SAISC TECHNICAL surfaces , so mechanical wire brushing which tends to polish the steel is not great for preparation for corrosion protection systems . iii . Sand / shot blasting does roughen the surface , we are looking for a profile of between 40 and 80 microns to get a good paint adhesion . iv . Fortunately sand / shot blasting is well specified in internationally accepted specifications . Swedish specification SIS05 59 00-1967 “ Pictorial surface preparation standards for painting steel surfaces ” was the original document in this regard . An updated version has been released in the form of ISO 8501-1:2007 . These documents have a series of full colour pictures that show what the various defined levels of cleanliness of the steel after preparation will look like based on the degree of surface rust before the cleaning process begins . ST specifications cover wire brushing , SA specifications cover sand / shot blasting . v . These documents do not touch on surface roughness requirements . ( The guidelines for the profile requirements comes from the paint manufacturers ). Refer to ISO8503 which covers “ Surface roughness characteristics of blast cleaned substrates ”. f . Quality assurance requirements . i . There are a few simple steps that if followed could implement a quality assurance programme for painted surfaces . ii . As the SAISC always does , we recommend that the contractor set up a quality control plan ( QCP ) which covers every step in the preparation , cleaning and painting process based on : 1 . Engineers / architects specifications 2 . Do ’ s and don ’ ts from SANS
1200HC and SANS / ISO 12944 3 . Paint manufacturers recommendations 4 . Blast / wire brush requirements 5 . Record measurements taken at relatively close centres on each piece of steel being treated such as visual inspection for removal of hydrocarbons etc , surface roughness , visual inspection of grade of cleanliness ( arguments in this regard can be settled by making sample pieces before work commences of what is agreed to be ( say SA2.5 , one kept by the applicator , one kept by the inspector ), wet film and dry film thicknesses , etc .
6 . Overview records of temperature and humidity read ( say hourly ).
Conclusion
There is no doubt that whatever corrosion protection system you choose to use , good preparation is basic to a long lasting life of the system .
This means attention to detail at every stage from detailed drawings , through cutting shaping and holing the steel right through to welding and final fabrication inspection , followed by hot dip galvanizing and / or painting with intermediate and / or final inspection .
By just taking a short cut bypassing any one of the preparation steps , your selected corrosion control systems could end up fatally flawed .
Steel Construction Vol . 40 No . 1 2016 23