General Principles of Surface Preparation for Strain Gage Bonding

The purpose of surface preparation is to develop a chemically clean surface having a roughness appropriate to the gage installation requirements, a surface alkalinity corresponding to a pH of 7 or so, and visible gage layout lines for locating and orienting the strain gage. It is toward this purpose that the operations described here are directed.

As noted earlier, cleanliness is vital throughout the surface preparation process. It is also important to guard against recontamination of a once-cleaned surface. Following are several examples of surface recontamination to be avoided:

• Touching the cleaned surface with the fingers.
  
• Wiping back and forth with a gauze sponge , or reusing a once-used surface of the sponge (or of a cotton swab ).
  
• Dragging contaminants into the cleaned area from the uncleaned boundary of that area.
  
• Allowing a cleaning solution to evaporate on the surface.
  
• Allowing a cleaned surface to sit for more than a few minutes before gage installation, or allowing a partially prepared surface to sit between steps in the cleaning procedure.

Beyond the above, it is good practice to approach the surface preparation task with freshly washed hands, and to wash hands as needed during the procedure.

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