How do I prepare metal fabrication for painting with a specialist industrial coating?
Surface preparation before painting any kind of metal product is key to ensuring the longevity of metal paint and other coatings.
Good surface preparation
Before applying a coating, it is critical to follow a specific surface preparation routine to ensure the coating is applied correctly, evenly and is taken by the material.
If a surface isn’t prepared, it doesn’t matter if you use premium or advanced metal primers or metal enamel paints, they will lose their sheen over time.
- In all cases surfaces should be cleaned and degreased prior to preparation.
- Depending on the object to be processed it may be necessary to steam clean first, to remove any obvious surface contamination. When this has been carried out and the surfaces are dry, degreasing can be commenced.
- A suitable degreasing material should be liberally applied to the surface and allowed a few minutes absorption time in order to loosen the surface contaminants.
- After this the degreasing material should be removed using clean cloths or better still, absorbent paper towel that is lint free and more likely to be changed regularly to avoid a build up of contaminants in the solvent.
Applied degreasing material should not be allowed to simply dry on the surface by evaporation as this does not remove the possible contamination.
Degreasing must be carried out before any flatting or surface preparation. Sanding or flatting carried out on a dirty surface will result in any contamination being spread across the surface and may also force this contamination into the flatting marks. If this occurs the surface could retain the contaminating materials and can cause adhesion and drying problems once a paint system is applied over the affected area.
Once a surface has been degreased it should be kept as clean as possible. After preparing a surface, remove flatting residues and wipe once more with a light application of degreasing material to ensure the removal of any remaining contaminates.
General surface preparation guidance:
Regardless of the type of substrate, the main requirement or preparation is to roughen the surface in order to provide a key for any paint film. A poorly prepared surface will reduce the adhesion of a paint film, leaving it open to premature breakdown and allow, in the case of metal, corrosion to develop.
Thoroughly abrade the surface to provide an improved key. Any rust present should be completely removed by the most appropriate method prior to painting.
Flat thoroughly with a suitable grade of abrasive paper (or disc and orbital sander) to provide a good key. Surfaces already primed at source of manufacture can present problems in that the primer may have been applied over a poorly prepared base. Rust may be present or the primer may be of a low quality.
If there is any suspicion about the quality of the adhesion of a works primer it should be removed. Applying a paint system over a suspect base will not improve its quality or longevity.
Blast cleaning is an efficient method of surface preparation and has two main functions, to remove surface contamination (rust, mill scale) and obtain the required degree of cleanliness to produce a surface profile to improve the adhesion of the paint system.
The accepted standard of defining the degree of cleanliness obtained is Swedish Standard S.I.S. 055900-1967.
The two degrees of cleanliness most quoted from this standard are SA2½ in which the surface is nearly white metal–usually accepted as the commercial standard- and SA3 where it is blasted to white metal with no contamination present.
This may be described as the degree of roughness of a surface after blasting. The peak to valley height of the surface-this is difficult to measure, is expressed in microns, a normal surface profile being in the range of 25-50 microns.
Pronto Paints have been working in metal fabrication for over 30 years and have an exhaustively researched range of metal fabrication coatings. Click here to check out our technical specifications.
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