Waffle slab is a base system and reinforced concrete slab. Builders use Styrofoam boxes (similar to broccoli boxes) between the blocks to create cavities for pouring concrete. In general, waffle slab pods are a less expensive construction than slabs because their builders use less concrete.
It is said that styrofoam (polystyrene) boxes give off CO2 because they are constantly in contact with moist acidic soil. This higher CO2 value makes the environment under the wafer plate more conducive to termite search. We have no scientific or field data to support these claims.
If you have the situation with an open termite nest directly under a concrete slab, you can apply a pesticide (liquid termiticide – Thermidor) directly to the nest.
Sometimes there are situations where homes have reported termite activity inside so a full chemical treatment of the outside perimeter has been carried out. But external treatment doesn't seem to solve the problem. This may indicate that there is a nest under the plate with access to moisture and wood (house).
Typically, you will apply the chemical under the slab by drilling the entire plate and injecting it into the lattice structure. This is much more difficult with wafer plate construction, as the thickness varies from 150 mm to 600 mm.
The option is to first use an above-ground bait program to uproot nests under the plate and apply continuous chemical treatment to the gut perimeter.