Poly Vs Epoxy resins

D

Dave Walker

Active member
I've been over in my head a 100 times the idea of making my own mold and building a small boat out of fiberglass. Nothing huge, layout style, or somethig that could handle a 2hp. Anyway I had spoke with a guy that had built his own out of a wooden kit that he used as a plug. His, it seems, was epoxy with fiberglass, but its been a while since I spoke with him (and he's in WI). Is there any benefit to epoxy over polyester resins? Strength, ease, cost, etc...?? I've built a wooden boat with epoxy and fiberglass wrap, now want to make an all fiberglass. Just curious for a little input from the pros who may have used both products. I know that polester is used for other layups, and I thought for commercial built boats. Any DIYers using it?




Thanks
Dave
 
Poly is cheaper, for a duck boat use the money you save to buy some foam for floatation.

Check out www.mertons.com

Joe is real helpful and has good prices on shipping.
 
Dave,
I went through this process several years ago (2002). We used poly resin. I was lucky in that I happened to meet a guy (Ben Gallup from MO that posts here once in a while) that had done all of this before and he helped me every step of the way. Here is the process that I went through:

1) build a boat (I built a modified Kara with a more pointed bow and a transom) This becomes the plug. EVERY detail of this boat will show up on the boats you make, including any blemishes, etc. My boat came out looking rather similar in shape and size to Ira's Fatboy boat. Makes sense since we had a lot of the same people and places inspiring our designs.

2) built a 2-part mold from the plug. Top and bottom halves. Make sure that you plan how you will fit the two halves together! We made the top mold a bit wider than the bottom. If you want to re-use the mold several times, then you will want to have a gel-coat on the inside of your mold. This is the same material they use on truck toppers, etc. It's extremely slick so that the part will slide out easily. If you are only doing a few casts, then you might be able to get away without this.

3) wax it like crazy! This may be out-dated, but Ben, my mentor, believed religiously in this. We used mold-release wax that can handle the temperatures created by the curing resin.

4) spray interior of mold with a thin layer of plastic like compound. I forget the name of this material, but basically it forms a cellophane like layer over the entire mold and keeps the boat from sticking.

5) spray in a layer of gel-coat which will become the outside coating of the boat

6) lay in the fiberglass mat and resin for the boat. We typically used a couple layers of glass.

7) Let it cure and then pop the part out (not always as easy as it sounds, it usually involved a crow bar and some shims to get it to pop out. Professional molds are built to handle this much better than ours)

8) fuse the two halves together and voila, you have a boat.

Counting the plug, mold and boats, I built 9 boats that year from March when I started the plug through the end of August. The boats went to various friends if they paid for materials and helped make their boat (plus a bit to help pay for the mold). The price of materials was probably around $300 per boat. Add in the expense of the plug and mold, and for a single boat you'll be at the price of a new momarsh, etc.

Depending on the size of your boat, you can lay out the two halves in a day. Put it in the sun and it will cure pretty fast. We were safe and usually let them sit for a couple of days before popping them out. Then it would take a few hours to get them fit together and a day for the seams to cure. I would estimate about 10 hours for two of us per boat once we had it figured out. The plug took longer to make as did the mold.

My boat is doing great after 7 seasons of moderate use (10-20 days each season). It weighs in at around 80 pounds. Using poly resin is fine for this application, that's what the commercial boats such as the 4-Rivers and MoMarsh boats are made from and it's MUCH cheaper than epoxy. I use a 3.3 hp motor on it and it works great for shallow marsh areas.

View attachment bellboatfront.JPGView attachment bellboatontrailerside.jpg
 
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Poly stinks unbelievably bad, especially in tight areas. Came right through 3M's organic vapor mask which was rated for it. Epoxy doesn't smell as bad.

Poly is cheaper, but not as good, but we are not talking about ocean going boat that never leaves the water.

I have used both and have boats made from each, prefer epoxy overall, yet mixing poly is way easier. If you need a "hotter" batch, just add more catalyst.

Pro's and con's to both. Good luck.
 
Thanks for the input guys. I'm still in the planning phase. My thoughts were that while the up front cost is more per boat, I could make a few and sell to locals while paying off my plug and mold costs. Mostly just for fun. I don't have any fantasy about recovering all my costs.


Dave
 
Dave ,

I'm probably the guy you talked to before . If you need to talk again just PM me and I'll send you my number. I agree with all that has been said on here. There are pros and cons to both poly and epoxy. I prefer epoxy myself but that is mainly because of the smell/fumes of poly. Epoxy also cleans up well off the skin and tools with vinegar instead of harsh chemicals.Epoxy is more expensive. Poly can be adjusted in batch by batch in how quickly it will "kick off" by the amount of catalyst you add. with Epoxy you have either slow , medium, or fast depending on what you bought. I prefer epoxy myself and use the medium from U.S. composites.

As far as applying them, the techniques are the same. One big difference will be in the matting if you use it. Matting made to use with poly is "glued" together. When you add the poly to it the the poly breaks down the "glue" and allows the matting to form to your shape. Epoxy matting is "sewn" . So, you have to work on wetting it out a bit more in the tight corners. Just make sure not to use matting made for poly with epoxy.

On top of using the mold wax I also spray this PVA release film on over the wax. Get it from fiberglast.com here:
http://www.fibreglast.com/showproducts-category-Wedges,%20Mold%20Releases%20and%20Clips-152.html
I have much easier times breaking a boat out of the mold using this on top of wax. The plastic wedges are great also.

I layout either the top or bottom working in the garage out of the sun. My table is on rollers and if its a nice day I then set it out to cure in the sun. Many times with the release, the shell will partially "pop" loose making total removal easier. In either case , I let the shell cure at least over nite so I don't damage any spots that are not cured yet. Then make the other half of the boat after prepping that part. You may need to make an adjustment to your plug so that the next half is a hair bigger so it will allow the other part to nest inside it for connection.

Add any handles/harware first that will be at hard to get to spots once the halves are connected. I use 3m 5200 as a joining agent plus seal the seams with a layer of matting and cloth on the inside. Once it is all set I then go in and add my bracing if needed.

good luck,

Dave B
 
I've been over in my head a 100 times the idea of making my own mold and building a small boat out of fiberglass. Nothing huge, layout style, or somethig that could handle a 2hp. Anyway I had spoke with a guy that had built his own out of a wooden kit that he used as a plug. His, it seems, was epoxy with fiberglass, but its been a while since I spoke with him (and he's in WI). Is there any benefit to epoxy over polyester resins? Strength, ease, cost, etc...?? I've built a wooden boat with epoxy and fiberglass wrap, now want to make an all fiberglass. Just curious for a little input from the pros who may have used both products. I know that polester is used for other layups, and I thought for commercial built boats. Any DIYers using it?




Thanks
Dave
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This is an interesting discussion with a few valid points, but I have never heard of a commercial manufacturer using epoxy for layup like you are talking about (and anyone who can point me to manufacturing materials saying otherwise, I'll happily eat my dish of crow). Poly resin is the stuff to use, it is WAY cheaper and is not inferior to epoxy for laying up a hull like you are talking about. Epoxy is a better adhesive and bonds to poly and epoxy and vinyl etc..., but that is not what you are talking about - you are asking about laying up a hull and poly is the way to go.
 
2 other very important points to mention on the build. 1. Be aware of your angles. Glass does not like square corners so if you can round them or angle them it will make laying it up easier. 2. Make sure your angles are appropriate to be able to pop off the shell.

Here is an example of what I mean by that. I have a friend who wanted to make a glass model of a wood skiff he made. The combing around the cockpit was V shaped (flared out). Therefore, if he just copies the plug exactly he won't be able to pull it off as the narrow part of the V won't pass over the wider flare of the top. You would have to make the deck without the cockpit combing making sure the opening is wide enough to go over the combing on the plug. You would then add the combing later. So, look ahead of time at your angles and how they effect the shell or you won't be able to get your shell off the plug.

dave b
 


This is an interesting discussion with a few valid points, but I have never heard of a commercial manufacturer using epoxy for layup like you are talking about (and anyone who can point me to manufacturing materials saying otherwise, I'll happily eat my dish of crow). Poly resin is the stuff to use, it is WAY cheaper and is not inferior to epoxy for laying up a hull like you are talking about. Epoxy is a better adhesive and bonds to poly and epoxy and vinyl etc..., but that is not what you are talking about - you are asking about laying up a hull and poly is the way to go.
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Don't get me wrong, I wasn't trying to imply they did use epoxy. I have seen enough discussion on boat pages about epoxy that its easy to conclude a lot of people use it for a number of projects outside of commercial work. So I'm trying to find out if there is a benefit to either product. It seemed to me the logical choice was poly as its the common commercial product. However I wanted to know that it isn't something I will need all sorts of special equipment, tools, skills to use compared to epoxy. Get my drift, just trying to learn more.
 


This is an interesting discussion with a few valid points, but I have never heard of a commercial manufacturer using epoxy for layup like you are talking about (and anyone who can point me to manufacturing materials saying otherwise, I'll happily eat my dish of crow). Poly resin is the stuff to use, it is WAY cheaper and is not inferior to epoxy for laying up a hull like you are talking about. Epoxy is a better adhesive and bonds to poly and epoxy and vinyl etc..., but that is not what you are talking about - you are asking about laying up a hull and poly is the way to go.
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Don't get me wrong, I wasn't trying to imply they did use epoxy. I have seen enough discussion on boat pages about epoxy that its easy to conclude a lot of people use it for a number of projects outside of commercial work. So I'm trying to find out if there is a benefit to either product. It seemed to me the logical choice was poly as its the common commercial product. However I wanted to know that it isn't something I will need all sorts of special equipment, tools, skills to use compared to epoxy. Get my drift, just trying to learn more.
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Yes, I understand, I wanted to make sure it was clear that epoxy wasn't superior. The materials designed for layup with poly are more readily available too. You don't need anything special for laying up with poly that you don't for epoxy other than a gel coat or one of the gelcoat-like materials out there that can be brushed on your mold. If you are hand laying you don't need anything special like a chopper gun either.
 
Here you go Tod. skaterpowerboats.com Vacumn bagged S glass/ epoxy. Saw a video where the call makers Haydel bros. were crow hunting and breasted them out for bbq. Might want to try that....
 
Here you go Tod. skaterpowerboats.com Vacumn bagged S glass/ epoxy. Saw a video where the call makers Haydel bros. were crow hunting and breasted them out for bbq. Might want to try that....
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I've eaten crow plenty of times and since Vacuum bagging is outside what he is looking to do, I think I'm still hungry.
 
Sorry, didnt notice him indicating either way. Just noticed a commercial builder using epoxy. Come to think of it, he didnt mention s glass either. Any other restrictions?
 
Sorry, didnt notice him indicating either way. Just noticed a commercial builder using epoxy. Come to think of it, he didnt mention s glass either. Any other restrictions?
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"but I have never heard of a commercial manufacturer using epoxy for layup like you are talking about (and anyone who can point me to manufacturing materials saying otherwise, I'll happily eat my dish of crow)."

Richard,

I was careful to limit my statement to small duckboats, note the portion of my statment where I said: " like you are talking about ". He is talking about a small marsh skiff type duckboat (to quote him: "small boat out of fiberglass. Nothing huge, layout style, or somethig that could handle a 2hp"), not an offshore racing catamaran as you posted.

You jousting with me in is post has more than doubled the number of words you have posted to this forum. Since you obviously have some interest and useful information, why don't you belly up to the bar and post up some information rather than sniping at me for trying to help.

T
 
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