Chemically-resistant paints
High gloss paints are durable under normal weathering conditions, but sometimes break down in chemi- cally polluted atmospheres or when exposed to chemical fumes and splashes. Other paints now available (Table 2) give much better per- formance under these conditions provided the surfaces are properly prepared. The most resistant of these are supplied in two parts, a base and a hardener, which must be mixed just before use. They usually need to be applied when the temperature is above about 45°F. and the humid- ity not too high. The paint hardens to a tough film a few days after application. Among the paints listed there is a considerable overlap of properties and the manufacturer should be consulted in making a choice to suit specific environments. Because of their toughness and re- sistance to abrasion. the epoxy and urethane paints and varnishes are also used as floor paints bar-top lacquers and furniture finishes.
Emulsion paints
Paints that are both resistant to alkali and permeable to water vapour
or
are useful on plaster, particularly where this has not dried out com- pletely. The older oil-bound distem. pers water paints have been considerably improved in recent years and have also been supplemented by emulsion paints based on a variety of resins. Emulsion paints are avail- able in a wide range of sheen and colour; they are less easily soiled and more easily cleaned than water paints. They are less susceptible to damage if moisture condenses on the surface immediately after application, but can be marred by excessive condensation in these circumstances. The cans should be protected from frost. The various types are review. ed in Table 3.
Special-purpose paints
Particular conditions on a job often call for special paints adapted to meet them. Although a manufac- turer may carry special lines. he may not find it worth while to stock a full range of special paints but may be able to formulate a special paint for a specific purpose. Table 4 gives notes on a number of examples. The adaptation of a paint to meet special
not
detra
requirements should materially from its other propertie but may well increase the pri especially if the general demand f the paint is not high.
REPAINTING
Where it is necessary to strip of the old coating before repainting. most types of paint can be removed either with the aid of a solvent pain! remover or by steam stripping of burning-off; however, the two-part. chemically resistant paints can only be dealt with by mechanical metho
If the old paint is sound and adher ing strongly. there is no need to remove it. The surface should be cleaned and rubbed down before repainting. To avoid any risk of incompatibility it is generally hest. where possible, to use the same type of paint as before. With some of the newer types of paint there is still some uncertainty about how they behave in contact with the same or with other paints; the manufacturers should therefore be asked about methods of stripping and methods of repainting before the paint is used on any large job.
92
H. K. HOUSING AUTHORITY
FUK LOI ESTATE
TSUEN WAN
2250 VIBRO PILES
by
THE VIBRO PILING
COMPANY LIMITED
LICENCEES OF
BRITISH STEEL PILING CO., LTD. LONDON.
ALEXANDRA HOUSE
HONG KONG
THE HONG KONG & FAR EAST BUILDER-VOLUME 17, NUMBER 3