Thick water is a generic name for a liquid that has been heavily loaded with fine material — most often cement, clay (bentonite) or silt — so that it becomes near pasty, and is used for soil injection, sealing or transporting excavated material. Its opposite is “thin water” or clean water.
Forms of thick water
In construction practice, “thick water” appears in several forms:
- Cement grout — water with cement, sometimes sand and admixtures, for injecting cracks, sealing joints or filling voids
- Bentonite slurry — water with clay, used as a support fluid for diaphragm walls and bored piles
- Slurry or silt — water with fine soil residues, generated by dredging and tunnel boring
- Cement-bentonite mix — combined for permanent sealing of sheet piles and membrane structures
Application
Thick water serves several roles in construction:
- Soil injection — in foundation repair, thick water is pumped under pressure into the ground to fill voids and raise soil strength
- Compensation grouting — during underground works, cement grout is injected to compensate for settlement of neighbouring buildings
- Support fluid — in diaphragm walls and bored piles, bentonite slurry keeps the soft soil walls open
- Joint filling — fluid cement grout penetrates even hairline cracks and seals them
- Drilling fluid — in directional drilling, thick water carries cuttings to the surface
Properties
A good thick water has:
- Sufficient density — to displace or support soil (1,050 – 1,300 kg/m³ for bentonite)
- Pumpability — viscosity suitable for hoses and grout lances
- Stability — does not separate quickly during transport
- Adequate penetration — fine enough to enter cracks or pore spaces
Processing
- Mix in a high-shear colloidal mixer for best results
- Transfer to an agitator (slow mixer) that keeps the paste homogeneous
- Pump with a mortar or injection pump
Related terms
- Bentonite
- Grout
- Grout injection
- Diaphragm wall
- Foundation repair
Want to know more about construction terms? Visit our knowledge base on fredsdiyplans.com.