Landcel tell you about”Causes of blackening and cracking in gypsum-based self-leveling mortars”.

Gypsum-based self-leveling mortar surface floating black

1. Influencing factor: the amount of water.

The more water is added, the easier it is for the mortar to secrete water, and the easier it is for the black residue to float on the surface.

2. Influencing factor:

Mixing mode mixing time is too short, the water reducing agent and cellulose ether fully dissolved water reducing agent did not play a dispersing role, cellulose ether does not play a thickening role.

3. Influence factor three:

Defoamer dosage is too high, or improper selection, will lead to more floating oil.
Note: During the construction process, there are black substances gradually floating to the surface, and pooled together, leaving a large number of black spots after hardening. The black color is electrolytic slag, fine particles, light weight, will float in the water.

Plastic cracking of gypsum-based self-leveling mortar

I. Influencing factors: interface agent treatment.

1、Did not brush the interface agent, or only water wetting 1~2 times.
2、Start pouring mortar without waiting for the interfacial agent to form a film.
3、Interfacial agent can not form a film.
4、The effective content of interface agent is low.
Note: Cracks appear before the initial setting. Cracks are deeper and longer. More penetration holes are visible on the surface.

Ⅱ, the influence of factors: gypsum characteristics and proportioning effects.

1、 gypsum undercooking phenomenon, dihydrate phase is high, for more than 5%.
2、 gypsum-based self-leveling mortar fluidity loss through time, 30min fluidity loss of more than 30mm.
3、long time to keep no mobility state, like false condensation. There is no internal moisture transfer, surface moisture evaporation, internal moisture can not be timely upward supplement.
4、The dosage of retarder is too much, and the condensation time is too long.
Note: High temperature and windy weather will further increase the cracking phenomenon.
Cracks are produced in the plastic phase and start to appear about 1h after the pouring is completed. Cracks are shallow and present only on the surface.

Late cracking of gypsum-based self-leveling mortar

Influencing factors: There is no uniformity yet.
1、Floor vibration
2、Constriction of grass-roots concrete
3、Excessive rate of dimensional change due to thermal expansion and contraction.
Note: Cracks are produced 1~2 months after construction, and the cracks are penetrating cracks. Across the whole room, from the surface to the bottom, not present in a small, localized area. When cracks appear, the strength of gypsum self-leveling has reached a high level. If the interface is not properly treated, the cracks will also appear hollow drums.