gel coat problem

[GarzaTaxidermy]

  what are your thoughts on what is going on?

  We are spraying our gel coat, letting it setup then laying up the glass without problems. Lately we have had a few fish come out with the gel rippled in a few spot. What is causing this?

[Pescado]

I would guess that the parts were not mixed up 100%. I do not use gelcoat but have had issues  with mo polyuretane if not mixed thoroughly. I wouldn't think a polyester or epoxy gelcoat would be much different.

 PB

[Mike B.]

Maybe moisture in your air line's ? Have you changed your filters lately.

[GarzaTaxidermy]

yes sir that was the first thing we checked also we switch to a new batch of gel coat just in case it was a bad batch

[beaker]

Don't know if it will help but a similar problem was discussed on a VERY different forum:
http://www.theeffectslab.com/forums/viewtopic.php?t=17104

[marshy creek]

garza....you problem is what called alligator....if you don't flash coat over the gel coat, this will happen.....once the gel coat gets tacky, it is then time to lay up your mat and resin....fiberglass resin is photo chemicly reactive....if you don't have the time,next time try this....gel coat and set in the sun......allow to dry 24hrs....next mix fiberglass resin, cover the gel coat and set in the sun......it should set in a very short period of time...this should solve your problem...anyone that thinks sunlight will not effect the set time of resin, try brushing some on cardboard, one left in the sun, one not....see the differance

[GarzaTaxidermy]

Thanks for all the help, we also found some good info at this site.
http://www.boatdesign.net/forums/

[Doug Bridges]

Sorry Marshy, but I don't think polyester resin is "Photo chemically reactive". I thought that statement was questionable based on what I know about polyester resins, so I did some research to confirm what I thought. It's a chemical reaction that "Cures or Polymerizes" the material. They don't dry. Here is some information on the process of adding a catalyst to the resin to start the curing process. I think the result that you are seeing is the effect of heat generated from the sun, not a photo reaction.

Here is a good resource for the information:    http://www.netcomposites.com/education.asp?sequence=9

"Resins can be formulated to requirements ready simply for the addition of the catalyst prior to moΩlding. As has been mentioned, given enough time an unsaturated polyester resin will set by itself. This rate of polymerisation is too slow for practical purposes and therefore catalysts and accelerators are used to achieve the polymerisation of the resin within a practical time period. Catalysts are added to the resin system shortly before use to initiate the polymerisation reaction. The catalyst does not take part in the chemical reaction but simply activates the process. An accelerator is added to the catalysed resin to enable the reaction to proceed at workshop temperature and/or at a greater rate. Since accelerators have little influence on the resin in the absence of a catalyst they are sometimes added to the resin by the polyester manufacturer to create a 'pre-accelerated' resin.The cross-linking or curing process is called 'polymerisation'. It is a non-reversible chemical reaction. The 'side-by-side' nature of this cross-linking of the molecular chains tends to means that polyester laminates suffer from brittleness when shock loadings are applied."

[Doug Bridges]

http://www.netcomposites.com/education.asp?sequence=12

Check out this page for a good explanation of the curing process and the effect that heat has on the time to cure.

[marshy creek]

no problem Doug...you might want to do some reasearch on "oxidizers".....a heat is created by the MEKP "oxidizer" without the heat of sunlight....resin can be kicked with very little MEKP since the process is already started.....I am sure you know this already....fact is:

"By contrast, polyester resins are usually made available in a 'promoted' form, such that the progress of previously-mixed resins from liquid to solid is already underway, albeit very slowly. The only variable available to the user is to change the rate of this process using a catalyst, often Methyl-Ethyl-Ketone-Peroxide (MEKP), which is an oxidizer and very toxic. The presence of the catalyst in the final product actually detracts from the desirable properties, so that small amounts of catalyst are preferable, so long as the hardening proceeds at an acceptable pace. The rate of cure of polyesters can therefore be controlled both by the amount of catalyst, the temperature at application and exposed light source"

[Doug Bridges]

Ok, I stand corrected. There are UV cure Polyester Resins that are a specialty product, but I doubt that most taxidermists are using UV cure resins. You listed MEKP which is an oxidizer and is added to the resin to accelerate the curing process. Even your statement above says the "heat of sunlight" not the uv rays of sunlight.

But to make a general statement that polyester resins are UV cure is not correct.

[marshy creek]

no problem Doug....although there are specialty UV resins, commonly used in the surf board and in the printing business, all Polyester Resins with the addition of the catalist, have UV properties.... the amount of "oxidizer" added does and will control cure rates without UV light, but adding a light source will promote the process.....the normal layup of resin usualy does not create enough "heat" in such thin applications....therefore, many add to much hardner to push the process....this changes the properties and strenght of the final cure....less hardner is better than more....a more active catalist like Hi Point 90 adds a much better UV reaction than the normal hardner that come with resin....thats why it should be stored in a cool, "dark" place...Blue Light Bulbs, used in the photo business produce very little heat, but have hi UV output.....I can't find anywhere in my posts, that I made the statement "heat of sunlight"......anyway Doug, I only responded to Garza to try and solve his problem, and not get into a pissing match with anyone....after almost 40 years of working with resins, I have experianced every problem you could have......and in that time, have tweeked the process for fish repo's....with the proper catalist, you can put a layed up fish blank out in the middle of winter and have it kick, as long as you have light....good luck Doug and thanks for your input

[nts2010]

Hey Doug . without trying to sound like a smart backside I have found that the curing of polyester resin can be reversed ! I discovered this when trying to clean the inside of a f/g deer mould , Some paint strippers designed to lift 2 pac industrial paints WILL break down the catalyst within the resin  leaving a gooey mess with matting fibres exposed . Just a bit of useless info for you to ponder .

[Doug Bridges]

Yep. Fiberglass resin is vulnerable to some solvents. I don't know if it reverses the chemical reaction or if it just breaks down the resin. Kind of like uncooking an egg, maybe?