Stick with it

Press, 8 May 1978, Page 24

Stick with it

The ca v e-dwelling people of Europe decorated their rock walls with coloured paintings, and since that time man has used various means of adding to the aesthetic appeal of his home. Over the past century or so, the most common method has been to cover the interior walls with patterned and coloured paper, and in most countries this practice still flourishes. As a means of attaching wallpaper, paste and mucilages made from starch, flour and natural gums have been used for a long time. In fact, a straight wheat flour paste, made in the old crockery mixing bowl, was in general use well into the thirties. The paste was good to use, cheap and easily made, but it stained the paper badly if not applied with care. Old-timers will remember working on scrim surface, lath and plaster or sometimes bare boards. But the paste stuck, so everybody was happy, even if the joins were lapped and not butted together. The next step was the marketing of a cold watermixing, pre-gelled type of paste powder. This gave an easily prepared paste with good working properties and reliable adhesion to the papers and base surfaces then in use. Pre-gelled pastes held the field for a long time, and over the years considerable improvements have been made in the stability, ease Of mixing and consistent quality of these products. A significant change, some years ago, was the appearance of paste powders or granules of modified cellulose, which were cold-water soluble. These pastes usually, but not always, had less marking effect if accidentally applied to the surface of the paper. Also the paste was quickly and easily made up, and was smooth, clear and colourless.

The cellulose paste, however, is not ideal, as it has been found by some to be too fast-drying, and also lacking in tack and body for very heavy papers. The low solids (usually 1-2 per cent), of the cellulose paste, has been thought a potential disadvantage compared to the higher, (10 per cent), ratio of starch-based pastes. However, some special heavy-duty cellulose pastes have been made to meet this problem. Papers have changed too. Durability was improved by applying a moisture and soil resistant ■ coating, and lately, even better, a fine film of P.V.C. (poly-vinyl chloride). These, changes did not require anything new in the way of adhesives. Of more significance has been a swing towards wall coverings of P.V.C. extruded onto a cloth backing. These materials can be relatively thin, but range up to very thick, heavily-embossed quality. The backing of some of the vinyls is not easy to bond, and adding to the problems of the adhesive manufacturer is the sheer weight of the material, and the fact that it has to be stuck on surfaces ranging from fibrous plaster to concrete. Starch and cellulose pastes were quickly found wanting in the hanging of vinyl, and it was found necessary to introduce a special dextrine adhesive, and for still more difficult jobs a P.V.A. (poly-vinyl acetate) synthetic resinbased adhesive. These two preparations gave better adhesion to both material and wall surface. Mould growth under the wall-covering became a problem after vinyl materials were introduced, as moisture from the adhesive cannot escape through the P.V.C. and final drying can be very slow, especially in cold weather. To prevent this

trouble, the adhesive must contain an effective fungicide. In fact, it is now normal practice for adhesive manufacturers to add a mould-preventive also to starch paste powders to avoid trouble in possible damp areas such as kitchen, bathrooms and the cold side of the house. Together, paste and paper allow the householder of today a wide choice, and it would seem that this method of decorating the interiors of houses will be with us for a long time yet. (Contributed by Davis Gelatine, (N.Z.) Ltd.).