How To Waterproof ICF Walls (Insulated Concrete Formwork)

How To Waterproof ICF Walls (Insulated Concrete Formwork)

How to waterproof insulated concrete formwork (ICF). Basement Retaining Walls.

Ensuring success when waterproofing ICF retaining walls: using the correct systems is key.

What are ICF  walls?

Insulated Concrete Formwork walls, also known as ICF, are hollow blocks of insulation that are locked together then filled with concrete. They are often used for retaining wall construction as they are cost effective and strong and also do not require a separate insulation layer. This saves time and money on the build process. When used for basements or retaining walls, ICF needs careful attention to make them waterproof.

Koster Deuxan 2C drum

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Waterproofing of new build basement walls – ICF

In order to prevent water ingress into a basement it is important to use an effective waterproofing system.

ICF walls will require a “post applied system”: this means that the waterproofing is applied to the wall – after it has been built.

There are two types of post applied waterproofing systems- Fully bonded, liquid applied such as Koster Deuxan 2c , or self adhesive such as Koster KSK.

Of the two systems we find the fully bonded liquid applied Deuxan 2c to be more reliable, as it is applied as a liquid and fully bonds to the outside of the wall.

Waterproof concrete is not effective for ICF walls. Its difficult to compact the concrete adequately in the ICF blocks and the structure of the blocks creates pathways for water to bypass the waterproof concrete

1- Access.

Good access is required to the outside of the ICF wall to allow for the application of the waterproofing. Remember the wall will be built and you will need space to accurately and carefully apply the waterproofing

2- Surface preparation.

The ICF  wall should be thoroughly cleaned to remove surface contamination before the waterproofing is applied.

3 – Pre treatment. 

Some building materials, such as new concrete, can generate free lime which could damage the tanking layer. This free lime should be encapsulated using a free lime blocker such as Koster Polysil TG500

4 – Internal Angles. Junction of Wall and Slab.

Right angles in the structure can create problems for waterproofing systems. Koster Repair Mortar Plus can be use to form nice, rounded fillets at internal angles. These fillets can spread the loading of any water ingress and remove any pinch points.

5 – Applying the waterproofing.

Koster Deuxan 2c is a two part thick film sealant. Deuxan 2c is applied in two coats to the outside surface of the ICF wall. Deuxan 2c can be hand applied with a trowel or, for larger areas, spray applied using a peristaltic pump.

6 – Backfill Protection.

It is likely that the walls will be backfilled against. This means it is a good idea to protect the waterproofing from damage. Delta Geodrain Quattro offers great protection against impact damage and also improves the external drainage around the structure to reduce the pressure on the waterproofing layer.

7 – Internal Systems. 

Often for new build residential projects it will be necessary to provide a secondary waterproofing system internally in order to meet the requirements of a structural warranty provider.  An internal Delta cavity drainage membrane is the best way to provide this extra system.


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Need help in selecting or installing the right waterproofing system?

Let us know our team of waterproofing experts will be happy to help.


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