In the presence of moisture, calcium chloride becomes visibly damp and copper sulphate turns blue, but the amount of moisture necessary to pro duce these changes is so small that they can occur even when the screed is sufficiently dry to install the floor finishes. It
It is generally believed that drops of an alcoholic solution of phenolphthalein placed on con- crete will always turn purple when the concrete is too wet to lay the finish. Unfortunately, the colour change can occur even when the con- crete is sufficiently dry, and in cer- tain circumstances it will even re- main colourless on wet concrete.
The effect of alkaline moisture is the same for all flexible floorings. The edges of the sheet or tile lift and bubbles appear in the surface. Usually the adhesive remains firmly attached to the underside of the finish but leaves the concrete sur- face completely. Occasionally the adhesive is attacked so severely that it is converted to a brown or black liquid that oozes up between the joints.
car.
Thermoplastic and vinyl asbestos tiles are much more resistant to al kaline moisture but sometimes the adhesive is attacked in the manner just described. Alkalis can, how- ever, produce a rare type of failure with these tiles. Water rising through the base concrete penetrates the joints and on evaporation de- posits salts, mainly sodium bonate, from the concrete
on the edges of the tiles: the salts tend to creep inwards from the joints over the surface of the tiles, and when dry, characteristic white bands about an inch wide are formed around the edges, which have been described as 'window framing'. Generally this condition, though unsightly, is harm- less and the salt deposits can be re- moved by careful cleaning. In severely damp conditions, however, thermoplastic tiles can absorb these salts, and the pressures set up within the tiles as the salts crystallize are sometimes sufficient to cause lamination and ultimately powdering of the edges of the tiles.
USES
de.
Thermoplastic tiles may be used in most non-industrial situations: the in. tile is adequate for housing but 3/16 in. tiles are more suitable for
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the heavier usage of shops. offices. and schools. The tiles are not re- sistant to grease
and oil but are satisfactorily used in domestic kitchens.
Vinyl asbestos tiles tend to have better abrasion resistance than ther- moplastic tiles. They have good grease and oil resistance and are more suitable for domestic kitchens or even industrial canteens: they are not, however, suitable for industrial kitchens.
Flexible PVC flooring is produced in such a wide variety of forms that a suitable type can be found for most non-industrial situations and in some instances for industrial situa- tions also. Some are tough enough to withstand truck traffic but it is difficult to fix them so as to prevent the stretching and splitting this pro- duces. In places where a jointless floor is desirable. such as in indus trial chemical laboratories or hos- pitals. it is possible to make a con- tinuous floor finish impervious to liquids by hot air welding of ad- jacent sheets. Sometimes sheets are butt jointed and welded: in other cases a rod of material of similar composition to the sheets is welded into a gap left between the sheets or one formed by edge trimming.
as an
The wear resistance of PVC floor- ing tends to increase as the propor- tion of filler in the material is reduc ed, material containing about 60% of resin wearing as well equivalent thickness of rubber. A disadvantage of PVC flooring is that it is more easily damaged by cigarette burns than some other materials, but it is doubtful whether any floor finish should be expected to withstand abuse of this kind.
The characteristics of synthetic rubber flooring are much the same as those of natural rubber flooring but they have the advantage of higher resistance to solvents, grease and oils, and freedom from the sur face crazing often associated with natural rubber flooring.
ADHESIVES
There are few difficulties associat- ed with adhesives for flooring so long as it is realised that adhesives cannot act as damp-proof mem- branes.
Even on a dry base there are some problems involved in lay-
ad-
ing flexible PVC flooring on hesives. Tar from an adhesive can diffuse slowly through the thickness of the flooring to produce indelible brown stains on the surface. Ad- hesives containing tar are not there- fore recommended.
Some adhesives cause flexible PVC flooring to shrink and produce unsightly gaps around the tiles. This shrinkage is quite different from that shown by undercured material (B.S. 3261: 1961 includes a test for this) and is produced by movement of plasticizer from the tile into the adhesive. The shrink- age is high (0.7% has been observ- ed) and because
because the
the plasticizer softens the adhesive there is a tendency for the tiles to move under traffic and very wide gaps to appear.
The problem can be solved by using an adhesive that is resistant to plasticizers. Water emulsions of synthetic resins or synthetic rubbers form the basis of most suitable adhesives but the choice of adhesive must normally be left to the manu- facturer of the flooring, since he is likely to use a range of plasticizers any of which might bleed into particular adhesives.
MAINTENANCE
To retain the initial appearance of the floor finishes discussed in this Digest it is necessary to maintain them by polishing. The polishes available may be divided into two categories: (i) emulsions in water of resins, waxes or blends of these, and (ii) pastes or liquids in which wax is dissolved in white spirit. tur- pentine or other solvent. Emulsion polishes can be used on all the ma- terials without risk of damaging the finish. but solvent-based polishes should never be used on thermoplas tic tiles since the solvents soften the binders in these. Excessive use of polish should always be avoided. since it leads to slipperiness and high dirt retention. Worn or dirty coats of polish can be removed by washing with a solution of a neutral detergent and subsequently rinsing with clean water.
Two common kinds of markings which
may present problems of flooring maintenance are those pro- duced by black rubber in footwear, castor tyres and protective thimbles on the legs of metal furniture, and
THE HONG KONG & FAR EAST BUILDER-VOLUME 18, NUMBER 2
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