Resin Questions

You're right, for a job this size the cost difference will be miminal.

Depending on the epoxy you get, it may be a little more difficult to work with than a polyester, but that's about it.

 

I was looking at the stuff from uscomposites, 635 thin epoxy with medium hardener.

 

Epoxies tend to drain out of the glass a little more than polyesters do, so you need to keep an eye on it until it starts to harden.

I can't tell you anything about the product your looking at though.

 

ondarvr, is right about all of it. Polyester is the way to go. It wets out better and does not drain as bad. I just had to write something.

 

Polyester isn't the product to use and frankly there isn't a debate to argue, the facts speak for themselves. Polyester makes a poor bond to itself and much worse on wood. It's not waterproof, which isn't good for wood and doesn't have the modulus of elasticity to compete with wood's physical properties (the primary reason it fails on wood). This isn't subject to debate, it's fact.

The only way to make polyester work on wood is to make the laminate as strong as the wood, which defeats the reason for using wood in the first place. Even if this thick laminate sheers, the wood is irrelevant as far as strength is concerned.

Epoxy on wood, if you don't want to do this again in the future.

I will agree with Ondarvr in that both products rely heavily on surface prep and sufficient cure times.

Skip the mat, which is a bulking agent in poly lay-ups, but completely unnecessary in epoxy laminates.

Epoxy is far easier to work with then polyester resins and much more forgiving to the novice. It smells a whole lot better too.

Log onto West System's web site and download their user's guide to familiarize yourself with its uses. Also perform a search on this site for transom repairs. It's a subject that's been covered many times with much useful information.

 

Yeah this site is great, I've looked at a lot of transom repairs, but the resin was still holding me up.
I had found the west system guide through another post on here a few weeks back. It really tied everything together.

I'm planning to use all 1708 in this repair, and epoxy thanks to all the good info.

 

sometimes the waiver of, is the wisemans comment.

 

I agree on Epoxy, specially for transom. However, I can make a mean boat out foam core, polyester resin, then epoxy. Polyester is stiffer, epoxy more flexible. Lighter and stronger than either alone. Consider alumimum plate to reinforce area of engine plate.

 

I've seen aluminum plate on transoms before, I thought it was just an attempt to fix a weak transom without doing the work of replacing it.

 

In a few boats, I have glued and bolted aluminum plates to transom with Epoxy. Sometimes on both sides It greatly strengths it. Many people put large engines on transom than the design entailed. Alumimum helps distribute forces.

 

PAR

I agree with you on many things and respect your opinion, I know many people on this site are anti-polyester, some for good reasons and some for not so good reasons, just bias.

Epoxy is vastly superior in many ways when compared to polyester, but frequently epoxy is overkill in many applications, and it is in a repair like this is one. We're looking at a very old boat with a small OB and when you look at what failed it wasn't the resin, it was the wood that rotted and the polyester is still there holding the pulp in place. Did the wood rot because the polyester wasn't water proof... no.... water gets in through unsealed holes and other similar shortcomings in construction, not through the laminate unless it was very thin ( and that happens, another shortcoming in construction). On this boat it looks like the trim cap on the transom is a good place to start looking for water intrusion and there are most likely other holes that leak also. These areas would leak whether the resin was epoxy or polyester and rot would be the result, with no difference between the two.

This boat looks to be from the late 60’s or early 70’s, so we’re looking at around 40 years of service out of the original construction, which may have been less than ideal. If he repairs it with similar products and probably more care than when first built, it will probably last that long again, not bad for a terrible product like polyester.

When bonding to wood there is no comparison, epoxy is far better and when building a wooden boat there is no question, epoxy is the product to use. But in this type of repair rarely is the bond stressed to the point of failure with polyester, the transoms on small power boats are thru-bolted in many places so the skins are secured in place.

The bonding, or should I say lack of bonding, of polyester to polyester is blown far out of proportion, while the bond isn’t as strong as when using epoxy, it’s more than strong enough to be reliable and durable.

I think the big difference is in the care and experience of those using the two products, plus the intended market of the finished craft.
Craftsmen using epoxy are taking extreme care to have the part engineered and well thought-out before starting the project and then proceed with great attention to detail, this includes original construction and repairs. These finished products are also valued for their design, workmanship and function over cost.
Until recent years it was rare to have an engineer working on production boats and even now many have no education in marine related composites. Production boats were built as needed to speed the build and lower the cost, these were the goals, “best practices” were rarely a concern. Resin choices were based on price and how fast they could build a boat with them, not strength or water resistance. Even to this day we make many resins that are far superior to what gets used in production. Now figure in low paid, poorly trained workers only looking forward to getting drunk on the weekend and the result is a mess. It was only the illusion of the supposed very forgiving chemistry of polyesters that made all of this possible. These shortcuts and/or bad decisions didn’t show up until a few years down the road, the boats more or less looked good going out the door.
The customer was buying based on style and price, not the quality of the finished product.


For the type of craft and customer base you have, epoxy is the product to use.
These small project boats are purchased for a couple hundred bucks and the budget for repairs is even less. Typically it’s a new boater that will only keep the boat for a few years at most before it’s sold at a loss, or is forgotten in the side yard. If the repair is small, as in this case, then the cost difference between the two products is marginal, if the project is larger, then the cost difference can be a deal breaker. 99% of people that finish a project like this, and many don’t finish them, will never see any difference in the final product with either resin, so I can’t see a reason for an “epoxy only” view point.

For decades I traveled around North America repairing, modifying, building, refinishing and installing just about anything you can imagine made from fiberglass. 95% of time it was some type of polyester or VE that was used, when needed I used epoxy. After doing it for that many years the numbers of call backs and/or failures were so few that I can’t really recall any (there must have been some minor ones though).

What it comes down to is that sometimes good enough, is, well, good enough.

OK, blast away.

 

Had to add one more thing.

One reason epoxies haven't been used more in production boats is because they are more difficult to use, it would be much harder to make 25+ boats a day using epoxy. I wish all my boats were made of epoxy, but if they were I don't think I could afford them.

 

I agree for the most part with you Ondarvr, in that well done repairs with poly work fine. The results will be heavier, more brittle and more effort for the novice. Epoxy is easier for the novice to work with then poly. It's strength can over come lamination mistakes made under the shade tree.

My experience has shown that back yard users, routinely screw up poly batches or laminate procedures more readily then when using epoxy.

Manufactures don't use it simply as a business decision based on end product cost and having to change a shop over to epoxy.

I'm like you in that I've done many poly repairs, with few difficulties, but this isn't our first picnic either.

On home brew transom jobs, I prefer epoxies repairs just to insure good tabbing and bonding to the substrate. One of the difficult things with these home grown repairs is getting sufficient bonding area, from old to new work and a good bond between the layers of plywood. I've seen shade tree jobs where the feathered back area was 1" wide and the tabbing overlap the same. To insure a limited access area stays stuck and the small amount of materials and work involved in these types of repairs, I tell folks epoxy. It's an easy way to get extra insurance the transom's not going to pop off when they gun the engine the first time.

You are also correct in that these era boats were poorly engineered, usually way heavier then necessary with pretty crappy resins and poor lay up procedures. I've repaired a lot of them and wondered why they used wood at all some times. I remember a particular sailboat, built in 1970 as a 22' centerboard cruiser. It had a 1" thick laminate near the keel and was about 3/8" at the rail, on a one ton boat! You could set a grenade off under this thing and it would have hurt it. Of course it sailed like a pig too.

Many of these boat survive purely by the ridiculousness of their laminate schedules. Then came the "dark years" and you know what era I'm talking about. They started fooling around with resins, fabrics, techniques, etc. and boy did they save money in manufacturing costs. These are showing up with more frequency in recent years. Some love the cool styling, other the prospect of a free or cheap boat.

I'm sure you and I could go on all day about the good, bad and ugly of it all, but I'll stick with telling amateurs to use epoxy, if for no other reason then it smells better and puts a pretty shine in your hair if you get some on you.

 

Well I got my runabout rennovation book, read up to the transom section. (not sure if any of you are familar with the book) He uses poly resin. Also he says he puts aluminum plate on the outside.
Not sure which resin I'm going to use still, epoxy really isn't much more money so I'll probably use it.

ondarvr, you are correct in the years, its a 1964 Crestliner, I'm supprised I didn't put that in my post originally.
The rating plate says its rated for 120 hp. Motor on the back when I got it is a chrysler 140, which by no means is putting out 140 hp but I'd still like any extra support I can add in.