At first, I was thinking that a stringer job done out of 1700 + epoxy would be cost-prohibitive due to the expense of the resin, but when I realized that 1700 cloth requires much less resin than 1708 cloth that would be used with vinylester resin, I decided to run the numbers and see.

What I came up with is assuming you use the same square footage of cloth, (just to have a figure I used 1125 sqft), and Vectorply's figures for open mold fiber/resin ratios:

vinylester resin + 1708 = $1470
epoxy resin + 1700 = $1325

So, I'm thinking there might not be much of a difference in cost. Maybe someone with more experience can tell me their opinions on this.

A second question would be why does the use of vinylester resin dictate the use of 1708 cloth?

The working time of epoxy pays dividends to your sanity....! I would pick epoxy just for that reason!

I've been using epoxy recently on all the structural work to my Magnum 27 and like Junior (J-bonz) said, for us DIYer's you can work slower and like a gentleman without the fear of it kicking fast like like poly or vinylester resin.........1708 has mat attached to it so it would take more to wet out than say 1700 which is used with epoxy resin.....To your question, I think 1708 has a styrine stitch in the mat that desolves with poly or vinylester to creat a stronger bond between the directional glass.............epoxy is more tanacious with just the 1700 alone.....I think??

..,,.

if your going to use epoxy you better make sure its grease free and bare to the resin or it will come apart..i would go with vinylester..chemical bond is much stronger then mechanical bond..

Can anyone answer my two questions?

1) Despite the difference in price per gallon of resin, does a job with vinyl ester + 1708 or epoxy + 1700 cost about the same to do, like my calculations suggest?

2) Why does the use of polyester or vinyl ester resin dictate the use of 1708 cloth? What is bad about using 1700 cloth with polyester or vinyl ester resin?

The 8 tenths of an ounce of chopped strand mat it the bedding for the stitched material. The surfaces are to flat so this additional mat fills the imperfections allowing for a better secondary bond.

The vinyl and poly do not dictate the use of 1708. You can use those resins with any glass. 1708 is great to work with, it forms very well and creates a strong bond with the mat. You should not use the 1708 or any mat with Epoxy as it does not have the ability to break down the binder in the mat. Epoxy does not have a long shelf life.

Thanks for your response! It's clear that 1700 and 1708 are the same other than the addition of CSM and a styrene binder in 1708. What's not yet clear to me is why 1708 is preferred for vinyl and poly. Or alternatively, would 1708 be preferred with epoxy if it could dissolve the styrene binder? If this is the case, the CSM must serve some mechanical purpose other than being able to absorb more resin.

Please forgive my ignorance, I've worked with neither material.

Actually most of the stitched mat fabrics have an epoxy soluble binder these days. The biggest reason for using a 1700 bi ax is no need for inter laminate bonding when using epoxy. The mat ends up being a resin sponge and a very weak layer in the stack. Epoxy does not like the disoriented strands in mat, it needs linear fibers to direct its properties. Also because it does not break down the binder as well as an ester it also looses some formability. I prefer VE to epoxy most times