of insulation, bur I find a liberal coating of oil prevents steel from rusting.

with insulated double skin,block all holes in the exterior skin to keep mice out,they love the warm cavity and ruin the insulation.

Also if it is timber lined this needs painting to prevent the timber being a source of humidity.

Yes I get that, and I’m not talking about the reinforcing but the generation of calcium bicarbonate by the reaction of atmospheric CO2 with the cement. As far as I can make out calcium bicarbonate can only exist in solution and as it dries it evolves CO2 which will acidify the solution by producing carbonic acid. So maybe concrete under cyclic dampness can act like an acid pump periodically creating a more than usual corrosive atmosphere. All this is just a hunch based on the anecdotal statements about concrete garages being the worst for corrosion. I need to ask a professional chemist really. These types of garages are bad for corrosion just because of their construction but it’s worth figuring out if there is something else going on. I will ask a chemist.

regards Martin

So I asked a professional and basically I'm chasing a non existant problem and talking a lot of tosh. Concrete does not chemically add to the rust problem of concrete garages which is nice to know and those of you who suggested such were correct.

regards Martin

Thanks for your findings. I actually analysed cement for about 3 years from late ‘69 (and occasionally concrete, too). That was predominantly wet analysis (XRF and XRD followed, as analytical methods progressed to more automated/advanced methods). Other lines, of mine, were recovery of precious metals Silver, gold, Platinum and Palladium, mainly), supply of aromatherapy-type ‘concoctions’ (oils, creams and other sundry products) and analysis of radio-isotope products (for both radioactivity and chemical purity).

Calcium ions are quite electropositive in nature and there was generally less than 3% ‘free lime’ (as CaO) in most cements (maximum amount varied depending on the source) but excessive amounts cause expansion as the cement cures (hydrates). Even at a 5:1 aggregate to cement ratio that small percentage of free lime would account for less than 0.5% of the concrete and would typically be converted to calcium carbonate early in its life. Concrete cover is used, as the only means of preventing reinforcement corrosion, in many structures.

Thin sections, such as in fence posts and garage panels can last decades without problems. Then there are the more specialised cements such as High Alumina and Sulphate Resisting. Quite a complex area in its own ‘niche’.🙂

Thanks all.
I’ll read though and decide what to do.

Chris

It's strange but I have a draughty 14X8 ft wooden lean to shed against the house, the floor is paving slabs , roof is corrugated plastic with shading screens, there are four vintage lathes, loads of tools etc and more or less nothing rusts at all.

Only problem is sometimes in Spring on a warmish day condensation can drip a few drops but this rarely happens

The mention of reinforcing steel in concrete is a further clue to the problem. the reinforcing adds two new causes of condensation - first it allows the concrete to be thinner so less insulating, and the steel conducts heat through it so even less insulating.

I now realise that although the Welsh Marches is not always a very good place to enjoy a garage hobby, it has one major advantage. We are only about five miles from a Kingspan factory. And they have off-cuts and rejects ...

Cheers, Tim

Interesting to read this thread and the many words of wisdom. If I may add a few comments of mine, even if not very wise :

Insulation: a key to avoiding rust is avoiding condensation, and the key to that is avoiding rapid temperature changes. Insulation slows down the rate of heat transfer and thus temperature changes and avoids condensation on surfaces where there is a temperature difference. It also helps a great deal in the summer, especially with roof insulation which avoids the effects of direct sunlight beating down on it.

Spray foam. Anyone who instals that is signing a pact with the devil. Yes, it insulates, and is easy to apply. After that, it's a nightmare with entrapped moisture, lack of ventilation, outgassing of nasty chemicals and difficulties in building maintenance. Slab foam or rockwool insulation is a much better way to go.

My own workshop is a reasonably substantial timber shed with 50mm of Rockwool RW4 grade** covered with 13mm OSB (Sterling) board panels for the walls and ceiling, which make for easy attachment of storage shelves, small tool racks etc. The floor is timber, laid on concrete slabs bedded on a very light dry sand/cement mix. Machines are mounted on anti-vibration pads through holes in the floor, resting on the concrete slabs underneath. A couple of holes at rafter height allow a through flow of ventilation which helps reduce humidity build-up.Windows are 'economy grade' commercial timber double glazed units.

A number of people have mentioned roofing felt; Onduline corrugated reinforced bitumen panels over battens laid on OSB panels are far more durable and easy to replace when eventually needed. The air space in-between adds to the insulation effectiveness. Sold at Wickes.

Heating is a small and simple oil-filled radiator with a thermostat.

It makes for a most comfortable working environment and even in recent -8C external night time temperatures was a pleasure to work in with the timber floor being easy on the feet and legs.

In your case, I would line out the concrete garage (internal shed approach as suggested) and insulate.

/John

**Rockwool in the more technical grades is available from Rockwool distributors over the counter, often a wider range than the usual DIY 'sheds'. Rockwool have a very helpful technical helpline. Google is your friend here.

Edited By John Abson on 18/12/2022 11:29:36

Just a warning to everyone today. My workshop is very well insulated (it's built from metal clad insulated panels) and I've never had the least bit of problems with condensation. Today's 14 degree rapid rise in temperature has actually made the ceiling damp and put a fine damp film on the stuff in my workshop and I've had to spend time wiping stuff off and applying water displacer to make sure noting rusts. Never had to do that since I built the place in 2008 but today is rather unusual circumstances.

I would advise anyone to go out and check their workshop over if they have bare metal they don't want rusting over.

My shop is 10' 9" x 6' 9" exterally, with 19 mm T&G cladding on 50 mm frames with 12mm ply inner. The gap is filled with glassfibre. The roof is 12mm ply on 50 mm frames, with 12 mm ply inner, again filled with glass fibre, now topped by a rubber membrane..

On the rear wall there is a high level, hooded, fixed vent (Actually a 6" ex equipment fan ) At floor level, there are two small, about 50 mm diameter fixed vents.

The floor is 19mm ply, supported on 8 x 2 bearers, which are shrouded on three sides, (Fence and low walls )

Condensation / rust has been no problem since it was built 19 years ago.

When it is cold, a thermostatically controlled 2 Kw heater runs for about 15 mins and then cuts in again about 45 - 60 minutes later, for a short time.

This is in East Anglia, U K.

Unless the weather is wet ans/or cold, often the door is left open.

When it is frosty, a 80 watt tubular heater, under the fitting bench is switched on, as a precaution.

The lack of rust problem is ascribed to good insulation, and good, but not excessive ventilation.

Howard

Pete. You have done me a massive favour! Read your post and went straight out to check my lathe. Horror! Surface rust! Wiped it all off with an oily cloth, but if I'd left it much longer there'd have been trouble. You've saved my bacon! Thanks fella!