When is epoxy a bad choice?

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

 

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

 

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 ??

 

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

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

 

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 . !!! So your saying just one epoxy fits all !! there should not be any yes and no answers to this subject !!

 

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.

 

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 !!

 

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.

 

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...

 

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

 

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..

 

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 !!

 

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...?

 

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.

 

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