How thick should my beeding layer be?

Patio flagstones (slabs), concrete flags, stone flags including yorkstone and imported flagstones.
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novicebob
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Post: # 20631Post 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.
gm

bobhughes
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Post: # 20636Post bobhughes

You're entitled to the work, not the reward.
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lutonlagerlout
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Post: # 20646Post 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 :)
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novicebob
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Post: # 20664Post 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.
gm

Tony McC
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Post: # 20670Post 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
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novicebob
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Location: Chelsfield

Post: # 20790Post 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.
gm

nelly05
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Location: South Cheshire

Post: # 20791Post 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
Thankyou

novicebob
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Post: # 20792Post novicebob

Thanks Nelly

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

nelly05
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Location: South Cheshire

Post: # 20793Post 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
Thankyou

lutonlagerlout
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Post: # 20806Post 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
"what,you want paying today??"

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matt h
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Post: # 20821Post matt h

bet he gets the point.lo
general builder, maintenance engineer, gas and plumbing installations, extensions etc

nelly05
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Location: South Cheshire

Post: # 20823Post nelly05

lutonlagerlout wrote: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
Thankyou

novicebob
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Joined: Mon Oct 17, 2005 12:54 pm
Location: Chelsfield

Post: # 20827Post 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.
gm

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