Repair mortar has strict requirements on materials. Controlling the quality of raw materials is a prerequisite for making good repair mortar. The lack of quality in one of these raw materials can lead to the collapse of the entire system.

1 Cement

At present, according to market conditions, P·O42.5 cement and P·O52.5 cement are generally chosen. 20~30min initial setting of sulphoaluminate cement or double fast cement. Because the cement quality of each cement manufacturer is different. A mortar laboratory is required to test cement indicators. It is necessary to choose the cement that suits you as the cementing material for the repair mortar.
In the author’s experience, it is best to choose products from local famous brand cement factories, which is beneficial to the stability of the product. Two types of cement may be used in repair mortar formulations. Ordinary Portland cement and double-fast cement are used together, and compatibility tests must be conducted on each batch of cement.

2 Silica fume

Silica fume is the smoke and dust that escapes with the exhaust gas during the high-temperature smelting of industrial silicon and ferrosilicon in industrial electric furnaces, and is collected and processed by a special collection device. In the escaping smoke, the SiO2 content accounts for about 90% of the total smoke, and the particle size is very small. The average particle size is almost in the nanometer range. Therefore it is called silicon powder.
At present, the quality of silica fume on the market is uneven, and it is difficult to distinguish between good and bad. Choosing high-quality silica fume can increase the surface strength of the repair mortar. Inferior silica fume not only fails to improve the performance of the repair mortar, but may also have the opposite effect.

3 Aggregate

Generally speaking, if you are repairing thick layers, use medium sand (6~120 mesh). If repairing in thin layers, use fine sand (40~120 mesh). Or adjust the fineness of the sand according to the actual requirements of the repair interface. If the repair project has high quality requirements, it is generally recommended to use quartz sand. You can also choose high-quality natural sand, manufactured sand, and tailings sand.
In terms of sand quality control, testing is carried out in strict accordance with national sand standards. Repair mortar has very high sand grading requirements. Reasonable sand gradation can produce high-quality repair mortar. Unreasonable sand gradation can easily lead to the collapse of the repair system.

4 Additives

Repair mortar generally uses polycarboxylate water-reducing agent, low-viscosity cellulose, redispersible polymer powder, reinforcing agent, rheology agent, defoaming agent, expansion agent, coagulant, interface agent, curing agent, etc. Due to the different quality standards of each additive factory, the performance varies.
If one additive in the formula does not perform up to standard, the entire repair system will suffer. It is best to use additives from the same manufacturer. Currently, the use of complex additives is popular on the market, making the repair mortar formula easier to prepare.
Landcel redispersible polymer powder