Two-pack primers are commonly used in the automotive repair industry and they are applied to vehicles for several different reasons. Because of their high solid content, two-pack primers are capable of producing a higher build which helps to achieve a flatter painting surface after it has been rubbed down. Etching properties also mean that two-pack primers will stick more readily to repairs and bare metal. A good two-pack primer will also repel moisture and alleviate the risk of corrosion for long periods of time.
Always wear latex gloves before handling solvent-based paint or primer products. Check the dates on the label of the primer against the technical data sheet provided to ensure the product has not exceeded the recommended shelf life.
Remove the metal seal on the tin of two-pack primer and take off the lid. Take a metal mixing stick and stir the primer continuously for several minutes. If two-pack primers have been in storage for long periods of time, the high-solid content will sink to the bottom of the tin and the product binders will float to the top. Do not stop stirring until the entire contents of the tin have merged. Once the primer is usable, remove the stirring stick and wipe clean with a general-purpose cloth.
Take a mixing pot and check inside to ensure there are no waste products from previous jobs. Contamination can lead to poor adhesion and slow drying times. Wipe the inside of the pot clean with a piece of general-purpose cloth soaked with cellulose thinners if any old materials are present. Take the mixing stick and place it upright against the inside wall of the pot with the ratio markings facing outward.
Refer to the technical data sheet to establish the mixing ratio. Most two-pack primers are mixed at a ratio of 3:1 or 4:1 with a compatible hardener. It is the presence of two separate packs (in this case, the primer and the hardener) that give two-pack materials their name. Establish how much mixed material you will need before continuing.
Check the left-hand markings on the mixing stick and choose a relevant number that reflects the amount of material you will need. Most mixing sticks are separated in measurements of one-tenth of a litre; if you need a half-litre quantity of primer, select the number 5 on the stirring stick. Pour in the primer carefully until it reaches the level you require. Stop pouring, replace the lid and store the primer away safely for future use.
Take the hardener and check the markings that run through the middle of the mixing stick. If you have poured enough primer into the mixing pot to reach number 5 on the left-hand markings, you will need to pour in enough hardener until it reaches the number 5 on the middle of the stick. Once sufficient hardener has been added, put the cap on the tin of hardener and store safely.
To establish flow through your paint spray gun, a small amount of thinners can be added. The right-hand side of the mixing stick will have markings at 5-percent intervals. Experienced painters will usually add thinners to a level of approximately 10 per cent but this can vary a little according to gun setups and spraying actions.
Stir the primer, hardener and thinner continually until all three products have merged. Wipe the mixing stick clean and pour the contents of the mixing pot into the paint gun, using a filter to remove any lumps or pieces of grit. Wash the mixing pot clean with cellulose thinners to finish.