putting a strip of 4mm glass mosaic between 6mm tiles

[AliGage]

I never did very well in chemistry at school so i hope i'm right with this one:

Glass is non-pourous. Therefore moisture resistant. Tubbed adhesive sets, cures, drys by disperssion of water. If what you are fixing is non-pourous then effectively it is resistant to the setting process.

Bagged adhesive works on a chemical reaction to harden, it's cementious.

That is about as much as i really know about the science behind it all, but i think basically, because of the way tubbed adhesive works to cure (using the moisture/water in the addy) and glass being non-pourous they will not bond well, if at all.

 

[John Wallace]

Thanks for the quick response, AliGage. As the glass tiles in the mosaic strip are only 20mm square, I think it is drying out OK, but I'll try an experiment with some scraps of mosaic on a scrap of aquapanel to confirm that. As you say, bagged adhesive uses hydration of the cement powder in it to form interlocking crystals that set it hard, so sets even if it hasn't dried. Chemistry isn't my best subject, though I did take it to A level, and covered the chemistry of cement during an engineering degree. The problem in this case is that I don't have any idea what is in White Star, and how it sets. Most adhesives go solid by some sort of polymerisation, where a short chain molecule assembles itself into longer chains. The polymerisation can be triggered by a catalyst, or by oxidation. Drying out of itself makes some things go solid (effectively the glue is in solution in water), but is usually reversible, so is unlikely to be used in a tile adhesive. I think water may be acting as an inhibitor in White Star, stopping the polymerisation, but that when polymerisation has made it set, it is not reversed by getting it wet again. Its very impressive how well it remains usable until the tub is almost empty - several times, I opened a near-empty tub, expecting to find it dry and solid, but it was still wet, smooth, and workable (yet the stuff would set on my fingers in minutes).

 

[AliGage]

Going a bit above my head there John. lol. Let me know your findings if you do any test though.

I don't use tubbed adhesive, but i have done in the past, quite a long time ago though. I'm pretty sure though if you wet/dampen something like white star it will "unset" in a manor of speaking. I.E soften up again. Don't know if that's 100% right as i've not used tubbed for a long while, but if it is and it helps you understand how it works i'm interested in knowing a bit of the science behind it myself.

 

[tilerjason]

4mm i think

 

[JHeff]

I had a problem like this last week, needed to pack out about 6mm for the mosaic strip to sit flush with the rest of the tiles. I got a sheet of 4mm Wedi, cut it into long strips 50mm wide (the width of the mosaic strip), then stuck them to the wall, then the mosaic on top. Finished perfectly flush.

 

[jwatson]

how u doing jason?? not seen you for a while

4mm i think

 

[robbbin]

What i do is cut a peace of plastic to a L shape, to a depth of the mosiac and the width of the border use rapid set fill the area and scrape off, when set fix border with rapid normally would tile up to border on all walls then when set tile up to ceiling.

 

[John Wallace]

Just an update, after finding I could only get the tile spacers mentioned by Rich online, which would take about 3 or 4 working days, (about 5 or 6 actual days because there was a weekend coming up), I did the mosaic along the second wall using a bed of tile cement. To make life easier, I cut a small piece of wood to shape so that I could level the tile cement at exactly the right depth (4mm below the surface) all the way along the wall (I screwed a 9mm strip of wood along the wall above the position of the mosaic so that the tool I made could be levelled on the tile surface below, and the strip of wood above). This worked well, except that I had to wait 2 days for the White Star to go hard before putting the mosaic up. I like JHeff's advice about using Wedi. If I can find that in the shops, might use it for the next wall. To avoid the delay in setting, I tried using finishing plaster for the same purpose in a few short lengths round the window alcove, but then was a bit dismayed by the advice on the tile cement to "let new plaster dry out for 4 weeks before tiling over" (!!!). Won't get on to the next wall for a few days, because now trying to solve problems putting a large heated mirror along the wall behind the basin.