Many house owners in Australia may have noted damage to the concrete floor slab around their house typically to the external perimeter both in and outside.
1.0 What is slab edge wetting.??
Generally pitting and fretting of the concrete is caused by the lateral ingress of moisture and ground salts into the concrete floor slab edge from the outside to the inside.
In most instances the salts and moisture are transmitted into the concrete where wet soil is directly up against the concrete floor slab outside without any plastic to waterproof the edge of the concrete.
This can cause many problems including,
-Mould under floor coverings to the perimeter of the house internally.
-Fretting of the concrete.
Caused by salt crystals expanding in the concrete causing the concrete to fret.
-Concrete cancer where the continual ingress of moisture and salts into the concrete causes the steel reinforcement inside of the concrete to rust thereby expanding and cracking the concrete.
-The moisture in the concrete under a timber floating floor can cause this to lift and bow.
-Tiles laid on the floor slab can have salts in the joints which can damage grout.
-A musty smell in the house.
3.0 Causes of slab edge wetting
In essence concrete is porous so if soil is constantly damp up against the concrete slab edge wetting will occur.
-Damp Soil up against the concrete.
-Clay soils directly up against concrete.
Clay soils will hold damp much longer than a free draining sand.
-Garden watering next to a floor slab.
-No measures to waterproof the edge of the concrete floor slab ie; The use of plastic.
-Minimal exposure of the concrete floor slab edge to the air.
Ie If the paving is too high up against the floor slab edge, the concrete cannot evaporate the dampness into the air.
-No falls on the paving away from the base of the wall.
-Clay soils under paving and also to the edge of the concrete floor slab.
4.0 How to avoid slab edge wetting.
We would advise on,
-Ensure plastic to the edge of the floor slab rises up to the top of the paving level. VIP!!
If the plastic is fully sealed to the edge of the slab it is unlikely that damp will enter into the concrete.
-Make sure that paving falls away from the wall.
-Ensure the concrete floor slab has a good exposure to the air. Ie Ensure paving is not placed too high up against the concrete slab edge.
-Do not have any garden beds to the edge of the floor slab.