For engineers and contractors, a concrete surface is often judged the moment the formwork comes off. Blowholes and porous patches mean remedial work, and on exposed concrete that reworking is both visible and costly. Controlled permeability formwork (CPF) liners were developed to address exactly this. They produce a dense, hard, virtually blowhole-free surface straight off the formwork and reduce the reworking that surface defects usually create, especially in exposed concrete areas.
Zemdrain and Zemfrasa
Silva Global supplies two Max Frank products for enhancing cast concrete surfaces in Australia: Zemdrain and Zemfrasa. Both draw water and air out of the concrete surface during the pour to produce a denser, harder surface, but they are distinct products with their own installation methods.
Zemdrain is a CPF liner made of polypropylene and supplied in rolls. It is fixed to the formwork with clamps or staples before the pour and completely removed afterwards, with no release agent required.
Zemfrasa delivers the same controlled permeability benefits as Zemdrain but incorporates a self-adhesive backing, making it particularly suitable for steel formwork, complex geometries and applications where stapling or clamping is impractical.
Zemdrain is available in single-use and reusable versions; the reusable MD version can be used two to three times, and testing at TU Munich found that surfaces cast even on its third use were smooth with very few visible pores. Zemfrasa can likewise be used two to three times.
Where it earns its place
CPF liners are particularly useful for concrete exposed to aggressive chemical or mechanical environments: wastewater and sewage treatment plants, drinking water structures, transport infrastructure, and structures near the sea and under water such as harbour walls, ports, locks and canals. For much of Australia’s coastal and marine infrastructure, where chlorides in the air and water drive premature deterioration, that resistance is a direct specification driver.
For drinking water tanks, Zemdrain Classic TW is tested and approved to the highest drinking water criteria and minimises the cavities where microorganisms and algae can otherwise colonise. For architectural and exposed concrete, it delivers the fair-faced finish described above. It can be made to measure for circular tank formwork and is also suitable for tank ceilings and slabs, as well as precast elements.
Why engineers and contractors specify it
The practical case for a CPF liner starts at stripping. The main reasons it is specified are:
- A dense, hard, virtually blowhole-free surface straight off the formwork
- Less remedial patching and reworking after stripping, especially on exposed concrete
- A high-quality architectural finish on fair-faced concrete
During compaction and for hours after the pour, the liner drains excess water and air out of the surface zone, lowering the water/cement ratio at the surface and drawing fine particles to it. Once the liner is removed, the result is a dense, hard surface with minimised blowholes.
For exposed and architectural concrete this matters on more than one front. Fewer blowholes means less remedial patching after the forms come off, and because the liner assists curing while it is in place, it also reduces the risk of the cracks and microcracks associated with early surface drying. The liner deaerates and drains the concrete as well, producing a characteristic almost void-free, matt, slightly textured surface with a more intense colour than conventional concrete, which reads as a genuine architectural finish rather than a repair job.
No release agent is needed, so there is no release-agent contamination on the finished face.
The finish also lasts
The benefits extend well beyond appearance. By producing a denser, harder concrete surface, controlled permeability formwork improves resistance to water ingress, chloride attack, carbonation and abrasion. Independent testing and long-term project performance have demonstrated improved durability, making the technology well suited to infrastructure expected to deliver decades of service.
Talk to Silva Global
Silva Global supplies both Zemdrain and Zemfrasa in Australia. Specifying either at the design stage improves the finish on day one and protects the asset over its service life. Our team can help match the right product and installation method to your formwork and your project.