On Sat, 26 Dec 2009 16:30:38 -0800 (PST), the infamous Robatoy scrawled the following:
Ooh, ooh! Bad toy. Go to your room.
-- REMEMBER: The sooner you fall behind, the more time you'll have to catch up!
Many products are deliberately 'aromatically' odourized.
Lew is right, though I couldn't give you any scientific explanation of their differences. I've used them both many times (since I first started piddling with fiberglass back in the seventies) and epoxy is definitely the superior substance. At the risk of starting a whole other tangent to this thread (!) one might say that epoxy is to polyester as Lee Valley is to Harbor Freight...
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A chemist I'm NOT and almost got tossed out of my chemical engineering course, but will attempt to answer.
Polyester resin requires a catalyst, usually from the peroxide family to activate the process which is highly temperature sensitive.
A catalyst, by definition, does not affect the chemical properties of the cured resin, but only assists in promoting the polymerization process.
The cured polyester is not water tight, is not an adhesive and is heavy and of relatively low strength.
One of the reasons polyester boats are hauled from time to time.
They get a new "bottom" and are allowed to dry out in the process.
Epoxy, OTOH, is an adhesive, is a polyamide based product consisting of a base resin and a "hardener".
The resin and the hardener MUST be mixed together in an exact ratio for the polymerization process to take place.
While temperature affects epoxy viscosity and the speed of the reaction, it does NOT affect the resin/hardener ratio.
The cured epoxy is water tight, is light weight and relatively high strength.
When used with fiberglass, polyester does not easily penetrate the glass strands thus requiring a layer of mat between the glass fibers to soak up the resin (It's not an adhesive).
About the best ratio you can obtain is 35% glass, 65% resin by weight.
OTOH, epoxy easily penetrates the glass fibers, thus a layer of mat is NOT required when laminating.
A ratio of 50% glass, 50% resin by weight is easily obtainable.
Epoxy and knitted glass provide the best commercial laminate available.
The next step up is to use carbon fiber which has been on allocation for the last 5 years.
Take a look at hockey sticks and golf club shafts if your curious where all the carbon goes.
As far as the "Bondo" that is sold to body shops for auto repair, it is the bottom of the bucket.
Polyester resin thickened with talc which while allowing a feathered edge will not bond to the metal which is why, even with holes poked thru the metal to give the Bondo patch something to hold on to, the patch often falls of the vehicle after a few months/years.
While not the high tech answer, hopefully you will find the info useful.
Lew
On Sat, 26 Dec 2009 20:51:24 -0800, the infamous "Lew Hodgett" scrawled the following:
I'm really surprised that polyester resin has any use in boatbuilding or surfboards, since both critically need the adhesive and watertight properties.
No kidding.
I've helped people NOT buy cars by removing the inner door panel or fender liners to show them the bondo "hair" underneath. It does require lots of holes to stick to the metal.
Thanks, Lew. You filled in lots of holes from the wiki on it and added valuable data.
I haven't tried any of the thin epoxies which are used to soak wood and harden it in rot areas on older homes, but I may sometime soon. (Luckily, it'll be on someone else's home. I replaced my rotted fascia and installed new gutters shortly after moving in. ;) It's all 'real' epoxy, too.
Oh, a kayak builder tested half a dozen epoxies and posted the results if anyone's interested.
It does a half assed job.
"Water tight" is a relative term.
You don't use polyester to build water tight storage vessels; however, surf boards and boats are not storage vessels either.
The wooden boat guys are light years ahead of you.
"Git-Rot" is a thinned epoxy you supposedly inject into rotten wood on a boat tom stabilize it.
Only problem after cost is about all it does is add weight but not restore strength.
Sooner or later, you replace the rotted wood.
Lew
On Sun, 27 Dec 2009 09:23:19 -0800, the infamous "Lew Hodgett" scrawled the following:
OK, acetone it is.
Sorta like pounding a cork into a hole, eh? It stops the leak but doesn't add anything to the integrity of the vessel.
Ayup. "Pay me now or pay me again later. It's up to you."
-- "I believe that sex is one of the most beautiful, natural, wholesome things that money can buy." --Tom Clancy
Rule 1: Wear disposable gloves.
Rule 2: Refer to Rule 1.
Actually hand cleaners like G-JO followed by soaps like Lava and water get the job done pretty well.
I learned to wear Tyvek suits and gloves to address the problem.
Lew
On Sun, 27 Dec 2009 18:31:39 -0800, the infamous "Lew Hodgett" scrawled the following:
Which gloves are resistant to acetone and epoxy? Nitrile? Thick latex?
Rule 3: Ventilate the area and wear a respirator (with organic vapor carts?)
Yeah, developing a sensitivity to epoxy hardener is definitely -not- an experience I wish to have in this lifetime.
-- "I believe that sex is one of the most beautiful, natural, wholesome things that money can buy." --Tom Clancy
Surgical latex works for me.
Also "canner's" gloves (cuff above the wrist), about $7-$8/doz, work for me.(Safety Clothing supply house)
Laminating epoxies do NOT contain VOCs.
OTOH, catalyzed resins that are sprayed are a whole different ball game.
Lew
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0--Tom Clancy
I'm rather fond of the polyisocyanate hardeners found in 3-part acrylic spray coatings. The transdermal nastiness is second to none. Touch it with a finger, and a toe nail falls off.... (okay.. I embellish..)
On Mon, 28 Dec 2009 10:39:09 -0800, the infamous "Lew Hodgett" scrawled the following:
They may not contain VOCs, but they smell. Is absolutely _all_ sensitivity to the hardeners from physical touch, or is some through the lungs? Cites, please.
So is sanding of any material, which requires both protective gear and ventilation.
-- "I believe that sex is one of the most beautiful, natural, wholesome things that money can buy." --Tom Clancy
Developing contact dermatitus is one thing, but hardeners do not cause lung problems.
You definitely want to wear protective clothing when working with epoxy.
Sanding almost anything requires protective breathing apparatus but VOCs are not involved with laminating epoxies.
Lew
Silly me, I thought they only came from dried grapes. their Raison d'tre, as it were.
Enjoy
Been around but it's BBQ season and a luau qualifies.
Lew
------------------------------------------------------- Keoki wants to have a luau.
He needs a pig for the luau, so he goes to a pig farm and asks the farmer for a twenty-pound pig.
The farmer goes into the pen and searches around for awhile.
Finally, he picks up a pig, puts its tail in his mouth and begins to swing the the pig around for a few seconds.
He puts the pig down and says, "Nope, not quite 20 pounds."
He picks up another, puts the tail in his mouth, swings the pig around awhile and declares "This one's 20 pounds!"
Keoki says, "You can't weigh a pig like that!"
"Sure I can," says the farmer, "Watch this."
So he calls his son over and asks him to weigh the pig.
The boy comes over, picks up the pig , puts its tail in his mouth, and swings it around for awhile.
Soon he puts the pig down and says, "This one weighs 20 pounds."
Keoki still doesn't believe they can weigh a pig this way, so the farmer tells his son to get his mother so she can weigh the pig.
After five minutes the boy returns alone.
"She can't come out just yet," he says, "She's weighing the mailman."
I wasn't expecting that. :-D mahalo, jo4hn
Not today, anyway! The mailman doesn't pass on July 4th. You have to get your pig weighed before the 4th, in order to expect something as that.
Sonny
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