Roncrete offers technical advice
Ronacrete is offering a range of technical articles to explain on various concrete repair techniques.
In Understanding Preparation of Concrete, Ronacrete’s Technical Manager, Mike Rhodes discusses the different methods of concrete preparation to ensure long lasting adhesion between concrete and new mortar / coating. He explains that adequate adhesion of screeds, renders, concrete repairs and floor coatings/membranes can only be achieved when correct substrate preparation has been carried out.
Finishing of concrete and screeds by trowelling, power-floating or tamping will leave a layer of laitance (a relatively weak layer of hydrated cement) on the surface which must be removed. Any adhesion to laitance will result in early failure of adhesion of floor screeds and coatings and early or eventual failure of adhesion of mortars to vertical and overhead surfaces.
The mode of failure is typically a breakdown of cohesion in the substrate at or close to the bond line and inspection of debonded mortars and coatings will reveal laitance and often parts of the concrete matrix adhered to the mortar or coating.