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