GB2398803A

GB2398803A - Walling blocks comprising clay and straw

Info

Publication number: GB2398803A
Application number: GB0304679A
Authority: GB
Inventors: Sam William Bernard Owen; Scott Parr
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-02-28
Filing date: 2003-02-28
Publication date: 2004-09-01
Anticipated expiration: 2023-02-28
Also published as: GB2398803B; GB0304679D0

Abstract

Walling for buildings comprises blocks formed from a soil-based material including clay and admixed with straw, the blocks being laid in courses and bonded together with a binder material.

Description

Walling for Buildings This invention relates to walling for buildings;

such walling may be of the load-bearing, typically but not necessarily external, type or of the non load-bearing, typically internal partition walling, type.

A walling material for buildings and which has been traditionally used for centuries, albeit typically in localities where suitable raw materials are available, is cob. Cob is essentially an intimate mixture of a clay-containing subsoil, straw and water, brought to a suitable consistency and placed in horizontal layers or "lifts" to form a mass wall. Typically, the lowermost or base layer is supported on a stone plinth and the completed wall, which may optionally be rendered, itself supports joists for upper floors and ultimately roof timbers, typically for a thatch roof. Buildings formed from cob can last for centuries, are visually compatible with local landscapes, do not consume energy or generate pollution in the construction process, and are generally at least as good as buildings constructed from more modern materials in terms of thermal insulation properties and resistance to propagation of moisture.

It has now been found that walling materials based on soil, such as cob (as it is known at least in the south-west of England, especially in the county of Devon), can be formed as regular-dimensioned blocks which can be laid in courses with a suitable binder material to form a wall.

According to one aspect of the present invention, therefore, walling for buildings comprises blocks formed from a soil-based material including clay and admixed with straw, the blocks being laid in courses and bonded together with a binder material.

Walling according to the invention may be single-skinned or doubleskinned with a cavity between the skins, and may be load-bearing.

The clay as a component of the soil-based material preferably contains a proportion of volumetrically-stable clay, that is, clays ol which the preponderant particle size is relatively coarse such that it neither expands nor contracts or shrinks excessively, thereby providing adequate cohesion under all conditions of use. The soil of which the clay forms a part preferably contains a well distributed range of aggregates from coarse gravel through to fine sands and silts, these being bonded together by the clay which forms a coating around the aggregate particles. The straw, which preferably comprises wheat or barley straw but may comprise other such materials including hay, has the effect of distributing shrinkage cracks through the block and increasing the resistance to shear failure in use.

The soil-based material also includes water, the quantity of which will vary according to the ingredients or properties of the soil but is generally present in an amount of from 10 to 12% by weight. Insufficient water results in inefficient distribution or dispersion of the clay fraction throughout the soil, whereas excess water reduces the soil component to a soft, plastic state, the mixture then requiring to be dried before being formed into blocks.

Aside from the water component, the soil-based material preferably contains stones and gravel (over 5 mm in diameter) in an amount of 30 40% by weight, fine and coarse sand in an amount of 25 - 30% by weight, silt in an amount of 10 - 20% by weight and clay in an amount of 10 - 25% by weight.

Optionally, the soil-based material also includes lime or cement in order to reduce the setting time, although the correct raw materials in the absence of lime or cement should result in building blocks which are as hard as required for structural walling purposes.

Thus, the presence of lime or cement makes little if any difference to the properties of the material itself, once fully set and hardened.

The material can be prepared by intimate mechanical mixing of the raw materials, adding water as required. Mixing the ingredients should include compaction or compression thereof and, conveniently, the use of a tractor with a fined apparatus attached to the front boom achieves both mixing and compaction, the materials being spread out on the floor of a barn or yard. Alternatively, the ingredients may be passed through a mixing/composition apparatus such as a screw conveyor. The mixed material may then be cast in blocks of the desired size and shape and allowed to dry and harden.

When using the blocks to form walling, a suitable binder material or bedding mortar comprises a mixture of earth, lime and sand, the proportions thereof varying according to whether the cob blocks are to be exposed and weathered or, alternatively, rendered or plastered. For example, a 5:1 mixture of coarse sand and lime putty would be suitable where the wall was to be rendered or plastered.

The use of cob blocks in walling according to the invention offers advantages over masonry and aerated blocks in that they have a uniform porosity and density, allowing even absorption and evaporation of water; uniform thermal expansion properties without hot or cold spots, whereby rendering and plaster will be less likely to crack as a result of differential thermal movement; and they are in visual harmony with other local raw materials, as well as being economical of energy requirements and low on pollution in the production thereof.

Claims

Claims 1. Walling for buildings comprising blocks formed from a soil-based

material including clay and admixed with straw, the blocks being laid in courses and bonded together with a binder material.
2. Walling according to claim 1, the courses being arranged in a doubleskinned array with a cavity between the skins.
3. Walling according to claim I or claim 2, in which the clay as a component of the soil-based material contains a proportion of volumetrically-stable clay.
4. Walling according to any preceding claim, in which the soil of which the clay forms a part contains a distribution of aggregates bonded together by the clay which forms a coating around the aggregate particles.
S. Walling according to any preceding claim, in which the soil-based material includes water in an amount of from 10 to 12% by weight.
6. Walling according to any preceding claim, in which the soil-based material contains stones and gravel (over 5 mm in diameter) in an amount of 30 - 40% by weight, fine and coarse sand in an amount of 25 - 30% by weight, silt in an amount of 10 - 20% by weight, clay in an amount of 10 25% by weight and water.
7. Walling according to any preceding claim, in which the soil-based material includes lime or cement.
8. Walling according to any preceding claim, in which the binder material comprises a mixture containing earth, lime and sand.
9. Walling blocks for use in walling according to any of claims I to 8.
10. A method of preparation of walling blocks according to claim 8, the method comprising intimate mechanical mixing of the raw materials and water, casting the mixed material in blocks of the desired size and shape and allowing the blocks to dry and harden.
11. A method according to claim 10, in which the mixing stage includes compaction or compression of the raw materials and water.
12. A method according to claim 11, in which the ingredients are passed through a screw conveyor apparatus.
13. A method of building a wall, the method comprising laying walling blocks according to claim 9 in courses and bonding the blocks together with a binder material.