Different types of primer. There are many different types of primer on sale, each with its’ own specific purpose. Below is a brief overview of their uses, including good points and bad points, to help decide which type to use for any particular job.
Etch primers Used as the first coat on any bare metal. Air drying like cellulose, but must usually be activated before use. Spray mist contains phosphoric acid, so adequate spray mask must be used.
** Etch Primers which contain zinc chromate are known to cause cancer and should be avoided **
Cellulose primers/fillers The most well known for diy work. Low-moderate filling properties. Fast drying, easy too use. Spray putties are basically just very thick cellulose primer filler. Normal spraymist precautions suffice.Tends to sink slightly over a longer period due to solvents leaching out. May cause old paints to lift or wrinkle.
Acrylic primers Very similar to cellulose but uses different resins. Slightly better resistance to sinkage.
2-pack Primer Fillers The best choice for quality. Must be activated before use. Excellent filling properties. Easy to apply with excellent resistance to sinkage when cured. Does not usually react with old paint films. Slower drying than cellulose. Isocyanate activators means that proper respirator cartridges or air-fed masks should be used when spraying.
Synthetic Primers/Fillers Not now in common use, except coachbuilders and commercial vehicles. Can be applied over virtually any prepared surface without problems. Fillers have excellent filling properties and very little sinkage when dry. Very slow drying, (up to 24hrs), can react with topcoats if not hard, thick coats may wrinkle.
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