Ordinary dry-mixed mortar bulges and cracks, what's going on?

[anna]

As shown in the picture, the overall smearing is okay, but the bulge appears within a few minutes after plastering and where is prone to cracking the next day; even watering cannot solve the bulge. Does anyone know what's going on?

 

[anna]

Here are the details

 

[Alex]

It has much to do with cellulose water retention, aggregate formulation, etc.

 

[Ramon Doria]

Have you brushed the interface agent? Another thing, you put plaster before the inner layer is dehydrated

 

[Ankur]

Don’t use silver sand, it is too tiny and thin.

 

[Cassie]

Isn't plastering supposed to apply on both sides, first laying the ground and then plastering the surface? Does this one have only been used one time? Also, if the sand is thin and the gradation is not good, it will be easy to hollow and crack, so you need to tell us the ratio and raw material conditions to find the specific reason.

 

[Scott Kaplan]

Look at the experimental data, the mortar is too thin, and the volume-weight may cause hollowing and cracking.

 

[Roy]

It foams after a few minutes of smearing. However, strictly speaking, it is not foaming but hollowing.
This one does not stick because the workability and initial viscosity of the mortar needs to be better. Try thickener.

 

[Luis]

Unreasonable gradation, thin sand, or low cement content may cause this issue.