Question about poly resin

[Daniel1947]

Like so many of you fellow forum members and friends, this guy "Andy" on Boatworks is definitely someone I consider very knowledgeable. He is a little "flakey" at times but his previous work and videos are always very informative and interesting. One of the things I have learned in the 4-1/2 years I have been on the forum is there are a number or ways to do things. Some will work OK, some won't work too well, and some are just asking for trouble. As I have said..."there is no right way to do it wrong." But at the same time, just about anything we do here is better than what the manufacture did.

I have a question: The ratio for MEKP to resin ranges from the usual 1% to 2%, usually because of the temperature, with an occasional drop to maybe 3/4%. Anyone have any hard evidence as to the "strength" of the finish product in relation to the % of MEKP. In other words, will the lay-up be stronger if the ratio is 2% compared to 3/4%?

 

[ondarvr]

I have a question: The ratio for MEKP to resin ranges from the usual 1% to 2%, usually because of the temperature, with an occasional drop to maybe 3/4%. Anyone have any hard evidence as to the "strength" of the finish product in relation to the % of MEKP. In other words, will the lay-up be stronger if the ratio is 2% compared to 3/4%?

Yes and no, but many things come into play. There have been a few studies done on this, but what happens in the lab can be difficult to replicate in the real world.

Catalyst % is normally best around 1.75%, but some resins are formulated for lower or higher %, and then there are several different catalysts that can be used that may require a different ratio. These catalysts would be tough to find in the retail market though.

Temperature comes into play also, so a low % at a higher temp could give a better cure than a higher % at a lower temp. And if the laminate is thick or thin it will influence the % also.

Your best bet is to stay around 1.25 to 1.75% if ambient temperatures allow it.

In a production shop the gel time of the resin is fine tuned for their application, this allows them to use the resin within the correct catalyst range. This can't really be done as easily for a DIY guy, so you adjust your techniques to fit your needs and stay in the correct range.

 

[SweeperForce]

Well I'm going to change lanes again. After a lot of Internet research, that gelcoat video and most people I talk to suggest using epoxy resin. I'm thinking about using West system 207 to layup my stringers and transom. Do all of you agree? Here is a great article I came across. that helped make my decision. I only ever used poly before so are there any tip I should know about? A huge THANKS to all who where involved.
Tom

 

[jbcurt00]

No, I think the posts above indicate most of us wouldn't choose epoxy over poly, we'd use poly.

If you use epoxy, I would paint after, not use gelcoat, again as noted in the posts above.

If YOU want to use epoxy, then use epoxy.

 

[Daniel1947]

Sweeper...just my opinion, but what I think the video from Boatworks showed was that there may not be a problem using gel coat over epoxy if the preparation is done properly. Since most of the boats here are probably poly to begin with, I can't really see any positive reason to use epoxy except for minor repairs. Anything major such as what I am doing...transom, stringers and deck, I can't see anything that would benefit my using epoxy instead of poly. My estimated cost alone will be almost 3 times as much for epoxy over resin.

I think the main concern is this.... we all know, beyond any doubts, that one can use gel coat or paint over the poly without any problems. I agree about 99.9% with Jbcurt00....I never give anyone 100% except my girlfriend. :facepalm:

Of course my advantage over many others, is that I have a local supplier for the Poly, so therefore I don't have shipping or hazmat to contend with. But as we all say, your boat your decision.

 

[zool]

The main benefit to using epoxy, aside from its inherent strength and flexibility, is its more forgiving in the prep than poly. In order for poly to adhere properly, the substrate needs to be totally clean down to fresh glass, and contaminate free..it also needs csm to gain its strength. Epoxy will stick to most any relatively clean surface. The mix ratio for epoxy should be spot on tho.

The main drawback of epoxy, aside from the price, is that if you are or become sensitized to it, like me, your hands and other parts start looking like a lizard..for a few weeks anyway. The price difference is kinda deceiving tho, because you use less epoxy to gain the same strength as poly.