Surface preparation for painting can be time-consuming and expensive, but it’s necessary in order to ensure that the asset you are protecting has a long lifespan. Without proper surface preparation (which means a clean, well-prepared surface area), you can run the risk of premature coating failure. 

We want to walk you through one of our favourite techniques for surface preparation in blast shops and provide 5 other techniques that we frequently use in our business on a day-to-day basis. 

Did you know that experts suspect nearly 75% of premature failures are a result of improper surface cleaning? Meaning, it doesn’t really matter how detailed and complex your systems are, if you aren’t preparing the surface properly, you have only a 25% chance of lifespan survival rate. This makes surface preparation for painting an incredibly important and integral step to the overall success and lifecycle of that asset.  

 

TIPS & TRICKS FOR SURFACE PREPARATION FOR PAINTING (MORE SPECIFICALLY IN BLAST SHOPS) 

 

A lot of blast shops that we encounter use steel grit and steel shot to remove the mill scale and get their surface profile. Inspectors that are new and unfamiliar with blasting of a steel plate at a shop facility vs. on-site may not be unaware that staining and discolouration can be a result of the plate sitting outside or getting stored in a certain way. This can result in confusion or mismanagement of surface preparation for those who are inexperienced. 

About Steel Plates & Mill Scale: Vis. Standards 

When dealing with surface preparation for painting in a blast shop, we generally use the vis standard- Vis-1, made by NACE and SSPCThe pictures provided in the VIS-1 standard were done by using silica sand to provide the surface cleanliness. Silica sand is white and leaves a very clean white surface, hence the term white metal or near white metal blast.   

Typically with a steel plate, depending on the size and the thickness, will have quite a bit of mill scale on it, requiring a very hard blast to properly remove the mill scale. This can lead to a lot of shadowing and discolouration.  

Though silica sand gives a nice white blast to the surface that you are preparing, here in Ontario you are not permitted to use silica sand for abrasive blasting due to the connection and relation it has to respiratory illnesses and it’s high water content (which can cause it to prematurely break down blasting equipment). 

So instead of silica sand to remove mill scale, we get a variety of grit such as garnet steel shot, steel grit, cornhusks, etc. There is a multitude of different media available for use, each giving its own appearance. So, when considering either hiring or working with a skilled inspector, make sure they know what appearance each abrasive will give in order to meet the specified surface preparation standard. 

Quick Tip for Surface Preparation Comparison 

If you’re having trouble using your vis standards, one of our favourite techniques for comparing surfaces in surface preparation is to get a steel plate that’s similar to the surface of the item thats being blasted. Once you have 2 surfaces to compare, blast the comparison steel plate and put it aside. Be sure to do this before you start the blasting job, to ensure you are getting the surface preparation to the highest standard possible. 

This way, if you happen to change inspectors or someone else shows up to the job, everyone involved will have a visual comparison that represents the surface preparation cleanliness that you are looking for and has been agreed to.  This will eliminate a lot of headaches and hassles down throad and relieves a lot of unnecessary discussions because everyone agrees to the same standard and all involved are on the same page.  

 

surface preparation for painting

Other Abrasive Blasting Tips & Techniques You Can Apply to Surface Preparation in Blast Shops 

1. Measure PSI at the Nozzle 

Never assume the reading on your compressor gauge is the true pressure as there are many areas that pressure loss can be attributed throughout your blasting system. Test the pressure PSI at the nozzle using a hypodermic needle-style nozzle pressure gauge. The ideal place to check for pressure is behind the nozzle holder. The ideal pressure rating is 90-100 PSI.  

2. Try a Gentler Medium First 

In order to avoid over pressurizing the surface area, and to avoid discolouration, try working with a gentler medium first before using a more abrasive material. This is why we work with corn husks instead of silica sand.  

3. Increase Shine with Glass Beads 

We recommend using glass beads made from soda-lime glass to achieving a smooth, bright finish. These glass beads are cost-effective and help with environmental impact as they are recyclable and can be used many times before you need to replace them.
 

4. Don’t Overuse Blast Nozzles 

We’ve seen this more times than we can count – overuse of blast nozzles while dealing with surface preparation for painting to help the contractor save money. This is something that should be avoided as a poorly performing nozzle can affect the overall results of the project.  For every 1psi of pressure loss at the nozzle contributes to 1.5% production loss. 
 

5. Use specialized media for polishing, etching and removal 

Consider specialized media for specific blasting features such as polishing, etching and removal. For example, silicon carbide works for fast etching of stone and glass. It also provides a sharp cutting action and can work well for paint and rust removal. Also, consider an aggressive steel media for polishing applications or removing rush, paint or mill scale from steel surfaces. Choosing a media that’s right for the job you are working on is vital to the longevity of the asset.  

If you would like more information on working in blast shops or would like us to come out and look at some of the materials you have that need to be fixed, contact us today for a free consultation.  

Jen Bourque

Author Jen Bourque

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