Patio Nightmare

[richard1600]

hi all,,, having a patio nightmare, have attempted to lay 3 times now and its just not happening,,, will attach pics.,,.

am happy with the ground, had my lines laid out for levels, was happy with that, so on first attempt done a dry mix sand/cement with 25 slabs,, looked great but the slabs just didnt bed properly, or i didnt bed them properly. they moved and could see cracks happening between slabs,

2nd attempt,, pulled all up and just laid on sand base, bedded much better but again its just not right, the slabs are all the same pattern and its suppose to be rustic looking so you dont need to follow pattern etc but again they move.. and its not looking good,

am pulling my hair out...

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[richard1600]

sorry,,

aslo, if just using sand wont the rain wash the sand out the gaps ?????

 

[ColJack]

what's under the sand?

try usind actual wet mortar if you don't like the sand moving..

or wet the sand once it's level etc..

 

[richard1600]

under the sand is just firm ground, it has had 6 inch thick concrete ontop for over 40 yrs so its def well compressed...

is it normal for the slabs to be able to move once laid???

i was told iniatially once the lines are set then do a dry mix of sand/cement level it all out, then spray to make wet, then use trowl to make a key, then lay slab,, this was going well but just doesnt seem right...

 

[lasors]

Out of curiosity, when you say dry mix you did add some water to it didn't you? It needs to be just damp enough to roll into a ball. And what sand did you use the second time around?

It doesn't look like you've compacted anything, it's too loose so the slabs will sink all over the place and float around when it rains. It needs to be a firm base.

Ideally you need to lay about 75mm of compacted type 1 hardcore, followed by 40mm of 3:1 dry mix. Leave 10mm gaps and mortar joint them.

 

[lasors]

You replied as I did. If the ground really is solid, and doesn't have a layer of earth on top of the concrete (which you should remove if it does) then great. If you use sand alone you need to border it with something to stop is falling out of the edges of the slabs, eventually the rain will wash all the sand out from under the slabs otherwise. It's far easier to use a sand/cement mix.

Don't mix it dry then spray it with water, it's not the same. Mix it with water to make damp then lay it on the ground as you go. Don't level the ground by making the sand/cement deeper and shallower, level it with compacted hardcore so you have a uniform 40mm layer of sand/cement mix over the whole area.

Mortar joints add rigidity as well and will help prevent movement, and weeds!

 

[richard1600]

i was told that wouldnt need hardcore base as ground has had concrete ontop of it for last 40yrs +...

i mixed sand/cement then level out as my bed,, then hose it lightly then keyed it with trowl,,

i am thinking my bed has not been thick enough,,,,

 

[richard1600]

just been checking my 2 previous bed depths, bot of witch around 20mm,,,

i got a feeling that muct be the problem...

so a 40mm bed is the way to go then....

 

[lasors]

You don't need hardcore because it has had concrete on it which has now been removed? I must admit I thought you meant the concrete remained and it had a blinding of soil over it in the photos :S

If you're confident the underlying ground is solid, fine, but I would still compact the surface, it looks loose to me, and it doesn't look level.

Spraying the bed with water will mean you get patches of dry material that might not go off properly. If it's all mixed together at the same rate, it all goes off at the same time.

 

[lasors]

No, 20mm isn't enough. When you dig down further you will disturb the solidity of the ground and it will need compacting. If the ground is not level and solid the mortar bed could sink and at the very least open up the joints, water gets in, freezes, and the thing starts falling apart.

 

[Thermo]

only 1 way to do it properly. lay on a wet mortar bed. anything else will not last and simply move over time.

 

[richard1600]

thx for advice guys,, i started again, gievn all advice, correct bed has def been the factor, slabs are bedding far better now and level,,,

can i ask, the slabs are good now well the 1st 10 anyways, 40 more to do, not pointed yet,, a couple have very slight movement in is this normal, does it settle over time?

 

[Thermo]

what are you bedding them on?

 

[richard1600]

as suggested, 40mm sand/cement mix (clay like texture,, the whole slab is sitting nicely on and not much movemnt just a little bit,

 

[freddiemercurystwin]

oops wrong thread.