The mosaic floor of the Old Public Trust Building's main entrance foyer is a most intricate pattern with the main body of mosaic tiles forming a fan, bordered by a decorative vine, leaf floral pattern, highlighting the cursive "PTO" lettering (Public Trust Office).

Within one fan pattern there are 200 small pieces of ceramic floor tile (tesserae), the tesserae vary in size from around 12mm -10mm long and approximately 8mm wide.

Within an area of one square metre of the fan pattern, there are approximately 16-17 fan patterns; the entire mosaic floor surface area is around 40 square metres.

The entire mosaic floor has around 128,000 Tesserae.

Mosaic execution: the process

The initial development of the concept or overall design would have been an extensive process, generally involving the architect, the mosaic production company and the builder.

Precise drawings and actual size, coloured art work (cartoon) for the decorative borders are developed from onsite measurements. Such measurements at the Public Trust Office are complex, given its circular internal stairway and external facade.

Within the workshop/studio, tesserae is hand cut (docked) from a long pencil type ceramic tile strip to irregular rectangular lengths, 10 - 12mm. (The ancient mosaicist used a wedged tipped hammer known as a Hardie to cut the tesserae)

These pieces are then shaped to size by further hand cutting with tile pinchers, to angular smaller pieces to form the intricate fan, floral, vine and lettering design elements.

The shaped tesserae are adhered to a full size, bulky brown paper drawing (a reversed copy of the cartoon) with a water soluble adhesive.

The cartoon is reversed from actual size detailed drawings (this process is termed the reverse or indirect method).

The bulky brown paper drawing is referenced on the backside, usually the length and height with a series of wavering hand drawn lines before the placement of the tesserae to the cartoon. The mosaic parcels are also numbered as further reference marks. However when inverted the paper is the actual face of the mosaic. Hence the term "Paper Faced Mosaic tiles".

At the completion of the placement process of the tesserae to the brown paper, the mosaic brown paper is cut into manageable pieces (parcels) for ease of transportation and on- site installation. This process is sometimes termed the Parcel method.

The intention with the reference lines and numbering sequence is to enable the mosaic tilers to interpret the exact position for each parcel, before setting the individual parcels into position on the screeded cement mortar tiling bed.

On-site installation 

 The entire mosaic floor is transported as a Parcel to the site for installation. A team of trained mosaic tilers are engaged to install the mosaic to the concrete floor. This installation requires a daily manageable, accurately screeded cement mortar bedding set to the nominated levels and heights. Whilst the cement mortar is still workable, the mosaic parcels are then set onto the cement mortar bedding, paper face up, as per the numerical and reference marks. 

An exacting step by step process is then undertaken, for example full contact of cement mortar to the rear of the Tesserae, wetting the bulky brown paper to dissolve the water soluble adhesive and the removal of the brown paper. Further cutting of tiles to abutments and alignment of the adjoining sheets may be necessary. At the completion of these steps, the mosaic tiles are grouted with sand and cement grout, then thoroughly washed and cleaned. This process is repeated until the entire mosaic floor is set into position.

Written by Barry Bulmer  Dip.Teach;Syd.CAE, B.Ed; UTS

Director

Mosaic Design Company P/L