What is a Waffle Concrete Slab?
A waffle slab is a reinforced concrete footing and slab system. Builders use Styrofoam Boxes ( look like broccoli boxes) between the beams to form voids where concrete is poured. Basically, waffle slabs are a cheaper slab construction as the Builder uses less concrete.
There is an argument that the Styrofoam Boxes (Polystyrene) emits CO2 as it is in constant contact with moist acidic soil. This higher levels of CO2 makes the environment under a waffle slab more conducive for foraging termites. We don’t have the science or field data to substantiate this claim.
But recently we were called out to a house where a Builder had created a cut-out to reposition some plumbing pipes and discovered a termite nest nestled in a Polystyrene box (see attached photo).
How to treat a waffle concrete slab for termites
When you find the situation we came across with the exposed termite nest directly under the concrete slab, you can apply a controlling agent (liquid termiticide – Termidor) directly into the nest.
Sometimes there is a situation where the house had reported termite activity inside so a full chemical treatment had been applied to the external perimeter. But the external treatment appears not to have eradicated the problem. This could suggest there is a nest under the slab with access to moisture and timber (the house).
Normally you would apply chemical under the slab by drilling and injecting the whole slab in a grid pattern. With waffle slab constructions, this is far more difficult as the thickness varies from 150mm to 600mm.