Efforts to reduce material and labor costs in the construction of stoppings have led to the introduction of newer lightweight materials for the construction of ventilation controls. Traditional stoppings are usually constructed of hollow-core concrete blocks by dry stacking or by binding with mortar between the block joints. A difficulty with using concrete blocks is they are heavy. A typical 20.32-cm wide by 20.32-cm high by 40.64-cm long hollow core concrete block weighs on average about 18 kg.Today, comparable lightweight blocks weigh much less, which can be one third or less weight, or around 12 kg or less. The lightweight blocks are generally available in various sizes from 15.24 cm thick and 20.32 cm or 30.48 cm high and 60.96 cm long.