Why is glass not wetting out? Pic.

Having some problems getting epoxy to saturate my 1708, so I did a test by completely submerging the glass in a container of epoxy for 20 minutes then pulling it out and letting it dry (this epoxy starts kicking around 40 minutes). Below is a picture of the glass after I shred it apart. It's relatively dry, flexible like a stiff bristled paintbrush, and can be bent in half without breaking.

I'm using US Composites epoxy, both their medium and slow setting epoxy yield similar results, although the slow set is a bit more watery and wets out a bit better. The 1708 was bought 6 months ago from FGCI and has been stored in my FL garage.

 

1708 has mat, which indicates it was most likely designed for use with polyester or vinylester. Because those resins have styrene (a solvent) the fabric should have a binder that gets dissolved by it. Epoxy does not have styrene and will not dissolve the binder, which may be preventing wetting. Check with the fiberglass supplier or manufacturer.

 

Will do, good call. I thought mat incorporated into 1708 was stitched in and therefore did not need a binder to hold it together. Versus straight CSM which virtually always has a binder and requires styrene to dissolve.

 

There typically isn’t any binder on 1708, but even if there is it doesn’t complicate things to a high degree. Even normal CSM will work with epoxy better than that.

Not sure what you have going on there.

 

If it is stitched, may not have a binder. I have never heard of a fabric so hard to wet, but am not familiar with the brand. The material could be contaminated. Maybe try to wash a small piece with acetone. Completely submerge it and try wetting it after it dries. I'm taking shots in the dark.

 

I have had water contamination prevent resin saturation. Had th use a chop saw to remove a foot off of an effected roll.

 

I'd go with some kind of contamination making it "resin-phobic". Even water shouldn't do that once its dried off. Maybe some kind of contaminate oil or chemical carried in the water?

 

These fibers have coating/binders or "sizing" for the fiber to wet out thoroughly. The sizing can be mechanical (pitted) or chemical suited for epoxy or polyester.

Most likely you have a chemical sizing that is not compatible with epoxy or has worn out. I have half a roll of 7781 that got wet and tried to save it by drying. It won't saturate anymore. Our purchaser also bought tons of fiberglass mat/cloth from China because the price was good. It would not wet out thoroughly with resin. We get only 90-95 wet out with poly resin even with a lot of rolling. Have to throw it away.

 

Update: I confirmed with the mfgr that this 1708 has no binders. I took my test piece into FGCI and they said everything looks okay and it’s a proper wet out. They said the epoxy “encapsulates” the fibers rather than fully “saturating” the fibers, so that if you pull away fibers from a propert layout those fibers will appear rather dry. They had some of their own sample pieces on hand and cut them up a bit and the results were similar to my test piece...seemingly dry fibers. I guess I was expecting all the fibers to be hard and brittle, but FGCI said that’s not what happens. Still not totally convinced though...

 

How hard are you pulling to get the fibers to separate? Any laminate can be broken, but shouldn't be easy. Even though it is not a calibrated test, try to find some old piece of laminate from a boat or bathtub. It is polyester and should delaminate much easier than the epoxy laminate. At least you can get a rough idea.

 

When I hear delaminate I think of the glass separating from the substrate. That isn't the issue for me, as the epoxy wetted glass is bonding very well with the honeycomb deck. It also visually appears to be an excellent layup as the glass turns virtually completely translucent.

The 'issue' I'm having is if I cut into the cured glass, such as with an oscillating tool, the glass fibers appear dry and are rather flexible similar to a stiff bristled paint brush. The fibers can then be separated from each other about as easily as detangling hair.

FGCI performed a test similar to my oscillating tool experiment and the results were similar to mine although not quite as exaggerated...dryish fibers inside of the layup. I was advised this was normal but would love other opinions as I'm going to perform more tests prior to moving forward with add'l glassing.

 

That depends on what you want to achieve. The coupler/binder/sizing is there to enhance the bond between the resin and fiber. It acts as an interphase. Sort of a primer in paint. Good adhesion between the matrix and fibers results in improved mechanical properties.

Test samples in small sheets would always show good encapsulation but requires a lot of rolling and pricking to get the bubbles out. That would equate to longer times during manufacture and quality issues with increases in voids (sometimes microscopic). This degrades the expected laminate strength.

There is a scientific test and formula done in the manufacturer's facility. It is called the fiber pull out test to determine the fiber adhesion to the matrix. This is best left to the manufacturers.

The only clue you will get is the suffix at the manufacturers product code which ranges from B to T with B having the smallest diameter fiber. "Fibers are as strong as their weakest point. Any defects such as nicks, cracks, or other discontinuities will be influenced by the fiber diameter. The finer the fiber is, the smaller the defect." Given a product code, it is best to consult the published data of the strength of the finished product. It is also good to note if the product comes with a finish. Silane and Volan are popular sizing finish.

 

You are expecting more than the resin can give.

What is your wetout rate?

You must wetout 1708 at 100%.

This means a yard of 1708 weighs 25 ounces and epoxy is typically 9.0 pounds per gallon. So a yard of 1708 weighs 25 ounces and 25 ounces of epoxy by weight is 128 oz per 9# or 22 ounces by volume if my math is right.

And that is all you can do is make sure enough resin gets into the fabric.

If the color does not change; try using a spiked roller or bubbles buster or squeegee and some pressure.

1708 is a bit hard to wetout. It just is...