No_5_February_1962 — Page 20

is an elderly chicken that comes

I home to roarty after four years, and

THE MASTER BUILDER exclusive handling trials feature marks the third report of long-term investigations.

The report dealt with here is devoted to specific practical trials of Glamorock, the now familiar mural decoration con- sisting of natural stone particles set in a resinbonded cementitious body.

Eye-Catching

The attraction of a multi-faceted wall surface, presenting a blend of colours and a bright, light-catching effect, is fairly obvious. What occurred to THE MASTER BUILDER representatives, and probably to practically every knowledgeable build- ing technician, when this material first made its appearance, was how long the material would stay on the wall. We are all familiar with pebble-dash that doesn't.

The sample sent for trial was applied strictly according to instructions, with surface

media also as preparation supplied. This undercoating

undercoating material appeared to be a plaster-type of paste, brownish-pink in colour to suit the similarly coloured particles of the finish.

These particles can be likened to de- merara sugar, in size and shape; rather like, perhaps, very sharp sand; individual particles being translucent and some- what like glass or quartz, with the same characteristic sharp edges.

Four years is a long time to remember the precise technique adopted for pre- paring the samples for testing and no notes appear to exist. In the course of making out this report the remainder of the sample material was found and dis- covered to be apparently serviceable—to our considerable surprise.

There had been about seven pounds of each, paste and finish. They had been sent to our research laboratories packed simply in double polythene bags, and we had left there when the small test samples had been removed.

A great deal can be said for sealing aqueous materials in polythene when it is realised that the bags contain sub- stances designed to go rock hard on set- ting but after four years were sufficiently soft to be knocked up again for a further series of tests.

The original four-year old test con- sisted of a simple attempt to see if the surfacing particles remained adherent to the backing or undercoat and, of course, to see if the backing coat also remained adherent.

For this purpose three similar bricks were chosen, cleaned and prepared with backing and finally with surfacing.

One brick was immediately placed out- doors on a corrugated iron roof, com- pletely exposed to the elements but with the treated surface vertical. In the course of years the face has turned to all points

of the compass.

warm

room

One of the remaining bricks was immediately shelved in a where it was left completely undisturbed for the whole period.

The last brick was subject to the cruellest treatment it was possible to devise, short of setting up a much quicker cycle of artificial weather conditions. This brick was alternately left in a domestic refrigerator for days at a time and then placed immediately on the hob of a working domestic boiler.

When this test brick was placed on the boiler hob it would have ice in the loose particle structure, or frosting from the ice making compartment.

It was expected that this treatment

HANDLING TRIALS

AFTER FOUR YEARS

Proof of the Pudding

remarkably tough and transparent skin which, although thin and almost in- visible, does succeed in making these particles stick to each other in an almost fantastic edge to edge manner.

Trowelling this material on the wall requires almost an act of faith. The material spreads out in a continuous screed and it is not until it is dry that the p.v.a. shrinks away from the surface leaving the separate granules individually identifiable. The change in appearance is quite remarkable but does serve to explain the adhesive action of the p.v.a. Writing this report was interrupted to seek out the remainder of the original material and to refresh

memory on method of application. When the bags

LONG-TERM TESTS WITH UNEXPECTED RESULTS

In an industry where products and methods less than 25 years old can be highly suspect, any new introduction needs practical tests. Results can sometimes run contrary to expectations.

would speedily lead to loss of material, at least a number of individual granules or some lumps. In fact, there was a most unexpected result.

As far as we are able to judge, and able to persuade the manufacturers to agree, the binding medium for both paste undercoat and granular finish is poly- vinyl acetate. This remarkable artificial resin emulsion has, of course, been the subject of many editorials in this publica- tion and will, in view of the nature of this universally applicable substance, be the subject of many more.

The open texture of Glamorock in its finished state is akin to that of a Tyro- lean cement rendering. Those who are familiar with the Building Station Digests will know the importance of an open texture, contradictory as it may seem, in preventing the penetration of moisture.

The p.v.a. binder used in Glamorock granular finish shrinks to a thin but

were opened it was found quite possible. to break down the granular material which was still damp: it was certainly not swilling in liquid as it had been originally. The paste undercoat was found to have stiffened and to have coloured layers, from deepish brown to grey, with fairly dry lumps.

Both materials were knocked up vigorously with trowel work and the addition of Croid p.v.a. and a very little water-that used for wetting the trowel, no more. The two mixes were halved and spread on to tiles-pieces of ancient clay roofing tiles. One appeared to have had more water in the granule coat and had a completely smooth look when trowelled out, the other almost at once took on the characteristic open appear- ance but with a rather unusually deep texture. These test pieces will be ex- posed in a similar way to the original brick surfaces.

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