Hullo New Tiler!
Just read your question about laying slate. From the
measurements you gave, the slate is about half inch thick?
Is it porous, ( i.e., absorbent), or is it dense?
Yes, you can lay up to 40millimeters, or one & a half inches of 3parts sand, to 1 part cement,to a consistency that will stand up on it's own, but is still wet enough to wet the back of the slate, but no deeper than one & a half inches of mix. Otherwise it will break up, or crack, because it needs larger size aggregate over that thickness.
When 'topping' an existing cement slab, it needs to be clean of dirt, oil, paint, etc. BTW, don't ever lay in a sand/cement bed less than 1 inch, it can let go of the slab it's sticking to, also.
I would advise using a polymer additive also, and follow the instructions on the label! This additive will strengthen the mix a lot, and stick better to the concrete underneath. It's well worth the money, and saves a lot of jobs that would otherwise fail.
The sand we use here, ( Australia), is Tiling sand, or washed beach sand.
However, sounds like you might go close to the limit in depth of the bed, so I would use what we call river sand. It's a coarser grade of sand, with particles up to about an eigth of an inch.
After you've mixed your 'mud', make a mix of neat cement powder and water, to the consistency of runny yogurt, and brush or broom it onto the immediate area you will lay your mud onto. Then lay the mud onto it, eg, with a spade, and roughly level it out to just above the required depth, so that when you lay the slate onto it, you have to tap it into the mix about half an inch, ( or less), to get the slate to the height you want. Any excess that oozes up above and over the edge of the slate, is just scooped off with your trowel, and you can clean out the joint with the trowel, or a rubber gloved finger, and sponge off the top of the tile IMMEDIATELY.
These joints, or grout lines, will have grout squeegeed into them the day after the last slate is set into the bed, and immediately sponged off with a wrung out, flat sponge. Only grout about a square yard at a time if you are a beginner.
As for levels, use your existing border as the guide, by stretching a string-line across the top of one side border, across in front of you where you're working, to the border on the other side of you. Just wrap the string around a brick a couple of times at both ends, and you can easily move the bricks around to tighten or slacken off the line, if you need to move it out of your way to place more mud, or while your working.
When your tapping your slate into the bed, use a rubber mallet. You'll know if you're tapping too hard, as the slate will simply crack or break.
Grout mix is 3 sand, to 1 cement, using the fine tiling sand, ( beach sand, washed.)
Hope this hasn't confused you. I usually grade the slate into thicknesses first, and then lay in thin-bed adhesive.
I've laid over 50 thousand square meters ( = square yards ) this way, but sometimes laying in thick-bed, the way I've described above.
There's lots of different ways to lay stone, some-times mixing different methods to suit the job, but the way I've described will do the job.
If you've got any more questions on this, I'll try and help you if I can.
I've also done large ( 10 sq.yds. of wall ) fireplaces and feature walls in slate and sandstone in thin-bed adhesive and sand-cement.
PS, make sure you wear rubber gloves when you grout, or you will be in pain for days from the raw fingertips, from the abrasion of the sand.
Good luck with your project,
Bruce.

How thin of a sand bed can I lay over an existing concrete patio to hold butted slate tiles in place.

>How thin of a sand bed can I lay over an existing concrete >patio to hold butted slate tiles in place.

Dude...

- stop hijacking other people's threads
- stop resurrecting ancient threads
- stop asking the same exact question in multiple threads

Can I add to that a message to you sbs9?
-stop posting pointless negativity.