Building Materials

This blog examines the uses, components and characteristics of four different building materials: concrete, mortar, clay and timber.

Concrete

Figure 1: Concrete

Image from Pexels

Concrete (see Figure 1) is a structural material used for foundations, floors and walls, building frames, roofs, windowsills and beams, all of which can be cast on site or pre-cast. Concrete can also be pre-cast into blocks (large) and bricks (smaller).

The main components of concrete are:

• Cement: a grey powder derived from limestone, shale and gypsum, which acts as the binder of the mix

• Water: the catalyst which triggers the chemical action

• Aggregate: the fillers, usually a mix of sand and gravel, with a variety of course and fine aggregates for better workability

Figure 2: Sand and Cement Mix

Image from mcmahons.ie

Figure 2 shows a 1:3 mix of cement to sand, however, the standard cement/aggregate/water ratio mix for concrete on site ranges from 1:6:0.5 to 1:8:0.5. Concrete should be thoroughly mixed and compacted at a suitable temperature and humidity.

There are two common tests for the strength and workability of concrete, and they are carried out as follows:

• Take a sample of concrete mix

• Fill a cylinder and a cone in three equal layers by volume, poking each layer with a rod 20 times to get rid of air voids

  • For the strength test, cure and send the cylinder to lab for testing

  • For the slump test, lift the cone, take a reading of height of the concrete versus the height of the cone, and determine if the cement has slumped

Mortar

Figure 3: Mortar

Image from Kilaran.ie

Mortar (Figure 3) is a material used to bond bricks or blocks together, to make bricks or blocks truly horizontal or vertical, to form screeds on floors, or to render buildings or walls.

The main components of mortar are:

• Cement: the binder

• Water: the catalyst

• Aggregates: the filler

• Hydrated lime / plasticiser: for workability and smoothness

Mortar can be made with different ratios of the above components. One example is a mix of cement, hydrated lime, sand at a ratio of 1:1:5. This is a standard mixture with good workability, used on the superstructure of buildings.

Mortar should be sufficiently pliable to enable ready application and to flow slightly, but it should not collapse under the weight of the units it is holding (Mortar, 2019).

Clay

Figure 4: Clay Bricks

Image from Kilaran.ie

The main building products made from clay are bricks (Figure 4), though bricks can also be made of calcium silicate and concrete.

Clay is made from fine particles of decomposed rocks and other organic matter. Clay is dug from the ground, washed, milled, shaped into a brick shape and burned at a high temperature in a kiln to fuse the particles together. It can vary a lot in composition based on where the clay is from. Finished structural clay products display properties such as high pliability, load-bearing strength, resistance to wear and an ability to take a decorative finish (Structural Clay Product, 2018).

Timber

Figure 5: Timber

Image from Goodwins.ie

Timber (Figure 5) can be used to form the entire fabric of a building, from walls, floors, roofs, windows, doors and foundations.

Timber can be classified as hardwood or softwood. This is a botanical classification, and does not have a direct weighting on the hardness or durability of the species. For instance oak is classified as a hard wood because its seed, the acorn, has a hard shell. Whereas pine is a soft wood because its seed, the pine, has a soft shell.

Heartwood (inner trunk) is more durable than sapwood (outer trunk). Sapwood therefore needs to be treated with a preservative if using outside to make it more durable. See Figure 6.

Figure 6: Sapwood and Heartwood

Image from civiljungle.com

Seasoning timber is the controlled drying out of timber to increase durability, strength and workability by taking the moisture content to below 20%. Seasoning can be done by air seasoning or kiln seasoning.

REFERENCES

Mortar (2019) Britannica, [online] Available from <https://www.britannica.com/technology/mortar-building-material> [accessed 21 February 2021]

Structural Clay Product (2018) Britannica [online] Available from <https://www.britannica.com/technology/structural-clay-product> [accessed 21 February 2021]