Resin and Fiberglass FAQs

It is important that only the recommended mixing ratio be used. Too much or too little hardener will produce inferior results. Never thin epoxy with solvents. Be sure to mix thoroughly, as incomplete mixing will produce an incomplete cure. Mix vigorously for two (2) minutes. Page 3 of Product Bulletin Premium Marine Grade Epoxy, the section on Mixing will answer this question in more detail.

Catalyst ratio can be varied to speed up or slow down the cure. Do NOT use less than 1% or more than 2% catalyst to the resin.

Use no more than a ratio of 10% by volume of the Styrene Monomer for thinning, as higher concentrations will degrade the resin's properties. Do NOT use with epoxy.

The coverage area for resin can vary dramatically depending on the particular application and the application technique. Here is a general "rule of thumb" for resin coverage: (per gallon)
Cloth: 40 sq. ft.
Mat: 20 sq. ft.
Roving: 15 sq. ft.
No Fabric: 100 sq. ft.

There are many resources on this site to help you make a choice. In particular please explore the Product Information section for numerous relevant pdfs. Here are a few advantages and disadvantages of each:

Polyester Advantages:
• Lower cost
• Cure time can be controlled by the catalyst ratio
• No sanding between layers
• UV resistant (Surfboard resin)

Polyester Disadvantages:
• Odor and flammability
• Need to establish a surface cure

Epoxy Advantages:
• Better adhesion
• Better chemical resistance overall
• Low or no odor

Epoxy Disadvantages:
• Requires accurate mix ratios
• More expensive
• If cured, requires sanding between layers.

Read Product Bulletin Premium Marine Grade Epoxy. The 143 B-Side Hardener (Slow) excels in penetration. It contains no solvents.

Permanent damage can result if a resin system is used in any kind of a paint sprayer. However, TAP sells the perfect answer, a GelCoat and Resin Spray Cup Gun.

Gel time (also called 'pot life') of resins depends on the resin, the volume, and the temperature. Higher volumes and higher temperatures accelerate the cure, shorten your working time. For typical gel times see our comparison chart.

TAP carries a variety of mold releases. See our Mold Release page: https://www.tapplastics.com/product/fiberglass/mold_releases

For a mildly dirty surface, use soap and water follwed by water. For faded, oxidized gel coat, use either 3M Marine Fiberglass Restorer.

Yes, nitrile gloves are fine for acrylic cement. For extensive exposure (which should not happen), many people recommend double gloving. However, proper use of the product should result in no contact with the cement.

Envirotex Lite may be used over the glass; however, the bond of the Envirotex Lite to the glass is not strong. The Envirotex Lite could be peeled off. A frame around the table edge so that the edges were not exposed would probably offer a solution.

Always experiment with a sample before attempting anything with irreplaceable parts. The release process for the master is different from that of the casting. Plaster can be sealed with potters’ soap or Murphy’s Oil Soap. Lather it into the damp surface of the plaster with a soft brush. Rinse and repeat several times.  Then polish with a soft cloth.  Once dry and sealed, you can use Rocket Release. It will not leave a residue in the mold that will make painting castings difficult. It can’t be over emphasized that it is important to practice in order to perfect the technique and learn the characteristics of these products.

The resin should cure, if given enough time; however, a cold environment is not good, Put it in the sun with a box over it to create a mini oven. If you can, paint the box black so it absorbs the sun’s heat. If that does not work, the mold may be cleaned. Casting resin can be cleaned off with acetone. Remove what you can with a spatula (or something like that). Just be careful not to damage the mold. Then wipe off the remaining resin with a rag and acetone. You will be good as new.

Casting is as much art as it is science. The shape of the casting can make a huge difference. If it is a thin casting with a lot of surface area, the cure will be very slow.  If it is in a mass, such as in a 3 oz. mixing cup, the cure will be much quicker. The shape factor dramatically affects your catalyst ratio. So, while we try to give guidelines, the ultimate answers for each situation come from experimentation. The other issue is how many layers the final casting will be. The more layers, the less catalyst per layer. The fewer layers, the more catalyst.

Latex Advantages: Advantages: Extremely economical. The mold could be made for just a few dollars. Also, it probably will not need a mold release, making the parts that come out of the mold ready to paint.

Latex Disadvantages: It takes longer to make a mold since 5-10 layers must be painted on. A ‘mother mold’ would need to be created to support the latex, since it is so thin. That can be easily done with plaster of Paris. See that demonstrated in our video.

Urethane RTV Advantages: Very tough, long lasting rubber. Easy one-to-one mix ratio. A poured-on block mold requires very little labor. Since it is a block mold, it will be self- supporting.  It is more economical than silicone.

Urethane Disadvantages: Since the master is painted with urethane, mold release is a must (urethane bonds to urethane, permanently). TAP sells a paintable mold release called Rocket Release. Practice with it before trying to make a mold of the good master.

Silicone RTV Advantages: Silicone does not require a mold release. Silicone RTV is less expensive than Platinum Silicone. Can be used to make a block mold, just like the Urethane RTV.

Silicone RTV Disadvantages: It is challenging to mix, due to its high viscosity.  Special precautions must be taken to avoid trapping air in the mold. . 

Platinum Silicone Advantages: It is the fastest with a 2 hour cure. Easy one to one mix. Good bubble release. No mold release required.

Platinum Silicone Disadvantages: It is the most expensive.

Casting fragile items such as flowers presents three issues. First, because the item is so fragile, it can come apart when put in resin. Try spraying the item with a thin coat of lacquer or clear coating of some kind. Another thing to try is thinning white glue with water with a ratio of four parts of water to one part of glue, and coat the item with that.

The second issue is bubbles. Complex shaped items tend to trap bubbles. Before embedding the item, try dipping it in catalyzed resin and then letting the resin drain off. Then embed the item.

Finally, there is the issue of color retention. Even though a flower or some other ‘living’ item may be embedded in plastic, it still continues to decay. Some materials retain their color over time and some fade with time. There is not good way to control that inevitable process.

Most food containers, like Tupperware, will work. Even butter tubs, the bottoms of squeeze bottles, etc. are usable.  However, if the plastic is hard and brittle, then it probably won’t work. One thing to look for is a recycle symbol on the bottom. Under the symbol you will see some letters. These letters will all work without a mold release: PE, LDPE, HDPE, and PP. Of course, as always, it is best to test before casting something irreplaceable.

When new resin is put over cured resin, the new resin must have good ‘sticking’ or adhesive properties. In other words it has to be a good glue in order to bond to a non-porous surface. If you go to the adhesives aisle in a store, you will find many epoxy glues, but no polyester glues. That is because polyester is really not an adhesive (glue); it does not glue itself well to epoxy. But epoxy is a good glue, so it will stick to polyester.

This relates to the question above. Carbon and Kevlar are difficult to bond to. The resin of choice must have good bonding properties, making epoxy a better choice than polyester.

Polyester and epoxy resins can be peeled off a sheet of glass. Fiberglass has a coating applied to it during manufacture. This coating is called a ‘sizing agent’. It is a special molecule in which one end bonds to the glass and the other to the resin, holding the two together. The glass fabrics TAP carries have a sizing agent that is designed to work with both polyester and epoxy resins.

Most of our customers are do-it-yourselfers who find it far more convenient to measure by volume than by weight. Our pump system makes that even easier. For those who wish to measure by weight the ratios are as follows:

• Marine Grade Epoxy Resin: 100
• Marine Grade Hardener 102 Fast: 22
• Marine Grade Hardener 109 Med: 22
• Marine Grade Hardener 143 Slow: 43
• Super Hard Epoxy: 100 resin: 22 hardener
• One-to-One General Purpose Epoxy: 100 resin: 85 hardener

That depends on how much time passed between layers. Resin goes through stages of curing. It starts out as a liquid, goes to a gel, then full cure. As long as the resin is not fully cured, each new layer will chemically bond to the prior layer. The best way to tell if it is still early enough in the cure process is to press your fingernail into the surface. If you can still indent it, then you can go ahead and add a layer without further preparation.

If you cannot dent the layer, it means the cure is too far along to get a chemical bond. Now the surface must be prepared for a mechanical bond. If the environment is cool or humidity is high, there may be an oily appearance to the surface. If so, wash it off with water and a scrub pad. Then sand with 80 grit sandpaper to roughen the surface. Wipe clean with acetone or alcohol. Then you can apply the next layer.

Keep in mind that even though the surface is hard, curing is still going on at a molecular level for up to a week. Do not put epoxy in water or expose it to chemicals before that time.

We have epoxy and vinyl ester resins that can be used with carbon fiber.  The vinyl ester has a higher heat distortion temperature and is more rigid and thus more brittle. You can find it HERE. Being a polyester, you will need to ensure surface cure and it will require sanding and buffing for a gloss finish.

Epoxy, on the other hand, fully surface cures, has better impact resistance, and cures to a gloss finish. I would recommend our Marine Grade Epoxy with either the fast or slow hardener. You can find it HERE. Read the product bulletin (link at the bottom of that page) to see the differences between the fast and slow hardeners.  Speed is not the only difference.

Sealing the foam depends on what kind of foam it is. If it is a urethane foam, you can seal it with the resin you use for the lay-up. If it is a Styrofoam type of foam, seal it with either epoxy, or Ultra-Seal. If you do not know what kind of foam it is, put a drop of acetone on it. If nothing happens, you have urethane. If it dissolves a hole, you have a Styrofoam type of foam.

Yes and no. Both types of resins go from a liquid state, to a gel, to a hard cure. There are two big differences, however. As epoxy is curing, while it is in its liquid state, it starts to warm up, giving you some warning of the curing status. After working with a particular epoxy, you will soon be able to judge when the resin is about to gel.

Polyester, on the other hand, gives virtually no temperature warning before it gels.

The second difference has to do with the surface cure. Epoxy cures completely in the presence of air. Polyester does not. The surface molecules of a layer of polyester do not fully cure (called crosslinking), yet everything below the surface layers does cure. The big advantage to that is that there is no need to sand between layers, since each layer seals the prior layer, resulting in a complete cure. When it comes to the final layer where surface cure is desired, wax is often added to the resin. As the resin cures, the wax floats to the surface, where it seals off the air, allowing the surface to fully cure.

Chopped strand mat consists of short strands of glass held together with a glue, called a binder. Polyester resin dissolves the binder, freeing the fibers to move independently. As a result, the mat can move in any direction, conforming to complex shapes. Epoxy does not dissolve the binder, so the mat stays relatively stiff.

Fiberglass fabric is made up of small strands of glass. The glass begins as a molten mass of chemicals that are stretched into small fibers. The chemical combination in e-glass is economical and easy to produce. It was originally used to make electrical insulators, hence the name ‘e-glass’, or electrical grade.

S-glass, also known as S-2 glass uses a different and more expensive chemical formula in the molten glass. This formula produces glass that is much stiffer and stronger that e-glass. It is a good choice for those who want increased strength, but do not want to pay a premium for carbon fiber.