Patio slabs / blocks directly onto old concrete

[numpty with a crowbar]

Morning folks,
Just trying to decide in my head which way to go with this: -

Just outside the back door is an area of smooth concrete which we're wanting to lay slabs over as it doesn't look very nice. The concrete itself is sound, no cracks or crumbling, so content to lay the slabs on top... But should I be using a dry mix or a wet mix to lay the slabs on? I'm pretty sure I'll just dry mix into the gaps between the slabs - but any thoughts on the mix for under??

 

[scatcat]

Have a look at http://www.pavingexpert.com it IS the answer to all these kind of questions.

I am doing a similar thing myself.

I am going for 10:1 mix sharp sand to cement. Dry mix, the natural moisture in the sand /atmosphere is enough to set it.

I am doing 20mm deep over the concrete apron round my house and 40-50mm deep else where.

Be careful of the finished level of the slabs relative to your damp course. It should ideally be 150mm, but there are things you can do if it is less. Ignore it being one of them.

As I said there is plenty of advice at the above site.

 

[Thermo]

if your happy the slab is sound, then i would do the following

give it a good clean with water and a brush

lay the slabs on a wet mix, it will give a much better result as youve got such a stable surface to go from. It does also depend on the slabs you use.

The paving expert site is very good, but dont believe every thing you read on it. e.g They poo poo the five spot method, but some manufacturers actually state this is the only way certain slabs they make should be laid

As for pointing i always go for a damp mix, especially in the hot weather to avoid cracking and powdering

 

[numpty with a crowbar]

Blimey! Paving expert do look down on the 5 spot method.....

Hmmm - Cheers for the advice folks... I'm starting to lean towards a wet mix now to bed the slabs onto - though if I end up leaving it till the autumn I might just go with a dry mix....

Aaaarrgghhhh!! Indecision!!!

 

[Thermo]

wet mix will adhere better, but its more difficult to lay and get all level, if you over tap one slab and have to take it back up it can get a bit messey!

Also if you do use a wet mix, knock up some neat cement in water and brush it over the surface of the slab to help adhesion.

 

[fathead]

if you use the 5 spot method, use tidy sized spots and once you tap the slab down level, the mix will basically spread out to the size of the slabs and practically leave no voids.

 

[Thermo]

absolutley nothing wrong with using the five spot method in this instance to bed it down on to the existing concrete. As fathead says it will spread. Try and lay it on a full bed and you will never get it level