How much cement ?

[Salop Matt]

This weekend I plan to put a concreate base down to put a steel shed on in my back garden. I am doing it myself with a friends help but neither of us are experts and I have some questions if anyone can help ?

 

I have bought a shed: 6ft x 7ft. I have dug out and shuttered a 7ft x 8ft Area to concreate.

 

My questions are:

 

* Is 4 inches of concreate going to be a deep enough base ? (it is deeper than is in patches)

* How much concreat do I need ? ie: sand /gravel mix and bags of cement ?

 

Iv used a online calculator from: "on site concreate calculator" which gave me the following :

 

Cement 7 x 25kg bags

Sand 13 x 25kg bags

aggregate 26 x 25kg bags

 

or ballast : 0.89 tons & 7 x 25kg bags of cement

 

Apparently this is a mix at 1:2:4 ! Iv only ever known 3:2:1, So will this mix be okay ?

 

Also how long should I leave it before drilling into it to fix the shed down ?

 

:unsure:

[al4x]

just call your local builders merchant and get them to deliver one dumpy bag of ballast and 7 bags of cement and you will have all you need

[Lloyd90]

Make sure the ground under is stable otherwise the cement will crack. We have a huge area that we are getting cemmented to be a parking area and enclosing the back garden. We have to put hardcore down first so it wont crack! :unsure:

[MPT1]

100mm over hardcore or 150mm concrete.

 

Put rods in ground where holes are needed bfore or at time of concreting to save drilling. then chemi fix fixings or put in rawlbolts.

[Cookiemonsterandmerlin.]

I would dig out 200mm of soil wack the sub soil then 100mm of hardcore or scalping wack that then 100mm concrete.

 

Make sure you tamp the concrete well to expell as much air as poss to gain max strength.

 

As said 7 bags of cement and one tonne of ballast.

 

Kind regards OTH

[activeviii]

adding a bag of chopped strand to every bag of cement will stop any of the cracking. you can get it from places like wickes for about a £1 a bag. worth the £7 extra if it helps stopping any cracking.

 

As said above, bulk sack and 7 bags its cheaper. or call in eazimix and they will mix on site to how you want so there is no extra to get rid of after.

 

Phil.

[al4x]

you could bung in reinforcing mesh if your really worried about cracking but having broken a few up a 4-5" slab isn't going to break if you mix it properly

[DSPUK]

If that was me I would shutter exact size of shed then when shed is on cover gap between shed and slab with piece of the tongue and groove they use for side of shed - one reason is stops rodents from nesting underneath and second if you do it the size you say water will splash up from concrete and eventually rot bottom part of shed - even putting gutters on doesn't help.

 

Dave

[Salop Matt]

Guys I got my slab down ( 7ft x 8ft and 6" thick) on saturday midafternoon. Its dry enough to walk on now but how long should i leave it for it to be cured ? Also could I get away with drilling into it after 7 days so I can put my shed on it ?

 

Cheers

[al4x]

drill it whenever you like and will be fine to put the shed on

[vampire]

Seven days is first initial cure for concrete and 29 days for final cure,although it never stops hardening,you were right to make base bigger this will stop it exploding when you drill fixings,if you do not have a base to the shed make sure you seal concrete with pva,this will add to the strength and prevent dusting of concrete.

[Salop Matt]

At what point should I PVA it ?

 

When i have assembled the shed on the base I plan to put a bead of clear silicone around the base strip to stop water being blown under to !