Results from Epoxy & Polyester testing

Well, The results are in.

We have done several tests as most readers of this blog will now. After removing the teak from our deck, we had some core to correct.  With that completed, we also knew we didn't want to go through this challenge again.  We had to make a decision on the best solution for ensuring that the 7000 or so screws that we removed from the deck didn't become places for water to leak in again in the future.  We filled each screw holes with epoxy through a syringe, but we felt we needed something that was a little bit more assuring.

We had heard from some that said removing the teak removed a bit of the rigidity of the deck even though the teak decks were not structural.  I didn't agree that this was the case but did agree that the extra strength certainly couldn't hurt.  Combining these two scenarios (possible water intrusion and strength of repair), we strongly believed that we needed or at least wanted to put an entire layer of fiberglass over the whole deck.  It may not be required, but after doing all the work we have done and are about to do over the next few years, I want a repair that is going to outlast any of the work I do and protect all the effort we will put into refitting and refinishing below deck.

So, with the decision made to pull up the teak and add a layer of fiberglass over the entire surface, the question now became what material to use.  We are certainly not experts at this point, and while I have used epoxy resin for waterproofing wood and painting bilge surfaces, I have never attempted a project of this size with it, nor had I explored other materials such as the materials used to build the boat.

I, like many others, have just heard that epoxy was a better solution and given the work I had done in the past and the quantity of epoxy needed, this made perfect sense.  But this job would be different; I would likely be using 6-7 gallons of material, and the difference in price is substantial between the options of Epoxy, Vynelester, and Polyester.  Fiber Carbon was ruled out right away due to cost and the idiocy of doing that on our Taiwanese built ketch

Based on all of my research, both epoxy and polyester would be laid and installed in a very similar way.  The big difference is the cost.  By way of example, when you mix epoxy, you add a resin and hardener in a 2 through 5 to 1 ratio depending on the manufacturer.  We use West Epoxy Systems for many small repairs, adhesive and even a waterproofing material for paint.  When you mix the one gallon of resin and the amount of hardener required for that, the total yield is 174 ounces, and the cost is $183 for a total per ounce cost of 95 cents.

Using Polyester resin and catalyst has a different mixing ratio.   One gallon of resin and the required amount of catalyst for 1 gallon which is only about 2 ounces of MEKP with the brand us used, the yield is 130 ounces, and the cost is $30 for a total per ounce cost of 30 cents.  The rest of the materials for the job are all essentially the same price such as fiberglass mat, cleaning supplies, tools, etc.

This significant cost difference made us look at polyester resin more seriously.  Before we did that, we wanted to answer two questions.
1)  What is the better material to use for this job and why?
2)  What does the surface preparation need to be?

Mainly we were hoping to avoid grinding the entire boat surface down to bare fiberglass if we could avoid that without compromising the results and strength.

We recorded videos for all of these tests and posted them to our youtbube channel.  Links to each video are below and will open in a new window.
Epoxy application and destruction test here
Polyester application test 1 - Failed and why
Polyester application test 2 - success
Polyester destruction and the results of the total experiment

Here are the facts we learned and the decision we made based on these tests.

First, epoxy is undeniably a stronger adhesive material and easier to work with in my experience.  That said, the bond between the existing deck and the new layers of glass, while slightly better-adhered when using epoxy it was more than sufficiently held with polyester.  I didn't measure this with a device at breaking strength, but I suspect that the polyester is still 3-4 times stronger than what is required of the job (adding a few layers of fiberglass on top of the existing deck), keeping in mind, this is the material used to build the original boat.

Second, the cost for polyester is significantly better, and without the strength of polyester to be a gating factor, the cost had to be factored in.  For those reading this that don't know us, I figure it is good to clarify a belief we hold.  If polyester were not going to be a viable strength and quality to be considered, the cost difference wouldn't matter.  Frankly masking tape would have been a cheaper option yet, but that would not be a sufficient material to use, so it is not considered as an option.  :)

Lastly, we spoke to an insurance adjuster who shared that when an insurance company authorizes a repair to a boat after an accident or damage, they require that the repair is done using the same material used to manufacture the vessel.  Not polyester because it happens to be the cheaper of the methods, but rather for the consistency of hardened strength.  The insurance company is worried about possible stress lines created between existing material and repaired areas if the repair is a different hardness than the original.  So for a boat made of vinylyester resin, the repair would have to be done using the same material.  The same holds true for epoxy, carbon fiber, and polyester.  

While this last bit of information was not a fact in the specific tests we performed, it was an interesting data point that helped in our decision-making process.

The second part of our test related to surface preparation was also a fascinating outcome.  Almost everyone said to grind the material all the way down to fiberglass for the new glass to be laid down.   After removing the teak and screws, I still had some old resin-based adhesive material on top of a fairing coat or gel coat and then fiberglass below that.  In each test, I prepared the surface two ways; one was down to bare glass the other was just smoothing the surface of the existing material with a 36 grit sanding disk.

With the epoxy test, when I removed the new layer, the existing glass lifted up and separated in the area where it was ground down to the bare glass, in the other area ts separated but was blended, in some cases the epoxy adhesive layer separated, other areas it was the existing glass.  What this told me was that either surface preparation would be strong enough, which was great news because the effort to grind to bare glass was significantly larger.

With polyester, the bond to the existing layers was not quite as strong as the epoxy but also separated in the same way, again demonstrating that the surface prep did not require the entire deck to be ground all the way down to glass.

I am hopeful that this information is helpful to others.  When I was doing research online for this job ahead of me, I found that there were so many differing opinions and all of those sharing the opinion seemed to be able to back up the recommendation with success stories.  The problem for me was that everywhere I opened up a dialogue on a boaters forum to ask this question, the conversations quickly disintegrated into an argument over which way was right or wrong and putting down the others opinions.  The entire experience left me very frustrated and lacked the actual information I needed to make my decision.

That is when I decided we needed to do our test, and come to our conclusions on this matter.  It was important, and I needed to know the pros and cons of each option without an agenda of trying to prove the method I used or sold to others was justified in a public forum.   I don't have a business to run or need to justify the ways of my shop; I am doing this just for me and for our boat repair.  And to add an exclamation point to this, I hope never to do this kind of a job again.  I am doing this for the strength of our blue water home and want that repair to outlast me and the boat

If you think this information may help others or they may find it useful, you are welcome to share it in its entirety in any public or private forum with proper credit.  I would also be willing to answer questions other may have in the way any of the tests were performed.

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The supplies we use for this job are listed below if you find this a convenient way to shop for them.    If you use these links, you get the same great Amazon pricing, but we get a small affiliate link credit.  Thank you.