Fiberglass resin hardener question

[snowman48047]

Is there a difference in hardener for polyester and/or epoxy resin? If the answer is yes;

Can they be switched without issue? If no;


How do I clean up the huge mess I now have with 2 solid layers and gravy in between? Cut it all out and start over?

 

[gm280]

Is your harder MEKP Methyl Ethyl Ketone Peroxide? If so are you using polyester or epoxy? If poly, no worries it will harden eventually even if mixed in wrong ratios. No so for epoxy though. There has to be a set ratio using epoxies...

 

[jbcurt00]

Are you asking about the compatibility of MEKP (polyester resin catalyst) and epoxy resin (part A) or polyester resin and epoxy hardener (part B)

Or there abouts?

For polyester resin, by volume, MEKP is added between 1% and 2% total volume of polyester resin. 100ml of resin gets 1-2ml of MEKP.

For epoxy resin, depending on working temps, desired cure rate and working consistancy you buy a hardener (epoxy part B) that matches your needs: a 4 to 1, 3 to 1, 2 to 1 or a 1 to 1. At 3 to 1 ratio, what is typically used for normal boat work iboats, 100ml of part A epoxy resin, would get 33ml of epoxy part B.

I suspect you already know the anwser to this question Snowman, but IMO, you need to remove everything down to before you applied whatever you are calling gravy under 2 layers of cured resin.

This is 1 of the reasons it's so important to speak in specifics, not fiberglass resin, which might be either polyester resin or epoxy resin.

 

[ondarvr]

The chemistry of the two types of resin and hardener are totally different and are not compatible.

 

[jigngrub]

What'cha workin' on Snow? Got any pics?

... Enquiring minds want to know!

 

[tpenfield]

So, I take you mixed up the wrong resin and hardener combination. The stuff in epoxy resin actually prevents poly resin from hardening . . .

Yes, trash it and start over.

 

[snowman48047]

Yes I think I'm screwed. Im working on a fiberglass mold with multiple layers over about a 2 hour timeframe. Using polyester resin and the hardener that comes with it in the quart sizes at box stores. Wax and applied mold release, mixed up about 1 cup of poly resin and hardener, apply with cloth and wait about 15 minutes to begin to set up. Mixed another cup of poly resin and grabbed the wrong tube of hardener (says $&@/blah blah peroxide, apply with cloth and wait again 15 or so minutes. Mixed up last cup and original hardener and same as above.... first layer appears solid, middle layer seems squishy like mashed potatoes or gravy, third layer is solid. I can press on mold and see tiny air bubbles moving around so assuming it didn't harden correctly/wrong type of hardener. Mixed in correct ratios but I just grabbed wrong hardener squeezer bottle.....I'll check again in morning. I think I have a big mess.

 

[gm280]

Yes I think I'm screwed. Im working on a fiberglass mold with multiple layers over about a 2 hour timeframe. Using polyester resin and the hardener that comes with it in the quart sizes at box stores. Wax and applied mold release, mixed up about 1 cup of poly resin and hardener, apply with cloth and wait about 15 minutes to begin to set up. Mixed another cup of poly resin and grabbed the wrong tube of hardener (says $&@/blah blah peroxide, apply with cloth and wait again 15 or so minutes. Mixed up last cup and original hardener and same as above.... first layer appears solid, middle layer seems squishy like mashed potatoes or gravy, third layer is solid. I can press on mold and see tiny air bubbles moving around so assuming it didn't harden correctly/wrong type of hardener. Mixed in correct ratios but I just grabbed wrong hardener squeezer bottle.....I'll check again in morning. I think I have a big mess.

Sorry to hear this Snowman. But yes your best fix is to remove the questionable stuff and start over. Also, if you are using off the shelf bondo type polyester, make sure the MEKP is still good by mixing up a little test batch. That stuff sits on the shelf well pass the usable dates and you never really know if the MEKP is still good or not. Just a suggestion... And you have to know that bondo polyester IS waxed type poly. And therefore if you mix up a batch and apply it, if you are going to layer on top of that previous application, you have to sand AND clean with "Acetone" first or the second layer will not chemically bond to the first. The wax will keep them separated forever...

 

[snowman48047]

I am sure that one little bottle is at least 2 years old. However, it seems to have cured with no negative effects. Since this is not on a boat, I will go ahead with this project. This is just a mold for future parts. The multiple layers I did were wet on wet, maybe 3/8" thick total, nothing cured in between so no sanding required. I will however for future projects make sure to use "new" material. Thanks for all the info guys!