Epoxy / Polyester Resins Question

[boatpoker]

Originally Posted by minaret

These are the same people who appear to believe that poly production boats are all built in a single 24 hour period, therefore within the bond window for poly! Fact is, every poly boat out there is chock full of major secondary structural bonds,

Thank you. I believe I've made that very point several times while noting I've seen hundreds of such failures in fairly new boats.
Please note there are no personal attacks in any of my posts. As this thread has long past the point of reasoned disagreement and has turned to childish cheap shots ...... I'm outahere.

[ramblinrod]

Originally Posted by Wotname

Hmm... I have found the epoxies I'm familiar with do cure somewhat faster when exposed to UV (leaving aside temperature) so I was asking if poly had a similar characteristic.

I note the dentist uses UV to cure his epoxy fillings

What source are you using for UV that does not include radiant heat and raise the ambient temp?

While I have zero experience with dental epoxy, I have the sneaking suspicion that it is different than marine epoxy.

Anyway, I have to go fix boats.

If you are interested in an FRP primer that covers polyester, epoxy, and the differences between them, I conduct regular seminars in the off-season at marine retailers and yacht clubs in South Central Ontario. Come and take one in, if you are in the area. (Every years sells out quickly, and last year, the first date booked up so fast, a popular marine retailer in Toronto requested a second date, that immediately sold out from folks on the waiting list for the first.)

I'll certainly consider this subject for a future article in a Canadian sailing magazine where I write a regular DIY feature.

[NevisDog]

Originally Posted by minaret

Now watch all of these people carefully ignore this question and refuse to answer it...

Okay, I guess that one is directed at me. I've built several boats in two halves and joined them down the middle (admittedly a long time back) so I guess that makes me a professional, as I wasn't working for nothing. All those boats where I worked were joined down the middle by bringing the two halves of the mould together as soon as the last layer of glass had kicked in. The job was completed within a day - never, ever attempted on cured polyester, not ever - that was an absolute no-no. Never, ever tried to attach poly to a fully cured hull. All of the literature in those days told us never to do this, so it was never done in a professional boatbuilding yard - not ever. Enough said?

[neilpride]

Originally Posted by NevisDog

Okay, I guess that one is directed at me. I've built several boats in two halves and joined them down the middle (admittedly a long time back) so I guess that makes me a professional, as I wasn't working for nothing. All those boats where I worked were joined down the middle by bringing the two halves of the mould together as soon as the last layer of glass had kicked in. The job was completed within a day - never, ever attempted on cured polyester, not ever - that was an absolute no-no. Never, ever tried to attach poly to a fully cured hull. All of the literature in those days told us never to do this, so it was never done in a professional boatbuilding yard - not ever. Enough said?

I dont agree , my last boat a old CSY was 2 halves hull joined in the midle to, and the layup Schedule is something between 7 to 10 days in those days, unless you work with really thin layups or thin core panels then maybe you can lay the expected thicknes in a day or 2 , simple as if you try to glass a hull halve in one shoot you can run in lots of troubles..

For example those boats are sanded and grounded down between glass layers, never ever see a CSY going down or with structural isues..

[NevisDog]

Originally Posted by neilpride

... layup Schedule is something between 7 to 10 days in those days...

No problem with layup over seven days - problems arise if the last layer is left to cure seven days before the next layup is applied - that was never permitted in a professional yard in my day. Green on green.

[neilpride]

Originally Posted by NevisDog

No problem with layup over seven days - problems arise if the last layer is left to cure seven days before the next layup is applied - that was never permitted in a professional yard in my day. Green on green.

No , they dont let the hulls cure for more than 7 days between layers but quite honest the midle joint is done in hulls cured between 7 and 10 days, i dont see any diference..

[lateral]

One rule I adhere to is when wood is involved use epoxy.
There are resins in some woods that retard or completely
render PE useless. ie WR cedar
That doesn't mean it won't cure at all, just varying degrees
of cure and interface strength.

Why compromise a project using semi-compatible products?
Why have a mechanical bond when with a bit of effort you can
do a longer stint and have a chemical bond and eliminate a stage?
e.g. glassing a hull then skimming with fairing compound on kick.
Dont sweat if you can't get a chemical bond boats are full of structural
secondary.
Why sand when you can use peelply?
Why use epoxy on a hole in a PE hull when you can feather both sides
an get a chemical bond in the middle of the hole locking it in place?

If you haven't done the process before, talk to people that have and listen to their logic & results. Base your decision on "proof of service" and be comfortable with it.
If you can't afford the "industry standard" and opt for something less than optimum you may get away with it, then you may not.
Look at all the carvel plankers that were glassed with PE and CSM that got a
little more life. (Most a death sentence )

[transmitterdan]

I don't see how you can have a chemical bond with wood.

[smj]

Originally Posted by ramblinrod

I did read your post completely, and I did not become unhinged.

I called you on a misquote.

Your misquote is clear to anyone who knows the difference.

If you can't comprehend the difference, you should not be attempting to quote others, due to the likelihood of misquote.

Case in point, you just did it again.

I declared that if your prior misquote was intentional, that was childish...

This is totally different than what you claim I stated.

Now please stop trying to divert attention away from your indefensible, illogical position, and answer this question...

If a poly boat can be constructed in two halves, and held together by a poly secondary bond attachment, right down the middle, over its entire length then why can't an adequate hull repair be performed with poly?

I'm waiting for a respectful, logical, direct to the point, answer.

If you can't provide one, I consider your position is proven flawed.

RR your not worth my time.

[NevisDog]

I like the idea of "reasoned disagreement."

1. Clearly some here will never allow repair work on their boats with polyester, regardless of skill or persuasive ability of repair-men. 2. Clearly some put their reputations on the line using polyester for repairs (to save the customer a few bucks) and since they are still in business, I guess they do a reasonable job. 3. It is also clear that very strict time limits are enforced by the better boatbuilders on how long poly can rest before the next layer is applied, and for very good reasons. If anyone can point me to a reputable, scientific/chemical engineering source that specifies later repairs to poly boats should be undertaken using poly resins then I'd very much like to hear about it. Until then I'm not going to be convinced, so best leave it as "reasoned disagreement."

[ramblinrod]

Originally Posted by NevisDog

No problem with layup over seven days - problems arise if the last layer is left to cure seven days before the next layup is applied - that was never permitted in a professional yard in my day. Green on green.

Agreed that the lay-up schedule is prepared to generally support primary bond lamination.

Unexpected equipment failure, vacations, or staff illness / turnover, weather, often results in schedule deviation.

However, most schedules include the structural joining of components from separate molds, or tabbing, post part cure employing only secondary (mechanical) bonds.

For hull half joining, the inside attachment may be green (not always), but the outside and centre attachment is pretty much always a secondary bond.

Note that the designer/naval architects layup plan calls for progressive layers extending way beyond the join, much further than necessary for a primary bond connection.

If the primary laminate is 1/4" thick, the seam will be much thicker, and will feather extending around 2 feet beyond the seam. Why? Because a primary bond is preferred when possible, but a secondary bond will suffice when not. The forces attempting to split those hull halves apart is absolutely incredible, and yet, a poly secondary bond will suffice.

[ramblinrod]

Originally Posted by smj

RR your not worth my time.

Hmmm, you have all of the time in the world to misquote, mislead, attempt to defame character, and post countless diatribe to support a your position in a debate you think you can win or at least gain support of others with.

But you do not have time to answer a simple if/then question (that you know the only logical answer proves your position invalid).

Therefore, I draw my only logical conclusion.

You realize you were wrong, but won't admit it.

Please remember this the next time a polyester vs epoxy question arises, and I take time out trying to assist fellow boaters with free advise based on my professional opinion and experience.

I certainly accept their are differences of opinion, and find healthy debate entertaining and educational, but disrespectful behaviour is never tolerable.

[transmitterdan]

There seems to be an underlying assumption by some that epoxy is always better than poly and can always be used over poly. I used to think that way too but experience has taught me that in truth neither of these are valid. Some repairs are better done with resin matching the original and there are good technical reasons for using poly besides "saving a few bucks". A good fiberglass person can make a hull repair with poly that is stronger than the original hull without creating stress discontinuities caused by dissimilar epoxy layups.

So in my old age I have come around to the view that the quality and experience of craftsman is more important than the choice of material. And a good craftsman knows the right material and process for each application. For me there is no hard and fast rule other than to only let experienced persons make safety critical fiberglass repairs.

[svrodeorm]

Originally Posted by transmitterdan

There seems to be an underlying assumption by some that epoxy is always better than poly and can always be used over poly. I used to think that way too but experience has taught me that in truth neither of these are valid. Some repairs are better done with resin matching the original and there are good technical reasons for using poly besides "saving a few bucks". A good fiberglass person can make a hull repair with poly that is stronger than the original hull without creating stress discontinuities caused by dissimilar epoxy layups.

So in my old age I have come around to the view that the quality and experience of craftsman is more important than the choice of material. And a good craftsman knows the right material and process for each application. For me there is no hard and fast rule other than to only let experienced persons make safety critical fiberglass repairs.

that's a very good sum up. Problem may be to know when you've found a good craftsman, particularly when cruising extensively. It's never a bad idea to accumulate own knowledge on everything boatrelated.

This thread has enlightened me quite a bit, for which I thank all participants refraining from ridiculous peeing contests

[NevisDog]

Originally Posted by ramblinrod

...For hull half joining, the inside attachment may be green (not always), but the outside and centre attachment is pretty much always a secondary bond.... The forces attempting to split those hull halves apart is absolutely incredible, and yet, a poly secondary bond will suffice.

Yes of course you are correct. Very valid point. It's a long time since I was up to my arm-pits in goop and my brain is likely addled from all those styrene fumes years ago. Sorry, I too have learned to think more rationally from this thread.