Prepare and Mix Paints, Coatings, and Allied Materials
This domain tests whether you can turn a container of coating into a usable, correctly proportioned product. Questions cover mixing ratios, pot life, induction time, thinning, viscosity, straining, colour tinting, shelf life, compatibility and allied materials such as primers, putties, sealants and hardeners.
Core rules
- Read the manufacturer's product data sheet and SDS. Confirm the base and hardener pair, the mix ratio by volume or weight, pot life at site temperature, induction time, and maximum thinner percentage.
- Measure, do not estimate. Use a graduated container or scale. Add hardener to base, not the reverse, and scrape the sides. Mix with a paddle at low speed to avoid air entrapment.
- Respect pot life. Mix only what can be applied within it; heat shortens pot life. Never thin a catalysed product beyond the stated limit or reactivate a gelled mix.
- Strain coatings through a filter bag or mesh to remove skins and grit.
- Check viscosity with a viscosity cup where specified. Thin in small increments and record the amount.
- Tint to an approved sample under the specified light; record batch numbers.
Worked example
An epoxy floor coating is 4:1 base to hardener by volume and has an 8-hour pot life at 25°C. You need 3.0 L of mixed product. Base required = 3.0 × 4/5 = 2.4 L; hardener = 0.6 L. At 35°C the pot life may fall by half, so mix in smaller batches. If the site needs only 2.0 L now, do not mix 3.0 L and leave it; the unused portion will gel and be wasted.
Traps
- Mixing a partial kit by eyeballing the ratio.
- Adding thinner to a waterborne coating because it looks thick.
- Using an expired hardener or a different brand's component.
- Forgetting induction time for products that require it.