What to use for thin mortar bed?

[Alien8]

I am kind of stuck at the moment with how to proceed with laying down a mortar bed to tile a covered patio area. The patio is a raised concrete slab.
My maximum bed height is only 20-25 mm down to a feathered edge. The area is 26 square meters. I found a product that will work. Lanco 136 rapid repair mortar but at 40 something dollars a bag this will cost a small fortune.Coverage of this product is 4 square meters at 3mm thickness. I know a standard mortar mix is just not going to be suitable for thickness down to a couple of mm’s.
The other option is to use levelling compound to fill low spots and use some sort of tile underlay. The only problem is that there will be very little fall and I haven’t been able to find a tile underlay suitable for exterior use. The patio is covered but if rain blows in the water will sit on the tile.

What are my options. I am really stuck.

[goldie1]

Could you attack part of the slab with a Kango to give your self some more thickness?

[Alien8]

Bit hesitant to start hacking into the patio. Its was built in the late 40's. The patio is a red brick box capped with concrete. About four and a half foot high. There is a few spots where the slab is cracked and has moved. Really want to avoid thicknessing it if I could.91558

[goldie1]

Just looking at your other thread. That slab certainly looks a bit sus. You might be better ripping it up and start

afresh. At least compare the cost of floor leveller with a new slab.

[Alien8]

I am considering that option too. I believe the slab movement is due to a drainage issue but thats just a guess. Next problem is the load bearing poles holding up the patio roof. Dont know if they are sitting on top of the brick. It looks like it because the outside edge of brick face is on the same vertical plain as the poles. Ths is starting to become quite a job.

[goldie1]

Is there any reo in the slab? Have a look at this thread there is a bit of info about columns.http://www.renovateforum.com/f208/replacing-verandah-ceiling-sheet-105570/

[Tim Burr]

If you dont stabilize the slab the cracks will just re-appear in your tiles. A new slab would be the best way or you could glue down tile underlay (use sika 221 or similar) and waterproof it before tiling.
The movement causing the cracking needs to be stopped first, they look like large cracks!!!

[Alien8]

Goldie1 I read that thread and am starting to get a better understanding on how these old places were built. I believe the columns sit on their own”stumps”which happen to be incorperated into the boxed structure for the patio slab to sit on. The slab is poured around the columns after the box is filled. I wonder what they used to fill these type of patios. Building waste? useless apprentices? haha. I don’t know if there is reo in this slab or not unless I start hacking. By the size and amount its cracked I wound say no.

The way the slab has cracked appears to be the two load bearing columns at the front of the patio sinking and kicking up the slab at the crack. The stormwater from downpipes around these footings is absorbed into the ground via pebble pits that run along the front of the patio right up against the brickwork. There is no where for the water to go but down. I do not know why the PO’s did not connect the downpipes to the stormwater out to the street. Anyway I am fixing this issue at the moment.

@ Tim Burr- I had considered this direction with the underlay. Still investigating.

If I pull the slab up I would most likely just deck it. I have no experience in concreting. Still working out cost (which is- I have none). Happy days!

[goldie1]

The brickwork was probably filled with site rubble and a layer of sand over the top and your most likely right

about the downpipes. A choice between a deck which needs refinishing every year or a new slab and tiles?

Concrete for me.

[Alien8]

The missus really wants a tiled patio. We already have the tiles sitting in the shed waiting for me to sort out the slab movement. I had an local underpinner out today to assess the situation. He said that the two front corners need to be raised and underpinned and a section of the slab cut out and raised and reinforced. His quote came in at $4500:oo:. I am getting a second quote tomorrow. Let the good times roll.