Epoxy / Polyester Resins Question

[Wotname]

Originally Posted by ramblinrod

......

Beware of epoxy manufactures who market (very well I may add) to DIYers.

They (naturally) will do everything possible to cast their product in a favourable light.

Whereas poly manufactures don't really market to the DIYer.

Follow the epoxy guys instructions when using poly (other than catalyst ratio) and there is very little difference.

.........

I think this is the key to my lack of knowledge about everything poly.

As a long term DIYer, I have used hundreds of litres of epoxy and of perhaps half a dozen manufacturers. You are correct, the instructions are in the main, very detailed and very clear about what and what not to do. In addition, they print booklets, run seminars, hold information nights and so on. Some even tell you the "why" as well as the "how". Pretty hard to get it wrong if one is willing to follow their instructions. With lots of use, comes ability and understanding of how the product behaves. So I used to use one product for one job and another for a different job etc.

With poly, it seems to me that the "how to use" detail just isn't so easily available, let alone the "why". Should I use waxed or unwaxed for a particular job and why, what is the difference between adding acetone and adding styrene, etc. I'm sure if I looked hard enough, google would tell me but only after trawling though lots of misinformation and going off on tangents.

With epoxy, I can go straight to WEST or Bote Cote or whoever, and all the information is in one spot.

Maybe the CF poly folk will end up teaching me everything I need to know about poly.

[Wotname]

OK, I hear the advice about preparation being essential for both resins so another question is why do I see so much poly (and glass) delaminating from plywood etc but have yet to see epoxy delaminate in the same way.

Is this because of poor preparation and /or wet wood or is there a real difference between poly and epoxy on timber?

[Wotname]

Sorry, more questions

Does UV affect the cure rate of poly?

[ramblinrod]

Originally Posted by smj

As usual, if someone doesn't agree with you they are amateurs, yet the man that calls polyester secondary bonds as strong or stronger than original you call a professional. Laughable.

Your attempt to deflect attention away from your logically indefensible position did not go unnoticed.

I said the "repair" can be as strong or stronger than the original.

That is significantly different than your misquote.

Was your misquote intentional?

If so, shame on you, that is childish and improper, especially when used in an attempt to defame.

If your context changing misquote was unintentional, I forgive you...this time, please don't let it happen again.

All one needs to do, to make a poly repair as strong as the original laminate, is a proper repair prep with sufficient overlap; to make it stronger, one extra layer of glass.

Viola, the "repair" is as strong or stronger than the original poly laminate.

If the vessel suffers catastrophic trauma (e.g. collision), the surrounding area is likely to be damaged before the repair area.

If one were to use epoxy for that same repair, they would use exactly the same prep and repair practices. Only the material, mix ratio, and finishing are different; the structural repair practice is virtually identical.

[ramblinrod]

Originally Posted by Wotname

OK, I hear the advice about preparation being essential for both resins so another question is why do I see so much poly (and glass) delaminating from plywood etc but have yet to see epoxy delaminate in the same way.

Is this because of poor preparation and /or wet wood or is there a real difference between poly and epoxy on timber?

Epoxy does tend to flow (overcome surface tension) around fibre and filler a bit better than poly. Nothing a small fraction more wetting and working doesn't overcome.

However, epoxy does delaminate in exactly the same way for exactly the same reason.

Hydrostatic force separating the materials and rot induced delamination, usually due to moisture ingress from poorly performed core penetrations, seams, or coverage.

However, epoxy has an additional very serious failure mode that poly doesn't; rapid material breakdown due to UV exposure.

If the finish over the epoxy fails, it will (not maybe) breakdown due to UV exposure and the delamination will advance very catastrophically and rapidly.

Some epoxies have UV inhibitors but these rarely work as well as materials that are not nearly as UV sensitive (such as poly) to begin with.

Whereas if the gelcoat wears through on poly FRP (gelcoat is much thicker and harder BTW, so this is less likely but regardless), the poly will last virtually forever with no finish at all.

If you haven't seen epoxy delaminating from wood, you haven't seen an epoxy constructed boat, the same age, and having the same annual maintenance, as the average poly boat.

Don't believe me?

Properly prep and completely coat one piece of wood with the most popular brand of DIY epoxy resin, coat another with poly, following exact same practice, lay them out in the weather, and check on them once per year. Before long, you will be shocked with how vastly superior the poly coated wood stood up.

[smj]

Thank you for calling me childish, improper and in need of forgiving. My quote was exactly yours except I used the words secondary bonds where you used repair. Surely you know that repairs on fiberglass require secondary bonds? Next time I suggest you read a post completely before becoming unhinged.

[smj]

From my knowledge there are zero boatbuilders producing wood/polyester boats, they're all using epoxy, and for good reason

[ramblinrod]

Originally Posted by Wotname

Sorry, more questions

Does UV affect the cure rate of poly?

Temperature certainly affects both.

In my experience, epoxy is more sensitive to temperature.

Epoxy manufacturers have a variety of different hardeners intended for use at different temps. (Whereas with poly, one just changes the catalyst ratio to suit temp and pot life requirements.)

If the epoxy manufacturer doesn't have at least slow, normal, and fast hardeners, the curing time will vary widely based on temp., and heat must be added in cooler temps, and cooling techniques employed in hot temps.

Epoxy tends to be much more sensitive to UV exposure post cure, from a material break and deterioration standpoint.

[ramblinrod]

Originally Posted by smj

From my knowledge there are zero boatbuilders producing wood/polyester boats, they're all using epoxy, and for good reason

Then your knowledge is extremely limited on this subject.

Millions and millions of boats have been and continue to be constructed of wood cored polyester.

[Wotname]

Originally Posted by ramblinrod

......
Properly prep and completely coat one piece of wood with the most popular brand of DIY epoxy resin, coat another with poly, following exact same practice, lay them out in the weather, and check on them once per year. Before long, you will be shocked with how vastly superior the poly coated wood stood up.

Well this isn't a good test as we both know that the epoxy will break down very quickly due to it being UV sensitive. I suspect that if both are coated (painted etc) to prevent UV damage, then the results will be very similar - no???

[smj]

Originally Posted by ramblinrod

Then your knowledge is extremely limited on this subject.



Millions and millions of boats have been and continue to be constructed of wood cored polyester.

Millions and millions of old ply/poly boats in the old wooden boat graveyard.
So RR show me some links to some well known boat builders that are producing wood/poly custom boats, or production.

[Wotname]

Originally Posted by ramblinrod

Temperature certainly affects both.

In my experience, epoxy is more sensitive to temperature.

Epoxy manufacturers have a variety of different hardeners intended for use at different temps. (Whereas with poly, one just changes the catalyst ratio to suit temp and pot life requirements.)

If the epoxy manufacturer doesn't have at least slow, normal, and fast hardeners, the curing time will vary widely based on temp., and heat must be added in cooler temps, and cooling techniques employed in hot temps.

Epoxy tends to be much more sensitive to UV exposure post cure, from a material break and deterioration standpoint.

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

[Wotname]

Originally Posted by smj

Millions and millions of old ply/poly boats in the old wooden boat graveyard.
So RR show me some links to some well known boat builders that are producing wood/poly custom boats, or production.

Aren't there poly coated balsa cored boats around????

[boatpoker]

Originally Posted by Sailmonkey

That sure looks like tabbing applied over gelcoat. Almost born to fail regardless of the resin.

The gelcoat is polyester.

[ramblinrod]

Originally Posted by smj

Thank you for calling me childish, improper and in need of forgiving. My quote was exactly yours except I used the words secondary bonds where you used repair. Surely you know that repairs on fiberglass require secondary bonds? Next time I suggest you read a post completely before becoming unhinged.

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.