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Basement Waterproofing

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Learn more about ICF Block Waterproofing System

Self-Adhesive External Waterproofing System for ICF Block

Protect  ICF (Insulating Concrete Formwork) Block Construction from water ingress with our highly effective, easily installed self-adhesive external waterproofing systems. With both primary and secondary waterproofing products available, you can ensure your ICF structure withstands hydrostatic water pressure.

What is ICF?

Insulating Concrete Formwork, commonly referred to as ICF, is an innovative and relatively modern type of building construction. It combines the strength of concrete with the excellent thermal performance of polystyrene. Pre-formed blocks are delivered to site ready for fast installation with the easy nature of the build often compared to constructing with large blocks of lego.

ICF is particularly good for basement construction, where the formwork provides the perfect void for cast, in situ concrete pour. If required, this can be waterproof concrete with steel reinforcement placed into the formwork voids.

How to waterproof ICF foundations

When it comes to waterproofing ICF walls, you need a full system that can withstand hydrostatic water pressure and prevent any water ingress. At Permagard, we offer the best ICF waterproof system, combining primary and secondary ICF waterproofing products along with the additional protection of a drainage membrane. Our self-adhesive ICF waterproof membranes are the most efficient and reliable method and a key component of the system.  

ICF Waterproofing Systems

The external polystyrene surface of ICF blockwork lends itself well to the application of a variety of ICF block waterproofing systems. 

One of the quickest and most cost effective options is a self-adhesive external waterproofing system. PermaSEAL Self-Adhesive Tanking Membrane offers a reliable and robust waterproof barrier, conforming to the BS8102:2022 standard.

The simple and fast installation requires the waterbased PermaSEAL ICF Primer followed by overlapping sheets of PermaSEAL Self-Adhesive Tanking Membrane. Benefits include:

  • Highly flexible and instantly waterproof
  • Fast application
  • Water-based primer specifically formulated for polystyrene for excellent adhesion
  • Fully bonded waterproof layer

This Type A (Barrier) system acts as the primary waterproofing to the ICF structure. Self-adhesive external waterproofing systems are considered a safe choice for ICF but it’s important to include further protection in the form of a drainage and protection membrane. PermaSEAL 8 or PermaSEAL 20 Geodrain Membrane protects the primary waterproofing from damage during backfill. At the same time, it helps alleviate water pressure from the surface by allowing water to depressurise into its 8mm or 20mm cavity and fall to a maintainable land drain at the foot of the foundation. A bonded geotextile filter fabric stops fines from clogging the cavity, providing fast and reliable drainage and further lowering the risk of water ingress into the structure.

Installation of PermaSEAL Self-Adhesive Tanking Membrane on ICF Block

PermaSEAL ICF Waterproofing System Diagram

Surface Preparation:

Check the ICF surface hasn’t become dirty after the installation. Any mud or contaminants need to be carefully sprayed or wiped off and the surface allowed to dry before the primer can be applied.


Once the surface is dry and dust and dirt free, roller or brush apply the PermaSEAL ICF Primer, making sure the entire surface is covered. This is a specially formulated water-based primer. Bitumen primers aren’t compatible with polystyrene and will damage the surface. The primer acts to consolidate any dust on the surface and provides the perfect surface for adhesion of the PermaSEAL Self-Adhesive Tanking Membrane.

Primary Waterproofing:

The 1m wide strips of PermaSEAL Self-Adhesive Tanking Membrane are applied to the primed surface of the ICF, with each sheet overlapping the last. A hard roller is used to smooth out the membrane and create a permanent, long lasting bond to the structure. Careful attention must be paid to corner and pipe detailing. Please refer to the installation guide for detailed instructions.

Protective Drainage Barrier:

Depending on the anticipated volume of water, PermaSEAL 8 Geodrain Membrane or PermaSEAL 20 Geodrain Membrane is installed in front of the primary waterproofing. The 2m wide sheets can be installed vertically (like wallpaper) or horizontally. Retaining walls 2m or under in depth allow the membrane to be rolled out in the full 10m or 20m lengths available, meaning less joints to tape. Anything over 2m would require vertical application. Please refer to the technical data sheet for detailed guidance on installation.

Permagard - Providing Solutions. Inspiring Confidence.

If you require further information on External Structural Waterproofing or ICF waterproofing please contact one of our technical advisors on 0117 982 3282. We’re here to help!

You can also benefit from big savings when you buy our PermaSEAL Geodrain Membranes in bulk.   

To find out more then read our Guide to External Waterproofing.