A brief understanding of the role of primers is helpful when choosing an exterior primer.

1. Priming creates a surface with even absorption so topcoats dont appear patchy. Bare substrates or dirty walls usually have variations in their absorption level and without a sealer/undercoat this can show through in the topcoats as uneven colour and varying sheen levels. ROCKCOTE Ecostyle Sealer/Undercoat or MUROBOND Primer are best for this job. 

2. Priming makes topcoats go on easier and spread further. Hence omitting a primer will not necessarily save on the overall cost of a job.

3. Priming increases topcoat adhesion. This may not be noticeable at first but can mean peeling paint in the future. Specialised primers such as ZINSSER Smart Prime and MUROBOND Primer can be used to adhere to glossy or hard to stick to surfaces.

4. Primers can enhance topcoat colour. A coat of primer is useful when trying to paint over strong colours. ROCKCOTE Ecostyle Sealer Undercoat has the best hiding power for this. It is also common to tint primers to grey, or half strength of the top coat colour, underneath strong coloured topcoats to help give the colour more opacity. ROCKCOTE Ecostyle Primer or MUROBOND Primer are the best ones for tinting. 

5. Priming can be used to seal in stains such as mould, watermarks, smoke, oils, tannins, efflorescence and rust. Zinsser Smart Prime is a specialised primer for this purpose.