What is Fabric Formwork?
Fabric formwork is a specialised construction method that uses engineered fabrics to shape and confine in situ concrete as it sets. Typically a lost formwork, the fabric remains in place after the pour, forming part of the final structure, though it rarely performs a structural role once the concrete has set. This technique is particularly valuable where traditional rigid formwork is impractical, such as underwater or in areas with restricted access or uneven profiles.
Key Benefits of Fabric Formwork
Flexible & Adaptable:
Forms around irregular terrain and structural footprints.
High-Quality Concrete Finish:
Porous fabrics allow controlled water bleed for dense, durable concrete.
Lightweight & Easy to Handle:
Ideal for remote, underwater, or congested work areas.
Engineered & Purpose-Made:
Custom-fabricated to suit each project’s specific needs.
Prevents Cement Washout:
Grout-tight yet porous, maintaining cement paste integrity.
Cost-Efficient:
Requires less concrete than traditional methods, reducing material and transport costs.
How Fabric Formwork Works
Porous Yet Grout-Tight Fabric
The woven synthetic fabrics used in fabric formwork are designed to allow water to escape while retaining sand and cement particles. As concrete is pumped in, excess water bleeds out through the pores, consolidating the mix and improving durability.
In Situ Filling
Fabric formwork is filled directly in place on the seabed, around piles, on slopes or attached to construction elements by pumping concrete or grout. The fabric adapts to the surrounding geometry, providing a precision-cast concrete structure with minimal preparatory work underwater.
Typical Concrete Performance
Mixes typically use a 0.55 water:cement ratio to ensure excellent pumpability and fully fill. Maximum aggregate size is usually 4mm to 10mm, depending on application.
Reinforcement can be used, but care must be taken to ensure full filling and concrete quality. Our standard mix design conforms to EC2 and BS6349, targeting a design life of 50–100 years.
Each formwork is engineered for its specific site conditions.
Typical positioning and filling techniques include:
Underwater Installation
In underwater applications, concrete is always filled in tremie fashion from the bottom up to displace water and ensure the formwork fully fills.
In-Air Installation
Above water, there is more flexibility in fill direction. However, bottom-up filling is still preferred to minimise trapped air and voids.
Quality Assurance
- Temporary works calculations ensure forms are not overstressed.
- Cut risks to fabric are removed during preparation.
- Filling is never done into a completely sealed compartment, avoiding rupture.
Applications
Fabric formwork is particularly well-suited to marine and coastal construction:
- Scour protection around Piled Jetties, Bridge Abutments, and Quay Walls
Long-Term Performance
Thanks to its water-management capabilities and tailored fit, fabric formwork produces:
- Dense, abrasion-resistant concrete surfaces
- Long-lasting protection in high-energy marine environments
- Reduced maintenance compared to rock armour or precast solutions
Proserve Expertise
With over 50 years of experience, Proserve has pioneered the use of fabric formwork in challenging construction environments. We develop concept solutions, perform detailed construction engineering, and provide installation guidance. On-site training and demonstration can also be arranged to ensure project success.
Contact The Expert
Contact The Expert
George Hawkswood
Engineering Director