When is epoxy a bad choice?

[souljour2000]

I am still just getting my sea-legs when it comes to epoxies and resins. Am I correct in my understanding that epoxy is much more brittle in general than your basic "boatyard" polyester resin? This seems correct from my experience with both. If so then,for you guys with experience...

What are some situations where the brittleness of epoxy makes it a bad choice?
Is this really only a worry under high shear loads where the two bonded areas could bend in different directions like corners? Will applying the epoxy in thin layers help this problem? I don't have a specific question regarding a project but am just wondering. Thanks!

[mark775]

Epoxy is less brittle than poly.

[rwatson]

True - and its the cloth that provides the significant sheer load strength no matter what 'goo' is used.

[PAR]

Epoxy is a better resin system in every way you can measure the differences between the two. I can think of no example of wanting to use polyester instead of epoxy.

[rwatson]

Epoxy is a better resin system in every way you can measure the differences between the two. I can think of no example of wanting to use polyester instead of epoxy.

Hmmmm -I can Par, when Cost matters, Polyester is waaaay better. Mind you, I wouldnt go lower down the food chain than VinylEster for a hull.

[alan white]

I chopped the cabin off an Alacrity 19 cruiser today in order to make it into a daysailer with a cuddy. This is particularly easy because the cabin is stepped and the forward part remains on the boat as a cuddy.
Why chop off the cabin (and the cockpit too)?
In a word, polyester resin. Virtually all of the structural and non-structural tabbing had let go when the boat sat with water in the bilge and the sun cooking it.
To get under the cockpit, let alone crawl into a small cabin to grind and rebuild would have nixed the whole rebuild project due to extreme hours of labor, but changing to a non-self-bailing cockpit from the original one gave access to the whole insides.
If epoxy had been used originally, I wouldn't have been able to afford the boat. The hull is absolutely like new (a testimonial to the proper use of polyester--- in large monolithic structures). Even the polyester gelcoat has taken sanding and buffing to the extent that it's hard to believe the boat is at least 40 yrs old.
The prudent use of both polyester and epoxy will yield the best of both worlds.
The tabbing in this boat in particular was very complicated and involved many wood parts. The parts were not totally encased in poly resin, but were allowed to take on water from other non-coated surfaces. This is what caused the tabbing to let go, but also actually reduced rot in the majority of the wood because for the most part, the wood could dry out once the water level in the bilge receded. Cutting through the overhead stringers (no balsa or ply coring, thank God), the wood was dry and strong.
The tabbing ought to have been done with epoxy. Each wood part attached should have also been sealed (though had it been polyester resin in the tabbing, sealing would have spelled doom for most all of the wood against the hull.
Bottom line, epoxy is just the right resin for building a boat that can stay rot-free for more than a quarter century, and probably longer. The hull is ployester, but any wood attached to it should be encapsulaed and bonded with epoxy.

[souljour2000]

Okay..well ..cost is a factor..will use resin on cabinetry areas for sure but flexibility was where I was really unsure of the properties of these two goos...I have it straight now... thx folks...btw..Alan...I am right behind you with my sawzall and a 1983 Hunter 20...oh..and a midget holding a stiff drink.

[souljour2000]

Alan...some pics of your project would be incredible...and no I am not really that close to hacking into my Hunter but I am curious how yours looks before /after

[alan white]

I took a couple today, very gruesome! It took about an hour and a half. Chose the coaming material also, will pick up tomorrow, two book-matched pc 1/2" x 8 3/4" x 10' african mahogany. The seats and sole will be port orford cedar from a local yard.
I'll take some pictures as I go along and post them here.

[Tony-Pion 30]

The main drawbacks with epoxy are alergies and cost. I am alergic to both the epoxy and the cost but persist in using it for its superior bonding properties. I need to don a chemical suit in order to avoid any adverse effects.

I would also avoid using epoxy where there will be prolonged exposure to sunlight as it deteriorates under UV bombardment.

Epoxy with its superior bonding properties makes it the only option in my mind for composite construction. Epoxy bonds extremely well to polyester and vinylester but not necessarily the other way around. So don't use epoxy in a situation where you will need to bond polyester to it in the future. Some paints and finishes also take exception to bonding to epoxy so consider the project as a whole when using epoxy.

[Roly]

When is epoxy a bad choice?
When clear epoxy is eposed to UV.

Brittle??
I am current using a specifically designed epoxy with a 50% tensile elongation.
Don't know of any modified poly that will do that.

[Herman]

Yes, there are polyesters that can do that as well. Mostly used for roofs. Not for construction work.

One other factor that must be kept in mind: Temperature resistance. In general, polyesters have a higher Tg then epoxies. (but keep in mind that both polyesters and epoxies are available with a Tg of over 200 degrees C)

[souljour2000]

Back to this thread for awhile...if I go with epoxy for my new coach roof on my Hunter 20 what do I need to consider as far as UV which I understand epoxy or clear epoxy cannot withstand well...is there a pigment added that counters the UV or does the right kind of paint over the epoxy protect it from the UV which a coach roof would be highly subject to?...thanks in advance.

[Submarine Tom]

Good question, I look forward to a good answer.

One heads up: Five Minute Epoxy is markedly more brittle than it's slow cure counter-part.

Cheers, Tom

[Herman]

On the 5 minutes epoxy: Depends on the brand. What they sell here is very flexible.

Coachroof: Apply epoxy as you are familiar with, then coat with a 2part PU paint with UV filter, minimum 2 coats.

[apex1]

You can apply almost any paint on Epoxy! Due to the fact that it is opaque, it usually will protect the Ep from UV rays. Sufficient thickness of the layer assumed.
When you varnish, you are in another world! The varnish not only has to be UV resistant (that means nothing but the varnish itself gets not destroyed by UV), it has to be UV "protectant" !!! And at least three layers are required for a first time protection varnish over Epoxy!

Regards
Richard

[PAR]

Richard has it, most any paint will do a good job against UV. For your cabin roof I wouldn't bother with 2 part LPU, I'd just use a single part polyurethane. Insure you get enough paint on the surface (several coats of primer, several coats of top coat).

5 minute epoxies can be brittle, but this isn't indicative of them, some are also quite flexible. Other then tacking together a template or something, I can see no use for these epoxies.

[souljour2000]

Thanks for clearing that up for me...two coats of primer and two coats of a good polyurethane topcoat...that should be enuff then. I have used 5-minute epoxy for small jobs...I usually get the marine epoxy which is a tube of stuff with a white and black tube side by side.When mixed they are of course grey in color and do in fact seem very brittle...something that I need to check on now that I think of it because I used it for small drill-hole patch or two at waterline from an old depth transducer and when I mounted my new transducer. The other kind of 5-minute epoxy I have gotten once or twice is clearish stuff that smells really awful and I have wondered if it wasnt really epoxy but instead might be this vinylester resin that people talk about which I have not tried. Like I said..this stuff has an unmistakeable odor but it DOES seem alot less brittle than the black/white marine 5-minute epoxy...Anyways...thanks guys for the other info on painting epoxy...

[apex1]

Take care,

some of the stuff named "marine Epoxy" or similar, is nothing but polyester!

Make sure you use really Epoxy resin.

And let the 5 minute stuff where it belongs, in the hands of RC model builders!

Regards
Richard

[Jimbo1490]

Back to this thread for awhile...if I go with epoxy for my new coach roof on my Hunter 20 what do I need to consider as far as UV which I understand epoxy or clear epoxy cannot withstand well...is there a pigment added that counters the UV or does the right kind of paint over the epoxy protect it from the UV which a coach roof would be highly subject to?...thanks in advance.

Just paint it with an opaque coating and that will do the trick. There are UV stable epoxy resins, BTW. They are a relatively new thing, only about 20 years old. Look at any chatachoochie stone company website. They will advertise their CLEAR epoxy bonding/coating with a 10 or 20 year warranty. And of course that's outdoors :p For some reason, these have not become popular in the marine industry.

I hate to say it, but the marine epoxy industry is kind of a rip-off. Everybody has this idea that epoxy costs like 3X or 6X what poly resin costs. I've bought both by the drum, and it just isn't so, at least not at the drum price. It's only after some re-seller gets a hold of the stuff that the price goes through the roof. Back in 2001, I paid $1.66 a pound for Epon 828 by the drum. As it was sold by weight, the drums were normalized to 500 lbs. At it's density, 500 lbs yielded ~51.5 gallons of resin which cost me $830.00, for a cost of ~$16/gallon. Quality poly resin was about $12 a gallon back then by the drum. Even back then, West was about $70/gallon, and West is (allegedly) just 828 plus a modifier or two. The resins have all doubled in cost since then, but that's true for poly too. I remember thinking at the time that the Vinylesters made no sense at all because they cost as much or more than standard (EEW190) epoxy resin.

If you need a lot of resin, then you need to worry about cost. That's when you need to buy drums, and not from a 'formulator', but a distributor for the manufacturer. They will give you all the FREE data you need to pick out curing agent(s).

Jimbo

[Fanie]

Neither polyester or epoxy last in sunlight, both has to be covered with ie paint. Over time the epoxy or polyester disintigrates and leaves the bare fiberglass.

Epoxy can bend a bit further than polyester, although I have yet to see a boat bend so far it will break.

The biggest difference is probably the application method. Polyesters cure fast above 15 deg C, epoxy 24 hours if you don't heat it up.

Epoxy bonds well to wood.

Epoxy is expensive compared to polyester.

When is epoxy a bad choice?
When is polyester a bad choice?

If poor preparation, poor method, wrong application.

[souljour2000]

Jimbo,

How long have you used this Chattahoochie Stone company clear epoxy resin?..I know it's got a 20 year guarantee and I have surmised often that there must be some marine grade stuff out there somewhere that is being used at $35.00/gallon to glue flagstones in someone's driveway...or other industrial applications...the plumbers use a two-part to re-line pipes but it seems to be expensive for them too...not to be a skeptic but I'm trying to sort out the myths ..if you have some fairly documented anecdotal experience with this Chattahoochie stuff or the like please embellish upon this if you can....the severely budget-conscious and monetarily-challenged portion of this online forum would be hugely indebted to you (in a sense..were broke as I said)

[Jimbo1490]

Jimbo,

How long have you used this Chattahoochie Stone company clear epoxy resin?..I know it's got a 20 year guarantee and I have surmised often that there must be some marine grade stuff out there somewhere that is being used at $35.00/gallon to glue flagstones in someone's driveway...or other industrial applications...the plumbers use a two-part to re-line pipes but it seems to be expensive for them too...not to be a skeptic but I'm trying to sort out the myths ..if you have some fairly documented anecdotal experience with this Chattahoochie stuff or the like please embellish upon this if you can....the severely budget-conscious and monetarily-challenged portion of this online forum would be hugely indebted to you (in a sense..were broke as I said)

I've never used chatahoochie stone bonding resin, but I've seen it in service on various buildings and been to the websites. Although it is clear, it seems to hold up just fine outdoors unpainted. The Shell website had a lot of tech data on the Epon 20XX series resins which are UV stable. This is the resin series that they use for this and also for durable outdoor tile grout. The UTS, e, viscosity were all in the 'normal' range of other liquid epoxy resins, but the stuff was just UV stable. I've never got a price quote; maybe its pricey.

Jimbo

[apex1]

Souljour,

I doubt any link or recommendation would help much. Jimbo was talking quantities for yards, not for homebuilders.
We are not even using barrels, we get the stuff in tank trucks.

Regards
Richard

[Jimbo1490]

Souljour,

I doubt any link or recommendation would help much. Jimbo was talking quantities for yards, not for homebuilders.
We are not even using barrels, we get the stuff in tank trucks.

Regards
Richard

A lot of posters to this forum (not necessarily this thread:D ) have embarked on a project to build a complete boat (and sometimes even the molds) from scratch. In that case a drum purchase makes perfect sense.

Jimbo

[apex1]

A lot of posters to this forum (not necessarily this thread:D ) have embarked on a project to build a complete boat (and sometimes even the molds) from scratch. In that case a drum purchase makes perfect sense.

Jimbo

Nothing to complain!

And I am absolutely pro support of a homebuilder. Just wanted to make clear that those quotations are not available for the average builder.

Regards
Richard

[souljour2000]

Hmm..I just need a three or four gallons but trying to save where I can...if I was building a boat from ground up you could try and grease someone's palm or were friends with a large builder and get it by the pallet I guess...

[PAR]

A three gallon kit from Bateau.com will run about $150 plus shipping or you can run up to St. Pete and use FGCI. Buying in those quantities (55 gallon drums) are for folks doing some serious building. The last drum I bought was $900+ after tax, so how much epoxy do you really need.

[souljour2000]

I just ordered about a gallon and a half from US composites (1 gal resin and 48 oz hardener)..thought I'd start with a small order and go from there..I think it comes to about $71.00 with shipping included ..they ship in 48 hours supposedly in FLA since they have a West Palm warehouse....alot of greenbacks for a gallon and a half of goo but at least I'm avoiding the West marine a few blocks from here....it's a medium-fast hardener though with the weather we've been getting here in FLA lately and the forecast it may require some patience...FGCI..hmm..in St Pete? ....will check them out PAR....I will need say 2-3 gallons more for the coach roof and a bow hatch re-model...don't need much at all really but the rebel in me wants to find a non-marine source that is essentially marine grade that some of the guys in here building ground up and needing 40 gallons or a pallet or two of barrels could use to save money.

[PAR]

Bateau.com is out of Vero beach and one day delivery to you. Epoxy isn't an area you want to skimp on.

You'll want slow and extra slow hardener in Florida, not fast. In the winter you can use fast hardeners, but not that often. Fast hardeners don't permit you the setup time, which is important for a novice user, so work in small batches of 6 ounces or less, to prevent waste. I'd rather have to post cure or wait for the weather to warm up, then not have enough time to get things in place before the goo is smoking.

[souljour2000]

Check that PAR..I got the medium fast hardener which with this weather we're havin' should give me some time..yeah..this is my first real amount of epoxy over an 8 oz. tube...should be fun...you guys have taught me alot though...will post pics...

[jonr]

I understand that cost and cure time are why so many boat builders are using vinyl-ester.

[apex1]

I understand that cost and cure time are why so many boat builders are using vinyl-ester.

Then you understand more than we builders do!:cool: Cost yes, but curing times I can order almost as I want them.

[souljour2000]

well...I'm not sure if my online order for epoxy from US composite went thru or not..I should have waited and phoned the order in this morning instead. If they didnt debit my card..I'll go to St.Pete to that place PAR mentioned..I have been meaning to go check out Don's boat junkyard in Clearwater..maybe hit that too..I hear that place is a south florida institution..

[Herman]

Then you understand more than we builders do!:cool: Cost yes, but curing times I can order almost as I want them.

I understand what you mean, but indeed jonr might be right. The fun thing about polyester and vinylester is that for 20 minutes (or longer, depends on what you ordered) nothing happens, then BANG!! The stuff is cured. I supply people that pop out 8 products from a single mould in a single shift. Every hour a product (including gelcoat!).

Viewed from that respect, epoxy is slow stuff... (which actually is not too bad)

[apex1]

Right,
though, as you know, I can have Ep curing in 15 minutes if I like. Less if quality does´nt matter.

[souljour2000]

Yeah..have to agree...the resin is pretty much the same down the line..but you have like 4 different hardener/catalyst choices from slow set to fast set and in-between ..at least with US composites ..which has a great website..well-explained....and they ship in 2-3 days in Florida...they say the medium speed hardener is their big seller...that's what I ordered and it did go thru...on Tues morning...just not on Monday..but I ordered Sunday night after a holiday so thats to be expected..they were backlogged with online orders.....but when does quality not matter Apex...am I missing something..? I am trying to ensure quality control in my project and then you who I respect as someone who knows something (at least more than I who am a novice with these materials) says that at times quality does not matter...expensive epoxy is involved so it must have to do with a project that matters is my thinking...not trying to bust your chops..well..okay maybe a little...:) anyways..I'm waiting for warmer weather before I do anything...pics will follow when i do...okay Fanie?..I know your out there some where...

[apex1]

...but when does quality not matter Apex...am I missing something..? I am trying to ensure quality control in my project and then you who I respect as someone who knows something (at least more than I who am a novice with these materials) says that at times quality does not matter...expensive epoxy is involved so it must have to do with a project that matters is my thinking...not trying to bust your chops..well..okay maybe a little...:) .

Who said quality does´nt matter?:?:

I did not.


Although that statement would be about right. There is in fact not such thing as different "qualities". We know different formulations, read: properties of the different resins and (more important) hardeners. But in terms of quality they are all equal.
For a homebuilt project it is easier to use formulations specially made for the given application, thats true, but one pays a high price, buying the West, SP, Mas or System Three stuff.
We are fine with less sophisticated formulations in professional boatbuilding.
But that has nothing to do with quality.
You could use the cheapest resin on the market and have as good a result as with any of the main suppliers stuff (given you use the right hardener)

I referred clearly to the curing time.

Regards
Richard

[souljour2000]

Okay..I thought that was what you meant...the resin quality..or brand-name used...okay..that is useful to know...and what I suspected...the hardener is where it's at...

[apex1]

Okay..I thought that was what you meant...the resin quality..or brand-name used...okay..that is useful to know...and what I suspected...the hardener is where it's at...

Let me say I´m not sure you´ve got it...........

[souljour2000]

Wouldn't be the first or last time..but I think I did get what you meant actually...or at I learned something at least...that hardener/activator is where the differences that matter are...that the resin worldwide is pretty much the same...but the catalysts and the speeds of them are quite different..is that right?

[Herman]

Basicly, yes.

In epoxy resins, there are basicly 2 different types:

Bisphenol-A based (gives the best mechanical properties, like Tg and stiffness)
Bisphenol-F based (gives more flexibility)

Both tend to crystallise. However, when you mix the 2 together, in a 70-30 to 30-70 blend, the mix will not crystallise. (so crystallisation-free epoxy is always a mix of A and F based materials).
This comes with a slight downside of somewhat reduced properties. (Tg and stiffness suffering somewhat).
There are also blends that are less prone to crystallisation, usually a 90/10 blend.

This is one side of the story.

Second is the thinning down of epoxy. Unmodified epoxy is a thick syrup at best. I have the stuff here, and below 10 degrees C I am not able to get it out of its jerrycan. Below 0 and bring in a knife and fork, please...

So to be nice to the customer, it needs thinning. This can be done in several ways:

-add a solvent. Cheap and quick. However does not improve properties, and makes the epoxy porous. Most popular solvent is benzyl alcohol.

-refraction the epoxy. Expensive process, where the chains of epoxy molecules are broken in smaller pieces, then the not usable stuff filtered out. Not many epoxy producers can do this process, and when the destilation installation of my supplier broke down, it took them 4 months to rebuild, bringing some clients in problems, because these products were hard to come by at other suppliers.

-add a reactive diluent. This is not a solvent, although the small molecule chain gives the same thinning. It differs from a solvent, though, because it does not evaporate, and co-cures with the epoxy. It has one or more epoxy groups (mono-functional of bi-functional) and this does make a difference as well. The mono-functional reactive diluents are cheaper, but as you can guess, will give less mechanical values.

For the fun of it, all above options can be mixed, to tailor the epoxy for a specific situation.
Also foreign additives can be added, to influence impregnation of fibers, toughness, surface quality, etc.

And I am only talking resins here...

For hardeners, there are even more options...

[apex1]

Talking hardeners would be harder.

Ähh, why did I say that?

Ahh, yes talking reactive diluents would complicate it.

And talking curing processes would drive a novice crazy.

But for the application given, one must say, there are worst choices than epoxy.

Regards
Richard

[Jimbo1490]

The bisphenol-F (BPF) resins are actually superior in all respects to the Bisphenol-A (BPA) resins, as certainly as epoxy is superior to polyester. They give outstanding UTS while also maintaining higher flexibility, fracture toughness and elongation. They always yield a higher Tg with a given curing agent. They start with a lower viscosity and are extremely resistant to crystallization, often being blended with the less costly BPA resin for the purpose of lowering viscosity and reducing the tendency toward crystalization.

All this is due to the BPF molecule having more reactive sites, thus allowing a more dense cross-link upon cure. This is reflected in the lower Epoxide Equivalent Weight (EEW) number, usually ~175 vs ~190 for standard BPA resin. As the number of reactive sites per molecule goes up, so does the resin's viscosity. The 'best' (strongest, toughest) epoxy resins of either type are unfortunately very viscous, many even solid at room temperature. So the fact that the BPF resins are substantially thinner while having more reactive sites per molecule is very significant. Another way of looking at it is that for a given reactivity and a given benchmark of cured state properties (UTS, Tg, Elongation, etc.), the formulation that starts with a BPF resin will have a lower viscosity than one that starts with a BPA resin.

The only disadvantage of the BPF resins is, of course, higher cost.

Jimbo

[souljour2000]

Okay...I wouldn't expect you to blind me with all the science..and I'm glad you didn't...but you guys did give me some good info that I can build on...thanks...

[tunnels]

I am still just getting my sea-legs when it comes to epoxies and resins. Am I correct in my understanding that epoxy is much more brittle in general than your basic "boatyard" polyester resin? This seems correct from my experience with both. If so then,for you guys with experience...

What are some situations where the brittleness of epoxy makes it a bad choice?
Is this really only a worry under high shear loads where the two bonded areas could bend in different directions like corners? Will applying the epoxy in thin layers help this problem? I don't have a specific question regarding a project but am just wondering. Thanks!

All resins are brittle !if you want them to be flexable then you buy just thaflexable resins . theres a million resins on the market no two are the same BE IT POLYESTER / VINYLESTER /or EPOXY . with out a fabric or material of some sort it isnt going to be flexable :D

[apex1]

All resins are brittle !if you want them to be flexable then you buy just thaflexable resins . theres a million resins on the market no two are the same BE IT POLYESTER / VINYLESTER /or EPOXY . with out a fabric or material of some sort it isnt going to be flexable :D

The embedded fibre does not change the flexibility of any resin!

[tunnels]

excuse me !! so if i have a sheet of just resin 12mm thick and a glassed sheet using the same resin at the same thickness which is going to hold together and which is going to break ??

[apex1]

Depends on the resin and on the fibre, of course.

But I was not talking layups. The statement was clear and valid.

[tunnels]

Epoxy is less brittle than poly.

SORRY !! i have been mucking about with resins for way to long ! that is not a good answer to that question ! you need to explain it a little further . !!!:confused: So your saying just one epoxy fits all !! there should not be any yes and no answers to this subject !!

[PAR]

A lot of this really depends on what you do. If you're building a boat for yourself in the garage, a single resin system is perfectly fine, with hardeners to suit conditions. Most small repair shops can live with this same arrangement as well. A small custom builder that produces only a few boats a year will also be quite content with a single resin system.

On the other hand if you're involved with more then one build a month, then you're probably looking into different resins to suit tasks, faster procedures and speeding up production times, so multiple resin systems would be employed.

Blanket statements, such as all resins being brittle are just ill informed nonsense. First we'd really be best served with a well defined idea of "brittle". Then comparisons of elongation and other physical properties of each resin system could be explored, which would take literally an book or two, the differences are this diverse.

[tunnels]

Gentle men we have to be very careful how we answer questions and the choice of words we use , we have people from differant countries and words that have little meaning to some of us are taken literal by others .It must be understood that for each resin system be it poly , vinyl , or epoxy there are a great long list of resins formulated for a million differant uses ranging from brittle and clear as glass to being as flexable as rubber and everything in between . Like another site i belong to resins and cores materials are very touchy subjects and can and do get heated most times . To the person asking the question be a little more spacific about what you want to know .Theres a lot of veryknowledgable people on these sites even if they have stiff collars everyone will give honest advise if you ask the right questions !!

[souljour2000]

Thanks for all the comments by everyone..it's been about 5 months since I asked the original question and I have learned a thing or two about epoxy and resin since...there is simply no end to what can be learned about all these products...from chemical/bonding properties/aspects to the myriad of ways they can be applied/should be applied/should not be applied...etc.
I am now prepped to the point where I am almost ready to lay down cloth/epoxy for my new cabin roof. I am currently planning on ordering a 600 cps thin resin with a medium fast hardener. This is a good laminating resin and is USC's normal big seller. Will I likely be okay with this as far as flexibility as long as I follow the instructions and don't use too much hardener which might make the roof set up more "brittle"...which is "Bad"...in my opinion ..I want a bit of flex under high loads..(like my own 230 lbs. of movable ballast)for exampe.

[souljour2000]

BTW. ...what weight cloth would you guys recommend?. I am thinking something that will wet out with little excess...something that I can keep weight down and avoid excess resin ...but give required strength...a medium weight biaxial? Would a Lightweight carbon or kevlar be worth it? I have alot more weight here than the original pop-top...so I may go that route...

[apex1]

Will I likely be okay with this as far as flexibility as long as I follow the instructions and don't use too much hardener which might make the roof set up more "brittle"...which is "Bad"...in my opinion ..I want a bit of flex under high loads..(like my own 230 lbs. of movable ballast)for exampe.

You do not use too much hardener! You STRICTLY have to follow the advice given by the manufacturer! It will not completely cure otherwise. And do´nt bother, it will flex under loads.

Do´nt get irritated by the dispute here, the standard Epoxy formulations are not brittle.

Regards
Richard

[souljour2000]

Okay..Apex..that is what I was planning to do...follow instructions to the letter..I will wait for 70 degree fahrenheit days also...75 is common here in winter..humidity usually fairly low...PAR...your advice is always very welcome ...you know the conditions here in FLA too...thanks everyone..

[tunnels]

BTW. ...what weight cloth would you guys recommend?. I am thinking something that will wet out with little excess...something that I can keep weight down and avoid excess resin ...but give required strength...a medium weight biaxial? Would a Lightweight carbon or kevlar be worth it? I have alot more weight here than the original pop-top...so I may go that route...

Just one little point i notice ! when you mix epoxy there is a very small amount of tolerance in the mixing ratio if they say 5 to 1 ratio then thats what you got a use! you need to understand you can not play with the ratio or you will end up with a disaster of resin not going hard or not curing or what ever . You need to be very accurate with your measureing
Also use shallow big diameter containers . In volumn the resin will heat up and shorten your working time and even start to smoke because it gets so hot . I would be inclined to start with a slow reaction hardener untill you get the feel of what you are doing . Glass weight for skinning 8 oz woven or could go to 12 oz woven but the weave takes a lot of filling . The over lap on corners and double up of glass will give you a good strength factor with the 8 oz glass . Theres a art in doing that type of glassing so watch what is happening and learn from it !!
:confused: :P

[souljour2000]

Good advice Tunnels...I'll have to think over the 8 oz -12 oz range and take a look at what they have here at Marine surplus store here...that seems like a good range for bi-axial for a coachroof...the first layer big layer of cloth over everything is key it seems...then smaller pieces/lighter laminations...maybe 6oz stuff at the joints...?

[tunnels]

just use all the same weight glass but plan out where you are going to put your overlaps on corners etc , thats where you can double the layers . one up and over and one down and over and the sand and fair the layers . trouble is with 6 os its very easy to sand right through even on flat areas if you dont take great care . DO NOT TRY TO FILL THE GLASS WEAVE ON THE FIRST WET OUT !!!!the glass will float if you have to much resin any where . if you do a second coat mix some q cells with the resin and it will help fill the glass weave and its easy to sand off the roughness after its hardened.

[souljour2000]

Okay...good stuff to know...thanks very much!

[apex1]

Okay...good stuff to know...thanks very much!

That unfortunately was NOT good advice. (apart from repeating my post)

You have to wet out every layer completely, otherwise you have entrapped air in the end. Sometimes the cloth "swims up" when you use much resin, that is true, but you soon get a handle on that and can avoid it.
Do NOT use too heavy fabric, better one more layer of lighter cloth. Otherwise the risk of voids raises, and you use substantially more resin to fill the voids in the cloth.
You do´nt easily sand through a fully cured 6oz glass epoxy layer, thats plain nonsense!

Do´nt make overlaps! For what? You make a roof top as far as I understand. So you will sand these overlaps plane anyway. That would be just added cost and labour, nonsense.

Do not use filler when you make your layup! Just work with the plain stuff and do your layup wet in wet (not fully cured between layers).

Regards
Richard


Tunnels
Gentle men we have to be very careful how we answer questions and the choice of words we use , !!
Thats so true.................
.....you should study and practice a bit on this, before contributing.:(

[PAR]

USC makes a good product. I don't personally use their stuff, but I know folks that do.

Their resins can tolerate slight ratio deviations, but you're goal is to not have any. Unlike polyester, you need to be fairly precise.

I'm not familiar with USC's formulations so cure times in our weather would be just a guess, so I will not bother, except that I almost always use slow or extra slow. This permits a relaxed layup process and chemical bonds on subsequent layers are easier to achieve.

Work small batches, until you get a feel for how long the goo takes to kick off. Avoid using brushes to spread goo and it's very wasteful. Use a squeegee or plastic applicator instead.

Log onto the System Three and West System sites, download their user's guides to get a handle on procedures. Practice on small stuff before committing to a sheathing application.

There are hundreds of tips and tricks. Flip through the previous threads and see how many you can pick up.

[souljour2000]

Okay..thanks everyone...much good info here...PAR ...very good info...slow hardener it is...makes lots of sense.Okay Thanks again everyone...

[Jimbo1490]

Just one little point i notice ! when you mix epoxy there is a very small amount of tolerance in the mixing ratio if they say 5 to 1 ratio then thats what you got a use! you need to understand you can not play with the ratio or you will end up with a disaster of resin not going hard or not curing or what ever . You need to be very accurate with your measureing


Even these statements are only true sometimes. The polyamide family of curing agents, notable for their very high and broad mix ratio, are a very common example of an epoxy resin system which is very forgiving of mixing ratio errors. The '5 minute' epoxies use such a curing agent. Gougeon selected such an agent for their new West adhesive line, and the mix ratio tolerance is very broad. The common one from Shell resins (I forget the part number :rolleyes: ) could be mixed in any ratio from 1:1 to 2:1 while still causing a full cure of the resin system.

Then there are the catalysts for epoxy like the Lewis acids and the imidazoles. These don't really have a set ratio at all and can be used in fractions from 1 to 5 %, all producing a full cure.

Jimbo

[souljour2000]

Interesting...I wonder which they are making the new B-787 with?...I digress...What is the difference between a catalyst and a curing agent Jimbo...I mean arent they the same thing? Or is the type of bond..e.g.- polyamide...the curing agent..and the chemicals are the catalyst..okay..I get it ...

[goodwilltoall]

Jimbo1490, you've used Epon 828 from 500lb. drums.

What type of formula with the harderer would you use to get below 1000cp. without using DETA or TETA hardeners? If needed lime or portland cement would be used as an inexpensive thickner.

I would like to use this as an adhesive for laminating wood free hand.
Barrier coat would be three coats wet on wet with final finish coat of premium exterior latex paint also applied wet on wet.