I need to set a mosaic onto cement paving slabs for use in a garden, 1.7m circle with square off set. this is a brand new set of slabs. I'll need to level off the surface of the slabs with a layer of cement, the mosaic will be done direct onto the surface and I'll be using 5mm thick marble tiles, roughly 10mm size with 1mm - 2mm gaps.

I was thinking of;

1. Cleaning the surface of the slabs, do I need to prime them?
2. To level off the surface, any particular type of cement?
3. Using Bostik Sticks Like or CT1 as the adhesive then sealing (LTP) and grouting with Mapei exterior grout.

I'm not sure if I'll need to use anything to avoid the surface being too slippery I'll have to see how they finish.

Any comments?

Ta,

How are the slabs fixed..laid on sand or fixed with sand/cement.

Originally Posted by Musivarius

I need to set a mosaic onto cement paving slabs for use in a garden, 1.7m circle with square off set. this is a brand new set of slabs. I'll need to level off the surface of the slabs with a layer of cement, the mosaic will be done direct onto the surface and I'll be using 5mm thick marble tiles, roughly 10mm size with 1mm - 2mm gaps.


I was thinking of;

1. Cleaning the surface of the slabs, do I need to prime them?
2. To level off the surface, any particular type of cement?
3. Using Bostik Sticks Like or CT1 as the adhesive then sealing (LTP) and grouting with Mapei exterior grout.

I'm not sure if I'll need to use anything to avoid the surface being too slippery I'll have to see how they finish.

Any comments?

Ta,

Hey, Lawrence, why do you want to use Bostic Stick Like or silicone in that situation that rather than any exterior grade cement adhesive and flatten your work with a grout float as you go along? Don't quite understand your reasoning there, explain it to me The grout and such small pieces should make it slip proof, really. Personally I would clean the slabs throughly, when dry prime them with 5:1 water: SBR bond, to avoid cement dust, and make sure to brush each section as you go along. Might be totally wrong but that's how I would approach it anyhow. Alslo would help myself with wooden or wire guides for accuracy.

So i take it they are small slabs laid in sand to make a large area you may not be able to cover the joints with mosaics as it will crack

Also if there laid on sand they tend to move after a few years..

A decoupler if suitable might be useful here, so important that the base is solid.
Even strong bases move too though.

Sorry, I took it that each slab would be mosaiced separately exactly to just inside the edge of each?

how are the slabs fixed? what are they fixed to? not convinced i would go ahead with that to be honest just my opinion tho

Mosaicing over the slabs' edges would mean getting rid of the drainage gaps, too.. nah, I think he means mosaicing each slap separately...

Originally Posted by Mosaic Girl

Mosaicing over the slabs' edges would mean getting rid of the drainage gaps, too.. nah, I think he means mosaicing each slap separately...

Think your right there G, slabs will be newly laid as well..

Thanks for the replies. I am setting the mosaic on each slab separately so no problem with any movement.

Gisela, I'll be scoring the designs direct onto the levelling cement bed.
I did think on using cement but I would need to change the way I work and it may sacrifice some speed, (with all the tesserae prepared and a fairly straight forward piece I aim to set 1m² in 2 days). If I use cement as the adhesive I use a latex additive to make it more ‘sticky’. This way the 2^nd line I set doesn’t push out the first one. The disadvantage is that you need to be quite scrupulous about cleaning away any excess from areas inbetween. With something like the classic twisted ribbon pattern (2 strand guilloche) I set all the black lines then go back later to set the colours.
If I use the glue then I have more control plus with the cement I’m always wary of too much of it pushing up over the sides before I’ve had a chance to put the pre grout layer of sealant on. If I had a gofer then I could leave them to clean away behind me so it's something to think about.

Thanks again,

PS Gisela, I tried that method of setting some tesserae direct onto mesh. I did a 20cm x 20cm piece and used the Bostik, left it for about 26 hours then to see if it was really stuck I took it outside, threw it across the yard 5 or 6 times, rolled it up threw it against the wall from about 6 feet away and at the end of that only 4 tesserae came off! Strong glue ;-)

Well done M G must of missed that bit

No Jay, that was me, I didn't specify that I would be setting them separately. It's too easy when you're experienced in any trade to think, 'I won't say that otherwise they'll think I'm treating them like they're an idiot'.

I'm always happy to get any comments and I never underestimate the power of the basic cock up

Originally Posted by Musivarius

Thanks for the replies. I am setting the mosaic on each slab separately so no problem with any movement.

Gisela, I'll be scoring the designs direct onto the levelling cement bed.
I did think on using cement but I would need to change the way I work and it may sacrifice some speed, (with all the tesserae prepared and a fairly straight forward piece I aim to set 1m² in 2 days). If I use cement as the adhesive I use a latex additive to make it more ‘sticky’. This way the 2^nd line I set doesn’t push out the first one. The disadvantage is that you need to be quite scrupulous about cleaning away any excess from areas inbetween. With something like the classic twisted ribbon pattern (2 strand guilloche) I set all the black lines then go back later to set the colours.
If I use the glue then I have more control plus with the cement I’m always wary of too much of it pushing up over the sides before I’ve had a chance to put the pre grout layer of sealant on. If I had a gofer then I could leave them to clean away behind me so it's something to think about.

Thanks again,

PS Gisela, I tried that method of setting some tesserae direct onto mesh. I did a 20cm x 20cm piece and used the Bostik, left it for about 26 hours then to see if it was really stuck I took it outside, threw it across the yard 5 or 6 times, rolled it up threw it against the wall from about 6 feet away and at the end of that only 4 tesserae came off! Strong glue ;-)

Glad I was able to help That was a jolly good test then...