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TO: Multi-Tech Products

I am a spa dealer with a customer that has reported a problem on the surface of his acrylic spa. The attached photos show marks appearing on acrylic shell surface. They were in the area around the filter canister, and looked small stone chips that you get on the front end of an automobile. The customer is one off our best on chemical management and takes great care throughout the year to service his tub.

Can you take a look at the pictures and give me your thoughts on the potential cause?  I have never seen this type of issue on a shell. It’s within about a 12″ area within the filter housing but doesn’t seem to be anywhere else.  Could it involve a previous surface repair?

Thanks,

Tony

 

To: Tony

The pictures indicate that this is another example of acrylic pigment fading and/or topical blistering due to exposure to a strong sanitizing agent (oxidizer).  Although rare, we have seen several similar examples over the years.  One acrylic manufacturer has even been able to duplicate this phenomena in the lab using “Tri-Chlor” tablets.  Someone has created this problem with pool chemicals either by using the wrong chemical, or using too much of an approved chemical. The appearance is consistent with what we have experienced with Tri-Chlor.

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The logical mechanism of your example is that a very strong oxidizing chemical (probably in solid form) sunk into the water, fell down the vertical surface creating surface damage as it sunk into the bottom of the foot well or seat.
Acrylic is by far the best material for spa construction, and withstands many harsh conditions, but it is not perfect.
Although this type of damage is rare, it suggests that the industry should increase it’s communications on chemicals to avoid, and how to use the recommended ones.  There is evidence of extreme chemical dispersion into the filter housing, and it reached a very high localized concentration.

From my observations from the photos, I see:

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1. A peeling effect of acrylic. This could happen where a tablet would set for a period of time in one spot on the acrylic.

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2. A scratching effect. This can be where a large round tablet would float and roll around creating damage to the surface. Or the scraping of chemical damaged or repaired acrylic.

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3. Rust in the affected areas. This would be from iron in the water reacting with the oxidizer, and depositing on the porous surface created from the chemical damage.

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4. Attack on the silicone in this area also suggests the presence of strong chemicals in the same area.

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5. Bleaching of the black filter fixture is an additional indication of chemical oxidation.

If there is a repair in this area, the peeling would be of a clear coat. However, the same chemical damage, described above, most likely would have caused the damage to the repair.  A pre-existing repair could only be determined by inspection by a repair pro that has experience with chemical damage.

The good news is that it can be removed by sanding through the oxidized layer (chemical damage) down to good acrylic.  Then it can be buffed and polished to a higher gloss. It will depend on how thick the oxidized layer is, which depends on how long the acrylic surface was exposed to the high concentration of oxidizing chemicals.  Hopefully, the discoloration is only “skin” deep. From my experience, it looks like it is less than a 1/16″ (1.6mm) deep.

The colors could change as you sand, and become darker or lighter.  It would be unpredictable based on the pigment mixing through the sheet. That should not be a big problem since it is in the filter area where it is hidden from view.   The gloss would be maintained through the proper buffing and polishing process.  If there is a repair, you should find a light-colored filler under the repair coating.  In this case, depending on the repair filler depth, it would need repair including a new coating and clear coat for protection. It could have been a surface repair that just covered up a light surface issue, and may buff and polish out to a normal appearance as well.

Here are other examples of the chemical issues and more explanations of causes. Follow the links in the articles to the proper remedies:
https://multitechproducts.wordpress.com/2014/12/15/surface-discoloration-in-an-acrylic-spa/
AND
https://multitechproducts.wordpress.com/2014/11/04/282/

To repair the surface, sand with a progression of 220, 320, 400 grit sandpaper. Finish with 600 grit wet/dry sandpaper. Then to recover the gloss, buff using a high-speed (variable to 2500rpms) with a good quality buffing pad and medium grit buffing compound.
We have a video demonstrating the entire procedure, and it can be down loaded.

http://www.multitechproducts.com/buffing-and-polishing-dvd/

Thanks,

Rob Clos

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Jeff Enswieler 4

We are occasionally asked what has caused a localized discoloration in a spa.  Most of the time, this change in color appears as a bleached surface.  There have even been examples where tiny blisters were present in the bleached area   In every case we have investigated, the root cause has been localized exposure to a strong sanitizing chemical.

The majority of spas are produced from  a  cross-linked, high molecular weight acrylic polymer sheet, a material that is very resistant to chemicals.  However, no product is perfect when it involves chemical resistance.   Spas require the use of sanitizing chemicals to maintain water chemistry.   Manufacturers provide recommendations on what products to use, and how to use them.  Failure to comply with these recommendations can lead to problems.  Even if a product might be used in a swimming pool, it may have issues when used in a spa.

Pure acrylic is clear with transparency better than most glass.  Pigments are added to the liquid acrylic to create the attractive colors and effects.  New colors often use exotic pigments.  Sanitizers for water are oxidizing agents used to kill bacteria, algae, etc.  Some are stronger than others.  The most common spa sanitizers are compounds of chlorine or bromine.   Some of these products have been found to bleach the acrylic pigments, and cause discoloration.  Manufacturers recommendations are always designed to prevent concentrated chemicals from long contact with the acrylic surface, and the plumbing system.  Water treatment chemicals for spas are best when in liquid form since they are easier to control concentration.  All examples of spa surface discoloration, that have been reported to MTP, have been caused by  one of these water treatment products.

Inorganic chlorine compounds such as calcium hypochlorite and sodium hypochlorite  commonly used sanitizers for swimming pools and spas.  However, they are both effected by sunlight, so they require the addition of cyanuric acid to stabilize the chlorine in outdoor pools and spas.  Organic chlorine compounds are products combined with cyanuric acid. Sodium dichlorostriazinetrione (“dichlor’) and trichloro-s-triazinetri-one (‘trichlor) are both popular stabilized chlorines for water treatment of outdoor pools.  Most of the spa discoloration cases we have seen have been the result of the use of “tri-chlor”.  Specifically, they have been due to the use of this chemical in the form of solid tablet.  This product dissolves slowly in water, and is a very strong oxidizer as well as increases the acidity of the water.  When these tablets are in contact or close proximity to the acrylic surface, it will attack the acrylic pigments and cause bleaching, and sometimes blistering.  Di-Chlor is a weaker chemical, and should be the stabilizer of choice for spas and is available in granular form.  Furthermore, when any sanitizer or acid is added to spa water, the circulating pump and jets should be running to assure rapid mixing of the chemical into the water.  This avoids creating localized regions of highly concentrated chemicals.

These problems have been verified by one of the acrylic sheet manufacturers.  They performed extensive testing of several water treatment products, and found that ‘trichlor” tablets can cause the bleaching similar to the examples that we have  observed and have been reported to us. They also found that when combined with hot water, it would cause blistering.  Some cases reported to MTP showed a red, rust-like material in the bleached area.  Their tests duplicated this phenomena when there was a source of iron in the water.   High concentration of the oxidizing chemical is a prerequisite for the discoloration.  This is facilitated by tablet form chemicals, since they can lay on the acrylic surface while dissolving.  If water is not being circulated, there will be a very high concentration at the interface of the acrylic and the tablet.

chem bleach1chem bleach

The two photos above show discoloration and blistering from the incorrect use of chemicals like “tri-chlor”.

Some people like to use floaters with a chemical inside.  Although it is a convenient way to treat water, it is not recommended, since it can cause problems.  The floater can rest against the side of the spa, and since it is in close proximity, it can cause bleaching of the surface.

Poor chemical control can also cause problems within the plumbing system by reacting with sealants, o-rings, etc.  There have  been reports of other spa components being compromised the use of bromine sanitizers, and ozonators (direct ozone addition).   Any chemical should be quickly dissolved and diluted with water to avoid problems.   It is very important for a spa owner to maintain total water chemistry (e.g. pH, chlorine, total solids, etc) as recommended by the manufacturer.  Various problems can occur if chemistry gets out of control.  For example, if chlorine level is too high the vapors  can bleach the under surface of a spa cover.   Excessive chemicals in water can also damage the jets, controls and fixtures.  Check with your manufacturer for their recommendations on how to maintain water chemistry in your spa.

Sometimes, the bleached surface can be removed by sanding and re-polishing, so surface appearance can be recovered.  However,  avoid repeating the factors which caused the original discoloration.

Following are some photos that provide examples to chemical bleaching (chemical burns).  The owner of at least one of these samples reported seeing pits in the bleached area.   There are chemicals that have been known to attack cross-linked acrylic.  One example is Wintergreen oil.  Although, the normal mode of failure from chemical attack on an acrylic surface is stress cracking, failure can occur in various ways.  Failure in a spa caused by wintergreen oil have been seen where it looked like a liquid had been poured on the surface , and it ran down the side.  The acrylic was discolored, and microscopic crazing was present.  Refer to information on stress-cracking in the website, http://www.multitechproducts.com.   So, unless a chemical has been approved for use in a spa, avoid using it.

The pictures above illustrate these problems in solid color and marble (multiple colored patterns) color spas.

The apparent defect can also occur in “granite” spas as shown below.    Again, they can be repaired using a sanding procedure.  You would start by using 80 or 100 grit sandpaper until the discolored area is removed, and you see the original color.  Then you would finish by using 320 grit wet/dry paper, and finally 400 grit.  If granite texture needs to be regained, you can use Multi-Tech Products K2000 clear topcoat with a brush.  Use the procedure provided to add texture.

Granite discolor

 

 

 

 

 

 

 

 

The picture below gives an example of the worst case of chemical attack we have seen on an acrylic spa.  This severe, widespread discoloration would not lend itself to sanding, buffing, and polishing to recover the original color(s).  Read the message at the link for more information on cause and refinish options on this case.

https://multitechproducts.wordpress.com/2013/11/04/282/

bilo-pic

 

 

 

 

 

Some general information on chemicals used for spas follows:

Calcium hypochlorite is available in granular or tablet form. It provides 65% available chlorine by weight and remains stable if stored in a dry, cool area. The chemical can be dissolved and introduced as a liquid, or it can be added in dry form. When
applied directly, it may cause a temporary cloudiness. Direct applications should be broadcast evenly over the water surface to avoid bleaching.
This chemical, when contaminated by or mixed with an organic compound, can produce a fire. A good rule is never to mix calcium hypochlorite with another chemical or store it in anything but the original container. Mix the chemical into water not water into the chemical. Calcium hypochlorite should not be handled with bare hands and must bekept off the operator’s clothes. As a chlorinating agent, calcium hypochlorite will slightly increase water pH. It’s pH is 11.8.

Sodium dichloro-s-triazinetrione and trichloro-s-tria zinetrione – chlorine compounds that contain cyanuric acid, and are used to stabilize chlorine.  The dichlor is more soluble and provides 56% or 62% available chlorine, depending on formulation.   The dichlor compound has little effect on pH, while trichlor is extremely acid (pH 2.8 -3.0).  Dichlor can be added directly to the water. The major effect of cyanuric acid on hypochlorous acid (HOCI) is to keep it from being decomposed by ultraviolet light contained in sunlight. Because it is readily decomposed by LTV light, the dosage of a chlorinating agent loke calcium hypochlorite that is sufficient for an indoor pool/spa is dissipated rapidly in an outdoor pool/spa.  Cyanuric acid bonds with the available chlorine in a manner that does not use up the chlorine.  At high stabilizer levels (over 100 ppm), chlorine’s efficiency may be reduced. The operator should consult the local codes and manufacturers’ recommendations on the proper use of stabilizers.

Regards,

Ken Wolfe (Chemical Engineer & Consultant)

To:  Multi-Tech Products

I am a spa dealer in Arizona, and I have a customer asking about extreme color fading in their 15 years-old, in-ground acrylic spa.  I have attached a photo.  What would cause this to occur?  Would spa chemicals be a likely culprit?  Please help.

Thanks,

Kevin

bilo pic

     (click to enlarge)

To Kevin,

Yes, your photo confirms a problem with extreme color fading.   There are two common causes of fading in an acrylic spa.  Pure acrylic is transparent, so pigments are added to achieve the attractive colors and effects.  These pigments are subject to fading from over exposure to chemicals and to a lesser degree sunlight  For example, it has been proven that high concentrations of chemicals like “tri-chlor” can completely bleach out spa surfaces.  UV light from the sun can also be a contributing factor.   Your spa may be suffering from a combination of both problems.  The cracks around the top edge are evidence of excessive exposure to the sun’s heat.  The sun’s radiant energy can result in very high acrylic surface temperatures during the day.  The cracks form as a result of repeated expansion and contraction from large swings in temperature from daylight to night.   This occurs frequently when a cover is not used when the spa is not in use.  If you look closely, the entire top surface is covered with cracks and crazing.  See our crazing blog entry below.   Manufacturers insist on  the use of a cover when the spa is not in use.  This is required to prevent cracks and crazing.  Most manufacturers will void a warranty when a spa cover is not used routinely.   See the “Why use a Spa Cover blog entry”.   It describes more on crazing.

https://multitechproducts.wordpress.com/2013/08/14/why-use-a-spa-cover/

Fading like your example would require years of exposure to strong sunlight, therefore, I believe excess sanitizing chemicals in the water is the prime cause of the fading.  Your case is the worst example of chemical/sunlight fading that I have personally seen in my 25 years’ experience.  You should also read the following blog entry.

Additional information at:   https://multitechproducts.wordpress.com/2012/04/20/surface-discoloration-in-an-acrylic-spa/

Early fading is usually limited to a thin layer on the surface.  In these cases it can be removed by sanding, buffing, and polishing the surface.  However, eliminate the source(s) of the problem.  Refer to our procedures in the website, or our Buffing and Polishing DVD for instructions on renewing the gloss on the surface.

https://multitechproducts.wordpress.com/2012/04/14/how-to-buff-and-polish-spa-surface/

You asked about chemicals used to maintain water chemistry.  Since they are strong oxidizing agents, it is a logical question.  First, if these chemicals are used properly, there will be no issue.  Some exceptionally strong oxidizers can create problems.  For example, it has been shown that high concentrations of “tri-chlor” in hot water can cause severe bleaching in acrylic spa surfaces.   Spa owners who use this chemical in the tablet form have real problems with fading, since they can rest on the acrylic surface, and dissolve slowly.  A high concentration of the chemical exists at the immediate area surrounding the tablet. When chemicals are involved, the fading is generally at the water line.  Generally speaking, we have witnessed very few issues with acrylic due to any of the common spa chemicals, which include bromine, chlorine, and ozone.  Acrylic is an outstanding product for spas, and has fewer problems than any material ever used for them.  But your photo shows what can happen when the spa is abused, and manufacturer recommendations are ignored.

I hope this helps.

Regards,

Rob

To Multi-Tech Products Corp.

Thanks for the great advice on this spa.  However, do you think it can be salvaged?

Kevin

To: Kevin

The simple answer is that it is possible to salvage.   We offer a FRL system that can be used to refinish  and create a completely new, attractive, long term surface that will last 15 to 20 years.  For information and instructions, go to http://www.multitechproducts.com/categories/frl-refinishing-system/

Also, refer to http://www.multitechproducts.com/content/procedures/frl%20PROCEDURE%20Final%20Draft.pdf

Your spa is a good candidate for the FRL resurfacing system, which is designed to create a new attractive surface on an aged spa that still is structurally sound, or is installed in a location that would be very expensive if one were to attempt to remove and replace it.  Even if there are structural issues, reinforcement can be added prior to the FRL application.  The FRL materials are applied directly on top of the acrylic surface.  Do not try this with bathtub, marine, or pool refinish coatings, since they will only provide a few years of service before peeling or delaminating from the surface.  Our FRL system has been proven to work in this application,and even over severely crazed acrylic, and is perfect for oxidized gelcoat surfaces.   However, it should only be performed by trained surface repair professionals, but we have seen people with handyman skills be successful with the process.  One important consideration is that the mechanical and electronic systems for hydrotherapy are still functional, and without issues.  Some of the advantages offered by the FRL system  include:

In ground spas may require a lot of costly work to remove and replace.  The FRL system will save dollars, and is a permanent solution.  The spa can be in service again in about one week.  Most structural problems can be fixed during the process.  Even modifications can be added to the steps, seats, and tile areas using standard composite methods prior to the FRL application

Please let us know if we can be of further help.

Good Luck,

Rob

To:  Multi-Tech Products

I want to thank you for your assistance in supplying a great system and help to replace and renew part of the surface of a swim spa installed in a home in Alaska.  The spa was originally produced from a co-extruded polymeric sheet with fiberglass reinforced resin for mechanical support.  Due to the presence of un-cured resin in the support structure, blisters had occurred around the bottom of the spa.  They were too numerous and widespread to repair with your standard procedure.  Furthermore, as the picture below shows, it would have been very expensive to remove and replace the entire spa   You can also see a photo showing some of the blisters..

IMG_3336.IMG950658

These blisters were located only around the lower portion of the spa, so your procedure for renewing a portion of a spa surface was ideal for this job.  As your procedures state, we created a line of demarcation establishing the boundary of the material to be removed and replaced.  Then we stripped this top layer from the spa with  the aid of a chisel and hammer.  We removed the entire bottom  of the spa.   Then we applied new fiberglass mat and resin using your FRL Kit to the affected surface.   See photos.

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Padres Spa Pictures 223

 

We completed the job following your recommendations using the products in your kit.  The following photo shows the final result.  The home owner was ecstatic about the appearance, and our ability to repair it without the demolition of replacing the entire spa.

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Thanks again,

Jeff

To:  Jeff

I want to thank you for your testimonial on our FRL (Fiberglass Reinforced Lining) System.  It was designed especially for this application, and we have had many satisfied customers including the San Diego Padres baseball team where the spa in their locker room was renewed.  We also want to thank you for trusting and using all of our products to repair spas and bathtubs made from acrylics, gelcoat, and other materials.

Regards,

Rob Clos

President

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?

Thanks,
Steve
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.

Thanks,

Rob Clos

To:  Multi-Tech Products

I am a new surface repair tech, and I am having difficulty getting a good cured repair on gel coat bathtub repairs. The surface remains tacky too long, and doesn’t achieve a satisfactory hardness. What am I doing wrong?
Thanks,
Richard
Richard,

The most common problem repair technicians have is “a tacky surface” after the sprayed gel coat has completed its heat cycle. The easy explanation is they have attempted to use a short cut in the application.
Many repair pros try to spray gel coat through a Preval® sprayer, since it is easy and convenient. This sprayer is an aerosol set up that allows mixing the ingredients in a glass jar. It is then atomized at low pressure using an aerosol source.
The low pressure requires the gel goat to be thinned excessively for spraying. This results in creating a recipe outside of the manufacturer’s requirements for optimum performance. Technicians have reported to us they try to use acetone as a thinner and create a 50% mixture. Every gel coat chemist says “do not thin gel goat more than 10-15% and use styrene only”

Gel coat is made for production factories “ready to spray” at 60-80 psi at the gun. Catalyzing at the gun tip yields optimum chemistry in this setting. The mold keeps oxygen away from the surface and gives the maximum hardness to the sprayed gel coat surface. When cured gel coat is pulled from the mold’s surface, there is absolutely no tackiness.

To duplicate this result in a repair application and achieve a tack free finish, you must:
-Spray pure gel coat at the recommended pressure (50-60psi). This requires an air compressor and proper spray gun or air brush.
-Spray it as close to the original manufacturer’s formula as possible (thin no more the 10-15%)
-Catalyze to between 1 to 3% with 90% MEKP
-Thin only with styrene.
-Most importantly, seal the surface at “peak exothermic cycle” with PVA.

All materials and tools are available from us. Using the proper materials and equipment will yield a more professional result, and a happier customer.

For more information on proper application of gel coat go to:

http://www.multitechproducts.com/content/Procedures/GELCOAT%20REPAIR%20GUIDELINE%20NCINSTGCGD-v%202.pdf

Ken Wolfe
Consulting Chemical Engineer
Multi-Tech Products Corp.

TO: Multi-Tech Products
Do you have a kit to repair ABS pans on a hottub?  We manufacture spas with a base (pan) made from ABS to protect the bottom frame from the outdoor weather, etc.   Sometimes, it gets damaged in transit to the dealer or customer. It is not cost effective to send an entire new pan, and some of our dealers have asked for a repair kit. I would appreciate any help.
Thank you,
Daniel
TO: Daniel

Yes, we offer a very good solution to your need for a kit to repair minor damage to ABS pans on the base of a portable spa. The kit contains the necessary components and procedure to repair moderate cracks, skid damage, and tears. You can read about the procedure by going to:

http://www.acrylicfiberglass.com/Procedures/ABS%20PLASTIC%20PAN%20REPAIR%20NCINSTABSPPR-v.2.pdf

You may order by calling Customer Service at 800-218-2066.
Thanks,
Rick Borden
Customer Service Dept.

TO:  Multi-Tech Products

I am repair technician and I can never achieve a hidden repair with your MMA system on acrylic.
My filler and contour application is perfect, but I always have a dark ring effect around the repair area after buffing.
I know factories use this product to get perfect repairs. What do they do differently? One factory even sends me the color. So I know it is the right color.
What am I doing wrong?  See photo.

John

Repair Technician

photo

 

 

 

 

 

 

Hello John,

This is one of the most common questions from repair technicians about achieving the perfect repair with our MMA System on acrylic bath and shower repairs.   The simple answer is the Clear Coat must be used.  Many technicians don’t understand the functions and importance of the clear coat, and therefore they think it is not necessary.

Some bath ware manufacturers send  only the product color coating (base coat) to technicians for warranty repairs. This certainly helps the contracted technician to use the proper color, but it might give the impression that only the base coat is needed for the repair.  I would also believe the customer service representative may not understand all of the requirements, as well.  However, the clear coat plays a role in both the dark ring, and the endurance of the repair.  The dark ring you mention develops when the base coat is sanded and polished without the presence of Clear Coat.

Since the MMA Basecoat is highly pigmented, it is not designed to withstand dirt, soap and general bath and shower environment usage.  Over a short period of time, the repair zone without Clear Coat will change color and become stained.  The Clear Coat is formulated to seal the base coat and give the repair its hardness, UV protection, and longevity.

How to remove the dark line?

With a good color match to the surface, the dark line will disappear when the Base coat color is sprayed on to the surface. This is done by  blending (feathering) the outer ring of the color application with the airbrush and spray process.  The dark ring appears, again, when the base coat is sanded. The sanding process  removes the hiding ability of the blend-out of the spray.  The clear coat, applied over the sanded base coat, can not remove the dark line. The clear coat must be sprayed over a “blended and without being sanded base coat”.  This will seal the feathered affect, and hide the dark line. Then the clear coat is sanded and polished. But the clear coat cannot be sanded excessively to remove the coatings, entirely.  The clear coat will then protect the colored base coat, and leave the blended area undisturbed.

Typically, this does not happen with gel coat repairs. Why does it happen on acrylic repairs?

Acrylic is a translucent material composed of a clear polymer with pigments added to achieve the desired color.  When compared to acrylic, gel coat is a resin with a higher loading of pigment.  Acrylic products are made by vacuum forming a flat sheet, heated to a high temperature, into the desired shape.  A highly loaded acrylic resin would be more brittle, and less able to be thermoformed.  Whereas, gel coat is sprayed onto a mold surface, so it can be highly loaded with pigment as long as it can be sprayed.  Higher-priced products are made from acrylic, since it is superior in properties needed for bath ware and spas compared to gelcoat resin.  When repairing a surface, a coating is used to match the color of the product.  It is sprayed over the repair filler and it’s adjacent area.  When the coating is applied to an acrylic surface, it creates a shadow at sharp, delineated edges of the coating. This is due to the thickness and transparency of the acrylic.  Even with a good repair base coat color match,  a dark halo is cast around the repair when sanded.  The only way to address the shadow casting effect, is to blend(feather) the base coat color, and apply (spray) a clear coat over it for protection and to preserve the appearance.

How to “blend” or “feather” the MMA base coat?

A single action (important) air brush operating at 35 psi (1 cfm air source) at the gun is required.  First, spray the base coat sufficiently to cover the filler area. This may take several layers (see MMA instructions).  Then open up the airbrush spray pattern to allow a higher volume of product to be sprayed. Using the correct temperature thinners and a smooth spray-out from the gun, pull the gun away (6-8 inches) from the spray surface, and feather coat the base coat around the edges of the previous sprayed area. Try to achieve a smooth surface that hides the edges of the over-spray.  If the product has sprayed a little dry and the surface around the area looks dull, wet-out those areas with straight MMA Finishing solvent from the gun in a clean separate jar. Do not over flood the area. Allow the coating and Finishing solvent to evaporate  (dry) before clear coating. This is the procedure required to create undetectable repairs on surfaces.  This spot repair technique also works with our Quick Glaze Systems.

Here is a summary of the important reasons to use Clear Coat over MMA Basecoats:

-Clear Coat seals the base coat color to retain its match and blend (feather effect) during the sanding and buffing process.
-Clear Coat is imperative for gloss and wear protection.
-Clear Coat adds depth to the acrylic look and effect matching the original surface.
-Clear Coat seals the color coat so it will not absorb detergents, dirt and elements from hard water.(most important) -Clear Coat is a necessary system component formulated and designed to be used with every MMA Basecoat application.

Other important MMA System components and tips are:

-The proper airbrush (Single action) 35 psi at the gun with a 1 cfm air source. Very important.
-Use MMA System Thinners, only. Alternative thinners will effect spray performance and final color.
-Use proper rated temperature thinners for ambient working conditions. The wrong thinner selection can cause dry spray out.
-Note: MMA Basecoats will darken as they dry. Decide on color adjustments after it dries.  Light forced heating is okay.
-Sanding can be performed on base coats, but reapply the base coat and perform the feathering prior to Clear Coating.

Here is a link to the MMA System repair instructions.

http://www.acrylicfiberglass.com/Procedures/BATH-REPAIR-MMA.pdf

Rob Clos

President

 

Dear Multi-Tech Products;

I have a crack in the radius at the bottom of an acrylic bathtub.  Must I contract someone to install an inlay to replace the entire bottom of the bath, or is their an acceptable, easier way to fix it?  See the photo.

Thanks,

Roger

photo 2 photo 1

To: Roger

The use of an inlay to repair cracks in the bottom of a bathtub is always the safest way to prevent re-occurrence.   However, after saying that, there can be some latitude in recommended repair techniques depending on the severity and exact location of the crack(s).  I would say that your example, where the one crack is located right at the radius does not require an inlay.  If the crack extended into the flat area, it would need a more stealthy repair offered by inlays.

Your crack, most likely, occurred due to either insufficient support under the base, or movement in the tub.  In sufficient support allows the tub bottom to flex under weight.  This repeated flexing eventually results in crack formation.  Therefore, my first recommendation is to add structural support by injecting our 5-lb. density polyurethane foam into the base cavity to restrict movement.  It does not increase basic structural strength, but it is effective in reducing movement.  If additional structure strength is necessary, it will need to be added using fiberglass resin over the top of the weak area.  The combination of these two processes will provide the permanent repair desired.

You can refer to the blog entry, FIXING A SQUEAKY, FLEXING BATHTUB OR SHOWER, for a description of how to add polyurethane foam.  Your small crack area can be fixed using a glass fiber stitch mat with our Binding resin.  The stitch mat should be cut to a size that completely covers the crack, and extends about 3 inches beyond it.  Refer to http://www.multitechproducts.com/content/Procedures/Binding-Resin-Spa-Blister-Repair-2010.pdf for instructions on laying down stitch mat.  Obviously, this means the repair zone will be raised in relation to the normal surface.  So you should use our Poly-Filler or Poly-Paste to buildup and transition smoothly to the existing surfaces.   Since this area is at the edge of the tub bottom, it will not effect water drainage.

Roger, theoretically,  any crack on a bathtub bottom could be repaired in this manner.  However, based on the size and exact location, it could significantly diminish the ability of the tub to drain, properly.  Your case is simple, and these procedures should result in a very satisfactory repair.  Crack size and location are the determining factors whether to resort to an inlay repair.  Inlays also offer the ability for a technician to offer the optimum warranty for a repair.

After these procedures are completed, the color needs to be restored to match the other surfaces.  Refer to the procedures on bathtub crack repair for directions on preparing the surface and spraying a colored coating over the repair.  You may also choose to use our color-matched repair paste.   In cases that the bathtub has a textured surface, the surface can be duplicated using the texture additive materials described in repairing granite spas.  However, you may decide that it is acceptable to leave a small smooth area at the repair, if it is not noticeable.

I hope this information helps you to resolve your problem.  Please call if you have further questions.

Regards,

Rob Clos

TO: Multi-Tech Products:

I am a repair technician; I have inspected a cultured marble whirlpool with a 4″ vertical crack on the tub. The crack is on the bottom radius around 12″ from the drain. The tub has leaked through due to the crack.  Do you have a method/product that we can use to repair cultured marble and guarantee that the tub would no longer leak.

Any help you can give us would be greatly appreciated.  We look forward to hearing back from you.  If you have any questions, please don’t hesitate to contact us. Otherwise, have a wonderful day.

All the best,
Maureen

TO: Maureen

You describe a thermal stress crack created by the shock of hot and cold water.  I have seen this type of crack go completely around the perimeter of the tub.

In order to repair it, and prevent future propagation of the same crack, you need to drill a hole at each end of the visible crack.  Be sure to drill through the entire depth of the tub with a ¼ drill.   Then grind a deep slot into the structure along the entire length of the crack. Just grinding an 1/8th inch groove in the top surface is insufficient since it will continue to crack. This is because the crack goes through the complete structure. The surface will continue to expand and contract as it is exposed to hot and cold water. This expansion and contraction will lead to a new crack directly through the repair. Cultured marble bathtubs aren’t reinforced with glass fibers, so they have less strength to resist failure from expansion cracks.   If there is access to the back of the bathtub, you should attempt to add reinforcement using fiberglass mat.  The combination of reinforcement on the back side and grinding the crack open through the structure will provide the best permanent repair.

The fact that this is a relatively short crack improves the probability that this crack can be satisfactorily fixed.

If there is no way to get glass on the backside, aggressive grinding and heavy glass reinforcement from the top side will achieve a good repair. The repair procedure should be:

  1. Grind the crack to create a recess in the top surface along the crack wide enough ( probably 2 to 3 inches) to accommodate the fiberglass mat.
  2. Using a heavy duty die grinder, grind a slot channel that would hold a recessed layer of heavy duty stitch mat. The stitch mat would be about an 1/8th of inch thick. A slot grove would need to be ground ¼ inch deep to hold the mat and the resin while leaving enough room for the poly filler after the mat and resin application. The slot groove would not go through the structure, but leave enough structure to bond to. The slot groove would hold the width of the Stitch mat to straddle the crack a little over an inch on each side of the crack. If the crack is 1/16th inch by 12 inches. The slot groove should straddle the crack by 1 ¼ on each side and extend past the end of the crack the same. Total groove over the crack 2 ½ inches x 14 ½ inch long by ¼ deep.
  3. With the groove and the crack prepared to except the fiberglass application, apply catalyzed Iso resin to the glass first and place it in the groove.  Smooth out and remove bubbles.
  4. Force cure with a heat gun.
  5. Fill with Poly-filler.
  6. Use our Quick Glaze system with the Clear Coat to achieve better color match and appearance.

You should charge your customer between $350 to $450 for this best-practice job, and it should take 3-4 hours to complete.

Hope this helps.

Rob Clos