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Posted: Fri Jul 13, 2012 11:27 am
by 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
Posted: Fri Jul 13, 2012 12:26 pm
by r896neo
I think you know the answer. 
get digging
Posted: Mon Jul 16, 2012 10:43 pm
by London Stone Paving
:laugh: :laugh: that made me chuckle
Posted: Mon Jul 16, 2012 11:15 pm
by 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.
Posted: Tue Jul 17, 2012 6:09 am
by 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.
Posted: Sun Jul 22, 2012 10:22 pm
by 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
Posted: Sun Jul 22, 2012 10:30 pm
by r896neo
probably worth putting some geotextile down then your new sub-base
Posted: Sun Jul 22, 2012 10:46 pm
by lutonlagerlout
i think after 30 year all the settlement has probably occurred
if you wack whats there it MAY work
LLL
Posted: Thu Jul 26, 2012 2:19 pm
by 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 
Posted: Thu Jul 26, 2012 5:47 pm
by Carberry
jamesgordon wrote: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:
Posted: Thu Jul 26, 2012 6:49 pm
by dig dug dan
whats the visqueen for on a garden shed base??
Posted: Thu Jul 26, 2012 7:15 pm
by 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
Posted: Thu Jul 26, 2012 7:19 pm
by 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
Posted: Thu Jul 26, 2012 7:19 pm
by Carberry
lutonlagerlout wrote: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
Posted: Thu Jul 26, 2012 7:58 pm
by 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!