Adobe - Adobe Bricks

Adobe Bricks

Bricks are made in an open frame, 25 cm (10 in) by 36 cm (14 in) being a reasonable size, but any convenient size is acceptable. The mixture is molded by the frame, and then the frame is removed quickly. After drying a few hours, the bricks are turned on edge to finish drying. Slow drying in shade reduces cracking.

The same mixture to make bricks, without the straw, is used for mortar and often for plaster on interior and exterior walls. Some ancient cultures used lime-based cement for the plaster to protect against rain damage.

The brick’s thickness is preferred partially due to its thermal characteristics, and partially due to the stability of a thicker brick versus a more standard-sized brick. Depending on the form into which the mixture is pressed, adobe can encompass nearly any shape or size, provided drying time is even and the mixture includes reinforcement for larger bricks. Reinforcement can include manure, straw, cement, rebar or wooden posts. Experience has shown straw, cement, or manure added to a standard adobe mixture can all produce a stronger, more crack-resistant brick. A general testing is done on the soil content first. To do so, a sample of the soil is mixed into a clear container with some water, creating an almost completely saturated liquid. After it is sealed, the container is shaken vigorously for at least one minute. It is then allowed to sit on a flat surface for a day or so until the soil has settled into layers or remains in suspension. Heavier particles settle out first, so gravel will be on the bottom, sand above, silt above that and very fine clay and organic matter will stay in suspension for days. After the water has cleared, percentages of the various particles can be determined. Fifty to 60 percent sand and 35 to 40 percent clay will yield strong bricks. The New Mexico US Extension Service recommends a mix of not more than 1/3 clay, not less than 1/2 sand, and never more than 1/3 silt. The largest structure ever made from adobe (bricks) was the Bam Citadel, which suffered serious damage (up to 80%) by an earthquake on December 26, 2003. Other large adobe structures are the Huaca del Sol in Peru, with 100 million signed bricks, the ciudellas of Chan Chan and Tambo Colorado, both in Peru (in South America).