Tag Archive: spa

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.








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.


Ken Wolfe (Chemical Engineer & Consultant)


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.


Repair Technician








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.


Rob Clos



TO:  Multi-Tech Products

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



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?




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.


Ken Wolfe

MTP Consulting Chemical Engineer


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.






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

Can you tell me what caused the clear coat, which was the final step in the spa repair,  to discolor (whiten) in less than a month?  I used brand new bottles of K2000 A and B parts, the customer did not fill the spa for about a week after the repair, and temperatures were in the 50 -60 degree range.  What will we have to do to repair this problem?


Warranty & Technical Dept.



This can happen due to a number of curing mistakes, which all involve premature exposure to water.   Here is an excerpt from the procedures available on our website that deal with this issue.

Click on the link below to see the complete instructions explaining what probably happened and how to fix it.

Somehow, the clear coat was exposed to water or moisture before the resin was completely cured.   Potential causes that could have led to incomplete curing are:

 1) Allowing moisture, water or dew to settle onto the fresh repair area within a few hours after completion.

 2) Closing the spa lid tight during curing.  This will generate moisture from the spa’s jet system causing the dry repair area and surface to stay wet.

 3) Filling the spa too soon (72 hours minimum @ 70°F) with water.  This stops the topcoat cure process  so that it fails to reach its peak hardness and chemical resistance.

 4) Extreme cold temperature during the cure period.  Low temperatures greatly increase coating cure time.   Then if water comes in contact with the coating it causes the whitening.

Go to:


to read complete description and instructions.


Rob Clos

Multi-Tech Products Corp.

41519 Cherry Street

Murrieta, CA 92562

Toll Free:        800.218.2066

Office:     951.834.9066

Fax:  951.834.9067

I have a 15+ year-old Jacuzzi® spa that I accidentally scrubbed a scum line from the surface until I reached a  white base underneath.   I would like to repair it.  Can you help me pick a product that will work?  Pictures are below.

Mike Buckley


Yes, this can be repaired. You may think you caused the problem by excessive scrubbing, but actually it is bleached from an oxidizing chemical caused by poor procedures during chemical addition.  A possible cause is just poor water circulation with a high concentration of chlorine or bromine at this surface location.

The original spa color is still there, but under the bleached surface.  The original color continues until you reach the fiberglass reinforcement.

We have a buffing and polishing video that you can purchase that will clearly demonstrate the procedure for renewing the surface color.

The video procedure starts with sanding using 320 grit wet/dry sandpaper.   However, for this chemical bleach, I would start with 220 or even 100 grit wet/dry sandpaper with a progression to finer grit.

The end result will bring back the color and granite effect without the texture. It will have a gloss in those areas from the sanding and polishing process.

If you want to bring back some texture, sand away the white surface, and apply our K2000 clear coat with a paint brush at the 320 grit sand paper stage. The dabbing  vs. brushing application will cause a stippled effect on the surface, which will mimic the original texture.

Rob Clos

Multi-Tech Products

 You can order from:

Multi-Tech Products Store


After years of service and use, the original surface of a spa may become faded, damaged, cracked, blistered, or defective in some way.  Mechanically, the spa is still  very functional, and it is leak-free, but the appearance of the surface is objectionable.  In these cases, the owner may prefer refurbishing the entire surface rather than purchasing a new replacement spa.  This should be performed by a professional, trained surface repair contractor.

Materials and procedures have been developed by Multi-Tech Products Corporation to renew the surface of spas with a white layer of reinforced resin.  The fiberglass reinforced lining system (FRL) includes a white polyester resin and fiberglass matting for reinforcement.  If applied properly, the products will extend the useful life of a spa for several years.  The materials and techniques provide an attractive, solid white textured surface.

Please call MTP for more information, and to order materials.


Spa blister repair



Yes, blisters can be repaired.  However, in rare instances there are too many to justify the expense.  Please visit http://www.multitechproducts.com to learn what causes blisters in spas, and how to repair them.  The repair requires grinding the blistered area down to the FRP layer, eliminating the root cause of the blister, filling the void, and finishing the repair with a system that recreates the original appearance.  The special, high performance acrylic filler should be used.

Go to http://www.multitechproducts.com/pages/procedures.html for more details on repairing blisters.




There are a few million portable spas and hottubs, mostly acrylic, in service today.  They get moved and are subject to damage.  They operate in a very harsh environment, so they develop minor surface problems that do not justify replacement, but the owner would take advantage of economical repairs.  Common problems range from simple scratches to cracks, crazing, blisters and bubbles.   These provide a great avenue for increased sales for enterprising, skilled repair craftsmen.

Many bathtub repair and refinish contractors decline jobs for spa surface repair, since they believe it exceeds their technical capability.  However, Multi-Tech Products offers repair kits, materials, tools, and training aids that can easily be used for becoming proficient in acrylic or gelcoat surface repair.  Even the ability to recreate the feared “marble” patterns can be learned by following and practicing a few simple steps and procedures with an airbrush.

And repairing the popular “granite-like” spas is very simple.

Multi-Tech Products Corporation (MTP) has been the leading supplier of bath and spa surface repair systems to manufacturers and professionals since 1992.  Information can be downloaded from the website, and training DVD’s can be purchased.  Explore the website for the information available, and to make purchases.

In order to develop competency for spa repair, a bathtub repair professional should purchase some material and arrange to practice the techniques before providing paid services.  Call MTP (800-218-2066) for ideas on how to facilitate practice jobs.  After completion of training, you must let potential customers know about your new capabilities.  You will know what advertising methods work best in your market area.    Customers of MTP are used for referral when manufacturers are looking for qualified repair contractors to perform warranty repairs or to help their customers locate a repair service nearby.  You may also want to contact these manufacturers, which are listed in our website.  Also, you should notify the spa retail stores in your area.

This blog has been created for multiple purposes.  One is to create a running dialog for information exchange between our hundreds of professional repair contractors.  We invite and encourage our existing customers to make contributions and write testimonials on how MTP repair technology has enabled them to expand their business.