When is epoxy a bad choice?

Originally Posted by souljour2000

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

Originally Posted by 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]

Originally Posted by tunnels

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 ) 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.