Archive for September, 2013

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



Cultured Marble Repair

TO:  Multi-Tech Products

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



Cultured Marble

TO:  Bill

Yes, our materials will repair cultured marble surfaces.  The most common burn is from a cigarette.  Most of these are repairable.  For information on how to accomplish a repair, and some of the limitations, see our procedure at:

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

I hope this helps.

Rob Clos


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