Mosaics & Tesserae
Although probably not suited for large areas of paving, if only for reasons of cost, panels of mosaic work can be very attractive and certainly, unique features within a larger area. It may be considered that mosaic materials are generally rounded, or small, flat pieces of stone, glass, ceramic or other hard material, that are curved at the edges and corners.
Tessaries are generally small pieces of the same materials, that are generally cubical or some other regular shape, known as tessera, (plural tesserae) which differed from the original natural pebbles (flat, rounded stones) that were used in Hellenisitic mosaics, and were made from marble or limestone.
In essence, there is no real difference between the art of creating mosaics or tessary works, as they both involve similar traditional techniques, so it could be held that mosaics are created using tessera. (Although both materials are commonly used in producing these works of art).
Mosaic tiles available today, are usually between 10mm x 10mm and 30mm x 30mm, as squares, hexagonal or round pieces of porcelain, glass and natural stones in variety, all very hard-wearing materials.
There are two methods of creating mosaics, dependent of the size on panel required. For larger projects, it is advisable to work from firm edges, set to levels as required to allow for water drain-off (1:60 minimum recommended. You need to avoid any chance of water laying between the tessara and suffering freeze/thaw during the winter) using boards, bricks, slates or any edge that you can traverse with a level board to ensure an even surface finish.
Depending on potential traffic – it would not be advisable to create mosaics in driveways where power steering may damage the work – a standard paving sub-base of 100mm MOT Type 1 laid over a non-woven geotextile membrane with a 50 – 75mm deep laying bed of semi-dry sharp sand and cement (1:4) may be lightly compacted ready to receive the tessera.
Each piece should be tightly packed, neighbour against neighbour, both to ensure stability and provide as smooth a surface as possible to prevent the small units from being damaged by shoes and high heels, to the chosen pattern. Each piece should be laid ‘damp’ and not dry, to ensure a ‘key’ with the laying bed. If the bed is too wet, as each new piece is introduced, it will push the next door unit upwards and away from its neighbour, and the integrity of the bed will be lost – as well as the pattern. The segments should be set slightly higher than the height of the laying bed to allow for pointing afterwards, using either a sand and cement mixture, or another jointing compound of a chosen colour. Once completed, clean as any other project, using water and brushes until all residue or hazing has been removed.
As the work progresses, a constant watch should be maintained to ensure an even plane across the project, as any low spot will collect water and dirt, spoiling the effect of the scheme.
Another system, occasionally seen at RHS Shows, where time is of the essence, is to prefabricate a smaller area of mosaic (which may be joined together if required once in situ) using a ‘crate’, or timber edged box (between 600mm x 600mm and 900mm x 900mm) with a floor strong enough to support the weight and transportation traumas of building off-site and laying each section as a unit.
The ‘floor’ of the crate or box should be formed using a section of reinforcing (BRC) mesh, covered in expanded metal sheeting (available in rolls from a Builder’s merchant) wired onto the mesh to prevent the laying bed from falling through the bottom. This has the advantage of not only being more friendly on your back – they may be created on a bench at waist height thereby reducing stress – but may also be constructed in the dry without risk or interruption by rainfall.
Once fully hardened – usually 28 days – the completed article, or section of a larger pattern, may be transported and placed carefully into position. This may be assisted by the use of thin nylon straps (used to bind packs of bricks together), laid underneath the tray and lowered by two people – depending on the weight – into position. The straps enable repositioning if required. Be careful when transporting the trays to lay them over polystyrene blocks/sheets on the floor of the vehicle to prevent vibration from damaging them.
