Knowing the substrate on which you are going to work and the coating that you are going to use before preparing the surface for subsequent painting is essential for ensuring a good result, one which is durable over time and against the external factors to which it will be subjected.
It is common to think that the covering or coating that is to be applied to a surface is the most important factor when protecting a part.
However, special attention must also be paid to the substrate or surface, as this is the base on which the subsequent coating will be applied.
The condition of the substrate directly affects the coating as regards its:
- Stability (Adhesion)
- Durability
- Effectiveness (Protection)
- Useful life
For example: A house built on sand or clay against one built on rock
If we were to build a house on sandy or clay terrain, it is most likely that the life of the construction would be shorter than that of a house built on rocky terrain. Therefore, the most satisfactory final construction result would be that built on rock.
The substrate and the coating
There are two determining factors when painting a surface: the substrate and the coating. The type of coating that we choose will depend on the nature of the substrate, and the substrate will require prior preparation that will depend on the coating.
Generally, coatings are developed for a particular type of substrate or material, so that if applied on another type of substrate for which it has not been designed, we would certainly not obtain the desired result.
All substrates require a minimum surface preparation. Depending on the type of coating to be applied, a more or less demanding surface preparation will be required. For example, a product for a sandblasted steel surface may not be appropriate for a different material, such as a wire brushed steel surface.
For this reason, it is very important to refer to the data sheet of the product that is going to be applied and follow all the application instructions.
How do you choose the preparation method?
Before starting the preparation of the surface, it is necessary to determine the methods and procedures that are going to be used depending on the specific characteristics of the substrate.
For example, to prepare a steel substrate, the criteria established in standard ISO 8504-1:2020 are taken as a reference.
The first aspect to bear in mind when choosing the preparation method is that the type of substrate on which you are going to work must be known.
According to this ISO standard, we can group metal substrates into three different types:
New metal
We must check:
- The type of initial metal.
- The degree of initial oxidization.
- The existence of any chemical treatment (chrome plating, phosphate coating).
- The presence of chemical substances or contaminants.
Previously coated metal
We must check:
- The type of existing coating to determine its nature, adhesion, DFT, presence of contaminants, etc.
Primed metal
Check the type of primer used in order to ascertain its nature and apply a compatible coating.
- The existence of damage or deficient underlying work (such as welding).
- The presence of contaminants on the surface.
The following variables must also be taken into consideration:
- Desired degrees and levels of preparation of the surface, if any.
- Equipment and personnel available for carrying out the work.
- The coating system that you are going to use.
- The regulations and laws that affect the preparation and coating process.
- The cost of the work.
A solid foundation before surface preparation
As we have seen, having a good understanding of the substrate and the coating to be updated is the first step before proceeding with surface preparation. This will determine the choice of coating and how we should treat the substrate to prepare it for application. Therefore, this step is the foundation for achieving the expected result.
