Who knows the Science of Polyester Resin and temperatures

[rbk]

Originally Posted by ShoreFun

Just a bit more.

I have garages, but they are kind of filled up and unheated. I have a couple of antique cars. Though I might make some room in the unpowered back garage.

I am aware of the toxic nature of the vapors and have been working outside with the resin. I could suit up and I even have a pressure fed hood from doing auto paint work. But that is too much work for these small jobs I need to do.

One of my learning tasks is how to get the repair over larger area below grade so I can lay in the gelcoat. I am learning as I go. I am used to making accurate patches in metal and then TIG welding them in place. Then I do finish work in the metal and only ever need a few coats of building primer to level. I mostly use a thin filler to cover some rust pitted areas.

These are just simple and really fun Sunfish. So I am forgoing making them perfect and working for nice looking and functional.

My belief is I need to get the resin cured enough to be hard before letting them get cool. I have to worry about condensation here where I live from temp changes and moisture is bad until cured enough is what I take out of various sources. So I believe I can get away with Halogen painting lamps to keep the temp up for a few hours. Then maybe expose the area to some sun for a few days.

This is the resin I have. https://www.aoc-resins.com/pdf/web_H596.pdf

If unwaxed (Doesn't say on your product sheet) build it up structurally until your close to happy, tint the last layer of resin and IMO if you want to keep the work down and avoid gel coating/painting the entire boat, send a chip into these guys: https://www.dolphinite.com/, spot repair then go sailing.

[Martkimwat]

You should only do GRP work at temperatures above 10ºC unless you can uniformly heat the working area and keep it warm till it cures, also use more catalyst up to 8% unless you are really concerned about ultimate strength. If you try to do it below that temperature it will not go off until the temperature increases, and by that time I think the styrene has vented off and the GRP will not cure properly and will be crumbly/rubbery and under-strength, and may even not cure properly at all.(remains tacky to the touch) don't ask me how I know!
I know the purists may say not to use more than 4% catalyst, and if your doing work to Lloyds spec, that's fair enough but for general GRP work I have found using higher amount of catalyst, certainly up to 8% has worked just fine. I understand that using more catalyst may also create bubbles in the layup but I have not noticed anything like that. If I was doing GRP work close to or below the waterline I might be more circumspect.

I'm not a chemist but I think the chemical reaction is much too slow below 10ºC, I believe that it needs a little exothermic reaction to set which can't get going if it is too cold.

[Locquatious]

In general, the rule of thumb is that for every 10 degrees C increase in temperature, the reaction rate doubles. Arrhenius theory.
At the higher temperatures diffusion increases allowing the reacting components to find each other more quickly.
That being said I have found that epoxy cures are more sensitive to heat.
As the cure continues, the viscosity increases to the point where the glass transition point is reached. The matrix becomes like a glass and molecular motion is severely slowed. The cure stops. If you raise the temperature above Tg, the reaction continues, raising the Tg even higher. There is a maximum Tg for a material system. Above that Tg, cure will continue but the Tg will not increase. The higher temperature may lead to deformation.
At the lower temperatures, below Tg, smaller molecule diffusion can cause problems even in the glass matrix. For example moisture may react with epoxy groups making them unavailable for an epoxy-amine reaction. Similarly, peroxide cures might be inhibited by oxygen.
So it is a good idea to bring the cure to completion by raising the temperature once the resin has started to harden. This will avoid a runaway exothermic reaction which often occurs when the resins are liquid and even viscous gels. But it will assure that the desired cure occurs without inhibition or moisture degradation.

[Moxie 38]

Hi, Much of this you have already learned about working with thermosets (irreversibly cured) systems. However. there are direct correlations between thermoset resin systems such as polyester (or improved, long standing vinyl ester) and your concern about ambient working temperatures. I would like to share these with you.

One requisite to successful thermoset repairs is understanding that there is a direct correlation between the amount of catalyst added and, just as important, the thoroughness of the mixing process. Once the catalyst is mixed into the resin thoroughly, the cure process is described as cross linking. I mention this only because there is no such thing as a 100% cured laminate. Catalyst react by cross linking with available resin molecules. They react only with what they come into contact with. Typically, even a well formulated and mixed catalyst does not cross link 100% during the published "cure time" as remaining non-linked catalyst will forever be suspended in the repair. Just aggressively sand any "well- cured" polyester product and you will typically smell a little MekP.

I realize you are contemplating good practices for repairing a Sunfish but, understanding the mechanisms in play here apply to all thermoset repairs - for both pond and blue water boating.

So, it's also important to understand that in addition to the ambient working temperature and the thoroughness of mixing, careful consideration of matching materials to the existing reinforcement in the structure must carefully be considered. When using a matte product, be careful not to use epoxy systems unless the matte is specifically approved for epoxies. Matte reinforcements typically have a binder which interferes with the glass to resin bond.

Also and, just as important, is the physical layout of the reinforcement in the repair and the available bond area to the first ply. There are many articles on how to prepare the surrounding area prior to laying up the first ply. There are also many articles on properly matching glass reinforcements to an existing structure. These practices provide homogeneity of performance between the repair and the surrounding area. So, the bond strength of all thermoset repairs depends on all of the above and the surface area to which it is to be bonded to.

Lastly, it's important to understand that the new composite will not cross link to the existing cured laminate. At the molecular level, it must rely on an adhesive bond rather than a cohesive bond as there will be no molecular reaction at the bonding surfaces. Cross linking will only take place between freshly laid up plies of reinforcement.

So, the success of your repair will also depend on the primary area of the repair and the preparation for the first bonded ply. Remember to role or squeegee out the air bubbles prior to cure! I hope this was useful.

[coopec43]

From years of experience I can say I agree with everything Squanderbucks says.

I would never fiberglass in cold or misty weather. I very much prefer to fiberglass under cover.