Fosroc construction chemicals
Structural Grouts
Structural grout transfers load from a steel baseplate, machine base or precast element into the supporting concrete. If the grout bridges and leaves a void under the plate, the load path is compromised no matter how strong the grout is. CSA supplies the Fosroc Conbextra range for structural contractors, precast installers and site engineers.
Grout selection follows the bay geometry, pour depth, required flow and the exposure the grout will see in service. The placement method decides whether the grout actually fills the void.
What decides the selection
- Bay size and pour distance under the plate
- Bed depth, including minimum and maximum limits
- Static, dynamic or vibrating load
- Chemical or marine exposure
- Required time to return to service
- Potable water contact (AS/NZS 4020)
- Ambient and substrate temperature at placement
Cementitious or epoxy
Shrinkage-compensated cementitious grouts cover the majority of baseplate and precast work. They are economical at volume, tolerate large bay sizes, handle deep pours where a deep-pour grade is specified, and can be extended with approved aggregate for thick sections. They suit general structural fixing where chemical attack is not a factor.
Epoxy grouts are used where the duty is severe: high dynamic or vibrating loads such as reciprocating machinery and crane rails, thin bed depths, chemical exposure, or where early return to service matters. They cost more per litre, are sensitive to temperature at mixing and placement, and generate heat in thick sections, so bed depth limits in the technical data sheet must be respected.
Placing grout so it fills the void
Pour from one side only and let the grout flow across and out the far side. Pouring from two sides traps air in the middle, which is the single most common cause of voids under a baseplate. Maintain a continuous head of grout using a header box or grout dam so the flow never breaks; once it breaks it entrains air.
Air relief holes in the baseplate help on larger plates, particularly where the plate is wide relative to the pour distance. Do not vibrate a flowable grout: these products are designed to flow under their own head, and vibration encourages segregation and air entrainment rather than compaction.
- Pour from one side only, never two
- Maintain a continuous head with a header box or dam
- Provide air relief holes on wide baseplates
- Do not vibrate flowable grout
- Confirm surface preparation and saturate cementitious substrates
Potable water and specialist duties
Where grout will be in contact with drinking water, AS/NZS 4020 testing of products in contact with drinking water is the relevant reference and the specific product grade matters. Check the product documentation for the grade you intend to use rather than assuming it applies across a whole family.
Underwater placement, high early strength requirements and very deep pours are all served by specific grades within the range. Selecting the general purpose grade for a specialist duty is a common and avoidable error.
Structural Grouts in the catalogue
All Fosroc products →
Structural Grouts: common questions
- Why is there a void under my baseplate after grouting?
- Almost always because the pour was made from more than one side, or because the head of grout was allowed to break part way through the pour. Both trap air under the plate. Pour from one side with a continuous head, and provide air relief holes on wide plates.
- Can I vibrate structural grout to compact it?
- No. Flowable structural grouts are formulated to place under their own head. Vibration promotes segregation and draws air in. Use a header box to maintain flow instead.
- When should I choose epoxy grout over cementitious?
- Where the load is dynamic or vibrating, where the bed is thin, where chemical exposure is expected, or where the plant must return to service quickly. For general static structural baseplates, a shrinkage-compensated cementitious grout is normally the appropriate and more economical choice.
- Can grout be extended with aggregate for a deep pour?
- Some cementitious grades allow extension with approved aggregate above a stated pour depth, and there are also dedicated deep pour grades. The permitted aggregate type, grading and addition rate are specific to the product, so follow the technical data sheet rather than a general rule.
Related systems
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Hand-applied and flowable repair mortars for spalled concrete, exposed reinforcement and structural reinstatement.
Joint Sealants
Polyurethane, polysulphide, silicone and hybrid sealants for movement joints, facades, floors and fire-rated penetrations.
Primers & Bonding Agents
Substrate primers, bonding agents and reinforcement primers that make the system above them work.