How to paint with primers and undercoats

1. Preparation

Before starting any job, the waterline must be protected as well as any other area which is not to be painted. This can be done with solvent resistant plastic tape.

2. Protection

It is also important to protect yourself with the proper overalls, gloves, goggles and mask. Adhere to safety instructions on the back labels and technical data sheets.

3. Stirring

It is essential to thoroughly stir any type of paint, it is even more critical for two component products. If not, correct drying will not be achieved and it will not provide the expected protection. It may also cause adhesion problems with the subsequent coats. For cans up to three litre, use a wooden/metallic stirrer, for bigger can sizes use a mechanical stirrer. The stirrer should be completely clean to avoid contamination of the paint.

4. Surface preparation

It is absolutely essential to apply paints over of totally clean surfaces, with a correct surface profile as this aids adhesion. Basic steps to follow are: 

  • Wash with fresh water to remove dust, salts and other contamination. If grease or oil are present, then the surface must be degreased.
  • Sand the surface with dry medium grade paper (P150–P180) for fibre glass and even coarser for wooden surfaces. On steel substrates, blasting is the best method but when not possible, matt the surface with very coarse grade paper or any other mechanical method. Always avoid polishing the metal as this will impare adhesion of the paint.
  • Apply the necessary coats of primers.
  • Finally, apply the topcoat or the antifouling.

5. Application tools

  • Roller: A medium or short pile mohair roller, resistant to solvent is recommended. A foam roller may also be used, but with this type of roller there will be more air entrapment, so extra brushing work to remove air will be needed. 
  • Brush: For small areas or touch up works, it should be solvent resistant. It is important to use a good quality brush as its will not loose fibres which may then be left on the paint film. 
  • Spray: Airless spray is the best method for priming, due to its better wetting properties, the film formation and thickness applied without dilution etc. Alternatively, conventional spray can be used, but more coats will be necessary to achieve the specified film thickness and protection. Spray application should only be done by professionals.

6. Application

Apply the recommended coats. Avoid applying under adverse conditions such as strong wind, high sunlight/heat (specially at noon in summer time), low temperatures, high humidity or rain. It is not recommended to add solvents as these reduce the thickness applied and there will be more risk of sagging, splashes, etc.

However, if necessary to apply paint in strong wind or in high temperatures, it is possible to add between 5% and 10% (maximum) of solvent. Only use Jotun thinners and carefully read the product specific technical data sheet prior to use.

Hints for successfull priming

  • Do not apply primers in very high or very low temperatures, in strong sunlight or strong wind.
  • Wet the surrounding floor area to avoid dust on wet paint.
  • Stir the product thoroughly and repeat during application.
  • Use high quality solvent resistant rollers and brushes (mohair or foam type).
  • Consider the pot life of the product after mixing two components products.
  • Check the minimum and maximum recoating interval as stated in the technical data sheets. This is a critical factor when using two components products.