Setting is the chemical process by which cement begins to harden when it comes into contact with water and develops its final strength. It is the first phase of the curing process of concrete, mortar and screed.
How does setting work?
When cement is mixed with water, chemical reactions begin (hydration). This process occurs in two phases:
- Initial set — the mix loses its workability and begins to stiffen. With Portland cement, this happens after approximately 1–2 hours
- Final set — the material is hard enough that it can no longer be deformed. This is reached after approximately 4–8 hours
After setting, the curing process continues for weeks. Concrete reaches its design strength after 28 days.
Application
Setting is relevant in virtually all work with cement-based materials:
- Concrete pouring — the concrete must be placed and finished before it begins to set
- Pointing — mortar in masonry must be allowed to set undisturbed, without drying too quickly
- Screeds — a sand-cement screed must be protected from draughts and direct sunlight during setting
- Tile adhesive — adhesive must be applied within its open time
Factors that affect setting
- Temperature — high temperatures accelerate setting; cold slows it down
- Water content — too much water slows and weakens; too little gives insufficient hydration
- Cement type — rapid-set cement sets in minutes; standard Portland cement in hours
- Admixtures — retarders and accelerators adjust the setting time
Related terms
- Concrete
- Cement
- Mortar
- Screed
- Hydration
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