Sheet and Tile Flooring made from Thermoplastic Binders
SHEET and tile floor finishes for non-industrial premises are nowadays
frequently made from mixtures consisting essentially of fillers, pigments and thermoplastic binders. In this digest materials other than linoleum and natural rubber are reviewed, together with some of the problems that have arisen in their use, and the sub-floor requirements. A section at the end describes the constitution of the various types of material, and their manufacture and availability, and will provide a background for an understanding of the problems discussed in the earlier sections.
The information given on the composition, manufacture and uses of flooring made from thermoplastic binders should be read in conjunc- tion with the relevant British Stan- dard Specifications and Codes of Practice. These are as follows:
B.S. 2592: 1955 Thermoplastic
flooring tiles
B.S. 2592: 1955 Thermoplastic
flooring tiles B.S. 3260: 1960 PVC (vinyl) asbestos tiles B.S. 3261: 1961 Flexible PVC
flooring
C.P. 203: 1961 Sheet and tile
flooring
In addition to the materials listed above, brief reference is made in this Digest to PVC floorings not covered by B.S. 3261, and to synthe- tic rubbers. The latter are introduc- ed for the sake of completeness. though the Station's experience of their behaviour in practice is not yet sufficient to provide detailed in- formation.
SUB-FLOORS
All the types of flooring described will conform to the contours of the sub-floor which should, therefore, be even, smooth and rigid. Otherwise the appearance of the finished floor will be affected and any raised por tions will show signs of wear more quickly than the rest of the floor. Any sub-floor can be levelled and smoothed, and suspended timber floors can be made more rigid by the use of suitable underlays. The choice of these depends on the situa tion in which they are to be used and
122
detailed consideration of underlays such as mastic asphalt, emulsion/ cement mixtures, plywood and hard- board is given in B.S. C.P. 203: 1961.
Whilst these sub-floor require- ments are comparatively easily met, the most difficult problem associated with sub-floors is the exclusion of moisture. Dampness in sub-floors is the commonest cause of premature failure of floorings fixed with ad- hesives. The problem arises because the finishes, the adhesives and in some cases the sub-floor magnesium oxychloride cement or timber) can be affected by moisture. The commonest sub-floor for any of the materials under discussion is. however, concrete used in the form of a cement/sand screed of mix pro- portions 1:3 or 1:4, and it is with moisture in this screed that the fol- lowing remarks are concerned.
(e.g.
Moisture in the screed can derive from water used to mix the screed or base concrete on which it is laid, and from water that can on wet sites rise through concrete in contact with the ground. In each case the water contains alkalis derived from the Portland cement, and can soften all adhesives normally used and give rise to considerable moisture ex- pansion of some of the finishes. With thermoplastic and vinyl asbestos tiles, alkaline moisture pro- duces a curious effect which will be discussed later.
Water rising from the ground or from the base concrete can be pre vented from reaching the screed by taking the precautions discussed in Digest 86 (first series) Damp-proof
treatments for solid floors and de- tailed in B.S. Code of Practice C.P. 102, 'Protection of buildings against water from the ground' shortly to be published.
In making the cement/sand screed the amount of water used is always much greater than that required to hydrate the cement. Nearly all the excess water must be removed before the floor finish is laid, irrespective of whether the finish, e.g. thermo- plastic and vinyl asbestos tiles, has good tolerance to moisture. The only way to eliminate excess water from the screed is to allow it to evaporate. No particular drying period can be specified because the time required will depend on many factors, such as the quality and thickness of the screed, and the heating and ventilation within the building. A rule-of-thumb method often quoted is that one
one month should be allowed for every inch of the screed thickness. This figure is useful for forward planning of building operations but no finish should be laid until the screed is shown to be sufficiently dry by a re- liable moisture test. Various test methods have been devised and of these a method based on the use of a paper hygrometer fitted into an in- sulated box has been found by the Station to be both simple and re- liable. Details of the apparatus and method of use are given in Digest 18 (second series) and B.S. C.P. 203: 1961.
Tests that are of little value are those relying on the use of anhy- drous calcium chloride, anhydrous copper sulphate or phenolphthalein.
THE HONG KONG & FAR EAST BUILDER—VOLUME 18. NUMBER 2