Cement and Lime Mortars

Cement mortar uses cement as its binder: it is stiffer and stronger, suited to repairs and modern masonry. Hydraulic lime mortar is more breathable and less rigid, and is used on historic masonry, where the wall must be allowed to breathe. Choosing the wrong mortar on an old wall can trap moisture and cause detachment. Always consider the type of masonry and the intended use.

To repair deteriorated concrete, use fibre-reinforced thixotropic mortars, applicable by hand or by spray, or flowable concrete for consolidation and casting. Exposed reinforcing bars first need a specific anti-corrosion mortar. The choice depends on the depth to be rebuilt and the application: vertical, overhead or poured.

Concrete repair products fall under the European EN 1504 series, which classifies structural and non-structural repair mortars in part 3. Look for the CE marking and the declared class on the technical data sheet, as they indicate the product's performance. For resin injection into concrete, the reference is part 5 of the same series.

Mortars for plasters and masonry follow the European EN 998 series: part 1 covers mortars for renders and skim coats, and part 2 masonry mortars. On the bag or in the technical data sheet, look for the declaration of performance and the mortar class. On an existing wall, check the suitability of the substrate and the amount of water to mix in.

For old damp walls use pure natural hydraulic lime mortars, such as the Tectoria line by Kimia. The dehumidifying version has macroporous pores that let moisture out; the one for plaster and masonry works is for repairs using the cut-and-stitch technique. Grouts consolidate rubble-filled walls, while a dedicated mix exists for detached frescoes. The substrate must be wetted before application.

The amount of water has the greatest effect on the final strength: too much water lowers strength and increases shrinkage. Mix in the quantity stated on the data sheet, add water gradually and respect the mixing time. For two-component mortars, weigh or measure the two components separately. Do not remix a mortar that has already set by adding water.

Building plaster is used on dry interior surfaces, as it does not tolerate moisture well and tends to crumble outdoors. Fine gypsum finishing plaster is used for smooth skim coats indoors. Fast-setting cement stops leaks and fills holes quickly, and can be used on damp substrates. Both the environment, interior or exterior, and the time available for the job matter.