Questions regarding causes of fisheyes in repaired bathtub surfaces have arisen over the years.  These can be created from in-plant repairs, or work performed by repair professionals.  They can occur in both MMA and Quick Glaze repairs.  One source for these problems is from oil or moisture in the spray. Following is a description of how they occur.

Rob Clos

1)  Oil and high moisture in the air lines:

It is common for compressed air source lines to carry a high concentration of oil and moisture.   Moisture is created from condensation as pressure and temperature are changed in the compressor.   This is especially true in high humidity regions.  With water present, the lines and tank reservoirs can also rust, carrying oxidation through the lines to the airbrush or spray gun onto the repair, which changes the spray color.  Oil  can impart a color  to the spray, also and it can cause fisheyes in the sprayed surface.

Water traps simply do not work efficiently to remove these liquids.

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The picture above shows a common  water trap, which our experience shows  are ineffective.  Regardless of the size or quality, it will  not remove 100% of the water or liquids.

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An industrial grade desiccant filter tower (shown above) works best to remove all foreign liquids.  This product is recommended, and can be installed at the air supply source to serve the repair area in manufacturing plants.

Contaminated compressed air enters the single tower desiccant dryer and flows downward through a bed of silica gel desiccant. As the desiccant removes the water and becomes saturated, the color of the desiccant life indicator turns from blue to white.  The air then flows through an integrated dust filter up to the outlet port of the dryer. The air is dried to a -40°F dew point and is ready for use.

The following picture shows an in-line desiccant air filter for portable use, especially for repair professionals, and where little moisture is present in the lines.   MTP sells these units. (click on picture)

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With the air lines drained of moisture, a desiccant air filter stops moisture and oil through to the repair surface. This filter will  prevent fisheyes from occurring in the repair surface during the spraying process.

It is common to have so much moisture in the lines that the water is visible when the air pressure is released through the lines.  Therefore, drain the compressor often so there is no visible sign of water.  Also, drain air source lines and hoses. With the compressor drained and air pressure recharged, open up and run dry/clean compressed air through the lines until the lines and hoses are cleared of moisture. Now attach an inline desiccant filter before or after the regulator and you will see a difference in the coating application performance.