If a bonding coat is to be applied (see mixing details under 6.4) the material should be sprayed to give a thin (nominal 2 mm thickness) coverage, and minimum air pressure should be used to give as heavy a textured finish as possible, to give a mechanical key to the subsequent coating of SLV. A coverage of 20% - 50% of the steel surface should be achieved.
The maximum thickness of SLV, which can be sprayed in one pass, will depend on the orientation of the steel surface and whether the steel is painted. (Whether or not the paint has been coated with Limpet Primer.) SLV can normally be applied in layers 10 - 25 mm in thickness. If the final coating thickness is 25 mm or greater, it is preferable to apply an initial thin coating of 10 - 12 mm and allow this to set off for a few hours, after which a thicker coating can be applied, this also achieves a neater finish.
Caution should be exercised with extended vertical surfaces. In contrast, 25 mm layers can be applied in one pass to horizontal steel members. Experience will soon determine the optimum approach to be taken.
The initial set of SLV is typically 4 - 8 hours, depending on ambient temperature and humidity. It is preferable to apply successive coats immediately after the initial set is obtained rather than leave the SLV for two to three days to cure. If the first sprayed coat has fully cured, then the surface should be wetted before applying more material, and care should be taken to ensure that the surface has not been contaminated by other trades. Where multi-layer applications are required, the surface texture of each sprayed layer should be left ‘as applied’ to provide the maximum keying power to subsequent coats.
Compressed Air Supply
Control the air supply at the nozzle to ensure that the desired coating thickness and texture are achieved. Too much air leads to overspray, bounce-off, fine texture and increased density, and hence increases material consumption.