Talk Composites - The Forum for Advanced Composites

RapidRepair epoxy resin incompatibility with West Systems epoxy

http://www.talkcomposites.com/Topic22303.aspx

By BoA kayak - 11/23/2016 3:43:48 PM

I’ve been repairing a carbon-kevlar kayak. I had used alayer of West System 105 epoxy resin with 205 hardener but did not like all thebubbles that appear on adding the hardener and are v difficult to get rid of.After a cure period of more than a month I sanded to 80-grit and recoated witheasycomposites RapidRepair epoxy resin and fast hardener. When these are mixedthere are no bubbles – so preferable to the other brand!( I cleaned aftersanding with acetone but waited for that to dry before re-applying resin).Where I applied easycomposites resin on top of the West Systems resin, theeasycomposites resin did not harden fully and went slightly milky. I know I hadthe resin/hardener mix correct (100-33) because the mix hardened in the mixingcup and on parts of the kayak where there was no West System resin underneath.After waiting a couple of weeks for it to cure, I found it was still a bit stickyon the surface and although it had hardened it had the texture of polyethylenerather than a hard clear resin and could be peeled off with a paint scraperblade (luckily because it won’t sand off easily). So there was low adhesion tothe West Systems resin underlayer as well as the hardening issue. Has anyoneelse experienced this? 

By Hanaldo - 12/5/2016 1:23:47 AM

Yeh, but it shouldn't ever really be a concern once the resin has cured. You should never mix two brands or different kinds of resin together while they are liquid or even partially cured, but once cross-linked they should be a hard surface just like any other thermoset polymer. Some may be harder to bond to than others, but I've never seen a properly cured thermoset resin react or cause a reaction with a similar or even completely different type of thermoset. 

Something must have happened to have caused one of the resins to not properly cure, and I'd say Warren hit the nail on the head with his last post.