Fabric formed concrete.
Fabric formwork is a construction method that uses engineered fabrics to shape and confine insitu concrete as it sets. It is typically a lost formwork: the fabric stays in place after the pour and becomes part of the finished structure. It earns its place where rigid formwork is impractical, underwater, on irregular profiles, or in areas with restricted access.
- 01 What it is
- 02 How it works
- 03 Concrete performance
- 04 Filling techniques
- 05 Applications
A form that takes the shape of the site.
Engineered woven fabrics shape and confine insitu concrete as it sets. The fabric is a lost formwork: it remains in place after the pour and forms part of the final structure, though it rarely performs a structural role once the concrete has cured.
That matters most where rigid formwork cannot go. Underwater, on an uneven seabed, around piles already driven, or in a space too tight to set shutters and strike them again afterwards.
Fabric formwork is the method. What we supply are the two systems built on it, below.
Two systems, one technique.
Concrete mattress
A continuous fabric-formed slab laid over the bed and filled in place, used for berth scour protection, slope protection and breakwater toe. Six variants, from thin flexible sections to 1.2 m bulk.
See the system
Grout bags and sock seals
Discrete fabric envelopes filled in place to close a gap, form a bearing foundation or wrap a connection. Most are small, routine jobs; the same system founded the MOSE caissons.
See the systemSix reasons it gets specified.
Flexible and adaptable
Forms around irregular terrain and structural footprints, rather than requiring the ground to be made to suit the form.
High-quality concrete finish
Porous fabrics allow controlled water bleed, which consolidates the mix and produces dense, durable concrete.
Lightweight and easy to handle
Suited to remote, underwater or congested work areas where craneage and rigid shutters are impractical.
Engineered and purpose-made
Custom fabricated to the geometry and loading of each project, not selected from a catalogue of standard sizes.
Prevents cement washout
Grout-tight yet porous, so the cement paste stays in the form while excess water escapes.
Cost-efficient
Requires less concrete than traditional methods, which reduces both material and transport cost.
Two things the fabric does at once.
Porous yet grout-tight
The woven synthetic fabrics let water 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. That is why a fabric-formed element can be denser than the same mix cast in a sealed shutter.
Insitu filling
The form is filled directly in place: on the seabed, around piles, on slopes, or attached to construction elements, by pumping concrete or grout into it. The fabric adapts to the surrounding geometry, giving a precision-cast element with minimal preparatory work underwater. More on how it is done on site is on installation.
The mix, and what it is designed against.
Each formwork is engineered for its site.
The technique follows the access, not the preference. Five projects, five different ways of getting the form where it needed to be.
La Reunion
Six compartments fitted beneath each pier base in the casting yard, then grouted from the surface once the unit was landed.
Read the case study →Dover Docks
The form goes in condensed and expands as it fills, which is how it reaches a gap it could not be carried into at full size.
Read the case study →Eilat, Israel
Divers position and secure the form on the bed, and the concrete is pumped down to it from the surface.
Read the case study →MOSE Project,
Venice
Filling and monitoring run entirely from a floating barge, with vent sensors confirming contact. No divers in the operation.
Read the case study →Al Faw pile
encasement
A jacket lifted into position around an existing pile, then filled to form a durable encasement in place.
Read the case study →Underwater installation
Concrete is always filled in tremie fashion, from the bottom up, so the rising concrete displaces the water ahead of it and the formwork fills completely.
In-air installation
Above water there is more flexibility in fill direction, but bottom-up filling is still preferred because it minimises trapped air and voids.
Temporary works calculations ensure forms are not overstressed.
Cut risks to the fabric are removed during preparation.
Filling is never done into a completely sealed compartment, which avoids rupture.
Where it is used.
The technique follows the access, not the preference. Five projects, five different ways of getting the form where it needed to be.
- Dense, abrasion-resistant concrete surfaces
- Long-lasting protection in high-energy marine environments, as at the Dunkirk RORO berth
- Reduced maintenance compared with rock armour or precast, and far less material: see Al Faw Grand Port
Over 50 years of getting concrete into places it should not fit.
Proserve pioneered the use of fabric formwork in challenging construction environments. We develop concept solutions, carry out detailed construction engineering, and provide installation guidance. On-site training and demonstration fillings can be arranged so the dive team handles the fabric before it matters.
The design basis is published. Our technical papers set out the research behind these systems, and design responsibility explains where we can take it on.
Frequently asked questions
What is fabric formwork?
Fabric formwork is a construction method that uses engineered woven fabrics to shape and confine insitu concrete as it sets. It is typically a lost formwork, so the fabric stays in place after the pour and becomes part of the finished structure, though it rarely performs a structural role once the concrete has cured.
It is used where rigid formwork is impractical: underwater, on uneven or irregular profiles, and in areas with restricted access.
How does fabric formwork produce better concrete?
The woven fabric is porous but grout-tight. As concrete is pumped in, excess water bleeds out through the pores while sand and cement particles are retained, which consolidates the mix and improves durability.
The result is a dense, abrasion-resistant surface. Proserve standard mix designs use a 0.55 water:cement ratio, conform to EC2 and BS6349, and target a design life of 50 to 100 years.
Can fabric formwork be filled underwater?
Yes. Underwater, concrete is always filled in tremie fashion from the bottom up, so the rising concrete displaces water ahead of it and the form fills completely.
Filling can be carried out by divers, or entirely by remote control from a vessel or platform with no divers in the water, as on the MOSE flood barrier caissons in Venice.
What concrete mix is used in fabric formwork?
Mixes typically use a 0.55 water:cement ratio to ensure excellent pumpability and full filling of the form. Maximum aggregate size is usually 4 mm to 10 mm depending on the application.
Reinforcement can be used, but care must be taken to ensure full filling and concrete quality around it.
Is fabric formwork cheaper than rock armour or precast?
It generally requires less concrete than traditional methods, which reduces both material and transport cost, and it needs no rigid shutters and no dewatering.
It also reduces maintenance compared with rock armour or precast solutions. At Al Faw Grand Port, 430,000 cubic metres of imported rock armour was replaced by 26,500 cubic metres of locally batched concrete.
See it built, or go deeper.
Al Faw Grand Port, 1.75 km piled jetty
Fabric formwork at full scale: 430,000 m³ of imported rock armour replaced by 26,500 m³ of locally batched concrete, with the works taken off the critical path.
Read the case study →Installation
How the forms are positioned, filled and monitored on site, above water and below it.
Read →Marine concretes and grouts
The mixes themselves: pumpability, aggregate, and what is specified for a 50 to 100 year design life.
Read →Technical papers
The published design basis, including PIANC world congress papers on berth scour and fabric formwork.
Read →Concrete somewhere a shutter will not go? Send us the geometry.
Send us the structure, the space you have to work in, and whether the pour is wet or dry. Our engineers will tell you whether a fabric-formed element suits it, what the form would look like and how it would be filled.