Admixtures

The strength and bonding of epoxy based material to the substrate is better than cement based materials. Make sure that you do proper surface preparation by removing dust and loose particles before applying the product. Also, the cleaned surface should be free from moisture while application of the product.

Goodluck.

A couple of points to remember:

1. Make sure you chip carefully and do not cause any damage to structure in the process. No making holes in the structure to support formwork for platforms.

2. Use a good mix design for the plaster, adequate cement, sieve the sand if it is coarse, use a mortar plasticizer or a liquid waterproofing admixture in the mortar, the most important thing is to have a control on the water to cement ratio.

3. Repair structural elements properly, where reinforcement is exposed,provide anti-corrosive coating on the reinforcement and use a bonding agent while patching the concrete.

4. While plastering make mortar in small batches. Workers generally have a tendency to make big batches and then add water when the mix gets drier. This will significantly reduce the water tighness of the structure. Quality control while plastering is the key.

5. If needed go for a double coat of plaster, do shotcrete if possible.

6. Do adequate curing after plastering.

7. Paint the finished building with a good waterproof paint.

8. Good materials, proper technique, workmanship and quality control are very important.

Hennie,

Since the bubbles get less on the 2nd and 3rd cast means either the mold reslease or its amount or application is one of the problems.

I had read in an article which said that mold release agents based on reactive agents generally perform better than barrier type mold release agents.

Try adjusting the mix design, especially the fines content and adjust the vibration time. Try spraying of the mold release using a finer size nozzle. It might be a trial and error process initially till you it right.

Goodluck.