What is PCC mortar?
PCC mortar (polymer cement concrete/mortar) is a cement-bound mortar to which a polymer dispersion or redispersible powder has been added. As it cures, the polymer forms a film between the cement crystals, so the mortar bonds better, shrinks less and absorbs less water.
The polymer content is typically anywhere from a few per cent up to around twenty per cent of the cement mass. Below that it behaves like ordinary mortar; above it, the mortar becomes expensive without much extra benefit.
Why add polymer?
A purely cement-bound repair bonds only moderately to old, smooth concrete and shrinks as it dries. That shrinkage pulls the repair away at the edges — the best-known cause of failed concrete repairs. The polymer film counters this in three ways:
- Better adhesion to the old concrete substrate and to the reinforcement.
- Lower shrinkage and a lower modulus of elasticity, so the repair moves with the concrete.
- Lower water absorption and chloride ingress, which helps prevent renewed concrete rot.
Unlike a resin-based PC mortar, PCC mortar remains vapour open: moisture from the structure can still pass through.
Classes under EN 1504-3
The concrete repair standard divides repair mortars into four classes:
- R1 and R2 — non-structural repair, such as levelling a surface or making good cosmetic damage.
- R3 and R4 — structural repair, where the patch has to transfer load. R4 is the highest class, used where reinforcement is corroded and in load-bearing elements.
Choose the class on the basis of the structural role, not on “stronger is better”: an over-strong, over-stiff mortar on weak old concrete creates stress in the bond line.
Application
Extensive concrete repairs: balconies and access decks, damaged concrete arrises, column bases, parking decks and viaducts. In outline: break out the loose concrete to behind the reinforcement, de-rust and coat the steel, pre-wet the substrate, apply a bonding coat if the manufacturer specifies one, and build up the mortar in layers within the stated minimum and maximum thickness. Curing against rapid drying matters just as much with PCC as with ordinary mortar.
Related terms
- PC mortar
- Mortar
- Concrete rot
- Cement
- Ready-mixed concrete
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