Concrete shed base with no DPM underneath

[Gossamer]

Afternoon,
I laid a concrete base for a shed a few months ago and forgot a DPM. I didn't realise they are good practice or essential.
Anyway, what's done is done and I was wondering what my expectations should be?
The slab was left to dry for 3-4 weeks before a shed was put on it (on a brick course with the concrete slab the floor) so it was pretty well dried out.
My worry is a damp problem / condensation and my tools getting rusty.
The walls and ceiling are insulated with rockwool, more for the sound proofing than warmth. If its really cold I might use a heater but generally it will be unheated.
Cheers.

 

[KenGMac]

Gossamer, good evening.

You could consider laying a layer of plastic DPM sheet, then a floating floor [timber treated battens and a floor surface -- ply -- OSB ---T&G boards, whatever?] and at the same time [if you can afford it] place some insulation in between the battens, much warmer as well.

Ken

 

[Gossamer]

Thanks. I suppose I'm wondering if I need to do anything?
I am planning on using the concrete as the shed floor and am worried about damp issues.

 

[geraldthehamster]

You could paint it with a liquid DPM, or with something bituminous

 

[Gossamer]

All good ideas but I'm wondering if it's likely to be a problem. Does omitting DPM = rising damp or whatever?

 

[geraldthehamster]

All good ideas but I'm wondering if it's likely to be a problem. Does omitting DPM = rising damp or whatever?

Yes, quite likely, But if you paint a bituminous or chemical layer on top of it, damp won't be able to rise into the timbers of any shed that you put on it

 

[Gossamer]

Yes, quite likely, But if you paint a bituminous or chemical layer on top of it, damp won't be able to rise into the timbers of any shed that you put on it

Great!

If only i'd put down a bl00dy DPM.....

 

[noseall]

Are we talking about a damp cold or otherwise generally moist garden shed or a habitable dwelling? Sheds are damp cold places usually with nothing more than a few council slabs beneath.

 

[Gossamer]

Its got rockwool insulation for sound proofing more than anything else. No heat source as such, albeit I might use a lecky heater to take the edge off in winter.

 

[Notch7]

All good ideas but I'm wondering if it's likely to be a problem. Does omitting DPM = rising damp or whatever?

The concrete is only likely to show damp near the edges. I expect the main part of the slab will stay pretty dry.

If you can keep the outside edges of the concrete dry -maybe treat them with liquid dpm and keep soil away, then the inside should stay fairly dry.

Whilst a dpm might be a good idea to keep the slab dry from underneath, on a shed base there is usually nowhere to tie in the dpm where it comes out around the perimeter.

 

[Gossamer]

'Interestingly' water is coming off the slab big time. I picked up a saw and can of paint last night and there was condensation under them.
The slab is 150mm thick and been down for 4 weeks and got soaked several times.
I assume this is the drying out process still going on?
Due to a brick course around it there has been several times when there has been standing water for a few days.

 

[Notch7]

'Interestingly' water is coming off the slab big time. I picked up a saw and can of paint last night and there was condensation under them.
The slab is 150mm thick and been down for 4 weeks and got soaked several times.
I assume this is the drying out process still going on?
Due to a brick course around it there has been several times when there has been standing water for a few days.

Thats not surprising, the weather is now damp and cold so the water isnt coming out of the concrete very quickly. thats not an indication the concrete will remain damp.