- Painting shall not be carried out under the following environmental conditions
- The environmental temperature is less than 50C.
- The surface temperature is less than 30C above the dew point.
- The relative humidity is over 85%.
- Surfaces are subjected to wetting before painting.
- Surface temperature is above 500C.
Checking of paints and thinners
Check whether paints and thinner supplied are the same as those described in the specification.
Mix the components of the paints according to the specific ratio and with the use of mechanical stirrers or paddle mixers. Stir sufficiently to allow the paint mixture to become homogeneous.
To improve the workability of the paint in accordance with the change of temperature, thinning is sometimes necessary. It should be noted that an excessive, deteriorate film properties and hiding power.
If the paint contains small pieces of skin or any small lumps, it should be filtered through a cloth filter or a wire filter with 60-100 mesh.
Once mixed, the paint supplied in two or three components in separate containers must be used within the specified time limit.
Over coating Interval
Paint should be allowed to dry in accordance with the manufacturer’s recommendation before over coating.
Inspecting of dry film thickness
The dry paint coating should be measured using a dry film thickness gauge. If the required coating thickness has not been achieved, it should be touched up with airless spray or by brush or roller.
- The brush should not be dropped deeply into the paint as this will overload the bristles and fill the brush heel with paint which ids difficult to remove.
- When paint is to be applied, the brush should be held at an angle of about degrees to the surface. Several light strokes will transfer much of the surface to be coated. The paint should then be spread to cover the surface and provide a uniform coating.
- After the surface is completely covered with paint, the painted area should be brushed crosswise to ensure uniformity, and finally brushed lightly to smooth out brush marks and laps.
- After the painting work is finished the brush should be well cleaned using specified thinners.
- The equipment used should be suitable for the intended purpose, capable of properly atomizing the paint to be applied, and have pressure regulators and gauges and parts as specified.
- Paint ingredients should be kept uniformly mixed in spray pots or other containers during painting, and while the paint is continuously or intermittently mixed mechanically.
- Spray equipment should be kept clean.
- Inbound pressure to the airless spray pump will vary with the length of the hose, the exterior temperature, and the viscosity of the material. An adjustment of air pressure should be made so as to achieve a uniform atomization of the material.
- The spray gun should be moved in a parallel direction and perpendicular to the surface to obtain a smooth and uniform coating. The overlap of each pass should be 50%.
- Be careful not to spray towards people, since the sprayed paint or thinner is under higher pressure.
- After an application of the multi-component type paint is finished, all airless spray machines should be well cleaned using specific thinners.
Film thickness control
The wet layer of film shall be measured using a wet film thickness gauge such as a roller gauge or a comb gauge, within a few seconds after the paint is applied to minimize the effect of solvent evaporation.
Any coated substrate should be kept as it is until the paint film completely dries. Paint applied to such areas where drying conditions are not ideal should be allowed to dry using ventilation.
Coating systems recommended per environment (with approximate comparison to SABS ISO 12944-5)
|Substrate||Recommended method of protection||Total DFT (um)||Environment||Equivalent system SABS ISO 12944-5|
|Steel||Alkyd + Alkyd(alk+alk)||70 – 100||*||S1.05|
|Steel||Zinc phosphate + alkyd (ZnPO4+alk)||100 – 125||*|
|Steel||Epoxy + epoxy(ep+ep)||225 – 275||*||S1.34|
|Steel||Epoxy + polyurethane (ep+PU)||150-225||*||S1.27|
|Steel||Epoxy + Epoxy + polyurethane (ep+ep+PU)||190 – 265||*||S1.34|
|Steel||Epoxy zinc + HBepoxy (ep+HB ep)||180 – 220||*||*||S3.21|
|Steel||inorganic zinc silicate + epoxy MIO + polyurethane (IOZ+MIO+PU)||200 – 275||*||S7.12|
|Steel||Steel epoxy + epoxy + polyurethane (ep+ep+PU)||450 – 530||*|
|Steel||epoxy zinc + epoxy + polyurethane (epz+ep+PU)||195 – 235||*||S7.07|
|Galvanized Steel||epoxy + HB epoxy (ep+HB ep)||260 – 320||*||*||S9.11|
|Galvanized Steel||epoxy + epoxy (ep+ep)||325 – 425||*||*||S9.12|
|Galvanized Steel||epoxy + polyurethane (ep+PU)||225 – 275||*||*||S9.12|
As defined in EN ISO 12944-2:1998
*C1-Very low corrosion environment
C3 – Medium corrosion environment
C5M – Very high (marine) corrosion environment