Polyurethane resin okay?

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Keith Medlkock

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I want to layup a bit of glass in a body tube end for landing durability. Is cheap polyurethane resin sufficient or is it worth cost for the extra epoxy resin durability? I guess I'm just thinking the fiberglass does the heavy lifting and any added strength from the resin is negligible. Thoughts?
 

rharshberger

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I want to layup a bit of glass in a body tube end for landing durability. Is cheap polyurethane resin sufficient or is it worth cost for the extra epoxy resin durability? I guess I'm just thinking the fiberglass does the heavy lifting and any added strength from the resin is negligible. Thoughts?
Epoxy resin is the best product for what we do, polyurethane resins are mostly used in casting iirc (I have done poly res casting) and the resin can set pretty quickly and is a bit thick generally for good fabric wet out. An excellent less expensive epoxy resin is US Composites 635 w/ the 3:1 hardener, at $71 per gallon (actually about 1.3 gallons, 1gallon resin and 42oz of hardner) its a value.

This link is to a recent epoxy comparison I put together for commonly used epoxies in our hobby along with their data sheets https://www.rocketryforum.com/showthread.php?138953-Epoxy-Comparisons-and-Technical-Data-Sheets
 

Steve Shannon

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I've never used (or even seen) polyurethane resins for glass lamination. I've only seen it used for casting and foaming. I can't even imagine what a mess laminating with it might be.
Frequently polyester resins are used for laminating, but they are smelly and they are much more heat sensitive and than epoxy. Plus, I think the fumes are flammable. I have received some rocketry parts over the years that were laid using polyester. As long as you're not building something that's going to spend much time over mach polyester works okay for laminating, but be sure and work outside with it.

I agree with Rich. I stick to epoxy, specifically Aeropoxy laminating resin which I buy from Aircraft Spruce. I've inherited a couple gallons of West Systems with different speed hardeners and I really like the wealth of information that West Systems publishes for their products so when my gallon of Aeropoxy is gone I'll try it.
 

Keith Medlkock

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I've never used (or even seen) polyurethane resins for glass lamination. I've only seen it used for casting and foaming. I can't even imagine what a mess laminating with it might be.
Frequently polyester resins are used for laminating, but they are smelly and they are much more heat sensitive and than epoxy. Plus, I think the fumes are flammable. I have received some rocketry parts over the years that were laid using polyester. As long as you're not building something that's going to spend much time over mach polyester works okay for laminating, but be sure and work outside with it.

I agree with Rich. I stick to epoxy, specifically Aeropoxy laminating resin which I buy from Aircraft Spruce. I've inherited a couple gallons of West Systems with different speed hardeners and I really like the wealth of information that West Systems publishes for their products so when my gallon of Aeropoxy is gone I'll try it.
Thanks, I'll grab some epoxy resin. Steve, the polyester resin I was thinking of is sold in 1qt quantities with the fg cloth & mat at Home Depot/Lowes, etc. Its intended for fg shower/bath patches.
 

rharshberger

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Thanks, I'll grab some epoxy resin. Steve, the polyester resin I was thinking of is sold in 1qt quantities with the fg cloth & mat at Home Depot/Lowes, etc. Its intended for fg shower/bath patches.
Polyester resins kick off pretty quickly, but are thin enough for laminating. My father used polyester resins in his custom tub, shower and cultured marble business, typically MEK is the catalyst. Without doing a data comparison, polyester has more flex than epoxy iirc. The FG cloth is between 6 or 8ozs, I have used it several times when I run out of other fabrics. My usual source for FG fabric is Raka Inc, and Carbon Fiber is Soller Composites.
 

Steve Shannon

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Thanks, I'll grab some epoxy resin. Steve, the polyester resin I was thinking of is sold in 1qt quantities with the fg cloth & mat at Home Depot/Lowes, etc. Its intended for fg shower/bath patches.
Two things to keep in mind:
1. Fabrics for laminating are sometimes treated with agents to allow them to wet out better with either polyester or epoxy. Some fabrics can be wetted out with either. Not all can, so you may find that a fabric that wets out great with epoxy doesn't work great with polyester and vice versa.
2. Epoxy depends on a precise mix of resin and hardener. If you have too much hardener in your mix that excess hardener remains unhardened. Same if you have too much resin although it's not quite as bad as too much hardener. With polyester the lesser component is a catalyst. Addition of the catalyst causes the resin to harden. Using too little catalyst may slow down the reaction but will not result in unreacted resin unless you do a lousy job of mixing. Adding more catalyst speeds up the reaction and it's an exothermic one, so be prepared for heat. Don't mix in a plastic container. I use uncoated paper hot drink cups for epoxy. Polyester with too much resin can be even worse as I understand it.
However, you should get a very nice end product.
I really enjoy laying out fabric and seeing it just completely disappear into epoxy; it's almost like magic.


Steve Shannon
 

Keith Medlkock

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Two things to keep in mind:
1. Fabrics for laminating are sometimes treated with agents to allow them to wet out better with either polyester or epoxy. Some fabrics can be wetted out with either. Not all can, so you may find that a fabric that wets out great with epoxy doesn't work great with polyester and vice versa.
2. Epoxy depends on a precise mix of resin and hardener. If you have too much hardener in your mix that excess hardener remains unhardened. Same if you have too much resin although it's not quite as bad as too much hardener. With polyester the lesser component is a catalyst. Addition of the catalyst causes the resin to harden. Using too little catalyst may slow down the reaction but will not result in unreacted resin unless you do a lousy job of mixing. Adding more catalyst speeds up the reaction and it's an exothermic one, so be prepared for heat. Don't mix in a plastic container. I use uncoated paper hot drink cups for epoxy. Polyester with too much resin can be even worse as I understand it.
However, you should get a very nice end product.
I really enjoy laying out fabric and seeing it just completely disappear into epoxy; it's almost like magic.


Steve Shannon
Good points and thanks again for the advice. FYI, I just picked us some West System 105 resin with 206 hardener. $114 out the door including cloth and metering pumps. Much more $ than polyurethane, but I specifically need rigidity which you guys have indicated is better with epoxy. I had another thread where people didn't believe a scratch built F motor fiberglass rocket could cost $1000, but here's a perfect example, lol.

I'll add to your info about poly being more exothermic than epoxy. In my experience, this is based on surface area. When I need more pot life from poly, I use a container that allows the active resin to be shallow and spread out. Conversely, I used poly to fill 6"x6"x6" plastic couch legs(faux wood plastic), and after 10 min they were too hot to touch bare handed! I conclude that a perfectly sphere shaped quantity of poly resin will kick the fastest.
 

Steve Shannon

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Good points and thanks again for the advice. FYI, I just picked us some West System 105 resin with 206 hardener. $114 out the door including cloth and metering pumps. Much more $ than polyurethane, but I specifically need rigidity which you guys have indicated is better with epoxy. I had another thread where people didn't believe a scratch built F motor fiberglass rocket could cost $1000, but here's a perfect example, lol.

I'll add to your info about poly being more exothermic than epoxy. In my experience, this is based on surface area. When I need more pot life from poly, I use a container that allows the active resin to be shallow and spread out. Conversely, I used poly to fill 6"x6"x6" plastic couch legs(faux wood plastic), and after 10 min they were too hot to touch bare handed! I conclude that a perfectly sphere shaped quantity of poly resin will kick the fastest.
You're exactly right about using shallow containers to prevent cooking off. I mix in the paper hot drink cups but never a large amount, then either work quickly or pour the mixture into a shallow container.
I was one who was skeptical about the $1,000 F rocket. I apologize if I offended you. I don't include tools or full details containers of epoxy in project costs because typically only a tiny portion of the epoxy gets used for that one project. Now in a larger project or where a person is making their own tube the epoxy gets used up faster.
I hope you love the experience. Not that you need them but TFish's videos on YouTube are very useful. The YouTube user name is TFish38 and he does a great job.
 

Keith Medlkock

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You're exactly right about using shallow containers to prevent cooking off. I mix in the paper hot drink cups but never a large amount, then either work quickly or pour the mixture into a shallow container.
I was one who was skeptical about the $1,000 F rocket. I apologize if I offended you. I don't include tools or full details containers of epoxy in project costs because typically only a tiny portion of the epoxy gets used for that one project. Now in a larger project or where a person is making their own tube the epoxy gets used up faster.
I hope you love the experience. Not that you need them but TFish's videos on YouTube are very useful. The YouTube user name is TFish38 and he does a great job.
Oh, no offense taken. It's like that with any hobby. I would say skydiving is cheap because I already own the gear and can get a ride up for $23. However, a new jumper would maybe pay $5000 total to get to being able to safely jump alone with their own gear for $23. My family's at that "new jumper" phase in rocketry.:)
 

Steve Shannon

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Oh, no offense taken. It's like that with any hobby. I would say skydiving is cheap because I already own the gear and can get a ride up for $23. However, a new jumper would maybe pay $5000 total to get to being able to safely jump alone with their own gear for $23. My family's at that "new jumper" phase in rocketry.:)
Training for my first jump plus all the costs of that first jump were $65. The second jump that same day would have been $10. That was a while ago. My mom, dad, and girlfriend all came to see. I had already finished the first jump before they got there; all that worrying my mom did and I was already done. Instead of the second jump we went to the bar for beer and pistachios. Funny how things are so clear after so many years.
 

terryg

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Polyester resin has an odor that last for years. Cut it or sand it extensively and there it is again.
 
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TheTellurian

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I'm wondering if people aren't confusing polyurethane with polyester? The polyurethane I have hardly smells at all where polyester and vinylester both reek. If you work with polyester cover it with a plastic tarp and the smell is contained inside. By the way the Task series from Smooth-on are nearly the same strength as epoxy.


Richard
 

Keith Medlkock

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I'm wondering if people aren't confusing polyurethane with polyester? The polyurethane I have hardly smells at all where polyester and vinylester both reek. If you work with polyester cover it with a plastic tarp and the smell is contained inside. By the way the Task series from Smooth-on are nearly the same strength as epoxy.


Richard
Yes, absolutely! I did mean polyester. Doh!
 
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