Create lightweight concrete by altering the standard concrete mix ratio, substituting a lightweight additive to the mix for a portion of sand. Altering the amount lightweight aggregate in the mixture alters the weight of the concrete, which also alters the strength of the final substance. The more lightweight material used, the weaker the concrete. This lowered strength reduces the number of uses of the mixture as you create a lighter building material. Lightweight concrete doesn't last as long as regular concrete, with heavily substituted mixes lasting only 30 to 50 years.
Pour 22.5 litres (5 gallons) of water into a concrete mixer. Add any additives or colourants you wish to use to the mix. Mix until the additives are thoroughly incorporated.
Add half of a 42.6 kg (94 lb) bag of Portland cement to the mixer along with a 22.5 litre (5 gallon) bucket of sand. Mix well and then add the second half of the bag of cement. Mix until the mixture is a soupy consistency.
Add five, 22.5 litre (5 gallon) buckets of perlite to the mixture at the rate of a single bucket at a time. Mix the added perlite completely into the cement before adding the next bucket. Add the perlite until the concrete mix thickens enough to pour. The mix should be of a consistency of thick pancake batter, mixed so that the perlite is completely integrated and covered with the cement.
Pour the lightweight concrete into the prepared concrete forms or moulds.
Expanded shale, volcanic rock, and vermiculite can be substituted for the perlite when creating lightweight concrete. Vibrate filled moulds or forms with a sander without attached sandpaper to stop bubbles from forming within the concrete.
Wear a dust mask and safety goggles when handling the perlite, as the dust is an irritant.