How long to kick off?

[Project_Mayhem]

I've been working on a lot of fiberglass right now and it's taking forever for the fiberglass to kick. Today it was in the low to mid 50's. I mixed a medium size batch for the length of my centerboard's leading edge, mixed in some 404 filler and started pouring. An hour and a half later and it doesnt appear as if it's hardened at all. It appears as if a lot of very small bubbles are forming after 30-45 mins. This happened on two separate occasions. I started packing up 1.5-2 hours later and It appeared to be the same viscosity as when I first mixed it. This is the third fiberglass project with this batch of resin. The fist two acted the same but they were hard when I came back the next day. I even used a heatgun on the second project with no noticeable difference.

We're seeing temperatures ranging from high 50's to low 70's right now. I'm using 205 fast hardener. Container dimensions don't seem to have an impact on cure times. How long does it take for your resin to kick?

 

[jssailem]

I would look up the West Systems info on cold temperature epoxy use. They have a report on how to use their epoxy under cold conditions. The issue is not just the air temp but the temp of the surfaces you are working on. You need to heat the surfaces with heat lamps or heaters and a tent to create a warm environment around the centerboard you are repairing.

 

[dlochner]

Epoxy resin takes much longer than polyester resin to cure.

One issue with epoxy is an improper mix ratio, the ratio of hardener to epoxy is critical. This happens when you lose count or on the first pump after the pump has been sitting a while. Some of the hardener or resin drains out of the pump, this causes the first pump to have a smaller volume of resin or hardener. Always prime the pump before dispensing the liquids by pumping until you get a full pump. You'll know it when it happens.

And, as John said air temp is only one factor. The temperature of the centerboard is a more important factor. While the air temp may be in the 70s the CB temp may only be in the 40s or 50s. If you an IR thermometer you can check the temperature and warm with heat lamps or a small heater.

 

[sailnoproblem]

I have had a lot of experience with polyester but not with epoxy, but it seems that you don't have the correct mixture. It should start kicking a lot sooner then what is happening in your situation. How old is your resin and hardener?

 

[daviddp]

I was advised to use a sheet of waxed paper over the repair to "hold the heat" while curing @ similar temps to what you are describing. It made a difference it time to harden. It also stopped the "sagging" that happened with the slow curing.

 

[dlochner]

I was advised to use a sheet of waxed paper over the repair to "hold the heat" while curing @ similar temps to what you are describing. It made a difference it time to harden. It also stopped the "sagging" that happened with the slow curing.

Yes, the reaction for both polyester and epoxy resins is exothermic, meaning it gives off heat. In colder conditions, retaining that heat will help to cure the resin. For this CB repair, it be helpful to cover the repair with peel ply or plastic wrap and then put an old blanket on top to slow the heat loss. Conversely, the working time for epoxy can be extended by using pouring it into a large flat pan instead of a cup. The greater the surface area, the more the heat will dissipate and slow the cure rate.

I prefer plastic wrap over wax paper because some of the wax on the paper may transfer to the epoxy. That will interfere with any additional layers of fiberglass, paint, or gelcoat.

 

[Project_Mayhem]

The centerboard was kept indoors until I started working on it last night. I used a large TotalBoat mixing container that's about 4" in diameter. I filled it up about 3-4" (10 pumps). Mixed for 90-120 seconds and then added filler. I layed the resin along the leading edge of the board. I filled a 2-3" wide area that stretched out about 24". It's a large area so it was easy for the heat to dissipate. Because it never really thickened it spread out more than I wanted. I mixed a second batch but suspecting there was a ratio issue I added 6 pumps of hardener and 3.5 pumps of resin. Yes, a bit extreme but it actually started to get warm after 15-20 minutes. As soon as it started to generate heat I dumped a large amount of filler in it and mixed to peanut butter consistency. It probably took me 15-20 minutes to clean up and I don't believe it thickened much before I brought it inside. The resin was purchased about a month ago. Something doesn't seem right. I've seen West resin melt plenty of cups and exotherm like crazy. This stuff barely gets warm. It will gel to the point that it's unworkable but we never see it get hard until we come back a few days later to do some more work

 

[dlochner]

I added 6 pumps of hardener and 3.5 pumps of resin. Yes, a bit extreme but it actually started to get warm after 15-20 minutes.

This is the issue. With polyester resins adding more catalyst will speed the cure time, adding more hardener to epoxy will not. What you have is partially cured epoxy and there is not enough epoxy resin to react with the hardener that you mixed with it.

The chemistry is different. Polyesters use a catalyst which stimulates a reaction in the resin. Epoxies don't have a catalyst, rather the 2 parts, resin and hardener react together to form a new compound.

A catalyst does not become part of the final solid whereas the epoxy hardener does become part of the final solid when the chemical reactions have been completed. Here's a couple of links:

https://www.westsystem.com/instruction-2/epoxy-basics/epoxy-chemistry/

https://www.sciencenewsforstudents.org/article/explainer-catalyst-chemistry

We have a couple of chemists on the forum, @thinwater and @rranger who can probably explain the difference between the chemical reactions better than I can.

I'm afraid your only option at this point is to remove the bad batch of epoxy. You can try mechanically removing it with a scraper, heating it with a hot air gun may make it easier to remove, it will soften even more at about 150° F. Vinegar or Denatured Alcohol can clean up the residual goo.

 

[shemandr]

If you are unsure of the mix volume from the pump weigh the two parts.

 

[daviddp]

You are correct David. I did use plastic wrap, not waxed paper. Of course, I still say "tin foil" vs aluminium foil. And I always make a "xerox" copy and store all my old stuff in the cellar.

 

[dlochner]

And I always make a "xerox" copy

Well you do live in Xerox country.

 

[Project_Mayhem]

This is the issue. With polyester resins adding more catalyst will speed the cure time, adding more hardener to epoxy will not. What you have is partially cured epoxy and there is not enough epoxy resin to react with the hardener that you mixed with it.

I used a different ratio as a test to see if my original ratio was off. The fact that it started generating heat in a reasonable amount of time suggests that the original ratio may be off

 

[dlochner]

I used a different ratio as a test to see if my original ratio was off. The fact that it started generating heat in a reasonable amount of time suggests that the original ratio may be off

With epoxies you have to precisely follow the manufacturer's instructions. Polyester resins are more forgiving, but not epoxy because of the difference in the chemistry.

 

[Ken Cross]

I accidentally mixed the wrong ratio (2 parts hardener with one part resin which should have been reversed) and after more than a week it was still a sticky mess. A heat gun and rags removed it with a little wipe of acetone and I started over. Mix per the directions only.

Ken

 

[Project_Mayhem]

I used a different ratio as a test to see if my original ratio was off. The fact that it started generating heat in a reasonable amount of time suggests that the original ratio may be off

 

[dlochner]

I used a different ratio as a test to see if my original ratio was off. The fact that it started generating heat in a reasonable amount of time suggests that the original ratio may be off

Heat is a by product of the chemical reaction of the hardener and the resin. If the resin and hardener are in the wrong proportions it will never fully cure. The reaction is not at all like drying paint, in which the solvent evaporates leaving a dry hard finish.

Think of it like baking a cake. If there is too much flour and not enough water, the cake will be dry and brittle. If there is too much water and not enough flour it will wet and soggy.

If you are measuring and mixing the components correctly you should barely notice any increase in temperature. The temperature rise will be slow. If the temperature of the epoxy is allowed to rise too quickly, it will become exothermic, meaning that the heat generated by the reaction is not dissipating quickly enough and the epoxy is over heating. When this happens the epoxy forms gas bubbles and it becomes very foamy and is structurally very weak. The main cause of becoming exothermic is too much epoxy in too small a space, the heat generated is contained which increases the reaction speed which raises the temperature and you get a run away chemical reaction.

What you did by adding too much hardener is to stimulate a rapid chemical reaction between the hardener and the epoxy, that cause the temperature to rise rapidly enough to perceive the temperature increase. However, once all the hardener was consumed there was nothing left for the epoxy to combine with, the chemical reaction stopped and you were left with a mess of uncured and partially cured epoxy.

 

[Project_Mayhem]

I prefer plastic wrap over wax paper because some of the wax on the paper may transfer to the epoxy. That will interfere with any additional layers of fiberglass, paint, or gelcoat.

Does the plastic wrap ever melt from the heat?

 

[dlochner]

Does the plastic wrap ever melt from the heat?

It shouldn't get that hot. Once cured epoxy gets to about 150° F it begins to soften that should be well below the melting point of the plastic wrap.

 

[jssailem]

You can get different types of plastic wrap. Different thickness.
Not just mothers saran wrap.

 

[Project_Mayhem]

Oh I have plenty of plastic drop cloths!