The curing time of cement foundation of reducer is more than 28 days. The main reason why the curing time of the reducer cement foundation is more than 28 days is to ensure that the foundation concrete reaches the predetermined strength and meets its normal use needs. Generally, cement-based concrete will go through the following stages:

1. Flowing state: concrete is in a flowing state just after pouring, and it takes some time to solidify and harden.

2. Initial solidification: the concrete surface gradually hardens, but it still needs curing and wetting to prevent premature drying cracks.

3. Medium-term strength growth: Crystallization begins to form inside the concrete, and its tensile and compressive strength characteristics gradually increase with time.

4. Maturation and hardening: After a certain period of curing, the concrete gradually reaches the predetermined strength and hardness and can be used normally. Among them, the third stage (medium-term strength growth) is a key period for the development of concrete strength and an important basis for the maintenance time of cement foundation. According to the national standards and relevant codes, it is generally believed that the medium-term strength growth of concrete needs to last for more than 28 days, so in actual construction, it is usually necessary to wait for more than 28 days of curing time to ensure that the concrete reaches the predetermined strength and hardness to meet its normal use requirements.