Learn about the different types of concrete, mortar and aggregates and how to choose the right materials for your project.
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Particles smaller than 3/8 inch in diameter are considered a fine aggregate; anything larger is a coarse aggregate. Both materials are used to make a mortar or concrete mix. Fine aggregate varies in color depending on where it comes from. Washed aggregate contains fewer of the impurities that can weaken the adhesion of a parging mix to the surface and stain the finish.
Crushed stone: Large stones and gravel — the coarsest aggregate. Used as a base for concrete and other hard-landscape surfacing.
Ballast: An "all-in-one" combination of fine aggregate and larger stones or gravel. Ideal for use in general concrete work where exact proportions of individual aggregates are not required.
Coarse aggregate: Graded stone, also known as gravel. It may be used in concrete, or as a drainage aid, or as a finished surface for a drive or path.
Sharp sand: Coarse sand with fairly large particles. Often used in concrete mixes, but may also be used to produce a very hard, durable mortar.
Builder's sand: Builder's sand is fine-textured and is used in mixes for laying blocks or bricks. An even finer grade of sharp sand is used for parging.
Kiln-dried silver sand: Very fine, dry sand, light in color. Mainly used dry to grout exterior paved areas.
These can be used in all mixes, according to your requirements.
Lime: Cement already contains lime, but adding more makes mortar easier to work with and less likely to crack when set. Traditional mortar mixes (without cement) are based on lime. Lime retains water well, and is less likely to shrink as it dries out. Nonhydraulic lime is sold as powder or as a putty containing water. Use powder for cement-based mortar, and putty for a traditional building mortar. Hydraulic lime sets more quickly, is harder and is less widely used.
Plasticizer: Makes mortar more workable, and is used as a modern equivalent of lime. It normally comes in liquid form.
Cement pigment: Powdered pigment that colors cement.
Waterproofer: May be mixed with mortar, especially when parging is to be applied in an area prone to damp. Some parging waterproofers slow down the parging's drying, keeping it workable for a longer period.
Accelerator: Speeds up curing time, and can be used to protect the mixture while it dries if frost may be a danger.
Excerpted from Do It Yourself Home Improvement
© Dorling Kindersley Limited 2009