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Posted: Thu Apr 26, 2007 5:17 pm
by rowland
I am creating a feature mosaic area for my daughter's school, its 4m2 in total, I understand I will need to form it on a concrete base, how thick, and what mix would be best? It will only be walked on very occasionally, its not in the playground. I dont really want to have to get a RMC lorry delivering concrete to school, will we be able to mix something by hand? ???
Posted: Thu Apr 26, 2007 6:53 pm
by bobhughes
This made me wonder how the Romans might have done it so a quick search gave me this:
"The tesserae were bedded in fine white or pink cement of great hardness, and the greatest care was exercised to obtain a good and level foundation. In the Basilica of Viroconium12 the white setting rested upon 2 1/2 ins. of fine brick concrete, which was spread over a foundation of broken stones levelled up with mortar p268 2 ft. thick. One of the mosaic floors of House 1, XIV, Silchester,13 had the following in descending order: red cement, 1 1/2 ins., upon which the tesserae, bedded in pink cement, were laid; white concrete, 3 ins.; and yellow mortar, 8 ins. Another in the same house had its tesserae similarly laid in pink cement, and resting on the following understructure: drab cement and mortar, 3 1/2 ins.; white cement and pebbles, 3 ins.; gravel, 5 ins.; and mortar, 1 in.
There is little doubt that the plain mosaics were laid by the direct process, that is, the cubes were placed directly on the prepared floor-surface; but whether this was the process adopted in the decorated ones is less certain. The usual method at present is first to cut a number of pieces of stout paper which fit together to correspond with the intended mosaic, and on these the pattern is traced. The cubes are then glued or pasted upside down on them, and when dry are ready to be transferred to the freshly cemented surface. The sections are applied with the cubes down wards, and, after being well pressed into the soft cement, the paper is moistened and stripped off, the final fixing process being to press into the joints a fine hard cement. It is probable that the Roman mosaists adopted this or some similar method for their more elaborate work."
No half measures there then.
Posted: Thu Apr 26, 2007 9:49 pm
by lutonlagerlout
we use a minimix company all the time on school work,they tip into barrows and we barrow to the area its needed(obviously a safety plan has to be agreed first) i would say 100mm of c25 concrete laid over 100mm of compacted type 1 stone,concrete needs to be levelled and trowelled up to a flat finish,then allowed to cure for about a week,then lay the mosaics with outdoor tile adhesive and grout,no point bodging it in a school and the poor little people tripping over
cheers LLL 
Posted: Fri Apr 27, 2007 10:28 pm
by bobhughes
And after it's finished and completely set - hire a polisher and grind and polish it flat.
Post some pics too please
Bob
Posted: Thu May 03, 2007 6:52 pm
by Tony McC
I had a very long and very detailed chat with a mosaicist a few years back, and she was after telling me that many of the more decorative features were "pre-formed" and set onto a hessian-like backing mesh, to be laid as a single unit onto a pozzolanic or opus signinum base. She reckons most of the popular 'characters' such as Athenae, Diana, Mercury, etc, and many of the traditional border patterns, such as Guillauche, were made in this way.
The thinking then was that a master mosaicist would nip around to your gaff with a pattern book, from which you'd select your chosen scene, add a border, and then he'd send in his lads with the factorium-made features and borders, and then the jobbing tessserae-installer would simply fill in the gaps.
Anyway, as for the school mosaic, 100mm of a 4:2:1 mix, as described here and laid according to the directions here