After applying and scoring the scratch coat of Portland cement mortar, what is the minimum time it should be set and cured?

After applying and scoring the scratch coat of Portland cement mortar, what is the minimum time it should be set and cured?

• A. Three Days
• B. One Day
• C. Two Days
• D. Five Days

Answer: (C)

The main idea is that the scratch coat must be given enough time to set and begin curing so it can develop enough strength to receive the next coat and form a good key for bonding. Portland cement needs hydration to gain strength, and until it reaches a basic set, the surface is too soft to support another layer without cracking or delamination. Waiting two days provides sufficient time for the mortar to stiffen and for moisture to hydrate the cement, making the surface stable enough for the brown coat to be applied and adhere properly to the scratch pattern. In normal conditions, this is the practical minimum. If the weather is hot and dry, you can still aim for around two days, but you might need to monitor moisture and cure appropriately; in cold or very damp conditions curing will take longer. Shorter waits, like one day, risk weak bonding, while longer waits (three or five days) unnecessarily slow the process unless adverse conditions require it.

The main idea is that the scratch coat must be given enough time to set and begin curing so it can develop enough strength to receive the next coat and form a good key for bonding. Portland cement needs hydration to gain strength, and until it reaches a basic set, the surface is too soft to support another layer without cracking or delamination. Waiting two days provides sufficient time for the mortar to stiffen and for moisture to hydrate the cement, making the surface stable enough for the brown coat to be applied and adhere properly to the scratch pattern. In normal conditions, this is the practical minimum. If the weather is hot and dry, you can still aim for around two days, but you might need to monitor moisture and cure appropriately; in cold or very damp conditions curing will take longer. Shorter waits, like one day, risk weak bonding, while longer waits (three or five days) unnecessarily slow the process unless adverse conditions require it.