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Our FAQ section is here to answer the most commonly asked questions. We have also added a glossary of terms in pdf form for your ease of use, feel free to download the glossary and use it as a reference.

Please take a look through our How To page if you can’t find the answer here. If it is a process you are wondering about you are more likely to find it there. It carries step-by-step instructions on several projects for do-it-yourselfers.

If you cannot find the answer to your question on the site please e-mail technical support or call us at 800-272-7890, one of our experienced techs will answer your question.

Glossary of Terms.pdf

FAQ Subjects

A hard white build up has accumulated on my mold – what is it?

Why are some resins called waxed and un-waxed?

What is Viscosity and Thixotropy?

What are the differences in Polyester Resins?


A hard white build up has accumulated on my mold – what is it?

The appearance of a hard white build up on the mold surface is commonly mistaken as evidence of styrene in the parting wax or wax build-up. The white substance is more likely styrene that has migrated from within the mold to the surface and broken through the wax barrier. Styrene molecules in the mold are attracted to styrene molecules in resins used to form the part and will bond if allowed to come into contact, causing the part to stick.

Waxes are applied to mold surfaces prior to the molding process in order to prevent bonding. However, heat generated during the molding process gradually softens wax and can inhibit its effectiveness as a barrier. In order to prevent styrene migration between mold and part a polyvinyl alcohol film (PVA) such as Partall ® #10 should be used in conjunction with wax. If applied properly, PVA creates a solvent resistant, yet water soluble barrier through which styrene molecules cannot penetrate. Wax and/or PVA must be applied properly and adequately in order to form an effective barrier.

The use of PVA is particularly necessary on new, repaired or reconditioned molds. Once a mold is seasoned wax alone is normally sufficient as a barrier when applied as needed but PVA can certainly be used as extra protection against costly and time-consuming molding hang ups, particularly on very large, intricate, or expensive molds.

If styrene migration does occur you will need to recondition the mold surface. This type of build up usually requires stripping down the mold with a proprietary mold cleaner or in extreme cases a power sander until styrene is no longer present on the surface.  In some cases buffing or hand rubbing the mold with fine abrasives or finishing compounds may be sufficient. The key is to remove all traces of styrene build up from the mold surface. Keep in mind that a reconditioned mold should be treated like a new mold in terms of the waxing/PVA process.


Why are some resins called waxed and un-waxed?

These terms usually talk about polyester resins, the first one waxed is an orthophthalic resin used in general fiberglass work where it is usually left a "natural" finish. This resin has a wax added to it to protect the resin
and underlying glass fibers from moisture penetration. The wax coming to the surface as the resin starts to cure (dry). for most diy repair projects the resin supplied in kits will be waxed resin.

The other resin which is called isophthalic resin is sold un-waxed, this resin is also a little bit more expensive to buy, is a higher quality resin being stronger in nature, has better chemical resistance
and is usually the preferred resin used in fiberglass boat building and repair work as it can be left for a day or two without sanding prior to further laminate build up.
Wax is best added to this resin on the last coat if it is being used under a boat floor/hull situation or left without surface finishing (e.g. painting) to protect from moisture entry.


What is Viscosity and Thixotropy?

The science of liquid movement is called “fluid dynamics”. We will take a look at two (2) simple parts of this known as “viscosity and thixotropy”.

Very simply, the “viscosity” of a liquid is how thick that liquid is. “Viscosity” can be measured in a number of ways and with different units of measure. Commonly used units of measure include stokes, poises and centipoises (cps). Scientifically speaking, it is the resistance of the liquid to oppose the energy being used to move it.

By examining water, which has a very low viscosity and comparing it to the “viscosity” of honey, which is higher, it would be much easier to stir the water and use less energy than stirring the honey. Both water and honey are called “Newtonian” fluids. This means the energy needed to move these materials is directly equal to the speed at which they are moved.

For instance, if it takes one unit of energy to move water at 1 mile per hour, it will take two (2) units of energy to move water at 2 miles per hour. It is directly proportionate.

“Thixotropy” is how much body or fluffiness there is in a material. A good example of a highly “thixotropic” liquid is mayonnaise. Mayonnaise has a high “viscosity” when stirred slowly but a much lower “viscosity” when stirred quickly. Because “thixotropic” liquids are called “Non-Newtonian” fluids, this means the energy to move them is NOT directly equal to the speed at which they are moved. So as in the above example of mayonnaise, “thixotropes” have a high viscosity when moved at a slow speed and a lower viscosity when moved at a higher speed.

The ratio of the slow speed viscosity or the “high speed number” divided by the high speed viscosity “low viscosity number” is called the “thixotropic index”. This refers to how much body the material has, how well it will hang and how well it will resist sagging, due to gravity.


What are the differences in Polyester Resins?

Unsaturated Polyester Resin Solution: Unsaturated refers to carbon-to-carbon double bonds, which have the ability to open up and crosslink with other unsaturated molecules such as styrene. The breakdown of the word polyester is poly meaning many and ester being a certain type of chemical connection that binds these molecules together. A solution indicates a mixture of different molecules; those that will crosslink together like the polyester and the styrene and those that will control the rate of the reaction such as the cobalt and various aniline accelerators.

There are basically 4 different types of Unsaturated Polyester Resin Solutions, which we sell and they are the low profile DCPD, Orthopthalic, Isopthalic, and Vinyl-Ester. The type of resin produced is dictated by the raw materials, which are used to make the polyester molecule and will result in these products having different end properties and different associated costs. While resins may be fit into these different classes, keep in mind many manufacturers will blend them together for their different products.

DCPD Type Resins are based on a chemical called Dicyclopentadiene and form a type of resin called Low Profile. Low Profile indicates resins, which are typically harder with less shrinkage, and most importantly, resist the tendency for resins to “print through”, that is to show the profile or outline of the underlying fibers of glass, carbon or aramid through the gel-coat surface.

Ortho Type Resins are based on Orthopthalic acid. These are the general purpose resins used in thicker laminates to build up thick sections of composites. They are easy to work with and usually cure with a slightly tacky outside layer, which is good in that it provides better inter-laminar adhesion to additional layers. The engineering parameters of these products such as tensile strength, flexural strength, impact resistance, and fatigue resistance are best described as good but not best.

Iso Type Resins are based on Isopthalic acid. These are generally considered a higher class of resin and a little more costly. They are not quite as user friendly but have improved engineering parameters such as tensile strength, flexural strength, impact resistance, and fatigue resistance. Additionally, they will also have much improved water and chemical resistance.

Vinyl Ester Resins are based on liquid epoxy resins. These Resins are considered the premium product in performance as well cost. Their downside is they have a tendency to foam with the wrong catalyst, which can result in porosity. The bigger advantages to these resins are their fatigue resistance and their high temperature resistance for chemicals and solvents. This makes them useful for a number of applications where no other product would suffice such as tanks for acid baths and containment for other chemicals. Additionally they have excellent water resistance and have become the resin of choice as a moisture barrier coat for submerged applications such as boats and pools.