If your industrial company is like many, you have a concrete floor that contains some oil contamination. Perhaps you would like to place safety lines on the floor, but will paint stick to oily concrete? Below are five things to keep in mind when painting lines on oil-contaminated concrete.[*]
#1: Even under the best of circumstances, concrete is not easy to paint
Even on a perfectly oil-free floor, paint does not stick easily to concrete. “Concrete is a surface,” notes one paint manufacturer, “that presents a number of challenges to paint in terms of adhesion and long-term durability, especially on horizontal concrete walking surfaces.”[1]
In order for the paint to stick, the concrete surface must be carefully prepared, and the prep work generally involves using machinery to roughen the concrete. In painters’ language, the roughening provides “teeth” to help the paint “bite.” Otherwise, paint tends to peel off of concrete due to insufficient bond strength, which is a frequent problem (see ASTM D4259, ASTM D7234, ICRI Guideline No. 310.2R).
#2: Paint does not stick to oil
Oil interferes with the bonding of coatings, which is why oil is referred to in the industry as a “bond-breaker” (see ASTM D4258, ICRI Guideline No. 310.2R, SSPC SP 13/NACE No. 6). All competent contractors know that oil should be removed from concrete before applying coatings such as paint.
#3: It is hard to get oil out of concrete
Getting oil out of concrete is easier said than done. Concrete is a porous material and oil can ooze into it, making it very difficult for detergents and other cleaning agents that are applied to the surface to work. Steam cleaning is somewhat more thorough, but it, too, is often only a temporary solution. With all of these cleaning methods, while the surface will be stain-free immediately afterwards, the oil may well return because oil trapped within the concrete tends to wick up to the surface. This wicking up to the surface is sometimes called bleedback.
#4: Oil bleeding back to the surface can loosen the paint
Oil returning to the surface will interfere with the adherence of the painted safety line, since (as noted) paint does not stick to oil. The paint may eventually start pulling loose from the concrete, especially in heavily trafficked work areas. In other words, oil bleedback can cause the painted safety line to pull up from the concrete.
#5: There is no cure-all for the problem of oil bleeding back to loosen safety lines
Some companies, recognizing the problem of oil bleedback, have sought to develop bonding primers that will emulsify the oil so that it does not loosen the paint or other coating. These products advertise that they reduce “oil bleedback in contaminated concrete.”[2] The existence of products of this kind highlights that oil bleedback is not an uncommon problem.
To use these primers, the concrete’s surface must first be roughened, as the product information sheets stress. Without a rough surface, the primer will not bond firmly to the concrete, and if the primer pulls up, it will take the paint with it.
It is not clear whether these primers, which are designed to reduce wicking up from below, will prevent the horizontal drift of oil onto painted safety lines from adjacent areas of the floor.
Conclusion
Oil-contaminated concrete poses a tricky problem for painting safety lines. If the safety lines pull loose due to the oil, repainting can be expensive.
One option is to use industrial floor marking tape. If the tape ever needs to be replaced, simply remove the affected section of tape, clean the floor, and lay down a new piece of tape.
References:
ASTM D4258, Standard Practice for Surface Cleaning Concrete for Coating (reapproved 2012), ASTM International, West Conshohocken, PA.
ASTM D4259, Standard Practice for Abrading Concrete (reapproved 2012), ASTM International, West Conshohocken, PA.
ASTM D4260, Standard Practice for Liquid and Gelled Acid Etching of Concrete (reapproved 2012), ASTM International, West Conshohocken, PA.
ASTM D4262, Standard Test Method for pH of Chemically Cleaned or Etched Concrete Surfaces (reapproved 2012), ASTM International, West Conshohocken, PA.
ASTM D6237, Standard Guide for Painting Inspectors (Concrete and Masonry Substrates) (2009), ASTM International, West Conshohocken, PA.
ASTM D7234, Test Method for Pull-Off Adhesion Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers (2012), ASTM International, West Conshoocken, PA.
ICRI Guideline No. 310.2R, Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair (2013), International Concrete Repair Institute, Rosemont, IL.
SSPC SP 13/NACE No. 6, Surface Preparation of Concrete (reaffirmed 2003), The Society for Protective Coatings, Pittsburgh, PA.
[*] All the same principles apply to grease-contaminated concrete.
[1] “Painting exterior concrete,” Valspar Paint, accessed December 8, 2014, https://www.valsparpaint.com/en/how-to/exterior/special-challenges/concrete-final.html.
[2] “Concrete Floor Coating Systems – Oil Contaminated Concrete,” CoverTec, accessed January 15, 2015, https://www.covertecproducts.com/concrete-floor-coating/.
