making shed base question on geotextile membrane

happyhero

Hi I am making a concrete shed base and I was told to put a Geotextile membrane down on the soil as it will stop the hardcore/mot1 migrating into the subsoil, but if I put that down first and then start smashing my leftover hardcore on it and adding some mot1 and then using a wacker plate on the whole lot wont it pierce the membrane and ruin it?

I cannot understand how you put down a membrane and then put a load of rough sharp stuff on top and then get rough with it and not damage the membrane. Am I missing something?

Appreciate any advice please.

stuart45

Who told you to put a geotextile under the hardcore?

Bendy_House

Hi HH.

Will this concrete base also act as the shed floor? And, how large is this shed going to be?

happyhero

stuart45 said:

Who told you to put a geotextile under the hardcore?

I showed my builder friend who I can't now get hold of this bit from the paving expert.com site and he told me I should do this

to summarise, its primary purpose is as a separation membrane , preventing the sub-base or bedding material mixing with the underlying layers, which can result in excess settlement or pumping of a particularly weak sub-grade, which, in turn, can cause settlement and rutting.

Makes me think it's obvious I should use it, are you suggesting I don't? If so can you explain why I don't need to worry about the bit mentioned above please, I'm just trying to understand it all?

happyhero

Bendy_House said:

Hi HH.

Will this concrete base also act as the shed floor? And, how large is this shed going to be?

I am making the concrete base 3.4m X 2.6m and I'm hoping to build a block built (3" block} walls. Yes base will act as shed floor.

Section62

happyhero said:

....to summarise, its primary purpose is as a separation membrane , preventing the sub-base or bedding material mixing with the underlying layers, which can result in excess settlement or pumping of a particularly weak sub-grade, which, in turn, can cause settlement and rutting.

Makes me think it's obvious I should use it, are you suggesting I don't? If so can you explain why I don't need to worry about the bit mentioned above please, I'm just trying to understand it all?

If you were building a road or driveway perhaps.

The migration of granular materials (e.g. hardcore) into the ground below is something you'd usually associate with an area having traffic, essentially the repeated loading and unloading causes the uncontained materials below to move around over time.

You wouldn't expect to get the same effect happening under a garden shed. You'd hope, once the shed was built, that the conditions were static, not dynamic.

There may be cases in which you'd use a membrane where there is no traffic, but those usually involve very weak ground below the sub-base where it isn't economic to dig out all the unsuitable material and replace it with something stronger.

There's no particular problem using a porous geotextile under a shed base, but if you needed to use one it suggests there was something very wrong with the plan.

Section62

happyhero said:

Bendy_House said:

Hi HH.

Will this concrete base also act as the shed floor? And, how large is this shed going to be?

I am making the concrete base 3.4m X 2.6m and I'm hoping to build a block built (3" block} walls. Yes base will act as shed floor.

3" rather than 4"?  How high will the walls be?

stuart45

3 inch blocks can be a bit tricky to lay. 4 inch are much more stable.
Having a strip foundation for the walls is better than building off the slab.
Geotex isn't normally used for a shed base.

happyhero

Section62 said:

happyhero said:

Bendy_House said:

Hi HH.

Will this concrete base also act as the shed floor? And, how large is this shed going to be?

I am making the concrete base 3.4m X 2.6m and I'm hoping to build a block built (3" block} walls. Yes base will act as shed floor.

3" rather than 4"?  How high will the walls be?

I was thinking I fancied a block built shed this time instead of timber and didn't think the blocks would weigh that much and so be fine on a concrete slab. My builder friend suggested 3" blocks would work well, which I would probably get him to lay. I was thinking making walls about 2.2 or 2.4m high, would that be so heavy. I would probably have double doors one end so hardly any blocks at one end.

My ground is very hard soil with clay and chalk at a deeper level with some roots I've tried to remove as much as possible. Its some of the hardest ground I've ever had to dig....its been tough going digging it to the right level.