How to choose the right patch repair mortar

Concrete patch repair

When looking to repair small patches of concrete, you may be wondering what type of repair mortar you need, as well as whether or not it’ll need a protective coating.

In this guide, we will teach you how to select a patch repair mortar, and what kinds of coatings you can use to protect the concrete.

What is a patch repair?

Patch repairs are small areas of concrete, or reinforced concrete which are in need of repairs up to about 0.5m² – anything larger than this and the job may require a poured or sprayed repair concrete.

Patch repairs can be due to various reasons such as mechanical damage, corrosion of steel reinforcement, carbonation, fire damage or even chemical attack, and can be in various places including:

  • Building repairs (including high rise before the replacement of facades)
  • Public buildings (including car parks and hospitals)
  • Concrete works (columns, beams, walls, soffits, and balconies)
  • Coastal defences (including sea walls and piers)
  • Highways (including bridges)

What should you be looking for in a repair mortar?

There are various different properties to be aware of when looking for a repair mortar, but the most important is to ensure it is compliant to BS EN 1504.

BS EN 1504 defines the properties needed for different types of repair to ensure an appropriate and durable product is used. Part 3 of this British Standard splits repair mortars into 4 different classifications.  The different classifications define where certain materials can be used, dependent on performance characteristics. The most well-known of these performance characteristics is compressive strength.


  • R1


    Only suitable for non-structural applications such as cosmetic repair, and has a minimum compressive strength of 10MPa.

  • R2


    Only suitable for non-structural applications, but slightly stronger than R1 at 15MPa compressive strength.

  • R3


    Suitable for structural repairs and has a compressive strength of at least 25MPa.

  • R4


    The highest classification, suitable for structural repairs and has a minimum compressive strength of 45MPa.

When selecting an appropriate patch repair mortar, the first step is to ensure a mortar is used that is suitable for the type of application.  This ensures a suitable, durable application is achieved which will extend the service life of the structure by the maximum possible extent.

Do you need additional coatings for patch repair?

Whilst it’s not always required, applying a further coating can provide a protective decorative finish which will extend the life of the repaired concrete.

There are various types of concrete coatings such as:

  • Fairing coats: Typically applied 3mm deep and gives a great cosmetic finish with additional CO2 protection. These are classified as repair mortar (in compliance with BS EN 1504) and can also be used as a coating applied on top of repairs.
  • Anti-carbonation coatings
  • Water repellents and proofers

Have you heard about webercem R4 duo?

webercem R4 duo is our very first 2-in-1 SMARTmortar and provides the ability to mix a top-strength R4 repair mortar, as well as an R3-classified fairing coat which will provide extra CO2 protection.

When using webercem R4 duo as a fairing coat, 3mm will provide the equivalent CO2 protection as 30mm of low permeability concrete or 300mm of high permeability concrete.

Work smarter with webercem R4 duo

Click Compare to help you choose the right product for your project, if you need further assistance please email