Portal: Repair

As long as the hollow clay tile wall is rigid and stable, the shotcrete application should not impact the finished side plaster. Shotcrete impacts in a very localized area directly where the material stream is hitting the substrate. Research shows that the localized force is about 90 to 100 lbs (40 to 45 kg) when shooting directly on the substrate. If shooting a thicker wall using a benching method, most of the force is carried by the previously shot material, so it would have less impact. If the clay tile needs to be stiffened, an initial thin layer could be shot to provide additional thickness before the final thickness is placed. Though we don’t have any specific information about vapor transmittal, concrete used in shotcrete placement inherently has a low w/cm and less water in the mixture to bleed or create vapor. We haven’t had any reports of plaster or grout falling off the inside of masonry walls that have been structurally enhanced with shotcrete.

Here are the answers in the same order as your list.

1. Shotcrete is just a placement method for concrete, so there is no “off-season.” However, as with cast concrete, cold weather placement needs more planning and material delivery controls. As wet-mix shotcrete material is predominately delivered by ready-mix trucks, the concrete should be delivered at 50°F (10°C) or higher. Then once shot, if temperatures are less than 50°F, the concrete should be protected by insulated blankets or the area enclosed by vented heaters to keep temperatures above 50°F. We also don’t want to shoot onto frozen surfaces.
2. We use small line concrete pumps standard in the concrete industry.
3. Concrete pumps and air compressors are generally diesel-powered engines. Pump engines range in horsepower from 75 to over 200 hp, depending on the pump size. Your application is of relatively low volume, so one of the smaller pumps should do fine. We also use relatively small air compressors, and many contractors who work in residential or metropolitan areas use equipment equipped with sound reduction. The sound at the point of placement where the air-accelerated material stream exits the nozzle is generally just the sound of the airflow.