I'm planning to lay an 80mm wide row of 25x25mm mosaics (which I think are marble, but could be travertine) mid-way up a wall tiled with 300x300 tiles.
The tiles are being laid with a 10mm trowel, and I'm planning to use a 6mm or 4mm trowel for the mosaics so they fall back flush with the other tiles, which are very slightly thinner. The adhesive for all the tiles is white Bal Mosaic Fix.

I've ordered a bottle of LTP Mattstone Stain Stop & Sealer to seal them before I lay them.

My main concern is keeping the mosaics clean while laying them and then more importantly while grouting them.

The Bal grout is cream/champagne in colour, and is somewhat lighter than the colour of the large tiles. I wanted something off-white to hide the dirt, but not something so dark you couldn't make out the grout lines. If at all possible, I want to keep it out of the nooks & crannies in the rather cavity-ridden mosaics (an effect I like). If grout gets in there, it will be almost impossible to clean it out, and I think it will look rather sub-standard. The only way I can imagine being able to do this is by injecting the grout into the gaps around the mosaics with a piping bag or similar and then smoothing it with small rounded stick or similar.

Has anyone done something like this?

Is there a specialist injection gun you can hire for this, or grout you can buy in a standard caulk tube?

I don't care if it takes time. This is a DIY job, and they're only a very small proportion of the total tile area.

Photos below for reference.

Thanks!

use a grout bag

Thanks!

Any particular model you'd recommend? These grout lines are rather narrow - about 2.0-2.5mm.

Grout bag (looks like a large icing bag) or I'm sure you can get a grout gun which works like the sealant guns

you can cut the nozzle pretty small

trade tiler sell them , you can click on the sponsor here for his website

cavity-ridden mosaics if you dont fill the cavitys with grout they may get filled with water i aways grout anything with cavitys first then seal later :Pete

same as Pete (pjc) for me!

Originally Posted by doug boardley

same as Pete (pjc) for me!

Doug is it a age thing ?

must be Pete! but personally, I think the cavities look better filled anyway

always seemed like common sense not to seal them first or the grout wouldn't adhere as well

As above, fill the cavities looks far neater

We did a conservatory floor once in unfilled stone and just before grouting I asked the lady if the limestone joint was the best colour for the tiles.
It was at this point that she informed me that she only wanted the joint filled and not the tile face!
What about the mud and dirt from the garden I said - Oh! its not going to get dirty she remarked!

Back to the thread - why not try covering the mosaic with clear masking tape and with a sharp knife cutting the 2mm joints into the tape face!
Then grout as normal and peel off the face tape when its set!

Thanks John, that's not a bad suggestion.

I think if I use a piping bag and go really carefully I should be able to fill the spaces between the tiles without affecting their faces. They're set high enough on the wall that the only place they're likely to catch water is inside the shower, and I can choose some with fewer cavities to run through there and make sure they're thoroughly sealed. They'll be laid on Aquapanel with a vapour sheet laid behind, so any water going through isn't going to cause any major problems.

I'll post some photos showing how I get on, but I won;t be starting to grout the mosaics for a week or so. I'm laying the main tiles first, leaving a 80mm gap all around in the middle of the wall.

Incidentally, is there a trick to hanging tiles going in the downwards direction while keeping them tight against the ones above? I need to hang starting at the midline going downwards. To prevent the bottom row from sagging I've had to run screws into the plasterboard below them for them to sit on while the addy dries, which obviously isn't ideal, and I don;t want to do this in the wet areas. I would have used a wood baton, but it's tricky to judge where it should be screwed as the tiles all seem to be very slightly different sizes.

batton stands are handy for this

or sticking the battens with a hot glue gun

Progress so far - started with the 'easy' wall to get some practice in before I attempt the ones with all the cuts. Plasterboard is primed with APD. This little lot took me about 6 hours including 3 lots of adhesive mixing and consequent cleanup - I don't think I'll be doing this for a living any time soon. Biggest problem is getting the lines of adhesive 'full' as more often than not they start going 'hollow' part way along the trowel pass. Not sure if this is because I'm going too fast, too slow or have too much air or lumps in the mix etc...

I was worried that the spacing baton would get stuck in the gap, but it came out OK without too much trouble.

I used a water filled tube to level around the room, and it turned out to be fantastically accurate, if a little slow. Can't stretch to a spinning laser though...

If you want to pretect form dirt in the future, go the tradetiler.com, Dave has a sprey that keeps grout clean.

Thanks!

Is grout sealer any good, or does it just trap water in the grout?

I used it on the grout when I re-tiled the kitchen splashback (foolishly consructed from moisture resistant MDF plus 3 coats of varnish) in an attempt to keep the water out. Almost went for epoxy grout - but in hindsight there's no way I would have gotten that neatly finished before it set hard - so a lucky escape. Just hoping this time the tiles stay put. The last lot lifted after a year when the original tiler laid the tiles on a piece of vinyl covered chipboard. Where he scribed it to get the tiles to 'key' it let water in and swelled up. Hoping my MR MDF plus grout sealer will be better, but probably a vain hope.

small point rob, clean the grout joints out before the addy sets up to hard

Thanks. I did clean them out a bit with the trowel, but maybe I should have another go and rake them right down. The first lot have been up for 2 days now, so probably hard as rock...

I use a small wet brush to wipe the joints out

Good tip, thanks. I was using a sponge, but it really wasn't getting in there very far. How far back do they need cleaning out? I figured if I took it back just 1-2mm from the face of the tile I'd save a bit on grout. Does the grout need a good depth to stay put, or will it adhere to the adhesive, assuming the adhesive is made a bit damp beforehand?

I would going deeper than 1-2mm, if it's grey adhesive it could grin through the grout

The adhesive is white. The grout will be champagne.

If all else fails, I guess I could use white grout instead.

Just clean the joints out deeper than you normally would, then your grout should be ok

Another small point - To get the mosaics flush with the face of the larger tiles, I'm going to need to use something like a 6mm trowel, which I know is large for mosaics. I used a 10mm trowel for the large tiles, but the mosaics are about 1.6mm thicker including the backing.

I planned to lay the 6mm bed between the two rows of tiles, offer up the strip of mosaics and them gently press them flush with a flat board.

Is the thicker bed going to cause them to sag/topple forward, or should this be OK if I use plenty of spacers after pushing them into position?

Thanks.

Whats the thickness difference between the tiles

I use a spacer to drag out the addy then clean off with a sponge, get right to the wall. Good idea with the sponge though, will give that a try

Also gonna try the baton with hot glue gun trick, not thought of that before. Cheers Mike

Wall tiles = 8.8mm

Mosaics = 10.5mm

So 1.7mm difference.

I'm using a 10mm trowel to lay the wall tiles.

Just use grouting tool to tamp the mosaic to flatten out, they may sit slightly proud of the face tiles though

Do you think a 6mm trowel will be OK to bed them on, or will small tiles like those tend to droop forwards?

I'm not exactly sure technically why a small trowel is better for mosaics...