November_1970 — Page 33

in set, and lower evaporation in warm weather with a consequent reduction in cracking and crazing.

Stuccos, levelling screeds, tile ce- ments, patching plasters and finishing plasters are among the products which employ cellulose ethers. Some tile cements contain only p.v.a. with a thickening agent such as a non-ionic cellulose ether, though it is more com- mon for these formulations to contain a hydraulic hardening agent such as gypsum or Portland cement in addi- tion. Patching plasters or joint fillers may incorporate up to some 0.5 per cent. non-ionic cellulose ether possibly with gypsum, a filler such as talc and sometimes p.v.a. A smooth paste is formed in water and pre-wetting is not required.

Spray applications

In spray applications inclusion of cellulose ether solutions gives less water separation, or syneresis, and splash back is reduced. In fire fighting the solutions are used to increase the size of drops of water in the spray and cellulose ether/di-ammonium phos phate is employed as a fire retardant to prevent the spread of flames.

Where exposed aggregate finishes are specified, two different methods have been suggested using cellulose ethers. In the first, an adhesive mix- ture of cellulose ether and sand in water is made up and spread on the mould surface to a depth half that of the aggregate nominal size. Aggregate is added and the mould allowed to dry, after which concrete is placed and the aggregate exposed by a water wash. In the second a retardant solu- tion incorporating a thickener such as cellulose ether is used to coat the mould surface, putting back the sur face setting of the concrete.

Probably the best known building application of cellulose ethers is that of an adhesive binder in wallpaper pastes. The long tacky period produc- ed gives time to position the wallpaper and the use demonstrates the non- toxic, easily mixed and thickening pro- perties of the solutions.

In addition to the above, paints, bitumen emulsions can be stabilised; the water demand of products employ. ing porous lightweight aggregates re- duced; boiler waters purified etc. by use of cellulose ethers. All these exam- ples of uses do show how, including

and beyond the factor of cost, an adaptable chemical product can be em- ployed in all manner of ways in build- ing and civil engineering.

References

Information and help given from the following organisations is grate- fully acknowledged (the opinions are those of the author): Bayer Chemicals Ltd.; British Celanese Ltd.; Joseph Crosfield & Sons Ltd.; Dow Chemicals Ltd.; Hercules Powder Co. Ltd.; Hoechst Chemicals; I.C.I. Ltd., Nobel Division.

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1. Davidson, R. L. & Sitting. M. "Water-Soluble Resins. Reinhold. 2nd Edition, 1968.

2. Uren, L. C. Petroleum Produc- tion Engineering. McGraw Hill. 3rd Edn. 1946.

3. "Oil Well Cementing Practices in the United States." Divn. of Produc- tion, American Petroleum Institute. 1959.

4. "History of Petroleum Engineer- ing." Divn. of Production, American Petroleum Institute. 1961.

5. Rogers, W. F. "Composition & Properties of Oil Well Drilling Fluids. Gulf. 3rd Edition. 1963.

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Far East BUILDER, November 1970

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