How thick should my beeding layer be?

[novicebob]

I have knocked down my garden shed which is away from the house and it has left a 100mm thick concrete base in good condition (approx 9m sq.). I am going to build a walled patio on this base using Bradstone Old Town slabs (6 sizes). Within this excellent website you recommend laying slabs on 40mm of sharp sand\cement mix (10:1). I am just wondering if this holds true considering the base I have or whether you would recommend something different.

[bobhughes]

Have a look here:
http://www.pavingexpert.com/faq_layover01.htm

[lutonlagerlout]

as long as the base is sound and crack free,30 -40 mm of bedding will be sound
i would be tempted to clean and prime the base and lay the flags/slabs on a wet mix for better adhesion
cheers LLL

[novicebob]

Thanks LLL.

As my name suggests I am a bit new to this paving game so can I ask for some clarification. The base is sound and uncracked.

What does "prime" mean?

Then you say a "wet mix". Is this 10 sharp sand, 1 cement and added water? Is this then spread all over the whole area and then the flags laid or do I use this wet mix to provide individual beds for each flag.

Hope this makes sense. And thanks again for your time.

[Tony McC]

Priming involves dampening the cleaned surface and coating it with PVA, SBR or a cement slurry. It's not always necessary, but when it is used, it does improve the bond between bedding and substrate.

Wet mix is explained here

Due to its limited working life, best to work with individual beds

[novicebob]

Thanks both for your answers.

I don't feel very confident of using a wet mix due to my inexperience. I would prefer to use the dry 10:1 mix if at all possible. Will it work having this dry mix on top of a concrete base? Will there be enough moisture in the sand for the mix to go hard?

Thanks again for your time.

[nelly05]

Noveicebob - dont be too afraid of using the wet mix, i found it easier to use than they dry mix, and managed to get the first part of my patio done ok.

You do get some playing time with a wet mix and i found levelling the dry mix was harder (for me!!)

Do be careful of the mix coming up between the slabs when laying - just feather the mix prior to laying and you should be fine.

I didnt and ended up with a couple of small cement stains along the edge of one or two slabs. Need to clean them off before i manage to get a dry day to seal the slabs!!

Regards

[novicebob]

Thanks Nelly

Told you I was a novice - what does "feather the mix" mean?

[nelly05]

LOL, i dont know m8, its just what LLL told me to do ;0)

Seriously, i took it to mean that you slope the mix that you lay under the joint, kind of like a v shape so the level is lower under the joint of the slabs, so when you level the slab all the mix doesnt come squirting up between the slabs causing them to become stained.

Someone will give you the technical term later - feather may not be quite the correct terminolgy.

regards

[lutonlagerlout]

firstly if you use a wet mix the mortar/bedding mix needs to be angled away from the adjoining slabs at 45 deg. to stop it squiting up between the slabs
feathering is running the trowel back and forward into the mix to introduce a small amount of air so that when you tap your slab it beds down nicely rather than push the slab next to it up
sort of like the mark of ZORRO but with a trowel instead of a rapier
cheers LLL

[matt h]

bet he gets the point.lo

[nelly05]

firstly if you use a wet mix the mortar/bedding mix needs to be angled away from the adjoining slabs at 45 deg. to stop it squiting up between the slabs
feathering is running the trowel back and forward into the mix to introduce a small amount of air so that when you tap your slab it beds down nicely rather than push the slab next to it up
sort of like the mark of ZORRO but with a trowel instead of a rapier
cheers LLL

Thats what i meant

Cheers

[novicebob]

Thanks again for your replies. Just a bit more clarification if you don't mind.

One of my earlier questions got missed I think. With my setup (ie laying on an existing concrete slab) can I get away with using a dry 10:1 mix or are you saying this won't work properly?

If I go for the wet mix can you clarify this 45 deg thing. Is the low part of the 45 deg next to the slab already laid? If so how do I manage when I am laying a flag ajoining 2 or even 3 slabs alrady laid (as might happen as I am laying a random pattern with 6 different size slabs).

Hope this makes sense.