Help with figuring out the problem of cracking putty on the decorative surface.

[Allen]

Please tell me about the problem of cracking putty on the decorative surface.
The formula is :

cement 400, quartz sand + heavy calcium carbonate gradation 600, Wacker redispersible polymer powder 3%, 20,000 viscosity cellulose ether 0.15%, water reducing agent 0.3%. 6mm glass fiber chopped strands 0.15%

 

[Cassie]

The cracking of this formula is normal; the more the rubber powder is, the more cracking it is, and the construction is not good. The formula should be sticky, but the strength is OK. To solve the cracking problem, you should add about 8kg redispersible polymer powder.

 

[Roy]

Double the amount of cellulose, and the viscosity should be more than doubled. 3 kg of water-reducing agent is too much; either stop adding or add 0.5 at most.

 

[Rony]

Pure redispersible polymer powder will not crack but can alleviate the rigid shrinkage cracks of cement and increase the flexibility/cohesion/bonding strength/impact resistance/aging resistance of mortar putty powder. Hydrophobic redispersible polymer powder is better than acrylic powder, and the cost is relatively higher. The film-forming is directly not water-resistant and needs to be saponified in the alkaline environment of cement to become water-resistant.

 

[Luis]

How much sand is this recipe? It is unnecessary to reduce the water; how thick is the wipe? The amount of cellulose must didn’t use enough.

 

[Scott Kaplan]

The amount of cellulose ether is low, and the water retention is not good

 

[Alex]

Even if the redispersible polymer powder is added to 20% and will not achieve the waterproof effect. Instead, the degree of cracking will be more serious, and may occur warping and peeling phenomenon because ordinary redispersible polymer powder will melt and rot when exposed to water.