Laying patio over concrete slab patio

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I currently have a concrete slab patio (600mm x 600mm x 2" slabs) covering an area of about 20ft x 30ft. I want to replace this patio with a more modern sandstone effect patio and wanted to know the views on over laying the slabs as there are so many slabs to would take ages to lift, then dispose of, where as overlaying would provide a solid level foundation.

could i over lay & what prep work would i need to do? also would i need to bed the new slabs down or could I simply rest them on the existing slabs with a bed of sand in between?
 
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the obvious question one would ask is, do you have the height tolerance?

the finished slab level needs to be 150mm below the damp course.

if you can lay your new patio within this measurement parameter then go ahead and leave them down.

make sure the existing slabs are free of crud and moss and grease.

you can give them a stiff brushing using some sharp sand and water as an abrasive.

we always solid bed slabs on a continuous bed of sharp sand mortar.

the only downside will be that there is no suction in the substrate due to the impervious nature of the slabs below. this may cause some water to sit on top of the slab joints for a while, and may delay the pointing.

a late Spring job me thinks. ;)
 
unless the existing slabs are mortared down i wouldnt recomend it, and then only as per Mr Ns comments above
 
the existing slabs are not bedded down, but have been in place for 15yrs plus as are rock steady.

I dont mind lifting them as thats not a major job, dispossing of the slabs will be the biggest problem.
 
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provided they don't rock, aren't hollow beneath and cannot shift in any way, then they will be as good as any hard core.
 
the existing slabs are not bedded down, but have been in place for 15yrs plus as are rock steady.

I dont mind lifting them as thats not a major job, dispossing of the slabs will be the biggest problem.
What's wrong with getting a big skip?
 
I have always found freecycle to be a useful way of getting rid of old slabs to save our customers the cost of a skip. All you need to do is join your local site. Post how many (approx) slabs you have and when they will be lifted and then get in contact with those that will take them off your hands. Usually saves £150 ish on a patio job as you would need an 8 cu yrd skip to take slab due to weight restrictions.

Hope that works for you


Lara
Warner Grounds
 
dont try to use a sand bed over ANYTHING, let alone an existing patio (I would lift that anyway). Use a full mortar bed - you'll find it easier to get the slabs right and it'll be a stronger result. Just need to hire a mixer.
 
Certainly all good advice here, but I personally would be worried on- What would happen if the area got waterlogged in winter to some extent and then freezing occured, you might get uneven lifting of the top layer of slabs- after all that work in getting them flat. :cry:
 
Certainly all good advice here, but I personally would be worried on- What would happen if the area got waterlogged in winter to some extent and then freezing occured, you might get uneven lifting of the top layer of slabs- after all that work in getting them flat. :cry:

this is made very difficult provided the installer lays the slabs on a solid bed.
 
never seen it happen. Once laid on a solid bed of mortar they dont move
 
I'm thinking of doing the same. About 11 Sq metre's of concrete slab patio. Been down for about 20 years & wanting to overlay with Indian Stone. There's plenty of distance from damp course & air bricks too.

Be a sight easier than taking the slabs up.
 

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