Tag Archive: FRP

To: Multi-Tech Products

I have attached a photo of a hot tub installed in a hotel. It is a plastered spa, and large chips are coming off of the surface. Can it be salvaged using your FRL System?


To: Jim

The quick, simple answer is yes, it can be used to renew the hot tub surface. However, before I give the complete answer on FRL resurfacing of a plaster finished hot tub, I want to address common issues with the practice of using fiberglass coatings over plastered swimming pools. Even though they are the same application, using a fiberglass coating on a plastered swimming pool brings much greater risks for failure than using fiberglass over plastered hot tubs.

There have been companies that specialize in a total refinish of pools by applying a fiberglass composite on top of the plaster. Therefore, there are a lot of these swimming pools in service today that have experienced a high rate of failure. Repairing these failed jobs have great appeal to repair technicians. Even complete pool resurfacing can be achieved with our FRL system. The larger the pool, the bigger the job, and bigger the pay check, right?  Our advice is don’t be quick to jump for that big pool job. Even though it might appear to be a great business opportunity, it is very risky to re-surface plastered swimming pools. Applying fiberglass resin systems over plaster does not always provide for resolution of the underlying issue, deteriorating plaster. These overlays of FRP usually fail as the plaster continues to deteriorate.

The explanation is that although advanced resins are utilized, and the top layer bond is great, adhesion between the different layers of fiberglass, plaster, and concrete base will decline. This leads to complete failure of the composite structure application. Some resurfacing will lose adhesion in big sections, and some will just have small areas that come loose. It is best to refer the major failures to a contractor that will completely re-plaster the pool. On the same note, the smaller failures provide the opportunity for repair professionals.

The following photos show one example of a swimming pool that had been completely over laid with fiberglass, and a partial repair was made, successfully. So, if the plaster has not become too brittle and chalky, a pool with small area(s) of failure can be repaired with the FRL System. It can provide a worthwhile extension to the life of the pool before a complete re-plastering is necessary. However, we would not recommend providing a warranty on these partial repairs.

2013-05-09 10.51.50 Before

2013-05-27 11.43.35After

Your hot tub can be refinished with our FRL system. It would require a complete resurfacing of the entire surface (nothing partial). Therefore, you should not commit without a prior inspection of the empty spa. Based on my analysis of your pictures, the glaze layer of the plaster is peeling. This layer is comprised of about .125″ thickness of the total original plaster finish. The glaze was created as part of the total installation process when the plaster was applied during the original construction.

The primary issue in resurfacing with any fiberglass product including our FRL system will be the ability to achieve prolonged adhesion to whatever you are applying it to – in this case the aged glaze or exposed plaster. But, if you re-surface the entire plastered hot tub, the FRL resin layer acts as a cap over the plaster, although it does rely on achieving a strong, long-term bond to the substrate. Hot tubs are smaller than pools so as the plaster layers deteriorate, the smaller bonding surface areas stay in place for the long-term. Ideally, the smaller volume allows for sufficient structural strength without the need for the strongest substrate composite integrity. Thus, it will stay in place and function correctly as a capped surface.

An inspection would be necessary to determine the condition of the plaster. Plaster fails by becoming brittle and chalky. The core plaster layer is under the glaze and on top of the concrete structure providing the shape of the hot tub. The primary cause for plaster becoming chalky, soft and brittle is from over-use of pool chemicals. So, you should remove the glaze in a few areas, and assess the condition of the plaster underneath, as well.

The FRL resurfacing procedure includes grinding and filling the substrate to assure smoothness, and provide a surface that allows the best possible bond with the FRL resin. That process will expose the core while leaving some of the glaze in place. If inspection confirms that the plaster is hard and shows little evidence of brittleness or chalkiness, then a re-surfacing with the FRL system would be advisable. One advantage of the FRL finish compared to a plaster surface is the ease of cleaning. The surface is much smoother, less porous and will be more durable.

Important Note: Resurfacing over peeling plaster is risky, and should be attempted only with everyone understanding the issues and potential for success or failure.

My experience is that plastered Hot Tub resurfacing with the FRL system has yielded long term adhesion and less call-backs when good judgment has been used during inspection and preparation for the refinishing stages. The same judgment should be used when establishing a warranty.

Rob Clos

TO; Multi-Tech Products

Wow, the before and after pictures of this hot tub are incredible. I’m amazed at how well it was repaired. Is an FRL system pretty common? Or do they use that on the newer hot tubs only? I’m just curious because I’ve got a pretty old hot tub that I need to get repaired.

Thanks Mia

To: Mia

If your hot tub is very old, 30 years or more, it is probably gel coat with a FRP backing, and installed in a cabinet or outside deck.  This type of product is suited well for resurfacing with the FRL system.  Refinishing a gel coat spa will give a permanent finish that will last 10 to 20 years.  The same applies to a spa made with an acrylic surface.  Acrylic spas were introduced in the early 1980’s, and quickly replaced gel coat products, due to superior performance.  These were offered as portable spas, but in-ground models were available.  Older plastered spas, which are frequently built with swimming pools, can also be resurfaced with the FRL system.

The pictures you referred to are actually a pool that was fiber glassed over plaster.  Fiber-glassing plastered pools and hot tubs is pretty common.  Companies that specialize in this service have come and gone over the years.  The business failures have been due to the liabilities from deterioration of plaster as described above.  Resins have improved over the years, which have made a difference in how long the new surface lasts.  But the main issue is that the plaster fails.  The FRL system is unique, and is designed for surface renewal.  It has proven performance in the right application.   See the above article for recommendations and limitations.  FRP is the acronym for Fiber Glass Reinforced Polyester.  This description encompasses a broad range of products with varying levels of quality.  The FRL system is designed to be used with numerous surfaces including acrylic, gel coat, ABS, and other spa surfaces.  We can refer you to a contractor that has been qualified to perform these applications.



To Multi-Tech Products

Hello, I have a customer that needs to add more mechanical support under their spa to distribute the weight more uniformly, and reduce stress levels to prevent cracking.  It is out of the manufacturer’s warranty. What do you suggest?



To: Joe

The following picture shows a very nice aftermarket adjustable support added to an FRP Spa shell.

Feb 2015 download 016

The most important requirement for installing additional support is to prevent the new beam from puncturing the wall of the spa.  The method used to accomplish this is to install the beam so it transfers the weight to a strong metal plate between the beam and wall.  Please reference the picture above.

If there is a seat, step or flat area that would accept a support beam, and if it is accessible, remove any foam and expose the structure of the shell.

If you believe there is a plate and need to confirm, grind off the resin/glass to expose the plate for confirmation. The picture above shows an intended design and original equipment manufacturer (OEM) requirement. The plates were built-in at the factory at the time of manufacture. That is not going to be the case on every spa shell.

There is a wrong way to add support. One example is adding 2″ x 4″ wood stud material directly to the shell without a  plate.


This is very bad practice since the large load of the spa will force the wood beam to eventually puncture the shell wall. I have seen this many times as a technician in the field. Even the nice support beam in the first picture above with its built-in,  top metal plate would pierce a normal spa wall without the addition of a strong weight distribution plate embedded in the structure or added in some alternative method.

Ideally, the best method would be a wood plate (as large as possible for the flat area). I would suggest a block of wood 2″ thick x 12″ x 12″ to start or as large as it can be while achieving good contact with the flat area. Be sure the plate sits flat against the spa structure.  Try to make it parallel to the spa base.  Use a 4″ x 4″ beam cut to size for the support. Be sure the 4″ x 4″ beam sits solidly on the deck, concrete pad or spa frame.  A plate may be necessary there as well.


It would be best to secure the plate and support to the spa shell.   It should be done with Multi-Tech Products Polyester resin paste. Resin paste will provide about 30 to 40 minutes working time before it sets.  It is somewhat temperature dependent. In weather below 55 degrees, it may be necessary to apply heat after the application to cure the paste.

Grind the surface with 50-100 grit sandpaper to accept the Paste for good adhesion.


Apply catalyzed paste to the plates prior to setting them in place.

Secure the plate to the bottom of the spa with Resin Paste. Secure the beam to the bottom of the plate with the same “Paste”. The “Paste” can also be used to achieve maximum contact between the plate and the bottom surface of the spa structure where angle changes or uneven surfaces prevent full contact.  Good, wide area contact is needed to distribute the load.

If the environment under the spa is frequently wet and the wood might eventually rot, use treated lumber, or the plate and the beam should be encased with resin and fiberglass prior to installing the beam and plate.  The following picture shows the wooden plate after encasing in fiberglass reinforced resin.








If the spa needs to be lifted to insert the beam device, install the plate with paste, and allow it to set (cure).  Then lift the area up with a hydraulic jack (car jacks work, also).  Push the new beam into place (adjust beam length, if needed), retract the jack and allow the spa to set on the new beam.












If additional supports are needed, repeat this process in order to distribute the total spa load throughout the spa.  One way to determine the need for additional support beams is to empty the spa, and put significant body weight in the unfilled spa shell.  If the shell moves, flexes, or the seats move downward with weight applied, this could indicate the need for additional under spa support.   This movement could would be due to either inadequate FRP reinforcement or insufficient mechanical support devices.  Properly distributed support is required to keep the spa shell from excessive downward movement due to the load derived from water and humans.  Pay close attention to the lip.  If a spa shell is built in a way to rely mostly on the edge support to provide the structure’s strength, the lip will move and deflect downward.  This would cause initial sagging and eventual cracking of the spa shell inner lip area.  Also, cracks inside the spa shell at upper corners could confirm inadequate supporting fixtures.  If the spa is within the manufacturers warranty, I would consult them before proceeding with an independent repair.  If it is not covered by warranty, good judgment must be used, but excessive movement begs for additional support to avoid problems.

Rob Clos



TO:  Multi-Tech Products

I am a professional spa surface repair contractor.  I frequently have to repair spa blisters.  Your procedure works very well, but it is more detailed.  Can I simplify the process by just injecting acrylic resin or an epoxy into the blister at the edges to create adhesion to the FRP?  This will save having to grind out the acrylic and causing a larger area to repair.

Thanks, John


Unfortunately, this method will not yield long-term repairs that you can apply a warranty to.  In order to achieve the desired result, a permanent repair that will not result in a call-back, we strongly recommend that you use the process that has been developed for spa applications, and has proven to work long term.  Since blisters are filled with a fluid, mainly water, the fluid will interfere with the polymerization of acrylic monomer resins, polyester resins, and epoxies. Even if there were a way to rinse out the fluid inside the blister, the root cause of the blister (wetness in the FRP) will still be there; not addressed, the same blistered area will have adhesion, wetness and continued bulging issues.

The method in question is often called the “poke and roll-out” procedure.  The blister is heated with a heat gun until a small hole can be punctured into the top surface.  The fluid is allowed to drain, and with the acrylic still soft and pliable, it is hopefully rolled or pushed back into its normal shape.


This photo shows a blister opened up.  Notice the fluid.  You can also see that the acrylic was not adhered to the FRP.

Theoretically, resin or adhesive of some type is injected into the blister to glue it into place.   This is not a permanent professional repair, since the same blister or a new blister will form when the hole(s) are filled, or if the hole(s) are left open, it will leak or ooze the fluid that will discolor the surrounding surface. Simply put, the root wetness needs to be addressed.




This photo shows an improperly repaired or rolled out blister that has the fluid, which was not removed during the repair,  seeping out of the repaired surface.




However, it could be a temporary fix if that serves a purpose. Normally, the manufacturer wants a permanent fix with a warranty.

Other problems can occur with heating a blister and laying it flat like:

-The acrylic will eventually crack causing a sharp or dangerous edge.

-The acrylic can split and melt during the process.

-The blister will not lay flat due to delaminated FRP behind the blister.

-Often large amounts of calcium builds up behind the blister keeping it from laying flat as well.

-All the above is the reason why a resin or adhesive will not adhere, let alone cure properly.




This photo shows acrylic removed from blister, and a perfect example of the laminate shredding as the blister forms.


A proper fix would consist of removing the blister, the fluid, force drying the FRP, sealing the area with the proper resin and matting, followed by the filler and color process.




This photo shows using a high temperature heat gun to dry the blister area.  Extreme heat must be applied to remove 100% of the fluid.  You will notice that the wetness extends deep into the FRP.




After the wetness is eliminated with heat, seal with our Binding Resin while saturating a layer of fiberglass matt.  The resin and matt thickness will eliminate a step in the filling procedure, making the filling process more efficient.



Following these instructions will assist in the prevention of repair failure due to fluid reformation in the repair zone.


You can also read about how blisters form:


This page will give customer relations tips, as well as other helpful information:



Rob Clos

TO:  Multi-Tech Products

I am a bathtub surface repair professional contractor.  I have a customer that has a combination tub and shower made from gelcoat reinforced with FRP.  They complain about the noise it makes while they are using it.  The bottom flexes and it squeaks.  How can I fix it?



To: Frank

This is a common problem experienced with any bath product produced from non-metal materials.  These types of bathtubs are produced from materials like acrylic sheet and gelcoat resins, and are reinforced with mixtures of polyester resins and glass fibers..  Furthermore, additional support features must be incorporated in the final product, and in the installation.  The following pictures show examples of how most manufacturers add support structure to their designs.  The most common examples are wooden boards fiber-glassed onto the base.

Bathtub/Shower Combination Unit                Bathtub Construction

Sometimes, manufacturers may add blocks of high density foam to aid in leveling the bathtub.  If blocks like the ones below are attached to the base, the bathtub must be installed properly to avoid developing flex in the bath bottom.  The best result is achieved when most of the space between the tub bottom and the sub-floor is filled with structural polyurethane foam or other filler designed for the purpose at the time of installation.


Construction with boards and blocks

So, squeaky bottoms are normally the result of inadequate support under the bathtub, between the tub bottom and the floor.  We have found that the distance from the tub bottom and the sub-floor can range from ½” to 5 inches.  This problem, if left alone, not only is annoying but it can lead to fatigue and severe cracking of the bath bottom.  However, the squeaking and flexing can be fixed by injecting structural polyurethane foam into the space(s) or cavities between the tub bottom and the sub-floor.  Refer to our procedure in our website for detailed instructions on how to accomplish the repair.  If the bathtub has developed a crack(s), we recommend using the Multi-Tech Products tub bottom replacement materials and procedures.  Refer to our Tub Inlay products.

This photo shows another type of structural board construction.  Strips of particle board are fiber-glassed onto the tub bottom.  This design is not as common as a one piece board. However, it is obvious that there are potential issues with the gaps and lack of support when installed improperly.

Cracks and Squeaking are very much repairable. Depending on the location of a structural fracture, a crack will require a composite rebuild of the bottom structure. This can typically be done with a structural patch or by bonding resins and fabricating a reinforced panel to the top of the floor bottom. The top side seams of the panel can then be repaired with composite resins, pastes and coatings to contour and complete the transition of the repair job. This can be done in such a way that the bottom inlay is not even seen. With all this said, what squeaking tub bottoms and fractured fiberglass floors requiring a rebuild do have in common is they both need this dense foam to stop movement.  Stopping the movement on a squeaking floor will require  2 or 5 lbs density pour or injection foam forced under the tub by injection, which will expand to provide the support. This can be performed through the access panel of a closet or other wall opening.  Or injections can be performed by drilling holes through the top of the floor of the unit to fill the void or space.

If the repair is performed by drilling small holes into the bath bottom, our experience shows that you should use either our 2 pound (2 lbs/cuft) or 5 # density foam to provide the necessary structural strength to stop the flex and squeaking.  When poured freely on a floor with no restrictions, 2# foam will expand and rise about 3 inches; whereas 5# foam only rises about 1 ½ inches.  The following picture illustrates the relative expanded volumes of the two foam products.

           5lbs/cuft                                2lbs/cuft

When mixed as an equal part (Parts A & B), an 8 oz. quantity of our 2 pound foam will expand to about 1 cubic foot.  The 5 # foam will expand to about ½ cuft.  These estimates can help determine the correct quantity of foam to use for a particular job.  However, it is possible to use too much foam resin, which may cause distortion in the bathtub bottom.  Our experience is that foams with higher densities than 5 lbs/cuft will not expand sufficiently to fill voids and cavities.  MTP provides these resins, which have been formulated to work.  The typical foam products you find in retail stores are only ½ pound density, and are only designed to provide insulation.  They should NOT be used for structural support.

The above photo shows some of the foam products offered by Multi-Tech Products Corp.  They include polyurethane foam ( parts A & B), and containers for injection.  Individual components as well as kits are available in quantities of a quart, gallon, and 5-gallons.  These products have been formulated to provide the best results in stopping squeaking and flexing in bath products.


A drill is used to drill through the first layer of fiberglass to inject a resin into the cavity, or to drill all the way through the support board to the empty space between the tub base and the sub-floor.  A 1/4″ diameter hole is best.

Polyurethane foam is injected to fill the void space.  Sometimes, the gap is so large that it may require more than one injection point.  The goal is to choose the right foam for the job.  If the gap is larger than 3 inches, the 2 lbs/cuft foam is recommended.

Another case is a very small cavity or gap between the sub-floor and tub bottom, or a de-lamination between the FRP reinforcement and top surface layer.  These problems can be handled with the injection of polyester resin or resin paste, also available from MTP.  This procedure can be accomplished using a caulking tube filled with our recommended resin or paste, with a standard applicator.

Or another option is to use a syringe applicator to inject the resin, as shown below.

After the foam has been injected, these small holes can be filled with a repair paste or putty and finished to match the color and surface texture with one of our spot repair systems.
One way  a Do It Yourself person could repair the holes is to apply a non-skid coating over the patched holes and create a non-skid area over the bottom of the unit. This would be the easiest way if one is not versed at matching colors and texture for spot repairs. We have a kit to make it easy.

Frank, I hope this answers your questions.  More information is available in our website, http://www.multitechproducts.com, and in procedures supplied with our products.  Squeaky, flexing bathtubs and showers are a common household issue, and most consumers are probably not aware of a remedy.  So this untapped market for the services of a repair professional offers a great opportunity for one to expand their business revenue and profits.  We wish you success in your business.  Call us 800-218-2066 for questions and assistance.

Best filler for injection holes:

Non-Skid Application:

Structural repair instructions: FYI


Rob Clos



There is no simple answer to this question.  Many factors need to be considered to develop the best, successful bid for a spa surface repair job.

First, is the request coming through the spa manufacturer, and is it under their warranty?   If so, they may have a standard fee schedule that applies.  Inquire about it.  Warranty repairs normally require the contractor to provide a guarantee of performance.  Higher prices are common on warranty jobs.

Additional information needed is:

  1. Does the job only require a cosmetic fix, or does it include a structure repair prior to the cosmetic repair?  Additional costs are required when a structure repair is necessary.
  2. If it is a warranty job, is the request simply for an evaluation visit to determine magnitude of the damage or is it for the actual repair.
  3. How far do you need to travel to get to the site?  Are other professional repair contractors closer, and are they bidding the job?
  4. What are the prevailing hourly rates for professional service contractors in your area?  Some contractors use job rates based on the magnitude and type of repair.  Obviously, it must take into consideration the time required to complete it, and a fair hourly wage.
  5. How does your skill level compare to your competitor’s?  There is an opportunity to earn more money if your skill level or materials provide a competitive advantage.  You can quote the cost based on what an average skill level contractor would charge, but your quicker completion and/or higher quality materials results in more profit at the same cost to the customer
  6. Would it be cheaper or wiser for the customer to replace the spa rather than repair it?  Reputable contractors will advise customers, accordingly.
  7. What is the defect being repaired?  Is it a blister(s)?  Is it a crack(s)?  Is it crazing?  Make sure you know what is involved before you make a quote.  Also, make sure the customer understands the scope of your quotation.
  8. Is the surface acrylic, or some other material?   Does the acrylic have an ABS reinforcement and/or fiberglass-polyester resin?
  9. Do you have all of the required materials for the repair, and what did they cost?   Typically, material costs are a small percentage of total cost for a repair.  These can be minimized when components are purchased in bulk quantities rather than single use kits with each required component.
  10. What color is the spa?  Granite-like acrylic colors are easiest to repair.  Marble patterned spas are the most difficult to repair, since it takes an experienced and skilled operator with an airbrush to duplicate the pattern so it is undistinguishable.  Some non-acrylic surface spas require special materials to repair.  Pearlescent colors also require special coatings to duplicate the appearance.


Visit http://www.multitechproducts.com/pages/Blisters.html for a technical discussion on what causes blisters.

Visit http://www.multitechproducts.com/categories/Instructional-Videos/  to order a copy of the DVD to learn everything on repairing spas.


1)  A 2” diameter blister in the lounge seat of a Granite colored spa.  The customer has drained the spa prior to your arrival.

–         Total time to prepare and complete repair by an average skill technician =  3 to 4 hours

–         Cost of materials ~  $50  (based on buying one single use repair kit)  Repair professionals that perform frequent spa repairs buy individual components, and can reduce their material costs for a single job.

–         Quotation Price ( including maximum of 1 hour travel time) = $250 to $300

Comment:   A similar repair on a Marble pattern spa would require an additional one hour, and the total Quotation price should increase to $300 to $350..

Additional blisters in the same granite spa should be quoted at a reduced cost.  The increase for the second blister should be 50% ($375), and the third blister should be an additional 30% ($450) of the first blister.  Reasonable judgment should be used for cases with numerous blisters.  It may get so costly that it would be cheaper to replace the spa, particularly if it is a portable one.

GO TO  http://www.multitechproducts.com/pages/Procedures.html for specific directions on repairing a spa blister with the MTP Binding Resin.

2)  A 6” long crack at the rim of a Granite colored spa.  The spa has been drained by the customer to provide a dry working space.

–         Total time to prepare and complete repair by an average skill technician = 2 hours

–         Cost of materials ~  $50 (based on buying one single use repair kit)

–         Quotation Price ( including maximum of 1 hour travel time) = $200 to $250

Comments:   A similar repair on a Marble pattern spa would require an additional one hour, and the total Quotation price should increase to $250 to $300.

Additional cracks in the same spa should be quoted at a reduced cost.  The increase for the second crack should be 50% ($300), and the third crack should be 30% ($375) of the cost of the first crack.

GO TO  http://www.multitechproducts.com/pages/Procedures.html for specific directions for a cosmetic repair of a spa crack.

3)  A 2” diameter hole in a spa, which requires rebuilding the FRP reinforcement.  Depending on what caused the hole, there could be spider cracks emanating from the circumference of the hole.  These will increase complexity of the repair, and the cost.

–         Total time to prepare and complete repair by an average skill technician = 4+ hours

–         Cost of materials ~  $30 for FRP structure materials and $50 for cosmetic repair kit

–         Quotation Price ( including maximum of 1 hour travel time) = $400 to $450

GO TO  http://www.multitechproducts.com/pages/Procedures.html for specific directions for a structural repair of a spa.

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.


Yes, cracks in spas or bathtubs can be fixed.  First, let us understand what a crack is.  Spas are subject to both cracks and crazing.  A crack is a well-defined, easily seen separation of the surface.  It can be a single crack or have a few branches.  Whereas, crazing consists of hundreds of small, often difficult to see without magnification, cracks covering a large area.  Cracks and crazing have different causes, and crazing is more difficult to repair.

CRACK                                                                CRAZING

Cracks can occur due to mechanical impact, or due to excessive stress in the surface, which becomes higher than the material strength. Multiple causes of excessive stress exist. These are exaggerated when the surface gets hot due to sunlight, etc. There can be multiple cracks in a surface, and they go through the entire surface layer.  Crazing is generally caused from chemical attack.  The chemical aatack can be from the visible surface side, or the underside.  Crazing from the underside has been predominately caused by excess styrene in the fiberglass reinforcement.  Numerous chemicals have been known to cause cracks and crazing from the visible surface.  These are normally caused by the owner.

Cracks in acrylic or gelcoat spas, bathtubs or showers can be repaired using Multi-Tech Products Corporation (MTP) surface repair kits and procedures.  Visit http://www.multitechproducts.com to order these materials, and to learn how to use them for repair.

Many bathrooms contain a combination, one piece shower and tub.  These are generally made from fiberglass reinforced plastic (FRP) coated with a gelcoat resin.  They can develop cracks in the tub bottom caused by inadequate support to withstand the weight of the users.  Repair of these cracks require adding reinforcement to the underlying support structure.  MTP also has products and procedures for this operation.  Please go to the website and find the procedure for tub bottom replacement.

Go to http://www.multitechproducts.com/pages/procedures.html for more information on repair procedures.