Shainwald, Ralph L., Jr.
Important facts about stucco, pp. 207-208
IMPORTANT FACTS ABOUT STUCCO only dainty fare, a craftsmanlike table and beautiful linen, but dishes which would add the completing touch to the sought-for har- mony. Pieces made with such an end in view cannot be hurried; but that is no drawback, for possession which is too easy leads to a certain carelessness of attitude toward the article so obtained and thence to the curse of wastefulness because it is "so easy to get another." We started our little industry in the cellar of a private dwelling, and today our plant occupies the first floor and basement of a house under the shadow of the old North Church where Paul Revere's signal lanterns were hung, and opposite the green turf and ancient elms which shade the resting places of some of Boston's first citizens in Copps Hill Burying Ground. Our pottery includes the usual necessities -clay bins, sifting, grinding and clay- pressing machinery, wheels, drying closets, racks innumerable, a whirler for mold work, tables for painters, a color mill for grinding glazes, benches for dipping ware and-most important of all-a good kiln. The utensils include vessels for glazes, modeling tools and painting materials, while the items which appear oftenest on the expense account are packing materials, clay, cones, fire brick, fuel, chemicals, "re- pairs on kiln and machinery," plaster for molds, and stilts. But equally important though less tangible factors in the work are the personal interest and craftsmanship that go into the making of Paul Revere pottery. IMPORTANT FACTS ABOUT STUCCO: RALPH L. SHAIN- WALD, JR., A.M. HE ease with which stucco lends it- self to artistic treatment, has tended toward a precocious devel- opment that has been harmful. The trouble is that a stucco job which at first appears to be an artistic gem, gradual- ly develops flaws which may finally over- shadow the original beauty. What is the cause of the "checking" and "hair-cracking?" Is it superficial, or is it hidden in the physiochemical composition of cement? Much valuable study has been devoted to the external treatment of stucco, but few have stopped to question its inter- nal composition. Let us therefore study some inside facts of stucco mortar. The subject is an interesting one and the conclusions startling. Who would have thought, for instance, that cement acts like wood: swelling up on wetting and contract- ing on drying? But this is proven by care- ful measurements. A. T. Goldbeck, of the U. S. Department of Agriculture, showed this in experiments described in the Engineering Record of July 8, 1911 (page 45). His researches were confirmed by Prof. A. H. White, working independently in the University of Michi- gan and published in the Engineering Rec- ord for July I5, 1911 (page 73). Both of these gentlemen proved scientifically and conclusively that mortar and concrete ex- pand on wetting and contract on drying, the action keeping up for years. In some cases the amount of expansion (due to wetting) was as great as that due to IOO degrees increase of temperature. This is a startling fact, when it is remem- bered that concrete expands with heat just as much as iron does. The strains due to wetting and drying are therefore very se- vere and come quickly and repeatedly. It is not difficult to see why this should be such a serious source of cracking. It is fortunate that only the cement is affected, the sand remaining practically un- influenced by moisture. Therefore lean mortars are much less affected than rich ones: a i :3 stucco when moistened expands much less than a I :2. But as Professor White says, "If a stucco is lean enough to avoid cracks water will go through it free- ly, and if it is rich enough to keep out wa- ter it will crack." In Italy, where stuccos have been used for centuries, masonry walls were thick and waterproof in themselves. Cement was made from pulverized natural rock, and lean stucco mixtures were a matter of economy. The passage of ages has devel- oped comparatively little checking in the Italian stuccos. But today, in America, Portland cement is cheap, walls are thin and climate severe, so that rich mixtures have been used in the attempt to get cheap waterproofing. The result is excessive hair- cracking. It is, of course, true that a T :2 stucco is more waterproof than a I :3, but it is very much more liable to crack. On the other hand, a I :3 stucco properly applied is safe from cracking, though very porous. This, then, is the dilemma which confronts the constructor: how to make stucco lean enough to avoid cracks, yet non-porous 207
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