Surface preparation is the most important job to be carried out prior to painting. It is very worthwhile noting that paint cannot help to hide defects in fabrication, or overcome the dents and bends or for that matter give aesthetic finish for the press parts Unless and until the surface is prepared properly.
Steps to be followed for Surface Preparation :
First of all clean the Surface to be painted by a suitable thinner so as to remove dust particles, grease, oil, loose matter and previous rust.
Sanding with suitable sand paper (emery paper) is very necessary to make the surface rough so as to get a proper adhesion and binding of paint to the surface.
Grinding with sander can remove the welding splatters and there by make the surface evenly levelled.
For removing the previous rust on the job pretreatment chemicals for eg. phosphating solutions or three in one solutions can be used.
For Control Panels or Furnitures like Steel Cupboards and decorative articles, Automotive parts, etc '7' Tanks system should be practised,
For heavy industrial jobs and structures like angles, channels, etc. and for heavy machineries, boilers, the jobs are to be sand blasted so as to remove the previous rust thorouqhly.
Primer Application. After proper preparation of the surface the job is now ready for painting,
Once the rust loose matter, etc. is, removed by sand blasting or by '7' tank system the surface has to be immediately given a coat of suitable primer so as to protect it further from getting rusted.
Primer can be applied by Brush, Spray, Airless Sprayguns, etc. as required and proper use of suitable thinners is very important for the brushability and sprayability of the paint.
Putty Filling After applying primer the uneven dents and cracks in the surface are to be taken care of by putty filling.
Before application of finish coats the putty applied has to be hard dry and the loose putty particles are to be removed by proper sanding.
Application of Finish Coat : Application of finish coat is done only after the primer coat is 'Hard Dry'. Loose primer surface or improper drying of primer may ruin the finish coat and proper adhesion cannot be achieved.
The primer surface is to be made a bit rough by sanding with a smooth emery paper, so as to yet a proper binding of the finish coat Filtering of the paint through a thin
muslin cloth or a nylon cloth with suitable mesh is necessary so as to remove the dust partlculars , and loose matter in the paint. Finish paint has to be diluted by suitable thinner in proper proportion so as to get the optimum brushability and sprayability.
As far as possible the finish coat has to he properly sprayed by using spraygun and proper compressor pressure. Improper brushing may leave brushmarks and affect the aesthetics of the finish.
Before applying any primer or paint by a spray gun the water and moisture from the compressor has to be thoroughly removed
A second coat of finish paint has to be applied if necessary so as to give a further protection and aesthetic finish only after the previous finish coat is thoroughly hard dry.