I have some "stepping stones" set in to my lawn: 9x18 cms and also a couple of paving slabs : 60x75 cms which have sunk. Is it better to relay them on "blobs" of cement rather than just trying to get a sand base nice and level. I am think if large blobs of cement are used it will be easier to get them level by tapping them down with a rubber mallet. (The paving slabs take no vehicles)
The dab and dot style of slab laying is always a bodge really - and the results never really lasts well IME.
Assuming the base if well compacted and firm (if not get a some bags of type 1 MoT, rake out a thin sub base screed of it, and then compact it down well (plank and a lump/sledge hammer will do small areas)
Then I would say you will find it easier to just knock up a dry[1] mix of weak sand and cement, and level them on that as if you were doing it on a screed of sand. Water them once down and the moisture in the soil and what you add will cure the mortar bed. The small amount of cement binder will then keep it in place and stop it being migrated by insects, or spreading out at the edges etc. It also means the slab is fully supported and should not crack with a load on it.
[1] Use sharp or "grit" sand, and no more added water than what is in the sand. Add cement at anything from 6:1 or even 10:1. That will be adequate to act as a binder - you don't need massive point load strength here.
Just use soil, you can get your level before putting down the slabs. in 2 or 3 years the slabs will appear to have sunk again, it is in fact the level of the lawn rising, thanks to worms. Remember you should keep the slabs just below the level of the lawn to prevent damage to your mower.
And sand also works fine. I've just reused a few random slabs as stepping stones. Yes - the first couple are a bit fiddly but it gets quicker and it's not really a huge hassle.
They sank because they are on topsoil which migrates out from under them helped by worms/moles etc. Lift them, dig out the topsoil and fill with hard core (any old bricks etc), tamp it down as hard as you can and top off with sand. Don't use any cement, there's no point, it's just a bodge method.
Have they sunk? Or has the lawn level risen. that seems to be the way things go around here. Brian
Blobbing paving slabs is a no no way to lay them.
Use sharp sand and cement at a ratio of about 8:1 and spread the mix all across where the slab will sit. Level it as required, and if too low in one corner , just put more sand under it.
As above except I find creating ridges in the sand/cement dry mix by drawing the surface with a garden rake helps with slab levelling.
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So far so good....
Could I suggest you go read some of the British standards on paving techniques? To describe using a bound bedding layer (i.e. one containing cement or lime) as a "bodge" is inaccurate and misleading.
Generally, "sand only" screeds tend to be used for smaller element paving such as blocks and sets, and screeds with a binder used for larger slabs - however this is not a hard and fast rule.
However the critical requirement of any sand only screed is that the edge is adequately retained - typically with a mortared in place bedded on course of blocks or edging stones, but sometimes just a concrete haunch. Without the edge restraint, the sand will migrate out, and will also get migrated by insects. and worms etc.
For chapter and verse on bedding courses, have a look at:
For general on flags:
The slabs in my garden were layed by my brother in about 1980; if there was any sand, it's long since disappeared. The slabs are still firm and dead level. This is almost certainly due to the soil being somewhat heavy and it hadn't been disturbed at all since at least WW2!
On the other hand, in a friend's garden that had a high water table, light soil and loadsamuck, some of the (fortunately 2x3) slabs were only about 25% supported by anything - they definitely needed sand and binder and probably some hardcore as well.
I will probably be at odds with everyone else but for any paths across grass I just use soil to level and lay, reason being it's easy to change your mind and move things, yes I sometimes have to re level a slab now and again but as the worms seem to raise soil levels anyway, its useful to be able to do it quickly and cheaply without making a mess.
The OP doesn't say when they were laid.
Personally I would use a lean mix of about 2" under the slab to raise it. Easier and more reliable than soils that are compressible.
Anything more for stepping stones is OTT.
Glad you agree Charlie, I said that when the item was first posted, anything more is just making unnecessary work, and inuring cost. David
So greenhouse bases put solely on a slab sand base - especially in a very wet area - will be fairly wobbly after about how long?
What about postcreting posts in for the corners for my greenhouse base, someone's suggested pressure treated boards around the bottom to make like a raised bed to sit it on.
For Gods sake read the OP.
"I have some "stepping stones" set in to my lawn: 9x18 cms and also a couple of paving slabs : 60x75 cms which have sunk."
He's not laying a patio or even a path.
They may never get wobbly - although the levels will usually shift. Often there will be no trace of the sand if you lift a slab later.
Frequently wet areas are worse - but the effect will vary with soil conditions.
If the slabs are above ground level (rather than on it "in" it) then the edge ones usually tip outward as the sand escapes from the edge.
What kind of soil do you have?
For slabs used as a shed or greenhouse base, adding enough cement to the sand to let it set a little once laid is usually all that's needed to keep it in place. (used as a dry mix - no need to actually turn it into mortar prior to laying)
Did you spot the "which have sunk" bit?
Assuming that was the problem he wanted to fix...
(note also the discussion has moved onto greenhouse bases)
So?
If you want to be able to level them and not have them sink again, do what has been suggested...
Lift the stone. Unless the soil is rock hard and stays that way all year, chuck in a thin layer of type 1 and ram it down so you have a good sub base to work from. Now rather than re-bedding the stone on just sharp sand, add a small amount of cement to it. Its only going to take 5 minutes to do it properly. That will stop the worms etc from romping off into the lawn with your bedding, or having it flushed out with too much water.
The plot I am thinking of has slabs covered with water when it rains a lot.
Soily with masses of clay underneath the wet plot. He tried digging through it but gave up.
Mine is much more loamy on the bit I want to put my greenhouse on and it's a bed I've dug and cultivated so it's a bit soft. Lovely for growing in though. Would I be better finding a different bit for the greenhouse? The whole plot gets the sun and there's no issue of shading another plot on most of it.
'k. Ta. I think they have just used sand from the bag - not seen cement bags anywhere.
About 30 years ago my dad and I put a new shed in the "woods" at the end of our garden. Ground was rough as s**te and not stable.
We levelled with a rake, dad made a boundary frame with some 3x1 (ish) pegged at each corner.
We filled it with dry 6:1 sand:cement. Rammed down by hand, levelled and slabs laid.
Gave it a good couple of hosings from the top then installed the shed.
Despite the frame being proud of the ground on 2 sides and the wooden frame eventually rotting and falling off the slabs stayed put.
6:1 is weak but it's enough to hold the general shape.HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.