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21/09/2017
Homepage - Preparation for Concrete Base


Concrete Base


Before beginning any work, you must be confident that you are able to complete this type of base. Corrections can be costly!

When laying the concrete please keep in mind the length of time it will take for the concrete to cure. Do not expect to site your building on a newly laid concrete pad.

For most buildings a concrete thickness of 3" (75mm) is fine, on some of the larger buildings & depending on use increase this to 4" (100mm) laid on compacted hardcore or Type 1 roadstone may be required. Approximately 1" -2" (25-50mm) of the depth of the base should be above the surrounding ground level.



Preparation:
Mark out where you want to place the building.
Tip: An additional border of approximately 6" (150mm) around the edge of the base will allow you to fill with pea shingle or a decorative stone preventing the possibility of 'splash-back' as rain drips to floor. This can be prepared before of after the base has been laid.
Clear the entire top layer of vegetation and compress the existing ground so that there will be no movement once the concrete has been laid.
Set out the Shuttering making sure that you measure from the inside of the shuttering at the same time keeping level, when pegging out keep checking the diagonals to make sure that they are equal this will ensure that the base will be square.
Double check all of the measurements and levels only when you are sure, will you be ready to lay the concrete.

Tip: It is advisable to place a polythene membrane down prior to the concrete being laid to prevent damp rising through the concrete to the building.


Materials Required

BALLAST
Ballast is usually sold in 25kg bags approximately 2 bags are needed to produce, 1 cubic foot of concrete.
Example: Shed Base 8' Long x 6' Wide x 3" deep the Volume = 8' x 6' x 0.25' = 12 cu ft
2 bags per cubic ft = 24 bags add 10%, 3 bags for compacting total 27 bags of ballast

CEMENT
1 bag (25kg) of cement mixed with the ballast in the ratio of 1:5, 1 bag of cement to 5 bags of ballast
27 bags of ballast divide by 5 and round up would = 6 bags of cement

WATER
Average 1.5 litres per bag of ballast = 40-45 litres

These quantities are for guidance purposes only. Always order more than you have calculated being needed. It's easier to return unused material than to get more materials as the concrete is going off.

Suggested Tools
Spade/Shovel Hammer & Saw Tape Measure & String Spirit Level & Square Concrete Mixer Rammer Tamping Beam Plastic or Wooden Float

MIXING
Make sure that you can get the materials and mixer as close to the base as possible this will save you a lot of time and effort, and unnecessary use of a wheelbarrow to transport the materials/concrete to the base.

Mix to the ratios that have been decided, in this case 1:5 whether it be 1 Shovel of cement & 5 shovels ballast, or you use 1 bucket of cement & 5 buckets of ballast, use of the same measuring device is essential.
Once you have mixed the first load you will know how much water you will need for all subsequent loads.
We are unable to describe the correct consistency, however you do not want to make the mix too wet as this may weaken the concrete.

LAYING
Starting at the furthest point of the base (so that you will not be walking over wet concrete) lay the concrete against the shuttering then using the front edge of the shovel tap the concrete down this will help the concrete reach into the edges, also tap the outside of the shuttering as you go this will help reduce air pockets.
Once you have filled the complete area you will need to use the tamping beam, first use the tamping motion to gain the rough level filling any voids as you go, then starting at one end using the same beam run this across the top of the shuttering moving from left to right in a sawing action this will give you the final level, you can then finish the surface using the wooden/plastic float.

As soon as the concrete has hardened enough not to be marked, it should be covered with a plastic sheet and weighted down.
This will stop it drying out too fast; the sheeting can then be removed after a couple of days.


Note: Concrete should not be allowed to freeze; additives or insulation during the drying process may be needed.

SAFETY
Care should always be taken when handling concrete, please read all packaging
Disclaimer: This information is to be used merely as a guide and as such Southern Sheds Ltd will be exempt from any liability, which may result in any way.


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