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A self-leveling mortar may look perfect immediately after mixing: high fluidity, easy spreading, and a smooth slurry.

But after several minutes, the mortar becomes noticeably thicker and stops flowing properly.

Adding more water may temporarily restore fluidity, but it can also cause segregation, lower strength, and surface defects.

The better question is:

Why is the mortar losing flow so quickly?

The polycarboxylate superplasticizer is one of the main components controlling flow in cement-based self-leveling mortar.

However, the same PCE can behave differently with different cement systems.

Flow loss may increase when:

• the cement source changes;
• the binder contains more reactive components;
• PCE dosage is too low;
• the selected PCE provides strong initial flow but poor retention;
• other additives interfere with dispersion.

Do not judge a PCE only from the initial flow diameter.

Measure the mortar again after 5, 10, and 20 minutes.

A slightly lower initial flow with better retention may sometimes perform better in actual application.

Self-leveling mortar needs enough working time to spread and heal before setting begins. If the accelerator-retarder balance is too aggressive, the mortar may start building structure too early.

Typical signs include:

• good initial flow;
• rapid thickening;
• shorter working time;
• poor self-healing;
• visible trowel or spike-roller marks.

When this happens, check the complete setting-control system rather than simply adding more PCE. Flow retention and healing time are recognized fresh-mortar properties in standardized self-leveling mortar testing.

A suitable amount of cellulose ether for self-leveling compounds helps improve water retention and stability.

But excessive dosage can increase viscosity and reduce flowability.

This creates a common formulation problem:

More cellulose ether improves stability, but the mortar becomes too resistant to flow.

SidleyChem’s existing self-leveling technical content also notes that cellulose ether dosage needs to stay within a reasonable range because excessive addition can reduce flowability.

The target is therefore not maximum viscosity, but enough stability without sacrificing self-leveling performance.

High temperature can shorten the usable working time of a self-leveling mortar. If laboratory tests are performed at 20–25°C but the product is later used in a much hotter environment, the field result may be very different.

When flow loss suddenly becomes worse, check:

• dry-mix temperature;
• mixing-water temperature;
• room or jobsite temperature;
• substrate temperature.

Do not change the formulation before confirming whether temperature is contributing to the problem.

Rapid flow loss in self-leveling mortar is not always caused by insufficient water.

The main causes may include:

• unsuitable PCE;
• poor PCE-cement compatibility;
• overly fast setting;
• excessive cellulose ether;
• high temperature;
• unbalanced formulation.

The best solution is to evaluate initial flow, flow retention, setting behavior, and mortar stability together.

The target is not simply high initial fluidity, but enough working time for the mortar to spread, level, and form a smooth surface.