Damproof membrane?

[wombats]

I have laid the dolomite and whacked it down now i need a damproof membrane for my shed base before the concrete goes in.

What do i need to look for to get the right one?
Does it just go on the flat part or should it come up the sides and be visable from ground level?

 

[freddiemercurystwin]

Why are you using a dpm under your shed floor slab?

 

[Richard C]

 

[theoldun]

Why are you using a dpm under your shed floor slab?

We always use a dpm in a garage or shed base to stop the concrete de-watering and stop the possibility of top of slab turning a shade of green in two or three years time. We find that your concrete will cure and harden a lot better with poly underneath, especially this time of year.
oldun

 

[wombats]

Why are you using a dpm under your shed floor slab?

I read somewhere that this will help prevent damp coming up through the floor when the shed is there. Don't want damp getting on items stored in the shed. (Have i got it wrong?)

 

[wombats]

Can anyone help?

 

[theoldun]

Why are you using a dpm under your shed floor slab?

I read somewhere that this will help prevent damp coming up through the floor when the shed is there. Don't want damp getting on items stored in the shed. (Have i got it wrong?)

No, you are not wrong. We list below an extract from Tony McCormack’s web site.
The purpose of the dpm is two-fold: Firstly, to protect the underside of the slab from attack by dampness and aggressive salts (such as chlorides) or other chemicals in the sub-base or sub-grade, and damaging the concrete, unseen, from beneath. Secondly, a dpm prevents the newly poured concrete from drying out too quickly (de-watering) because of water absorption by the sub-base or sub-grade, which will adversely affect finished strength and can cause hundreds of tiny surface cracks.

Use either blue or black Visqueen 1000 gauge. Lay it over sub base and over top of shutter board, lay base, strike shutter, back fill edge and cut dpm of 25mm above ground level.
oldun

 

[freddiemercurystwin]

For a poxy shed it won't make any difference.

 

[Richard C]

I’ve always covered the bottom of all my sheds with roofing felt & stood them on 2” paving slabs or reinforced fence gravel boards, bedded in 25-30mm of sharp sand; no movement, no damp & no rot.

One left behind at my previous property is now around 25 years old, still standing & got years left in it.

 

[wombats]

Use either blue or black Visqueen 1000 gauge. Lay it over sub base and over top of shutter board, lay base, strike shutter, back fill edge and cut dpm of 25mm above ground level.

Thanks that is what i needed to know. Is This What i need? Should i get the 250mu or 300mu ( i don't know what this is).

What does strike shutter mean?

 

[wombats]

For a poxy shed it won't make any difference.

This is no poxy shed it is costing me over £3000 so i want to get it right.

 

[freddiemercurystwin]

A dpm under the slab will not make any difference to the shed if it is a conventional shed sat on bearers, as DickieC says, the key is to isolate the shed from the slab not the slab from the earth. When you post a question about a 'shed' how are we to know whether its a £3K outbuilding or a £100 piece of crap from B&Q? Muppet!

 

[wombats]

Sorry for not stating the value of the shed or type! It is a concrete sectional shed and will be sitting directly on the concrete slab.

ps.

Muppet!

no need for the attitude for a misunderstanding

 

[hotrod]

Thanks that is what i needed to know. Is This What i need? Should i get the 250mu or 300mu ( i don't know what this is).

What does strike shutter mean?

Hi wombats, Get the 1200g (300mu) - it relates to the thickness and is just slightly thicker than the 1000g. For what it's worth, for the sake of £10-£20, I would always put a DPM down.

'Strike' the shutter just means to remove the wood (or whatever you've used) from the concrete you've poured.

 

[wombats]

Thanks hotrod much appreciated now i can get on with the job need it all doing today for the concrete to come tomorrow.