Epoxy / Polyester Resins Question

[smj]

Originally Posted by ramblinrod

Your statement is illogical. If a structural repair only requires 10% of the adhesive strength of polyester resin, then polyester resin is more than adequate for the structural repair.

My mistake, misread your post. We've argued this many times before and gotten nowhere. If you like to use polyester for structural repairs that's your decision, never on my boat.

[ramblinrod]

Originally Posted by transmitterdan

If you substitute vinyl for poly in the above statement I would agree. I don't think pure polyester resin has a good rep below the waterline. It requires an epoxy seal coat.

I have seen many polyester repairs above the waterline work quite well. But it does require someone of many years experience and innate skill to get it right the first time.

We use polyester under the waterline all the time. 4 coats of Interprotect (much faster curing in thin film than normal epoxy) and all is fine in the world.

[Lake-Effect]

Originally Posted by ramblinrod

Sometimes a repair guy will recommend using epoxy because, either:

a) That is what they were trained on, and they don't know that either will work fine.

b) Maximize profit (both parts and labour).

c) It makes sense to the customer if the original failed, to use something "better" the next time. (Even though the something better, would have failed too, if used under the original conditions, but of course, the customer wouldn't understand that.)

Forgive me if this has already been answered, but is there a labour difference between professional repairs done in polyester vs epoxy? Seems to me that the effort is pretty much the same for either, and that the labour costs will swamp the materials cost?

[neilpride]

Originally Posted by Lake-Effect

Forgive me if this has already been answered, but is there a labour difference between professional repairs done in polyester vs epoxy? Seems to me that the effort is pretty much the same for either, and that the labour costs will swamp the materials cost?

If there is a cosmetic finish at the end then sure there is a diference, patching a hole in a hull side in epoxy call for spray painting in most cases when done in poly you can match in gelcoat ...

[DeepFrz]

You can also use gel coat over epoxy repairs.

[NevisDog]

Originally Posted by neilpride

... patching a hole in a hull side in epoxy call for spray painting in most cases when done in poly you can match in gelcoat...

No one in their right mind would repair "a hole in the hull" using poly!

[neilpride]

Originally Posted by NevisDog

No one in their right mind would repair "a hole in the hull" using poly!

Why not, here in the island is a regular job , hundreds of boats repaired in Poly and doing fine, even after years, if you can make a multi stern extensión in poly you can patch a big hole in poly, usually do it by Pro´s.

[smj]

Originally Posted by neilpride

Why not, here in the island is a regular job , hundreds of boats repaired in Poly and doing fine, even after years, if you can make a multi stern extensión in poly you can patch a big hole in poly, usually do it by Pro´s.

So if I understand this correctly, a very well prepped hole in the boat or stern extension done by a good fiberglass professional in polyester can give results that are satisfactory. I'm guessing the only way you will find out if the prep was good enough or the fiberglass man was a true polyester wizard is if you stress the boat enough and she comes out unscathed. Now if for some reason the prep wasn't good enough or the glass guy wasn't a wizard you'll find out when the patch peels of the hull or the extension falls of, usually when the boat is being put through some serious stress? If it were my house or possibly a house boat on a benign lake I may take the chance as the results wouldn't be as catastrophic as this happening in the middle of the ocean. I do believe I will shell out a few more $'s for epoxy and feel better about my chances. This is coming from a guy who had a pro glass man do a patch on our keel that was hanging on by a thread the next time we hauled.

[neilpride]

Originally Posted by smj

So if I understand this correctly, a very well prepped hole in the boat or stern extension done by a good fiberglass professional in polyester can give results that are satisfactory. I'm guessing the only way you will find out if the prep was good enough or the fiberglass man was a true polyester wizard is if you stress the boat enough and she comes out unscathed. Now if for some reason the prep wasn't good enough or the glass guy wasn't a wizard you'll find out when the patch peels of the hull or the extension falls of, usually when the boat is being put through some serious stress? If it were my house or possibly a house boat on a benign lake I may take the chance as the results wouldn't be as catastrophic as this happening in the middle of the ocean. I do believe I will shell out a few more $'s for epoxy and feel better about my chances. This is coming from a guy who had a pro glass man do a patch on our keel that was hanging on by a thread the next time we hauled.

Diferent materials diferent properties, as far i know you dont want a hard spot in a topside, also as well some insurance companys call for OEM material repairs, having done a long extensions in a power multihull in poly im pretty confident in the material used,, and also cheaper because we match the hull gel with the sterns in gel to, the other way its a $$$ bill in a Awlgrip job ,, epoxy for a keel stub or keel repair job is fine and i dont see any flaw for using epoxy as far the repair is done respecting the surrounding mechanical properties...

The pics show some poly glass repairs done, i see some of those chárter multis loosing a bow after a collision ....

[lateral]

Firstly, from my experience epoxy does not spontaneously combust.

It can exotherm to highish temperatures (400°+), but 100% solids west does not support combustion well at all. Try burning epoxy laminate. But it could set fire to inflammable material adjacent whose ignition temperature is way lower.
Exotherm in structural epoxies should be controlled with thickness of laminate for optimum physical results.

Whereas Poly curing, is exothermic + vigorously supports combustion on its own, and burns ferociously.
Poly "bombs" are easy to make, never seen an epoxy one.

If your project requires a glue why not use one instead of something designed as matrix filler that has adhesive qualities?

If your project's substrate is poly, but if you need reassurance on adhesion, prep an area and run a peel test side by side of each.
Pretty easy & fundamental. Why introduce a material of different mechanical
properties if you can avoid?

I think your prep practices will have a bigger significance than your choice.
The deck of my boat is poly gelcoat over poly /0.75oz over epoxy balsa composite. No gelcoat failure. (Laid up in reverse in female mold.)

[smj]

Nothing personal to those wanting to use polyester, but epoxy when it comes to secondary bonds is far superior and is my choice based on what I've seen. We all make decisions on how we spend our money, and when it comes to the structure of my boat a few extra $'s to me is worth the peace of mind.

[ramblinrod]

Originally Posted by Lake-Effect

Forgive me if this has already been answered, but is there a labour difference between professional repairs done in polyester vs epoxy? Seems to me that the effort is pretty much the same for either, and that the labour costs will swamp the materials cost?

Poly tends to cure faster so WIP time is reduced. Otherwise, everything else is pretty much equal.

When I prepare an estimate in Poly, and a customer asks about the same repair in epoxy (when possible) the epoxy estimate, parts and labour is about 10% more.

[ramblinrod]

Originally Posted by DeepFrz

You can also use gel coat over epoxy repairs.

One can do all kinds of things. But poly doesn't always play nicely over epoxy.

I remember one cold night, hours before a hard launch date, running out of
Watertite epoxy fairing a hull / keel join. With no other option, I mixed up
some poly and filler. Nope, didn't play nice. I ended up scraping all of that mess off, and redoing completely in poly. Finished just as the sun was coming up. Kicked myself for even starting with the watertite. Ate the 6 hours of prime billable hours it cost me.

[ramblinrod]

Originally Posted by NevisDog

No one in their right mind would repair "a hole in the hull" using poly!

Why not?

Many polyester boats were/are built in two halves, joined together with poly, right down the middle. If it can hold 2 halves of a boat together, certainly it can hold a hole patch of any size.

[ramblinrod]

Originally Posted by smj

Nothing personal to those wanting to use polyester, but epoxy when it comes to secondary bonds is far superior and is my choice based on what I've seen. We all make decisions on how we spend our money, and when it comes to the structure of my boat a few extra $'s to me is worth the peace of mind.

Again, epoxy only has marginally stronger adhesive properties. If only 10% of
poly adhesion strength is required to hold the repair together, what does additional adhesion strength do?

Obviously, a tad more margin for error, but it is just a tad, and the error has to be huge. In fact, so severe, that it may just as easily exceed the epoxy strength too. When people do things wrong, results aren't great. Using epoxy instead of
Poly doesn't change that.