Keeping stuff mould and rust free in integral garage

[Sparrowhawk]

Quick recap:

• 300m from sea (south coast)
• Garage faces the sea

 

I want to use my garage as a workshop but, having just cleaned mould off a bunch of pine timber (stacked with spacers in between), and selected more MDF to take to the tip as it's mouldy, it's not in a fit state yet.

 

Normally I'd think "ventilation" but:

• even with brush strips added the up-and-over garage door is nowhere near draughtproof
• there's a 12"x12" air brick next to the door

 

So then I thought "damp":

• no damp is coming up through the floor - I've done the paper-on-floor check
  • I also painted the floor with single pack garage paint when we moved in
• but I do wonder if driving rain / general mist and damp air gets in via the air brick and around the garage door

 

And if damp, salt-laden air gets in and leaves the salt behind, that keeps everything a bit moist.

 

The metal garage door means big temperature swings inside on sunny days, as it heats up.

 

My thinking is that replacing the garage door, with a wall and door or anything more airtight, would improve things.

 

But before I do anything, what's BuildHub's diagnosis? Am I chasing the wrong problem?

 

[SteamyTea]

I have just started to clear out my shed so that I can replace it.

Just about everything in it has mould or rust.

 

Timber going mouldy is a tricky one, some just attracts it, other timbers don't.

 

Ventilation and keeping the RH low is the only answer. The easy way to do that is with heating and a small wall fan.

You could try a tray of water softener salt, that absorbs what when the RH is above 50%

[ProDave]

I suspect it's the sea air?

 

I am 3 miles from the sea and garage door faces north.  My integral garage is never damp, my tools don't rust, bits of wood stored in the garage remain mould free. My classic car in there stays dry and fresh.

 

The garage is well insulated, the wall make up is pretty much the same as the house, but I did not bother with an air tight membrane.  2G version of the same windows we have in the house (3g).  A reasonable but not expensive pedestrian door and an "insulated" roller door.

 

One difference is my garage was under the size that mandated air bricks for ventilation, so I have none. The only ventilation is the trickle vents in the windows and the leaks around the roller door, and the letter box in the pedestrian door.

[saveasteading]

It's most likely dampness through the floor but you've checked that....so driving through some weakness.. under the door, through the wall.

 

The simplest answer is much more ventilation.

 

But first walk all round it and go into it during heavy rain.  You'll often find a drip or dribble.

[LnP]

I don't think you need more ventilation. You mentioned that you have large temperature variations. The items in your garage are heating up and cooling down. Because of their thermal mass, if the garage is drafty, that process will lag the temperature of the air coming into your garage. The relative humidity of the air coming in, will go up and down with its temperature. After a cold night when the contents of the garage have had time to cool down, as the day warms, warm moist air getting into your garage will come into contact with items which are still colder than the air, and water will condense out on them.

Reduce the temperature fluctuations by insulation and perhaps some background heat. Slow down the rate at which the garage air is replaced by trying to get your garage door less leaky. You don't need much ventilation in a garage; trickle vents etc are there because we introduce moisture into our houses by living in them.

[LnP]

Correction, I should have said, actual humidity (g/m³ ) will go up and down, not relative humidity (%)

[JohnMo]

Insulate, that helps mitigate temp swings, which helps stop water condensing on thing in your garage. 

5 hours ago, Sparrowhawk said:

• 300m from sea (south coast)
• Garage faces the sea

That will never help the situation

 

5 hours ago, Sparrowhawk said:

thinking is that replacing the garage door

Get an insulated one, or just add 25mm PIR to your existing door.

[-rick-]

5 hours ago, SteamyTea said:

Ventilation and keeping the RH low is the only answer. The easy way to do that is with heating and a small wall fan.

 

1 hour ago, LnP said:

Reduce the temperature fluctuations by insulation and perhaps some background heat.

 

If you are considering background heat, think differently. You can get the same heat output from a dehumidifier of the same wattage and then you effectively get dehumidification for free. (They aren't designed as heaters but the electricity used ends up as heat). Dehumidifier will have a fan to keep the air circulating inside the room and will reduce the need for active ventilation to the outside (less air changes reduces the amount of work it will have to do).

 

It's not an air sealed space so the dehumidifier will likely work hard which is a consideration and they are more expensive than a small bar heater but I'd guess they are going to be much more effective even if not perfect.

[Roger440]

As above. Make sure its as airtight as possible, and get a dessicant dehumidifier. Problem solved, though with some running costs.

 

Insulating will help a lot, but thats not going to be so easy.

 

You absolutely do not want more ventilation. If its 95% RH outside, it will be 95% inside. If its ventilated you cannot possibly get any other outcome.

 

Steel wont rust below 65%, and nor will mould grow on wood at that either.

 

I keep my workshop at 50%. Nothing degrades in any way. It does, however form part of my largest expense, electricity. But its a big workshop.

 

 

[-rick-]

11 hours ago, Roger440 said:

As above. Make sure its as airtight as possible, and get a dessicant dehumidifier. Problem solved, though with some running costs.

 

Can't say I was thinking of a desiccant type rather a compressor type.

 

11 hours ago, Roger440 said:

Insulating will help a lot, but thats not going to be so easy.

 

It should be the first thing to do if you can. Makes anything else more effective and lower cost.

 

11 hours ago, Roger440 said:

Steel wont rust below 65%, and nor will mould grow on wood at that either.

 

Rust happens due to two things, temperature changes and humidity. If the steel is kept above dew point then rust will be much less of a problem even if the humidity is relatively high. So if you can attack the problem from both sides it's likely easier/cheaper than just trying to solve the problem via either one or the other.

[ProDave]

Re running a dehumidifier.  Check the spec before you buy.

 

We have one, and it does not have any defrost function, so if you try and use it somewhere cold, the evaporator ices up and it shuts down.  So check what you buy will actually work in a cold unheated garage.

[SteamyTea]

14 hours ago, Roger440 said:

If its 95% RH outside, it will be 95% inside

Only if they are at the same temperature, which they won't be very often.

[SteamyTea]

3 hours ago, -rick- said:

Rust happens due to two things

I see it happening for only one reason, iron reacting with oxygen.

Everything else just affects the speed and penetration.

 

[Iron can react with other elements i.e. hydrogen, fluorine]

[Roger440]

7 hours ago, ProDave said:

Re running a dehumidifier.  Check the spec before you buy.

 

We have one, and it does not have any defrost function, so if you try and use it somewhere cold, the evaporator ices up and it shuts down.  So check what you buy will actually work in a cold unheated garage.

 

Which is why you use a dessicant one in low temp environments.

 

They also generate significantly more heat, which is useful in the OP's situation. And mine.

[Roger440]

4 hours ago, SteamyTea said:

Only if they are at the same temperature, which they won't be very often.

 

Techincally correct. But my barn was, before i made it somewhat airtight,  rarely more than a couple of degrees adrift from outside. Because it was well ventilated.

 

A couple of degrees difference isnt not that critical, a building full of damp air is. 

[Roger440]

8 hours ago, -rick- said:

 

Can't say I was thinking of a desiccant type rather a compressor type.

 

 

It should be the first thing to do if you can. Makes anything else more effective and lower cost.

 

 

Rust happens due to two things, temperature changes and humidity. If the steel is kept above dew point then rust will be much less of a problem even if the humidity is relatively high. So if you can attack the problem from both sides it's likely easier/cheaper than just trying to solve the problem via either one or the other.

 

Insulating properly is expensive. You can run a dehumidifier for many years before you get close to the cost on insulating effectively. Its also quick and easy.

[Sparrowhawk]

Thanks all, so I either want more or less ventilation, a larger or smaller temperature differential, but we all agree on more insulation  

 

To get me through the winter, I think the starting point is sticking PIR on the garage door, and trying to improve how the door seals without jamming it (any ideas?). Then to figure out a longer term solution (conversion or replacement door).

 

The garage has heated spaces above, to the side and back, and the remaining wall is double skin with partial fill insulation, so this may even reduce heat loss from the rest of the house. We run a dehumidifier in the house from autumn to spring, so if I get the garage airtight enough I'll run another in there.

 

The two positions on ventilation both make sense because I could see how sealed + moisture control would work, but so could e.g. an extractor fan installed and higher airflow through the garage. Though the wind pressure from the 40mph gusts now having a path through the enclosed garage might bring in more moisture. Like @SteamyTea everything in our dry-and-well-ventilated shed rusted and some went mouldy, and that's why I'll try less ventilation first as high ventilation there didn't seem to work.

[marshian]

Late to the party but I'll add my thoughts

 

Background (to my garage issues)

 

Attached single garage, single skin brick, wooden trusses with concrete tiled roof, no insulation, no loft boarded - only entry point up and over metal door and no window

 

It was horrible in summer as the south facing roof gathered all the heat from the sun and radiated it down into the garage - with only one entry it was impossible to get a airflow thro it

 

It was horrible in winter, pretty much same temp as outside - tools went rusty, wood got mouldy

 

In spring and autumn I saw lots of issues with condensation as a result of temp swings

 

It was too small to store both a car and a motorcycle so sub optimal for my car and motorcycle habit

 

Action

 

I extended it (doubled the length to a tandem garage) added a SUDG'd side door and a SUDG'd window at the back of the extension - same roof type. Fully boarded the ceiling with plasterboard, Added loft insulation between the trusses and then chip-boarded the floor for light storage. Fitted an insulated roller shutter door.

 

According to my temp monitoring

 

It's never been below freezing in the winter - typically it never goes below 5 Deg C 

 

It's never been above 26 Deg C in the summer - I can open side door, window at the back and the roller shutter a foot or so and when I'm fabricating in there the thro draft keeps the air clear.

 

I bare metalled a car door that had a big crease in it filled with filler - pulled the crease out welded up the holes and was going to put some paint on it but hung it on the wall awaiting paint - I've never actually got round to that - it's still not rusty!!!

 

I've a complete bare shell from a classic rally car that was shot blasted and etch primed years ago (it's my retirement project if I ever get to retire!!!)

 

So my advice is insulate the heck out of it - make sure you have the option to ventilate when needed and set up some form of monitoring that can give you the heads up when humidity or temp is likely to be a problem

 

I use sonoff TH-100 with a single sensor for temp and humidity and it will log hourly data for both temp and humidity and store it for up to a year - it uses a tiny amount of power and it's connected to the house wifi and with an app on my phone I can view it whenever I want. I think I paid £25 for the unit and sensor (It can be linked to devices and programmed to switch on or off at preset points - ideal if you want to run a dehumidifier or greenhouse tub heater) 

 

[-rick-]

19 hours ago, Sparrowhawk said:

The two positions on ventilation both make sense because I could see how sealed + moisture control would work, but so could e.g. an extractor fan installed and higher airflow through the garage. Though the wind pressure from the 40mph gusts now having a path through the enclosed garage might bring in more moisture. Like @SteamyTea everything in our dry-and-well-ventilated shed rusted and some went mouldy, and that's why I'll try less ventilation first as high ventilation there didn't seem to work.

 

High ventilation will work in some situations, but will lead to the inside of the garage being near the outside temperature. If you have big swings overnight so its 15C during the day but falls closer to freezing overnight then you will likely find chunky metal objects don't change temperature as fast as the room so as the room warms, higher humidity (warm) air enters and touches still cold metal and condenses. If you live near the sea this will be particularly bad as the sea air will be more humid than average.