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Dear Multi-Tech,

Hello,  I have a question about your acrylic filler and granite materials.. One, should the clear coat be white in color,  it looks cloudy, not clear. Two, everything for the repairs pastes are different in consistency from body fillers for spreading and shaping. Third, the product is very hard when cured making it harder to sand. Is this how it’s supposed to be? It doesn’t seem correct to me being a body repair tech for 25 years, clear is never cloudy and this filler repair when cured is hard as nails and not easy to sand?

Max

Hello Max,

The cloudiness of the clear is correct for the product. It is rich in resin bringing a high solids content to the product. However, this will not cause it to be visible on the surface of the repair.

Everything else you describe is normal. The hardness of the end product will provide a higher quality repair with greater endurance in the spa and bath surface repair applications.

Your comments about the consistency of the acrylic resins are normal opinions from an auto body person’s experience base.

Most auto body products are developed for ease of workability, while giving good performance in the relatively dry environment that vehicle surfaces must endure.

Body filler, spot putty’s, primers and automotive coatings (having ease of use) will all absorb water and fail, especially when used for a bath tub or spa surface repair.

photo 1

 

 

 

 

 

 

 

The picture shows how auto body fillers fail when used for bath or spa repairs.

Since bath tub and hot tub environments are wet environments (water, heat and chemicals), they require resins which contain high levels of special additives to prevent moisture absorption, so they will provide the expected durability and performance.

Thus, the completed repair is much harder than in auto body repair materials.

At the same time, these special additives impart color and translucency to the initial clear resin.

The chemistry of these additives are designed to be compatible with the base resin and provide the desired properties for superior performance.  Unfortunately, this means they may be more difficult to work with.  A hard surface in a bathtub or spa repair results in better performance.

A good rule of thumb; if the product sands, shapes and works easily (softer), it will absorb water and deteriorate in a very wet environment.  Auto body pastes and epoxies fall in this category.

Even though these plastic products may be more difficult to work with, they have been designed for the purpose. These issues are minimized with the use of proper tools.

Aggressive grinding and shaping will require applying the filler in multiple layers. To fill voids, skim coat applications, using the same filler, will provide maximum performance in the finished repair.

Your comments and observations are expected. We have many repair techs from the auto body industry using our products.  Understand there will be a learning curve while adjusting application and working techniques when transferring to Multi-Tech surface repair products.

I hope this helps, and good luck with your repairs.

Rob Clos

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TO:  Multi-Tech Products

I have a spa that has developed crazing in the acrylic surface.  See the photo.  How can it be repaired?

John

Crazing2

TO:  John

Repairing a large, crazed area is complicated, since it requires removal of the affected acrylic surface.  A hammer and chisel is normally required to remove this material.  Be carefult not to punch a hole completely through the wall structure.  Then our Acrylic Filler and color-matched coatings are required to refinish the area.  Refer to the procedures for repairing spas with the Quick Glaze system.  Often, the cause of crazed acrylic is the presence of trapped styrene in the polyester resin backing system.  So to prevent re-occurrence, you should use a heat gun to evaporate any residual chemicals in the exposed FRP prior to starting to apply the acrylic filler.  See our explanation of crazing in the website, http://www.multitechproducts.com.

Remember that crazing affects only the appearance of the surface.  It will not result in water leaking through the structure.  In some instances, where there is minimal crazing, it can be softened with heat.  Using a heat gun, you would heat the surface up to about 220ºF, which will cause the crazing to relax and reduce the severity of the micro-cracks.  One acrylic manufacturer suggests that wiping the area with a paste wax, or equivalent, sometimes works to fill in the micro-cracks to make them less visible.  You could try some of the MTP paste repair kits.  Using a cover on spas is very important in avoiding these and other surface issues.

I hope this has been helpful.

Rob Clos

TO:  Multi-Tech Products

I am a spa surface repair contractor. and have been asked to inspect and repair an acrylic spa for a manufacturer.  What should I do to provide a comprehensive inspection report to the manufacturer?

Thanks,

David

 

TO:  David

The most frequent types of surface damage to acrylic spas are blisters, discoloration, cracks and crazing.  Please read our website to gain and understanding of the description and causes for each of these problems.  You will see that a common thread through many of the problems is a chemical attack.  Therefore, when your mission is to repair the surface, you should also look for signs of a chemical exposure.  Since misuse of chemicals can void a warranty, the manufacturer will be very interested when there is indisputable evidence of neglect and misuse.  Chemical damage to the acrylic surface or mechanical components can be clear evidence of a contributing factor to the surface failure being reported by the customer.  Staining, fading, cracking, crazing, and blisters can all be at least partially due to improper maintenance of water chemistry, or the use of strong chemicals for cleaning, etc.  For example, organic chemical solvents can be absorbed by the acrylic, which weakens it, and contributes to cracking or crazing due to excessive stress.  Certain chemicals can attack the pigments, and cause fading or discoloration.  There have been past reports of problems caused by aromatherapy chemicals added to water by the owner.  Repair contractors often see calcium deposits at various locations in a spa.  This is a clear indication that water chemistry is not properly maintained.  Even some of the chlorinating chemicals (e.g. solid tablets)  can cause discoloration when they are in close contact with the surface for extended periods.  So, you should ask the owner questions to determine their practices for maintaining water chemistry, and list the chemicals they use.  Also, inquire about any other type of chemical that has been added to water for any reason.  You want to help educate the owner about proper chemical use, and warn them about things that cause problems.  If you do not know this, check with the manufacturer.

I hope this information helps to improve your expertise as a professional.

Regards,

Ken Wolfe

MTP Consulting Chemical Engineer

 

Cultured Marble Repair

TO:  Multi-Tech Products

I know you specialize in repair of bathtubs and spas, but will your materials serve as a repair for a burn on a cultured marble sink countertop?  See the picture.

Thanks,

Bill

Cultured Marble

TO:  Bill

Yes, our materials will repair cultured marble surfaces.  The most common burn is from a cigarette.  Most of these are repairable.  For information on how to accomplish a repair, and some of the limitations, see our procedure at: http://www.multitechproducts.com/content/Procedures/Cultured%20Marble%20Repair%20Procedures.pdf

Cultured marble products normally have a clear topcoat over a colored surface.  If the burn goes into the colored portion, repair becomes more complex.

I hope this helps.

Rob Clos

President

TO: Multi-Tech Products Corp.

I have a new acrylic spa that has brown spots all over the acrylic and the side panels.  What caused it, and how do I get rid of them?  Please see the attached photos.

Thanks,

Kevin

SPA 2 SPA

 

 

To: Kevin

The brown spots appear to be diphenylmethane diisocyanate (MDI), which is the most common isocyanate used in polyurethane foam.  Polyurethane coatings and foam are used both as reinforcing and insulating materials in spas.  MDI is the “A” component in the two-part resin system, and has an amber color.  Part “B” is an organic alcohol, and is normally white.  The MDI will continue to get darker in color as it oxidizes with age.

The MDI can be on these surfaces due to over spray during the manufacturing process.  Since it can take hours for the color to appear, the manufacturer may not have seen it during their cleaning steps.  Also, if the workers have it on their hands and tools, and touch these surfaces, it will leave a residue.  This occurs when factory workers are not diligent in maintaining cleanliness.

There are multiple considerations for removal.  If it is foam ( i.e. mixed parts “A” & “B”), sanding may be required.  Also, if the chemical has been absorbed into the surface, it may require sanding.  Sand in a circular motion with 400 grit followed with 600 grit wet/dry sandpaper using water.  The acrylic surface can be renewed after removal by following our “Buffing and Polishing” procedures and/or video.  Polishing with medium grit compound using a 2500rpm electric buffer will bring back gloss.  Polishing would not be required on granite textured surfaces.   See our procedures for granite repair for more details.  If it is on the artificial wood or plastic side panels, sanding may remove the color making it necessary to re-stain or paint.  You can test in a non-conspicuous area.  You can inquire with the manufacturer about their repair recommendations.

If you desire to avoid sanding and surface renewal, you can test the effectiveness of using solvents to remove the foam chemicals.  Start by using plain water with about 10% ammonia and some household dish detergent.  Water reacts with isocyanate to form non-toxic carbon dioxide gas.  If it fails, try isopropyl alcohol, which has low risk.  Again, if unsuccessful, try standard paint lacquer thinner.  Finally, try a commercial xylene solvent, being careful to use a minimum quantity.  When finished, the xylene should be completely cleaned from the surface using water and the alcohol.  Xylene is not recommended for long exposure to acrylics, since it will lead to stress cracking.  The acrylic used for spas is cross-linked to impart superior chemical resistance compared with standard acrylic products.  So be careful to remove all excess solvent.

I hope this helps to resolve your problems.

Ken Wolfe,

Consulting Chemical Engineer

To:  Multi-Tech Products Corporation

I have recently purchased an acrylic spa, and the salesman strongly recommended that I keep a cover over it when it isn’t being used.  Why is this?

Thanks,

Jim

To: Jim

There are several valid reasons for using a cover on a spa when it is not in use.

The first is obvious.  A properly designed and insulated cover greatly improves the energy efficiency of the unit.  The cover slows the rate of water evaporation, which removes heat from the water remaining in the spa.  Also,  evaporation control will result in maintaining proper chemistry of the water, which will reduce usage of the chemicals needed.  These facts help control operating costs of the spa.

It is probably understood by everyone that ultra-violet radiation from the sun is deleterious to all plastic materials.  Acrylics have very good resistance to sunlight, which is why it is commonly use for windows, skylights, aircraft canopies, etc.  But, it is not perfect.  Although, we may not understand all of the ways sunlight harms polymers, we know we should minimize exposure.  So, we strongly recommend using a cover when the spa is not in use.

Another issue regarding acrylic spas is the formation of cracks or crazes.  Both of these phenomena involve failures due to excessive stress.   First, lets review the construction process.  Acrylic spas are produced by heating and forming a flat sheet into a mold shaped like the spa.  The sheet is stretched from the top rim into the bottom of the mold cavity (foot well of the spa).  Obviously, several things happen.  As the sheet is stretched, it becomes thinner, and weaker.  The acrylic thickness in the foot well is normally in the range of .030″.   This stretching imparts stresses, and some of the stress remains after it is cool.  Then most “spa shells” are reinforced with polyester resins containing chopped fibers of glass.  So it becomes a composite structure with each material having unique properties.  Stresses exist throughout the spa shell, and arise from the thermoforming and reinforcing steps, and from the weight of water and people using the spa.  Material strength is effected by temperature and exposure to chemicals.

Crack(s) in the acrylic layer occur when stress exceeds the material strength.   Stress can be based on thermal changes or induced mechanically.  If covers are not used properly, the surface (acrylic) is subject to wide swings in temperature from  sunlight during the day to very cool night temperatures.  This heating and cooling can result in fatigue failure cracks from repeated expansion and contraction.  The mechanical stress created by the combined  weight of water and people also can lead to cracks.  Therefore, these need to be minimized using adequate support devices under the shell – particularly under the seats.  Increased temperature reduces material strength, so if stress and temperatures are high, a crack can occur.  Since stress is typically highest at the spa rim, cracks generally start there, and propagate into the center.  The use of a cover will minimize effects of temperature, and reduce probability of crack formation.  See the picture for an example. of cracks at the rim.

Cracks.

 

 

 

 

 

Another type of crack phenomena is crazing.  A craze is different from a crack in that it can’t be felt on the surface, and it may be able to support a load.  Many studies have demonstrated that two conditions must be present for stress crazing to occur on an acrylic spa surface.  They are 1) high stresses within the acrylic and the 2) presence of a stress-cracking liquid or solvent. The presence of only one of these conditions does not cause crazing.  Both must be present.  Crazes form at highly stressed regions.  Stress can occur due to thermal or mechanical forces.  Crazing occurs mostly in amorphous, brittle polymers like polystyrene (PS), acrylic (PMMA), and polycarbonate (PC).  The acrylic used for spas is a specially designed to withstand the normal spa environment, but it will fail under harsh conditions.

Crazing2

Crazing appears as very small micro-cracks on the surface (see photo).  The stress pulls apart the tightly coiled polymer chains in the material. This condition makes it easier for liquid molecules to penetrate the molecular structure of the acrylic and diffuse throughout the polymer chains.  The crazing mechanism is the stress cracking molecules act as a lubricant, which allows the polymer chains to separate from one another when stressed, creating very small cracks. Depending upon the amount of stress and the aggressiveness of the chemical agent, the small cracks continue to grow in size.   Since the strength of the acrylic declines with temperature,  the use of a cover will minimize thermal stress, and lower the risk of crazing.  Since the over-riding cause of crazing is the presence of a chemical, it shows the importance of avoiding the use of stress-cracking chemicals on the acrylic surface.  Only use approved chemicals for cleaning and maintenance of water chemistry.

Finally, many manufacturer’s warranties are voided when covers are not used.

For more information on crazing, please click on the link below:

Tech Bulletin Stress Crazing.pdf

I hope this helps to explain your question.

Ken Wolfe

Consulting Chemical Engineer

Effects of Hard Water in Spas

TO:  MULTI-TECH PRODUCTS CORP.

ACRYLIC SPA REPAIR CONSULTANTS AND MATERIAL SUPPLIERS

I am the manager of warranty service for a major manufacturer.  One of my customers has provided these pictures, and asked for our opinion of the cause of the white deposits around the surface.  Can you help?

Thanks,

John

image (1)image (2)image

To: John

The pictures indicate a common problem associated with hard water that is prevalent in many areas of the country.  You probably have experienced the same hard water problems in coffee makers, bathtubs and shower devices.  They are found frequently on household faucets, drains and bathroom grout.  When appliances are not regularly cleaned with products formulated to remove calcium (e.g. Lime Away®), they develop deposits of the chemical salts present in hard water.  These deposits are basic, and need a weak acid to dissolve them.   When commercial products do not do a complete removal, a stronger acid solution is required.  An economical and readily available product, muriatic acid,  can be used.  Muriatic acid is actually hydrochloric acid, and is commonly used for swimming pool water chlorine maintenance.  However, it must be diluted with water before use in removing hard deposits.  Muriatic acid is a strong oxidizer, and should be used very cautiously.  It is also recommended to use heavy kitchen-type latex gloves, goggles, and a chemical cartridge respirator with cartridge(s) when using strong acid solutions.  You can also refer to the safe handling recommendations of the manufacturer of the chemicals.  A fan can be used to blow harmful vapors away from the work location.  Pure acid is likely to do damage to some surfaces, so it should be diluted using equal amounts of acid and  distilled water.  You may even want to test a small area to confirm that it does not attack the surface.  Be especially careful using it on vinyl covers, electronic devices and other plastic components within the spa.   Apply the solution with a clean towel, scrub with a nylon bristle brush, and rinse with clean water.  You may need to repeat the process to remove 100% of the deposit.  A wet/dry vacuum can be used to remove the acid solution and rinse water.

In order to prevent a new build-up of calcium, the owner should use calcium deposit removal products in a regular maintenance program.  The frequency will depend on the hardness level of the water, and the frequency of total water replacement in the spa.  It is also imperative to maintain overall water chemistry.  Improper use of water chemicals can also lead to deposits.

Total hardness is one measure that is used to maintain water chemistry.  It is a measure of all the dissolved minerals such as calcium, magnesium and sodium. For practical purposes, calcium hardness is the common reference used in pool and spa water chemistry.  The recommended level for calcium hardness is 200 – 400 parts per million, and both high and low levels can result in problems.  It should be closely monitored.

High calcium hardness results in scale formation on surfaces as well as scaling in the pipes, plumbing and filter. In extreme cases the water becomes dull and cloudy with the calcium precipitating out into the water rather than onto a surface.  High calcium levels will also irritate users, causing sore eyes as an example.

If high calcium level is a result of spa chemicals, draining some or all of the water and replacing it with fresh water will lower calcium hardness.  If the cause is the fill water, commercial hardness reducers or chelating agents will bond with the calcium to keep it trapped in solution.  If the user is uncomfortable using the home kits for water maintenance, a professional can provide the service at most spa/pool dealerships.

I hope this helps.

Ken Wolfe

Consulting Chemical Engineer

Customers frequently inquire about whether their problems could be occurring due to contamination in their repair materials purchased from MTP.  So here is an explanation for most of these issues.

Rob Clos

  •   Contaminated product

It is highly unlikely to receive MMA or Quick Glaze components from MTP with contamination.  Contamination usually happens when multiple technicians handle the same product in the factory or in the field. This can happen where two or three shifts occur in a factory. Contamination can occur from alternative products being substituted for MTP products for solvents, reducers, thinners, hardeners and toners. To assure trouble-free results, use only MTP brand components to assure compatibility and quality consistency.

When finished with a repair session discard any remaining mixed products.  Do not attempt to re-use at a later time or date.   This can be especially unforgiving when multiple technicians are using the same product or mixtures from one shift to the next production shift.  The paint products, both basecoats and topcoats, are mixed with various thinners and other special purpose chemicals prior to spraying on the surface to be repaired.  Therefore, a prepared mixture may last for days before becoming unsprayable.   If they are stored and used later, there is high risk of changing the formula, creating issues, if additional chemicals are added to the mixture.  For example, multiple temperature thinners added to the product can have an adverse effect on the performance of the product.

The absolute best practice is to prepare fresh materials using proper components each time a surface repair session is initiated. Check for contamination, yellowing or amber tones in the product source before mixing.

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.

untitled1 (2)

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)

untitled3 (2)

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.

Topcoat1 topcoat2TO: Multi-Tech Products

We are having problems with the MMA system products we recently purchased for repairing our acrylic bathtubs.  See photos.  The white basecoat is becoming yellow after we apply it.  After we fix the defect and refinish it in our plant, the repaired area of the bathtub becomes yellow. We have many difficulties with it. We’d like to know why this is happening.

I hope to hear from you soon.

Thanks,

Danilo

Dear Danilo;

The most common cause of MMA basecoat yellowing is the absence of the protective clear topcoat.  It is either that it was not used at all, or it was accidentally removed by sanding and buffing excessively.

It is imperative that all repairs have the clear coat designated for that repair system. The MMA system basecoats will yield a good initial repair without clear coat. However, overtime, yellowing and discoloring can occur under the right conditions.

It appears that the unit in your picture had not been sold and installed.  If it has been stored outside, and exposed to sunlight and weather, the basecoat will turn yellowish due to the effects of this exposure.  Even indoors, soaps, cleaners, shampoos, hard water, dirt and UV will yellow the base coat that has not been clear coated.

The MMA System must be used with the MMA clear topcoat. It should be thinned only with the MMA Monomer to be effective. A factory can experience excellent long term repairs on bathware using the MMA System complete with Clear Coat.  I would recommend getting this information to your production and QC department so they can incorporate the clear coat into the process.

The Quick Glaze and Granite Repair Systems must be clear coated with the K2000 Clear Coat.  Professional repair contractors should be equally diligent in always using the appropriate clear topcoat to avoid call back complaints.

Please let me know if this resolves the issue or if you experience any other performance issues with our systems.

Thank you for asking the question about yellowing.

Rob Clos

Danilo, just in case that there might be another problem source, I have included the following information that has been known to cause yellowing and other issues in an MMA system repair.  It for sure will be helpful in your quality control procedures.

1)  Oil and high moisture in the air lines:

It is typical for factory air source lines to carry a high concentration of oil and moisture. The compressor itself can be a moisture producing machine. Even small portable compressors produce heat, that in return generate moisture in the lines. 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. Oil by nature can create a amber color to it however, oil typically will cause fisheye and effect smooth flow out of the spray coating.

Water traps simply do not work efficiently.

untitled1 (2)

This picture  shows a common type water trap, which our experience shows  are ineffective in eliminating all liquids from the compressed air.   Regardless of the size or quality of the device, it will retain a portion of the water, but not 100%.

An industrial grade desiccant filter tower works best.  This product is recommended, and can be installed at the air supply source to serve the repair area in manufacturing plants.

untitled2 (2)

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 and where little moisture is present in the lines.   MTP sells these units for use by repair professionals.

untitled3 (2)

With the air lines drained of moisture, a desiccant air filter stops moisture and oil from going through to the repair surface. This filter will also 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.

2)  Contaminated product:

It is highly unlikely to receive new product from MTP with contamination. Contamination usually happens when multiple technicians handle the same product in the factory or in the field. This can happen where two or three shifts occur in a factory. Contamination can occur from alternative products being substituted for MTP products for solvents, reducers, thinners, hardeners and toners. To assure trouble-free results, use only MTP brand components to assure compatibility and quality consistency.

Do not re-use or mix old, used product for multiple applications. This can be especially unforgiving when multiple technicians are using the same product or mixtures from one shift to the next production shift.  The MMA product, both basecoat and the topcoat, are mixed with thinners and air dry on the sprayed surface.  Therefore, a prepared mixture may last for days before solidifying when stored. But it can lead to over thinning or  contamination when left on the shelf or mixed in the pot.  For example, multiple temperature thinners added to the product can have an adverse effect on the performance of the product.

The absolute best practice is to prepare fresh materials using proper components each time a repair job is initiated. Check for contamination, yellowing or amber tones in the product source before mixing.