Shed base using slabs

[lms78]

Hi,

I am planning on installing a 8x6 foot garden shed.

I had planned on using a pro-base style base, but I have a load of 2x2 foot paving slabs that are otherwise going to waste, so it probably makes more sense to recycle these as a base instead.

I have read various instructions on how to lay slabs for a base and am a bit confused.

As I understand I need to dig out and level the ground. I have done this, and the ground is quite well compacted and reasonably level. I then need to lay a dry mixture of sharp sand and cement (8 to 1) to make completely flat, then simply place the slabs down and ensure they are level. Does this sound ok? If so, I have the following questions:

How deep do I need the sand/cement or is it a case of as much as is required to make a completely level surface?

Do I need anything around the outside slabs to hold them in place?

Should I lay all the sand/cement first and then place all the slabs or do a slab at a time?

I assume that as my slabs are 2x2 and my shed is 8x6, I will actually need to make a base that is 10x8 (I don't have any tools to cut the slabs) as it will need to be bigger rather than exactly the same size?

Any advice would be very gratefully received and apologies if some of the above questions fall into the "stupid" category!

 

[r896neo]

Personally I think you will find a wet mix easier because the mix will flow under the flag as you tap it down level. A dry mix will not spread so the bed had to be right before you put it down. I would also go 6:1. Aim to make it between 25-50mm. If you need it deeper than 50mm for a low spot etc then add some gravel to bulk it into a basic concrete before laying.

Check out paving expert.com for how to guides. If you have any spare flags you could try breaking them with a bolster. It doesnt work well at all but you might get lucky and if you dont want to hire a stihl saw then give it a go.

 

[lms78]

Thanks r896neo, do I lay the wet mix directly onto the soil I have flattened? Should I aim to to lay a smooth level of the mix and then put the slabs on that, or should I "dot and dab" on each slab?

 

[r896neo]

Yep mortar straight on the ground.

Lay a full base, create ridges with the trowel that will push flat when you set the weight of the flag down. Check out a vid or two to see the mortar consistancy you want as getting that right makes it much easier.

 

[lms78]

Thanks again. I have looked on pavingexpert.com and will continue to do so between now and laying and try and catch a few videos as well, but just a couple more questions before this thread goes cold....

I have roughly levelled out the soil. I assume that given the size of the area and the size of the slabs, I do one slab at a time, is that correct? If so, at what points do you check the levels? I assume you'd put the mix down roughly to the height you want it (I assume you don't want to be putting spirit levels on this?) then put the grooves in (using an adhesive trowel - like you use for tiling?) and place the slab then push down to level. At that point I assume you check the level of that slab and its level compared to the adjacent slabs?

Sorry again for the complete lack of knowledge. It goes without saying that I have never done this before!

 

[r896neo]

You need to decide on your finished height, this would be dictated by the surface you are coming up to meet such as existing flags or a lawn etc. Then you decide on your fall and what direction it will fall. So say your existing flags where your starting is at 0cm you want to fall the flags away towards a fence behind. Your flagged area will be 2.4m (8ft) long so you want a small fall on the paving of say 1:60 so 2400mm divided by 60 = 40mm.

You use a long straight edge with a level on top and hammer in a peg 2.5m away from your starting point and you make it 40mm lower. Now all you need to do is use your long straight timber to check the level of the flags. Place the mortar down for the first one and riplle the mortar with your trowel, set the flag on and tap it down gently, check with your straight edge to match it up with your peg.

Its hard to explain but very straight forward if you think about it methodically

check this video for the actual bedding

 

[angelboy]

check this video for the actual bedding

Out of interest, is there any reason not to point up the joints as you're laying them so that bedding layer and joints are all continuous as they're drying at the same time?

I ask because I laid a load of Marshals heritage paving as per the video, but a few years later a good portion needs repointing - mainly because my wife loves to get the jet washer on them twice a year.

I wondered if it was a continuous bed I would have the same problem in future.

 

[r896neo]

Most professionals lay and point as a seperate process. This is for practical reasons such as using a specialist jointing compound or complex layouts where there may be some grinding and normalising of joints needed post laying. Also there is the issue of having to get on the paving when the bedding is not fully hardened which can leave rocking flags. That said though there is merit in continuous bed and joint.

The problem however is you cant or shouldn't use the same mix for both. Bedding should be 6:1 grit sand to cement and pointing should be 4:1 plastering sand/ building sand to cement.

Repointing is a waste of time if the paving is moving at all or is not laid on a rigid mortar bedding.

Proper jointing should withstand moderate jetwashing but it will always speed up pointings deterioration.

 

[angelboy]

Most professionals lay and point as a seperate process. This is for practical reasons such as using a specialist jointing compound or complex layouts where there may be some grinding and normalising of joints needed post laying. Also there is the issue of having to get on the paving when the bedding is not fully hardened which can leave rocking flags. That said though there is merit in continuous bed and joint.

The problem however is you cant or shouldn't use the same mix for both. Bedding should be 6:1 grit sand to cement and pointing should be 4:1 plastering sand/ building sand to cement.

Repointing is a waste of time if the paving is moving at all or is not laid on a rigid mortar bedding.

Proper jointing should withstand moderate jetwashing but it will always speed up pointings deterioration.

Thanks for that. I think I probably jointed them with grit sand if I remember right.

So what's the issue with bedding with builders sand?

 

[r896neo]

Its too small grained and therefore too weak when used in a thick bed like a 40mm bedding. It also holds too much water making it turn into a soup when you tap a flag into it.