Epoxy resin and CSM. Is this OK?

[farmer9009]

While researching supplies for my upcoming project I ran across this statement from a supplier "Chopped strand mat contains a binder which prevents proper bonding with any epoxy resins. Use our polyester or vinyl ester resins with chopped strand mat."
This statement is at the bottom of this link:
http://www.fibreglast.com/product/System_2000_Epoxy_Resin_2000/Epoxy_Resins

I never saw it mentioned anywhere else to not use Epoxy resin with CSM.
If this is the case what should I use in place of CSM when using epoxy resin? For example when installing a new sheet of plywood transom to the existing hull of the boat. I understand epoxy has the best adhesion qualities and from what I have read CMS is preferred for this due to its moisture sealing qualities.
Thanks.

 

[drewpster]

Re: Epoxy resin and CSM. Is this OK?

The random pattern of the CSM works to hold resin suspended throughout the fiber. This makes it more watertight by helping to prevent dry areas and it will help to hold resin on to vertical surfaces. It also helps to localize fracturing in polyester resin or prevent it alltogether. Epoxy has these qualities by nature in the resin alone, therefore CSM is not needed in most instances. When coating with epoxy it is generally accepted that light and medium weight cloth is all that is needed. Epoxy is also stronger and less likely to fracture when mixed correctly and is more watertight. That is why you can build stronger, lighter parts out of epoxy and cloth.
Epoxy has superior qualities than polyester in many ways, however there are trade-offs in using it.
In my opinion epoxy is overkill is doing boat repairs but it does have its uses. For large layups like transoms, stringers and decks, polyester works perfectly well when used correctly and is generally half the price of epoxy. Epoxy cannot be finished using polyester gelcoat. Generally hulls that have repairs using epoxy will have to be painted.

 

[Peteco]

Re: Epoxy resin and CSM. Is this OK?

Generally, no. The binder in CSM is not broken down by epoxy, unless the CSM is specially formulated for use with epoxy. Use cloth, which as drewpster said is usually overkill.

Epoxy structures have the advantages of:

- Providing a stronger finished matrix.
- Generally can be set up for longer working times for large layups
- Able to use them over foam - If you are building structure with foam as a core rather than plywood
- Tend to be useful when laying up complex shaped items, since you can hotwire, mold, and shape foam more easily than a wooden core
- Are concerned about weight (in which case you wouldn't be using CSM)
- Can use peel-ply for secondary bonding rather than sanding
- Stronger secondary bonds over older structures

If cloth were the same price as mat, there are times when you might use mat anyway because it's an easy way to build stiffness in the finished part.

 

[Yacht Dr.]

Re: Epoxy resin and CSM. Is this OK?

While researching supplies for my upcoming project I ran across this statement from a supplier "Chopped strand mat contains a binder which prevents proper bonding with any epoxy resins. Use our polyester or vinyl ester resins with chopped strand mat."

I never saw it mentioned anywhere else to not use Epoxy resin with CSM.

Actually its been mentioned here on Iboats in several posts

Poly and/or vinylester is just fine for basically anything you need for repairs ( I like using VE resin for under the waterline repairs ).

YD.

 

[farmer9009]

Re: Epoxy resin and CSM. Is this OK?

Thanks for the information.