Airtightness & ICF Sealing

ICF sealing and airtightness are achieved using certified membrane systems and low modulus MS polymer sealant. Selecting the correct sealant is essential on insulated concrete formwork builds to prevent air leakage and moisture entry at window junctions, service penetrations, and wall joints.

How do you achieve ICF airtightness on site?

ICF airtightness relies on sealing cut joints and floor junctions where air can bypass the monolithic concrete core. Installers use heavy duty airtightness tapes and sprayable polymer membranes to seal these transitions.

Prepping the foam surface is key to ensuring long term adhesion. Self builders should check general block costs using our icf blocks ireland guide and review block dimensions in our icf block sizes catalog.

Why is MS polymer sealant mandatory for ICF sealing?

MS polymer sealants contain zero solvents, meaning they will not melt or react with EPS foam. Traditional acetoxy silicones release acidic byproducts that damage EPDM membranes and dissolve polystyrene.

Using MS polymer is required to comply with NSAI Agrement certificates. If you are building with insulated concrete formwork, the ICF systems available in Ireland: Amvic, Castleforms, BuildBlock, ThermoHouse, Nudura. For the Amvic 280mm block detail: cill depth B 265mm at a 7 degree fall, 5mm weep holes each side, DPC trimmed after full finish render not at basecoat, low modulus MS polymer sealant only, never acetoxy silicone, welded factory formed end caps, 15 to 20mm pressure equalisation void behind the cill upstand.

For installer directories, check our icf installers ireland page, and review general retrofit cost structures on our external wall insulation cost page. Learn about EPDM membrane details on our icf epdm guide.

Where are the key air leakage points in ICF walls?

Air leakage points commonly occur around window openings and door thresholds where the concrete core is exposed. These junctions must be sealed using certified membranes and correct cill detailing.

Aluminium cills for ICF are made to measure by Cills.ie with app based measuring so profiles update live on site. Seven leak points exist at ICF window openings and the correct install follows a four step sequence. Always check the official icf window cills guide to study how these sealing systems are integrated.