Slabs on sand and sleepers - How to fix the slabs

[Heathy]

Good evening, I'm really confused and really need help! I've read so much info and advice about how to bed slabs. I'm helping prepare a fairly large area ( approx 20ft x 20ft) . We've used sleepers to edge it and have put down a good rubble and MOT hard core base, used a whacker and topped with a sand and cement mix (10-2), this has been whackered and levelled with the top of the sleeper and is nice and firm and level. I have two questions:
1. Can I simply lay the slaps on the sand and cement mix and let moisture bind them or should I dab them with mortar? Which is best?
2. Can I lay the slabs on top of the sleeper (approx 4 inches of the slab will be on top of the sleeper, the rest of the slab on the sand or dab. Can I use mortar on the top of the sleeper to stick to the slab.
I can provide photos if needed, I would really appreciate any advice. Thank you. Here's the link to photos: https://www.dropbox.com/s....pg?dl=0
https://www.dropbox.com/s....pg?dl=0
https://www.dropbox.com/s....pg?dl=0
https://www.dropbox.com/s....pg?dl=0

[lutonlagerlout]

this is doomed to failure
the sleepers will expand and contract and pop your edge slabs
I know this as years ago i was party to a very similar structure,and it failed
sleepers are not suitable for any masonry,or flags slabs to be laid on as they will always move slightly
you could lay the slabs up to the edge of the sleepers but it will look cat

LLL

[GB_Groundworks]

as tony said bound to fail, dig 50mm off lay some gravel grid and gravel it

or dig it down lay the slab up to the sleepers but its going to loo funny

sleepers out and build brick walls would be what wed do for a paying customer if they insisted on wanting wood, block walls and clad in timber

[Heathy]

Thank you both for taking the time to reply, I'll pass that on and have a rethink. What about the bedding of the slabs on the 10-2 sand cement mix? What is the best way? Full mortar bed, dabs or straight onto the sand mix?

[seanandruby]

What is the best way? Full mortar bed, dabs or straight onto the sand mix?

No bad language allowed here ( dabs ) :;):
6/1 mix.

[Heathy]

Sorry!! Reading other threads I see the D#%s method is not liked!! So a full mortar bed of 6-1 is the best way?

[seanandruby]

Full bed every time.

[lemoncurd1702]

Heathy, why have you laid a sand screed over the sub-base?

As said above lay to the edge and not over. You could dress the top of the sleepers with a decking board to make the same level as the paving.

If you really want to go over the top of the sleepers there is a possible work around without bedding onto the timber.
Use the larger slabs around the edge, 600x600, 900x600, bedded on a wet mix with a very good slap of bonding slurry on their underside.
Overhang the sleepers by around 25mm leaving a gap underneath, maybe 10mm, so the paving is not touching the timber.
With a deep bed and bonding slurry those slabs will not move but it may leave the edge fragile if something drops on it.

You need to do away with that screed whichever way you do it.

[seanandruby]

One i wad going to try once ( as an experiment) for a guy.screw some marine ply to top of sleeper and use flexible stuff they use for tiling bathrooms/kitchens etc: to lay some cut slabs same width as sleeper on the ply. A gap between main body of slabs for movement. Never got round to it though. Would of been easy to break off the slabs if it failed. But expensive experiment for someone with a few quid to spare ???

[Heathy]

Heathy, why have you laid a sand screed over the sub-base?

As said above lay to the edge and not over. You could dress the top of the sleepers with a decking board to make the same level as the paving.

If you really want to go over the top of the sleepers there is a possible work around without bedding onto the timber.
Use the larger slabs around the edge, 600x600, 900x600, bedded on a wet mix with a very good slap of bonding slurry on their underside.
Overhang the sleepers by around 25mm leaving a gap underneath, maybe 10mm, so the paving is not touching the timber.
With a deep bed and bonding slurry those slabs will not move but it may leave the edge fragile if something drops on it.

You need to do away with that screed whichever way you do it.

The advice given and the plan is to just lay 600x600 slabs/flags on top of the sand/cement mix scree, including bedding on top of the sleepers. Landscapers and builders have advised the owner that this is ok and to use pva glue to adhere the slab to the sleeper. I'm just helping out, thanks for taking the time to reply and offer advice.

[seanandruby]

PVA ? SBR is the stuff needed. Bedding on the screed and the sleepers in one ...massive fail.

[Heathy]

Thanks again for all the advice and guidance, I will pass it on.

[Heathy]

Advice taken, slabs laid level with with the top of the sleepers on a mortar bed with a gravel edge all round. Looks great and very stable. The advice and tips were very helpful, thank you.

[seanandruby]

Reason why i suggested a rip of ply over the sleeper and a cut flag same width as sleeper...because, you seem hell bent on it and if/ when it fails your not damaging the top of sleeper and can unscrew it. ??? The suggestion of PVA says they haven't a clue, concrete and timber don't go together without movement.

[lutonlagerlout]

good job heathy
its good that you asked first
cheers LLL