PROGRESS REPORT ON THE EFFLORESCENCE AND SCUMMING OF MORTAR MATERIALS1

A general discussion is given on soluble salts in clays, clay products, and mortar materials and on the addition of barium compounds to make the salts insoluble. Twenty-one, 4- × 4-foot panels, 8 inches thick were constructed of the same glacial-clay, red, face brick with variations in the following common mortar materials: sand, slaked lime, hydrated lime, and Portland cement. Saturated brick was tried versus dry brick; sea water was used to replace fresh water; machine-mixing of the mortar batch was tried against hand-mixing; and various percentages of barium carbonate, barium hydroxide, and barium chloride were introduced to make the calcium sulphate insoluble. Temporary scum or that obtained in the original drying of the wall was noted and later or permanent scums, produced by artificial and natural soaking and drying the walls were studied for over a year. Results All the mortars studied can be made to scum if sufficient water and time of contact of water and mortar are provided. The troublesome salts are: (1) calcium sulphate largely introduced by the Portland cement, which makes a very bad, early scum; (2) calcium hydroxide from the free lime and hydrolyzed calcium aluminates and silicates in Portland cement and from uncarbonated lumps of lime in the lime mortars; in addition, some minor salts from special sources, such as sodium chloride from sea water Lime mortar streaks were only produced after a large quantity of water had been washed through the panel, and were apparently formed by finely divided or colloidal lime hydroxide or carbonate in suspension in the water running from the porous mortar down the side of the wall. This is a very severe soaking condition and is not common in the ordinary building wall. The lime sulphate dissolves readily enough to pass in solution through the pores of the brick and t o spread uniformly over the brick surface. Lumps of hardened lime should he removed from both slaked and hydrated lime to prevent streaks of lime hydroxide and carbonate on the surface under wet conditions for long periods of time. Lumps of lime also produce spalling. The interior of a wall should be well protected from leaky drains, gutters, etc., which permit water to get inside. A hard rain of short duration is not as bad as a long, soaking drizzle which permits the water t o remain in contact with the mortar for a longer period of time. Cement products, such as artificial cement stone, commonly release salts which drain onto other facing materials. The tests indicated that barium carbonate is effective under normal conditions in preventing or minimizing calcium sulphate scum from Portland cement. This has been checked on large Seattle school buildings where the conditions are favorable for scum. Five per cent barium carbonate in terms of Portland cement has been used successfully. I t has been suggested (but not tried) that diatomaceous earth may combine with the free lime of the mortar materials to produce a more insoluble calcium silicate and reduce the temporary scum of lime hydroxide. The study is being continued on the chemical analysis and composition of the scums taken from the surface of the walls and leached in the laboratory from separate batches of the mortar materials. Preliminary analyses have already been made. The strength of the mortar materials to note the effect of barium salts is also under study. No deleterious effects have been found from barium salts.     

NOTES ON SHAPE CONSTRUCTION1

The lines of development of a course for training ceramic artists, who are very much in demand, are outlined. Ceramic shape design for quantity production involves a study of factory processes, product specifications, both consumer's and factory, and manufacturing specifications. Examples of commercial designing are demonstrated, using drawings of a series of glass designs as illustrations for various points made. The filing of research studies in design, relation of shapes to product specification, and product development are discussed. The difference between the art engineer and the craftsman is pointed out.     

NOTES ON CASTING SLIP1

This is a note showing the unreliability of viscosimeter control for casting slip. A rule is given for control of the “hardness” and thickness of slip.     

NOTES ON FIRING TERRA COTTA1

Some notes are given on the firing behavior of a 14-foot diameter muffle type terra cotta kiln, using coal as a fuel. The need of more data on periodic fired kilns in all branches of the ceramic field is stressed.     

NOTES ON CYANITE AND DIASPOR REFRACTORIES1

This investigation covers a survey of some cyanite, diaspor, and clay refractories. The work is divided into three phases: (1) diasporcyanite study, (2) diaspor-clay and cyanite-clay study, and (3) commercial production and tests. Results of routine tests made with each set of test specimens are given. The addition of 20% or more cyanite to diaspor tends to counteract the shrinkage of diaspor during continued use at high temperatures.     

NOTES ON DRYING AND DRIER OPERATION1

A brief résumé is given, comparing drying shrinkage with the action of clay slaking in a bank. The drying of Missouri dry-press refractories in summer versus winter and blistering and mcans of prevention are discussed. The operation of three Harrop type driers and an ordinary waste-heat tunnel drier are described.     

NOTES ON TERRA COTTA BODY SHRINKAGE1

Notes on method of preparing a terra cotta body, proportioning by volume and using unground material, and method of preparing body, proportioning with ground materials, using disc feeders, are given. Notes on checking laboratory work with these two methods and variation in shrinkage due to amount of water in the body are also considered.     

NOTES ON DRY-PAN AND WET-PAN OPERATION1

The article is a discussion of the following points: (1) improvement in dry and wet pans with the introduction of high capacity heavy-duty units to replace several units and requiring less power and maintenance; (2) engineering cost data with respect to economical operating speeds, results of which were obtained from an actual installation calculated on an average power rate; (3) relation of rotation rate to capacity, considering the effect of the speed of rotation on the efficiency of the emptying device; (4) the optimum size for economical operations at various capacities, an intelligent answer to which cannot be given without a thorough study of the many factors involved, some of which are discussed in the article.     

NOTES ON SHIVERING OF TERRA COTTA1

Six terra cotta clays are tested for shivering as a body trouble using a white mat glaze, at cone 3 starting. One non-shivering clay and one badly shivering clay are experimented with, to produce and overcome shivering. Causes of Shivering .—From this work and that of others which has been checked, uses are

• 1 presence of finely divided silica in the body, from

• (a) highly siliceous clays
• (b) finely ground grog of a siliceous nature

• 2 presence of soluble salts in the clay, grog, or tempering water
• 3 longer firing periods

Methods of Eliminating Shivering.

• 1 Use of a flux such as feldspar, felsite, or similar rock to overcome action of fine silica
• 2 Use of coarse grog or sand
• 3 Use of barium carbonate to overcame effects of salts

     

NOTES ON TERRA COTTA GLAZE CONSISTENCY1

Some of the difficulties encountered in applying glaze to terra cotta are discussed. The use of a hydrometer to test glazes is misleading as a hydrometer supplies gravity indication only in true solutions and glazes are not true solutions; furthermore the viscosity of a glaze may obscure the real specific gravity. It is suggested that in order to Control a glaze it should first be made to a desirable specific gravity and then the desired viscosity at that gravity be ascertained by experiment. A viscosimeter and specific gravity bottle are suggested for this purpose. The effect of change of alkalinity and of bacteria together with the control of glaze wastage are also discussed.     

SOME NOTES ON THE NATURE OF CLAY1

The porosity and particle spacing was determined for a number of plastic and non-plastic materials under various conditions of wetness and pressure. This was done by pressing the material in a cylindrical mold and measuring the resultant density of both the freshly-molded and the dried specimen. The results show that all of the materials at the lower pressures have a critical water content, beyond which the particles re-orient themselves into a denser packing. This point corresponds to the pores being one-half filled. The clays are differentiated from the nonplastic materials by their ability to hold a stable water film onto the surface of the particles. The maximum stable thickness of this film occurs at or beyond the point where the pores are filled, and for the clays tested averages about 3 × 10⁻⁶ Cm. in thickness. This film is so stable as not to be influenced by pressures as high as 800 kilograms per square centimeter. A size analysis of the particles of all the materials was made, and their average sue and diameter computed. All of the materials were found to have some elasticity when the pressure was relieved. These data taken as a whole allow the construction of a comparatively accurate picture of the clay structure.     

NOTES ON FIRING IN DOWNDRAFT PERIODIC KILNS1

The results of a series of investigations chiefly in connection with firing are presented, with a general discussion of factors entering into the heat treatment of silicate materials. These include (1) factors controlling firing, (a) specific heat of the clay body, (b) heat of dissociation of the hydroxides, (c) latent heat of fusion, and (d) heat of reactions which take place under fusion, (2) fuel consumption and temperature rise, (3) heat distribution in the kilns, (4) firing economies, (5) cooling, and (6) dehydration and shrinkage.     

SOME NOTES ON THE COLOR OF ANTIMONY ENAMELS1

Pure white antimony oxide does not give as good a color or opacity in enamel as the gray, impure, domestic product. The better color and opacity of enamels made with the latter is probably due to the impurities contained in the antimony.     

SOME ASPECTS OF THE SCUMMING PROBLEM*

The two general types of scumming and their causes are discussed. The sulfate type of scumming is caused by sulfates either in the enamel materials or in the atmosphere to which the ware is exposed. Nonsulfate types of scums are usually caused by a combination of factors, which include underfiring, excess water vapor in the furnace atmosphere, fineness of grinding, and mill additions, especially clays and opacifiers.     

NOTES ON KALLAUNER AND SEGER METHODS OF RATIONAL ANALYSIS1

A comparison of the Seger, Kallauner, and calculated rational analysis is made, using a Florida kaolin and a Tennessee ball clay. Results obtained are observed and discussed.