Epoxy on epoxy – chemical vs mechanical bond. Does it matter

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LesForgue
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Epoxy on epoxy – chemical vs mechanical bond. Does it matter

Post by LesForgue » Mon Mar 05, 2012 12:23 pm

Epoxy on epoxy – chemical vs mechanical bond.
Does it matter much for structural integrity?

My question is …
Should we bend over backwards to achieve more chemical bonds and fewer mechanical bonds?
Sometimes our family-job-church-whatever schedules will force us to miss opportunities for chemical bonds, making us settle for mechanical bonds at times.
I am thinking (and hoping) that mechanical bonds will be more than enough for a strong, long lasting, safe canoe.

I do understand (I think) that putting epoxy onto epoxy that has not cured will save sanding and reduce risk of amine blush, so there are advantages besides the chemical bond.
But there will surely be steps in the S&G process where epoxy will be put on fairly well cured epoxy, losing the chance for a chemical bond. I also think I understand that if the chance for a chemical bond is missed, that sanding first will make for a better mechanical bond.

I’d appreciate some opinions on whether it’s advisable to try very hard to get chemical bonds as much as possible, or whether it would be okay to let delays in getting to the next building step make us settle for a mechanical bond.

Thanks.

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jem
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Re: Epoxy on epoxy – chemical vs mechanical bond. Does it ma

Post by jem » Mon Mar 05, 2012 12:36 pm

As a general rule, I try and get the chemical bond when possible. Sometimes I can pull if off, other times life jumps up and gets in the way.

This is why I prefer not to do an initial "sealer" coat on the hull before applying fiberglass. It ensures a strong bond to the bare wood and I don't have to worry if something interrupts me between the "sealer" coat and actual fiberglass application.
-Matt. Designer.

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Re: Epoxy on epoxy – chemical vs mechanical bond. Does it ma

Post by LesForgue » Mon Mar 05, 2012 7:44 pm

Thanks Matt... I reckon I'll go your way instead of that of the much-repected elder with his own forum who advocates complete epoxy saturation of every panel as a first step.... I was wondering anyhow would that not make the panels that much more harder to bend at the bows... since I got 5 mm (and he uses 1/8 inch stock). I am gleaning advice from both you and Old Sparkey, (and others on the forums) but when there's a big difference I will go with what the designer says and does. (If Old Sparkey happens to read this here, I do want him to know I place a high value on his experience and wisdom, whether I choose to follow every detail or not.)

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Re: Epoxy on epoxy – chemical vs mechanical bond. Does it ma

Post by jem » Mon Mar 05, 2012 7:51 pm

It can be done either way with success.

Chuck, if that's who you're speaking of, stitches the hull, then applies a coat of epoxy, then applies the fiberglass.
-Matt. Designer.

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Re: Epoxy on epoxy – chemical vs mechanical bond. Does it ma

Post by tx river rat » Mon Mar 05, 2012 9:57 pm

I have applied it both ways and I cant tell the difference .
Chuck does his boats different than most because he has medical reasons to be extremely light. He is a top crafts man and does it well.
If I am glassing a boat in hot weather I use a saturation coat to seal the hull and stop the out gassing. I just rough sand after the saturation coat and the apply the glass.
Ron

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Re: Epoxy on epoxy – chemical vs mechanical bond. Does it ma

Post by Oldsparkey » Tue Mar 06, 2012 9:57 am

LesForgue wrote:Thanks Matt... I reckon I'll go your way instead of that of the much-repected elder with his own forum who advocates complete epoxy saturation of every panel as a first step.... I was wondering anyhow would that not make the panels that much more harder to bend at the bows... since I got 5 mm (and he uses 1/8 inch stock). I am gleaning advice from both you and Old Sparkey, (and others on the forums) but when there's a big difference I will go with what the designer says and does. (If Old Sparkey happens to read this here, I do want him to know I place a high value on his experience and wisdom, whether I choose to follow every detail or not.)
We have a lack of communication here or a gross misunderstanding ...BOSS. :lol: If you are referring to how I make a boat.

I do not recommend the saturation of each piece before attaching them together , only after the boat is together and ready for glassing. If each panel is saturated before assembling you will have a hard time bending it since the epoxy stiffens the wood , some folks ( Not Myself ) do make boats that way.
Someone was asking that on my forum and he was advised of that fact if he tried doing it , it could be done , but it is not my way of doing it. If memory serves me he was also asking about glassing each piece after it was saturated. He was advised that he would be doing double the work since each seam would have to be glassed or the whole boat re glassed when it was together doubling the weight of the glass on the boat. Basically doing the same job , twice.
As I recall he was wanting to have a slick glass finish on the boat and figured it would be easier to do each piece individually and then assemble them then to do them when the boat was together.

I saturate the wood before glassing ( after the boat is together ) but I make sure that I have the time to do that. The wood is saturated , then sanded (lightly ) when cured , then glassed the next day. The epoxy I use there is a 72 hour time span in there as an buffer but when I do it it is the next day. The time is set aside for me to do that , priority job #1.

There is one exception and so far it works for me. When doing the fillets I saturate the wood on each side of the seam so when tape is applied it has something to stick to. I did that one time without the epoxy on each side of the filleted seam and when I pulled the tape some wood came up with it. SO....I always put down a inch to 1 ,1/2 inch line of epoxy on each side of the seam. Later ( it might be a month or more depending on how fast I am with the construction ) when the boat lightly sanded and then saturated. The epoxy and glass adheres to what is already there and everything comes out as planned.

Everyone has a different way of making a boat , the biggest job is figuring out how you want to do it. All of my boats , if you checked them , do not have the 1st piece of metal holding them together. Just wood , epoxy and glass and as light as possible. :D

Chuck.........
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Re: Epoxy on epoxy – chemical vs mechanical bond. Does it ma

Post by jem » Tue Mar 06, 2012 10:09 am

tx river rat wrote:I have applied it both ways and I cant tell the difference .
Chuck does his boats different than most because he has medical reasons to be extremely light. He is a top crafts man and does it well.
If I am glassing a boat in hot weather I use a saturation coat to seal the hull and stop the out gassing. I just rough sand after the saturation coat and the apply the glass.
Ron
Thanks for mentioning that. I forgot that part.

If you do perform a sealer coat first, then it's easier to deal with any outgassing bubbles that form than if you had a layer of fiberglass over the wood. Outgassing happens as epoxy coated wood is changing temperature and expanding/contracting. If the wood cools and contracts, it forces air out of its pours into your epoxy (even if the air cools and contracts a little). If temp in the wood increases, the air heats up, it and the wood expands, and the air works it's way out into the epoxy. I've found I get less bubbles as the temp decreases.

If you apply your epoxy when the temperature of the wood is stable/constant, you'll have very little outgassing bubbles. Chuck builds down in Florida where the temperature is about as stable as a pack of Mentos in a bottle of Pepsi. So he is constantly fighting gas... er augh... from the boat. :lol:
-Matt. Designer.

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Re: Epoxy on epoxy – chemical vs mechanical bond. Does it ma

Post by Oldsparkey » Tue Mar 06, 2012 5:22 pm

jem wrote: If you apply your epoxy when the temperature of the wood is stable/constant, you'll have very little outgassing bubbles. Chuck builds down in Florida where the temperature is about as stable as a pack of Mentos in a bottle of Pepsi. So he is constantly fighting gas... er augh... from the boat. :lol:
One I can handle but the gas from the wood as it heats up is a real pain in the posterior. I try my best to do the saturation when the temp is falling and the wood is cooling. The way I see it is as the wood cools and the air is being absorbed by the wood it helps to absorb more of the epoxy. Plus by doing it that way the epoxy has all night to cure so I can glass it in the morning. Since that problem is over after that saturation coat so glassing the boat is not a problem.
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