Slabs on patio keep moving

It sounds to me as if the builder did not compress the ground and level it correctly, you should not be having this type of problem. My patio was laid years ago and I don't have this problem.
As it's years ago since you had it put down I don't think you have any recall.
Could you get 4 builders round and see what they say and make a decision after about taking them all up or not.
If you need them relaying ask for references next time, ask to see work they have done previously.
Thing is you can't be putting up with the chance of falling so something needs to be done.

There should be a decent layer of compacted hardcore beneath the sand. Sounds like corners have been cut and you’ve been fobbed off.

We have a lot of ants (a lot!!) and I think that they can cause problems by undermining the sand or anything that is underneath the slabs.

We were having some rough stony ground cleared to prepare for slabbing. Couldn’t believe my eyes when three frogs started moving when we lifted some heavy boulders! On first site I picked one up thinking it was a stone then the blooming thing started to wriggle!!

Haven’t a clue as to how long they may have been under these boulders.

If he had put down a thick enough layer of sand down and then tamped it firm and levelled it before laying the slabes, they shouldn't have moved.

If they have and keep doing so, they have been laid badly, probably too little sand, not rpoperly tamped.

Our patio has become very uneven after about 35 yrs . Ours really needs some work before one or other of us will trip A over T. Ours is quite large. OH does not like the stress of the changing and faffing about.

I would imagine it would depend on your ground. If it is clay then it would dry and expand, perhaps more noticeably than other soil. I wonder if you have large trees in the vicinity that are drying up the soil. Possibly you need a deeper foundation, I would think a job for the experts and it may need relaying. Ask for local recommendations.

The slabs should be sitting on a bed of mortar then they wouldn't move. I had my patio laid twenty years ago and have no slabs that have sunk or moved. He's bullshitting.

‘Slabs on patio keep moving’ - is there anyone buried underneath? ?

We've had to have someone in to re-lay some of our slabs as it is laid on sand.

If you want to put sand in between slabs, the easiest way is to pour it as well as you can in the gaps and use a yard brush. There are stones around the edge, at one point we removed the old ones and replaced them which made it look a whole lot better. However, it does get weeds growing in the stones, but they are easy to pull out as they don't seem to develop very firm roots.

The little stones round the edge provide drainage and I try and remove the debris from them round my patio - a nuisance, but better than a patio that is one big puddle.

I think the builder is blagging you a bit as, although sand is the right thing, the slabs should not be sinking. He has simply not done a good job would be my thought.