Garden office base query

[jamesgordon]

Hi All,

Been through the site, and also spent a while trawling the forum, but would be grateful for some opinions on the following.

Just removed a large wooden workshop that had been in situ for nearly 30years which was sitting on 3 rows of sandbags filled with concrete with 6 x 3 wooden bearers across. The sub-base seems to be Hardcore with a blinding layer of granite chippings mixed with sand/soil.

I am planning to lay a 15m2 concrete slab onto which I am putting a garden office/log cabin, but was wondering if I can use the existing sub-base with a 20-30mm layer of sharp sand just to level off and stop any perforation of the visqueen before pouring a 100mm thick concrete slab. Or should I go belt and braces and dig out existing and stick another sub-base down using Mill Waste before the slab.

Grateful for any assistance

[r896neo]

I think you know the answer. get digging

[London Stone Paving]

:laugh: :laugh: that made me chuckle

[GB_Groundworks]

can you do a little test hole into the subbase in a few spots see what it is, or go the raft route with some mesh or fibres and should be fine, but without seeing it its hard to say. digging it out and starting again is the only for sure way to know.

[Dave_L]

If it's been there 30yrs and it hasn't sunk/fallen over then the chances are its is OK - but as GB says, dig a couple of test holes and see what you find.

[jamesgordon]

Thanks all, took a pick axe to it and there is around 18inches of hardcore/bricks/old garden ornaments e.t.c and then around 3-4 inches of some sort of crusher run.

No way it's coming out, so I'm going to stick a bit more sub-base on it and borrow the neighbours wacker plate and hope for the best.

When the floor breaks into 50 pieces I'll let you know.

Rgds

[r896neo]

probably worth putting some geotextile down then your new sub-base

[lutonlagerlout]

i think after 30 year all the settlement has probably occurred
if you wack whats there it MAY work
LLL

[jamesgordon]

just stuck a load more MOT1 down (about 50mm) and done around 8 passes with the whacker plate, got the missus to walk on it and it didn't sink, so I think it'll be fine

[Carberry]

just stuck a load more MOT1 down (about 50mm) and done around 8 passes with the whacker plate, got the missus to walk on it and it didn't sink, so I think it'll be fine

Don't let the wife see that post... we see "got the missus to walk on it and it didn't sink, so I think it'll be fine "
Women see "She's a disgusting fatty"

:laugh:

[dig dug dan]

whats the visqueen for on a garden shed base??

[lutonlagerlout]

visqueen which is a trade name for DPM is an enhancement to any concrete slab that you pour
I am sure brucie boy can tell us why scientifically but it is a better job all round
LLL

[msh paving]

^^^^^ main reason for putting poly sheet down is to stop water and grout loss into the sub-base, so the concrete don't dry out to quick and crack, and allows for finishing time MSH

[Carberry]

visqueen which is a trade name for DPM is an enhancement to any concrete slab that you pour
I am sure brucie boy can tell us why scientifically but it is a better job all round
LLL

Keeps the water in for curing I believe

[dig dug dan]

main reason for putting poly sheet down is to stop water and grout loss into the sub-base, so the concrete don't dry out to quick and crack, and allows for finishing time MSH

that was what i thought. unnecesaary for a shed base surely?
but as lll says, it adds enhancement!