Grantville Gazette - Volume V (42 page)

This presents a new problem. Brick is not a popular construction material in Thuringia, the area in Germany where Grantville has been deposited by the Assiti shard. This means that there will be few brickmakers near Grantville, but more importantly for the short term, there will be no infrastructure in place for the production of bricks in volume. There will be no large stockpiles of clay dug up last autumn and left to weather over the winter. There will be no drying sheds, nor will there be permanent kilns. Worse still, there will be insufficient dry wood, the fuel of choice until the nineteenth century, available for firing bricks. Any brickmakers in the area will be refugees or itinerant brickmakers moving from job to job. Either way, without up-time assistance, they will be unable to produce bricks in any volume until the brickmaking season of 1632.

The brickmaker is responsible for the following tasks:

Preparation of brick earth.

Molding of the bricks.

Drying of the freshly molded bricks.

Firing of the dry bricks.

Earths (the technical term used to refer to soils as opposed to rocks) suitable for brickmaking fall into three principal classes:

1) Plastic or strong clays, which are chiefly a silicate of alumina. Often called
Foul clays
by the workmen because of the odor they give off, they are also known as
Pure clays
 

2)
Loams
and mild clays are those with a considerable proportion of sand intermixed.

3)
Marls
or calcareous clays are, as the name suggests, clays containing a notable proportion of carbonate of lime.

As both the Grantville area of West Virginia and Thuringia abound in suitable earths a down-time brickmaker will easily locate clay suitable for brickmaking within or close to the Ring of Fire, He will then have to prepare it for molding. It is rare to find naturally occurring clay that is suitable for brickmaking. Thus the preparation of clay becomes an important step. Our skilled brickmaker will examine the available earths and decide what has to be added to it for successful brickmaking. The pure clays require the addition of sand or loam, while the loams often need the addition of lime to flux and bind the earth. Pure clay or clays with little sand content will shrink and crack while drying no matter how carefully and slowly the bricks are dried. They will not stand firing, as a red heat will cause the mass to rend and warp. To overcome this problem substances that do not combine with water and do not contract when heated are mixed with the clays. It is common practice to mix in ground-up burnt clay (grog) from failed bricks. This is especially true when making fire bricks, as the fire clay tends to be expensive. For example, considerable savings can be made by mixing two parts by weight of burnt clay to one part Stourbridge clay to produce a good firebrick.

Once the brickmaker has located a suitable supply of clay and decided what to add to make it suitable for brickmaking, he has to extract the clay and then prepare it. Digging the clay and transporting it to where the bricks are to be made and fired is going to be labor intensive. It takes about two cubic yards of clay to make one thousand bricks. A single
pallet
molding
team consisting of a molder and three or more assistants can mold and lay out to dry something like three to five thousand bricks per fourteen hour day. Just to keep one team working, the clay diggers are going to have to dig six to ten cubic yards per day of brick making. A single worker can dig wet clay (as opposed to mining dry clay) at about fifteen cubic feet per hour. At this rate, ten cubic yards requires eighteen man-hours of digging.

Before the introduction of large-scale mechanization, clay was usually dug in the autumn. It was then transported to a level place prepared to receive it and left in heaps several feet high to weather over the winter. The winter frosts would help break up and crumble the lumps. Clay that has been dug in the spring will not have benefited from the frost action and, apparently, will produce inferior bricks. The object of the weathering process is to open the pores of the clay and to separate the particles so that the clay can absorb water more readily when it is mellowed (made pliable and plastic).

At the start of the next brickmaking season, which normally starts in April, the clay is removed from the heaps and thrown into treading pits where water is added, and with a combination of spade labor and treading by barefooted humans and animals, the clay is tempered to the desired plasticity. Throughout the tempering process any stones that may be found in the clay must be carefully picked out by hand. This is a tedious and time consuming operation, but one which cannot be neglected, as the presence of a pebble in a brick will result in an unsatisfactory brick. Usually the different density of the pebble compared to the clay will result in cracking of the brick.

For earths that contain a lot of gravel the only option is to wash them and run them over a grating so sufficiently fine that not even small stones can pass through. The liquid pulp has to then be run into a pit that is prepared for it and left until sufficient water has evaporated. This process produces clay that is perfectly uniform in texture throughout the mix. However, it is expensive to prepare and therefore to be avoided unless the bricks you are making require the perfectly uniform texture, such as in cutting, or rubbing bricks. Rubbing bricks are laid with almost no mortar between them, and are "rubbed" or cut to give a very close fit, such as in gauged arches.

When working with
marls
care must be taken that no lumps of limestone survive the tempering process. Even a piece of limestone no bigger than a pea in a molded brick is sufficient to destroy that brick. The carbolic acid is driven off by the heat of the kiln and forces a vent through the side of the brick. This creates a cavity that water can enter. The first sharp frost this brick is exposed to will freeze water in the cavity and will generally be sufficient to destroy the face. Over time the entire brick will disintegrate as the exposed area takes in water that will freeze and thaw.

The people from Grantville can contribute to the preparation of the earths in a number of ways. Principally, their contribution will be finding ways to mechanize the processes. When it comes to digging the clay, the introduction of mechanical diggers will not only increase the rate at which clay can be dug and loaded onto wagons and carts, but it will also extend the digging season. In seventeenth-century Europe the earths are dug in the autumn for a number of reasons. Probably the most important reason is that autumn digging allows weathering over the winter. During the summer the laborers who could be digging clay will be busy tempering the previous year's clay. This leaves only autumn and winter for digging. Winter digging is not desirable as not only does it reduce the amount of weathering the clay can undergo, but also there are the problems associated with trying to dig in wet and maybe frozen earth using wooden or poor iron shovels. Not only will the laborers have difficulty digging, but also standing in wet earth under winter conditions for hours on end will damage their health.

Figure 1. Grinding clay in a ring pit. (
Dobson
)

Mechanization of the digging process means that we now have earths being delivered to the brickworks right through the year. This means that not all the earth will benefit from weathering. We know that this will result in inferior bricks. Therefore something has to be done to replicate the weathering process. The easiest methods of breaking down the earth, and for that matter, any small stones and clumps of limestone, is to use the grinding mill.

Figure 2. A single pair of rollers for crushing clay.
g
and
g'
are the two counter rotating rollers.
h
is the feed hopper,
i
is the separation distance between the rollers. (
Dobson
)

The simplest grinding-mill consists of a ring-pit around which a draft animal drags a heavy cast-iron roller (figure 1). Clay is spread around in the pit and the roller is repeatedly rolled over the clay. Water and additional earths such as sand are added until the clay is the desired plasticity. Men then empty the pit with shovels. Because the pit is out of service while being emptied it is useful to have more than one ring-pit, allowing grinding to continue. An alternative to the ring pit is to use pairs of counter rotating cast-iron rollers arranged similar to an old-time wringer or mangle to crush clay, stones, and lumps of limestone (figure 2). It has several advantages over the ring-pit: first, it uses much less land, and second, it is an all-in-one process. Instead of loading the pit, grinding the clay, then unloading the pit, the pairs of counter-rotating rollers allow raw clay to fall through the machine, compressing the clay and crushing anything larger than the separation gap between the rollers. With multiple pairs of rollers, the separation gap can be reduced pair by pair until the final pair is almost touching. The resulting product is not as good as that from a ring pit, but it is usually good enough for most purposes, and more importantly, it is cheaper than using the ring-pit. Clay going through the counter-rotating rollers will still have to go through a pug mill, but by placing the pug mill below the roller arrangement the clay can fall directly into the pug mill, greatly reducing the amount of handling, and thus the cost of brickmaking.

The pug mill can either be used on it's own, when earths are known to be free of stones and limestone lumps, or used in conjunction with the grinding mill. A pug mill is usually a cylindrical vessel with a central shaft that holds a number of knives, which by their motion, cut and knead the clay. The knives are arranged so that the clay is gradually forced through the mill so that the finished product is thoroughly tempered ready for molding, and is similar in principal to a kitchen mincer. It is possible to have twin-shaft pug mills. The counter-rotating shafts temper the clay more efficiently than a single shaft, but the arrangement of the shafts, and the casing surrounding them are more complex. Energy to rotate the rollers of the grinding mill, or the shaft or shafts of a pug mill can be provided by draft animals pulling a sweep, water wheels, windmills, or some type of engine, either an internal combustion engine or a steam engine.

There are two methods of hand molding that may be current in seventeenth-century Europe. They are
slop molding
and
pallet molding
. The difference between the two is principally in the release agent used to prevent the clay adhering to the mold. In slop molding the mold is dipped in water from time to time, while in pallet molding the mold is sanded, rather like flour is used as a release agent in baking. Generally the slop molder needs at least two molds, while the pallet molder makes each brick with the same mold. It appears that there is little difference between the two methods in terms of product quality, and except for having a wetter surface on the brick, which means it can't be immediately tipped out of the mold and then hacked, there is little difference in how the bricks are handled. The following is a description of pallet molding.

The pallet molder makes his new brick by throwing a clot of clay forcefully into the mold using a two-handed throw. Using the hands to force the clay into the corners of the mold is undesirable, as it changes the density of the clay in that area and any uneven pressure exerted in forming the brick will show up as distortions in its shape as it dries or is fired. The molder then uses a
strike
to level off any surplus clay before turning out the molded brick onto a pallet. The pallet, a small board slightly larger than the brick, is then put to one side for an assistant to put onto a hack-barrow. When the barrow is full it is wheeled off to the drying ground where the bricks are stacked for drying (except for the case of bricks to be fired in a clamp or scove, where the bricks are taken to the hacking-ground and stacked into hacks). Our single pallet molder can keep two people wheeling barrows (wheelers) constantly employed, with two barrows being always in work while a third is being loaded at the molding stool. The drying floor for a brickworks producing over thirty thousand bricks a week can cover a large area, so it is not uncommon for bricks to be wheeled over fifty yards from the molding stool to where they will be stacked for drying.