Tag Archive: bathtub

TO: Multi-Tech Products

I recently completed a cosmetic damage repair on a shower wall surround. I used my standard repair filler, color coating and methods. The repair failed as the filler fell out of the prepared area while the coating bonded well. I remember not recognizing the material but proceeded with my usual methods anyway. It was a small crack and the structure was solid. When I used my grinder to prepare the crack, I found a material with two or three layers. It had different colors to the layers. The thin bath ware top white color, a pure white plastic like layer, and the structural layer similar to a composite reinforced structure. The structure layer did not smell like fiberglass when I ground into it some. What do you think it was, and what is the proper way to repair it so it will hold?

Dear Steve;

It sounds like you found a product made from what is called “co-extruded” in the industry. This material is less expensive than traditional materials and is becoming more popular in economy products. You will find them at your local Home Centers. Manufacturers continually seek materials and processes to lower manufacturing costs. Historically, most bath tubs and shower products have been manufactured from cross-linked, cast acrylic sheet or gel coat. Both are reinforced with FRP (polyester resin with embedded glass fibers). Cast acrylic sheet is the most expensive acrylic on the market, and the cross-linked variety was specifically engineered for bathtubs and spas. Therefore, it has the best balance of physical and chemical properties for these applications.

The co-ex product you experienced is made by extruding a two-layer sheet – the top is a lower molecular weight, un-cross-linked acrylic, and the bottom is ABS (acrylonitrile-butadiene-styrene copolymer). Typically, the sheet is .125″ thick with the top layer being about .025″ and the bottom layer about .100″. When formed into bathtubs or shower walls, it can then be reinforced with FRP, polyurethane (PU), or have no reinforcement. PU may have glass fibers in the resin, and it can be a high density foam or a smooth coating. Sometimes it is reinforced with fiberboard strips or panels.

You mentioned there was an odor when grinding the structure. This is usually the best way to establish identity of a polyester resin. Simply use sand paper (320 grit) to sand the material in question before proceeding with a repair. Grinding may be required to expose the different layers. Polyester resins will have a distinct sweet smell with sanding or grinding friction. After the sanding test to confirm that it is a polyester, it is safe to use similar polyester resins for filling and reinforcement purposes. If there is no polyester odor, use our binding resin for reinforcement. It is formulated to adhere to PU and other plastic surfaces.

We would also recommend verifying the structural strength and integrity of the repair zone before applying the color coatings. Be certain there is no movement or stress to the area when hand pressure is applied. If there is, remove any filler and start over with the repair.

When repairing the cosmetic surface of bath products made with “co-ex” , our materials and processes work well. Our MMA or Quick Glaze systems perform very well as the color coating. In fact, since the lower molecular weight acrylic is not cross-linked, coatings adhere to it better. However, compared to polyester resins, it is more difficult to achieve adhesion on ABS or PU. So, you should not use Poly-Filler or any polyester resin based crack or putty fillers. The deceiving factor is that most polyester fillers will initially bond to the material for a short period.   However, after time it will lose its adhesion to the ABS or PU, and will break away from the repair zone. Our acrylic filler should be used for this application.

I hope this provides you the necessary information to perform the best repair.  If you need more help, please call or email.


Rob Clos


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.

I would like to add a slip-resistant surface to the bottom of my bathtub.  How do I do it?

Multi-Tech Products Corporation offers components capable of providing a slip-resistant surface to bathtub bottoms, shower bases, tile or concrete floors.  The system was designed for applications where a patch area or a defined non-slip surface area is required to avoiding the entire surface.  Obviously, no surface treatment can totally prevent falls.  These products will increase friction and reduce the likelihood of a fall.  The components include either a clear coat or a color-matched coating with a semi-transparent powder added to provide a textured surface.  The Quick Glaze system provides a great textured surface for porcelain, cast iron, gelcoat and acrylic bath products as well as tile, concrete or metal surfaces.  If the procedure is followed, the final result will have great adhesion to the existing surface, and the appearance will be a consistent textured surface as shown.