What a bricks made of?

Factual Questions
1

Simple question, but search engines don’t help much.

I was reading Conrad’s “Heart of Darkness” and at one point the character mentions some of the people trying to make bricks out of straw, but it wasn’t working. I know bricks aren’t made out of straw, but what are they made out of? Clay? And exactly how are they made?

2

Take a bunch of clay, make it into a rough brick-type shape, then cook it in a very very hot kiln for a while, and you have a brick.

3

Most bricks I am familiar with are indeed made of clay. They are really just low grade pottery and are fired in a kiln. This is quite an industrial process however and in the past not everyone would have had the ability or resources to build adequate kilns. More primitive bricks can be made from clay or even mud by adding straw as a binder and just drying rather than firing. They will not have the strength of a modern brick but the straw helps to keep the brick together rather than crumble away, hench the saying “You can’t make bricks without straw”. Adobe is made this way.

4
      • There’s unfired brick and fired brick. What we see mostly in modern times are fired bricks, and the reason shall soon be apparent:
  • In “The Ten Books On Architecture” by Vitruvius [translated by M. H. Morgan, ISBN 0-486-20645-9] the chapter on bricks states that they should be made of white chalky clay or red clay, with no pebbles or sand and little or no gravel because “the straw in them does not hold together on account of the roughness of the material”. {He never explains how much straw is used or when it is added at all} At this time bricks were not fired so the bricks were air-dried (enough of any fuel to do so would have been cost-prohibitive, if they wanted something harder than clay brick they used cut stone) . They must be made in Spring or Autumn, because if they are made in summer or winter they do not dry evenly enough and crack the first season. It was common practice to let bricks air dry for two years before use, and in some special or critical structures, only bricks that had dried for five years were used.
  • Because they had to air-dry, bricks then tended to be relatively larger and flatter than what we are used to. No thicknesses are specified, but Lydian bricks were normally 1.5 x 1 foot long and only perhaps 2-3 inches thick (this I guess from the illustrations and photos in the book). Roman bricks were about the same thickness, but either the length of five hands (pentadoron), or four hands square (tetradoron). The 5-hand bricks were only allowed for public buildings while the 4-hand bricks were for private dwellings; restrictions on Lydian bricks aren’t noted either way. Each of these also had a half-brick size, to allow alternating the layers when stacked. Another common practice was to use bricks as roof tiles for two years, and if they survived without breaking then they were removed and used to build walls. The roof was then recovered with fresh tile. There are some Greek and Roman structures made of such brick still standing. Kind of.
    —Fun fact: - Also noted is that there are certain bricks made in Spain and Asia Minor that are light enough when dry to float in water.
  • So anyway, this is the reason for baked bricks: you can make them quickly and year-round in any climate, because you don’t have to worry about inconsistencies when drying them naturally. Different materials work better for baked bricks, so air-dried and baked bricks do not use the same materials. Air-dried bricks of ancient times were white or red clay combined somehow with straw.
    ~