Gel coat mechanical/physical properties

[SLO240]

I am new to the composites world and have attempted to read as much as possible. I have made it to about page 100 thus far, so thank you all for the wealth of knowledge.

My question which I have not found an answer to, even reading product sheets is; What are the physical properties of a gel coat or even molecular properties of a gel coat that would explain why it is recomended and commonly used for the surface layer of molds?

Similarly what would be the difference between something labeled gel coat versus tooling gel coat? Same question with an epoxy top coat and regular epoxy resin?

-Sean

[wyowindworks]

I am new to the composites world and have attempted to read as much as possible. I have made it to about page 100 thus far, so thank you all for the wealth of knowledge.

My question which I have not found an answer to, even reading product sheets is; What are the physical properties of a gel coat or even molecular properties of a gel coat that would explain why it is recomended and commonly used for the surface layer of molds?

Similarly what would be the difference between something labeled gel coat versus tooling gel coat? Same question with an epoxy top coat and regular epoxy resin?

-Sean

A gel-coat is typically polyester or vinyl ester based. Some gel-coats are designed for in-mold coatings and others are designed for fabricating tooling. Epoxy based products that are used to make surfaces for molds are typically called surface coats. Gel-coats and surface coats have thickeners/modifiers/fillers so they don’t run off of vertical surfaces. You wouldn’t use these to saturate fibers. You saturate fibers with laminating resins.

Polyester based gel-coats are typically easier to polish than epoxy surface coats. Epoxy surface coats are typically more durable than gel-coats.

Epoxy top coats often refer to table top coating systems.

[SLO240]

Thank you for the correction wyowindworks, epoxy surface coats.

So it is the addition of the thickeners to polyester, vinyl ester, and epoxy that give it its UV resistance, higher viscosity(thixotropic), and higher durability.

The base resin, the thing that does all the cross linking is basically the same between a laminating resin/epoxy and gel coat/ surface coat?

Not that I am ever going to make my own, but what are the typical thickeners added to the resin?

[wyowindworks]

Thank you for the correction wyowindworks, epoxy surface coats.

So it is the addition of the thickeners to polyester, vinyl ester, and epoxy that give it its UV resistance, higher viscosity(thixotropic), and higher durability.

The base resin, the thing that does all the cross linking is basically the same between a laminating resin/epoxy and gel coat/ surface coat?

Not that I am ever going to make my own, but what are the typical thickeners added to the resin?

Typically the fillers don’t give the resin any UV resistance. They can change the physical properties.

The base resin can be the same as the laminating resin or it can be different.

I often make my own epoxy surface coats by adding 27% West Systems 404 High Density filler and 9% graphite powder (West Systems 423) by weight to my laminating epoxy.

[herman]

As for tooling products and part products (whether epoxy, polyester, vinylester or even PU based).

All are formulated for a specific purpose. There are many variables, and manufacturers usually have products targeted at different applications.

gloss retention, easy of application, sprayable or brushable, chemical resistance, ease of repair, sandability, heat resistance, these are all variables that can be changed.

Polyester gelcoats usually have better weather resistance and gloss retention (and higher gloss to begin with), but epoxy gelcoats might be more durable.