No_2_August_1963 — Page 134

SHEET & TILE FLOORING (From page 126)

of binder. whereas others may con- tain only 25% or even less. The prices of finished products when compared on the basis of equivalent thicknesses give some indication of the proportion of binder, as this is the most expensive ingredient.

in

The most important processes the manufacture of PVC flooring in- clude the following:

(1) The binder and its compound- ing ingredients are heated and mas- ticated to form a hot mass

from which sheets are produced by calen- dering. Sheets up to 0.125 in. thick can he satisfactorily produced in this way but it is often easier to manufacture thinner sheets which are then pressed together in layers or laminated with other materials such as bitumen-saturated paper felt. cellular rubber and cellular PVC.

When similar sheets of thin ma- terial are laminated together it is often difficult and sometimes impos-

SHRINKAGE OF AGGREGATES

sible to distinguish the finished pro- duct from one made to the full thick. ness in one operation. Frequently the backing has the same composi tion, apart from pigmentation, as the face, so as to allow trimmings or off-cuts. which would otherwise be scrapped, to be reused.

(2) A cold paste of the plasticized binder is spread on to a supporting layer such as needleloom felt or hes sian. The paste is then heated and a tough film is formed when it gels. This process lends itself to the pro- duction of embossed patterns.

(3) Pelletized material is formed into blocks and these blocks are sliced into tiles. Particular patterns, e.g. simulated terrazzo. can

be

pro- duced by this method.

Methods (1) and (2) are used for the production of PVC flooring hay- ing a jute hessian backing. Hessian may also be used to support ma-

(From page 120)

above at a temperature of 14 - 19°C (58 - 66°F).

After a further week in the oven, the cycle of drying, cooling and measuring shall be repeated until constant length is attained, constant length being regarded as the state when the difference between two consecutive readings separated by a period of drying of at least 44 h. followed by cooling for at least 4 h,

is less than 0.0003 in. The final reading shall be taken as the 'dry measurement."

During the drying process, fur- ther wet prisms shall not be placed in the same oven and there shall be free access of air to all surfaces of the prisms.

After the dry measurement has been taken, the nominal 8 in. length of the prisms shall be mca-

terial during production in which case it is stripped from the product before it is distributed.

Synthetic rubbers

re-

There is a small but increasing use for flooring of a group of ma terials generally referred to as syn- thetic rubbers. These materials semble natural rubber flooring in appearance and can be produced on conventional rubber manufacturing equipment. Tile may be cut from calendered sheet or produced in- dividually in moulds to give the same wide range of thicknesses and sizes that are available for natural rubber flooring. The binders used include chlorosulphonated polyethy- lene, styrene-butadiene copolymers, and butyl and nitrile rubbers.

Prepared at the British Building Research Station (Digest 33-2nd series). Crown Copyright.

sured adjacent to the balls to the nearest 1/32 in. and this shall be taken as the 'dry length'.

The drying shrinkage' shall be calculated as the difference between the 'original wet measurement' and the 'dry measurement' expressed as a percentage of the dry length.

Prepared at the British Building Research Station, Garston, Ilerts Crown Copyright.

HONG KONG HOUSING Authority CONTRACTS AWARDED

MAY 1963

128

Particulars

Contractor

Amount

Ma Tau Wai Estate Phase II Demolition Contract

General Contract

Governinent Low Cost Housing Estate Cheung Sha Wan Clean-

ing contract

Fuk Loi Estate. Tsuen Wan Cleaning Contract

Government Low Cost Housing, Wong Tai Sin Estate Cleaning

Contract

Wo Lok Estate, Kwun Tong. Phase II Lift Contract

Piling Contract

Kin Tại & Cọ.

$ 5,000

(Credit to the Authority)

2.932,857

Goodman Co.

Chuen Fat Service

A.B.C. Service Bureau

Pang Kee Sanitary Co.

49,680 (per annum) 72,864 (per annum)

18,585 (per annum)

British General Electric Co. Ltd. Pressure Piling Co. (H.K.) Ltd.

322,500

215.250

THE HONG KONG & FAR EAST BUILDER-VOLUME 18, NUMBER 2