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Working with 1208 Biaxial Glass


Howard
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Rather than hijack the Princess 26 thread on the B&B, I figured I'd start a new thread thread here on the topic of working with 1208 biaxial glass. Intent here is to have a self contained reference thread for builders to turn to for answers.

The reason for the question is it is being specified, but most of us don't have much experience using it. Builders are experiencing difficulty getting it to lay down, getting it fully wetted out and adhered to the hull as intended and later on, faired to a smooth hull.

Further, why that type of cloth on the outside, and why glass vs. alternatives like 4 oz xynole polyester, which despite it's harmless appearance, is also difficult to work with and soaks up epoxy like crazy. Both leave a thick, durable coating that has to be faired.

With that as an introduction, what do those of you with experience have to recommend?

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What project is this for? I assume it's not one of ours, as we've never called for bi-ax in our plans.

As to why I'd use it one something, because it adds far more stiffness than cloth. I'm assuming whatever project this is for, that they called for bi-ax for the structural properties it supplies. On our plans projects, we're only calling for glass as a weather-resistant element (as opposed to personal projects, which have certainly used bi and tri-ax for their strength.)

The knitted fabrics (bi and tri-ax) are a bit harder to get into tight shapes, as compared with woven cloths, so we usually try to dry-fit things as closely as possible before beginning to mix resin. Don't try to dry-fit after you've started the reaction! Time seems to speed way up then...

As I recall, xynole-type fabrics are a good alternative to thin glass cloth as a weather-beating layer. Not much for structure, though, if I remember right.

Mike

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Mike:

Graham on the B&B forum often specifies 1208 biaxial on many if not most of his larger designs. Inside and out. Inside, I can understand. A glass lined boat, with all the tabbed partitions and bulkheads along with a glass lining of this stuff is going to be very strong.

Outside, it may be a way to quickly build a reinforced epoxy skin, adding both strength and abrasion resistance. However, for plywood boats, I don't know at what point you go from protection to structural on the thickness of the glass. I was of the opinion that for most epoxy covered plywood boats, the epoxy was for protection, not structural strength. Any amount of glass basically give more structure to the epoxy that several thin coats of epoxy alone would do.

This is a test panel I put together to measure some of the thicknesses:

IMG_2945.jpg

These were stuck to 3/16" luan subfloor plywood (20 year old version......current stuff is pure crapola). Strip on top is 1208 biaxial. Middle is simple 6 oz glass. Below that is plain luan. Bottom is 4 oz Xynole polyester. Benefits of the latter are supposed to be a bit more flexible, good abrasion resistance, soft and supply to lay in complex curves, and isn't glass, so doesn't itch. It sucks up incredible amounts of epoxy and leaves a rough, pebbly texture that is tough to fair. As near as I can tell, after the first wet out coat is tacky, you start rolling on slightly thickened coats....2 or 3 more of them to even the texture. I agree, I don't think it offers much structural strength the the plywood.

1208 Glass is definitely more rigid and structural and also sucks up the epoxy.....about the same as xynole.

The lighter spots on the samples are where I whacked each with a ball peen hammer. All three deformed and where damaged about the same amount, the lighter glass fractured noticeably more.

As far as working with these, the best advice I've heard is to use "smallish" batches of epoxy, taking care to fully wet them out. It also appears to help if you use the thinner, less viscous epoxies, such as System 3 Silver Tip or MAS (not FLAG), vs. the general all purpose marine epoxies, which tend to be a bit thicker and don't wet out as well. And some also suggest you pre-coat the plywood to get it fully sealed.

Pre-coat opens a new can of worms. If you lay your dry glass cloth on wet epoxy, will it fully lay down and conform to the shape? If you let the epoxy cure, there is the blush issue with some epoxies, and if you let it go too far, you won't get the chemical bond you want vs. a mechanical bond.

There probably is a best method, but I don't know what it is.

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I can find no reason to use any of the combo fabrics in epoxy applications. It's just a waste of resin and tends to make the resin/'glass ratio go way up, which isn't good.

Mat knitted to biax (or what ever) is strictly for polyester and vinylester resin systems, where the need for the additional modulus of elongation, that these high resin content laminates offer. A straight epoxy and biax laminate is stronger in every regard then a combo fabric (such as 1708), plus 3 to 4 times less resin is used with a cost, application and weight savings coming along with it.

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Paul:

Good call on the 1208. I"m sure to you the error stood out like a neon light.

The 12 being reference to the 12 oz weight of the biaxial glass. The 08 being reference to 8 oz mat stitched to the back. The biaxial tape shown above in my photo is NOT 1208. It is either 6 oz or 12 oz biaxial and does not have the mat. It was purchased to do some tests with and that was some time back. I can't remember which it is but my guess is 12 oz. It came from Raka:

http://www.raka.com/fiberglass_tape.html

The reference to the 1208 came on Scott's Princess 26 thread he started a week or so ago. He, Ray and all of us called it 1208. Not sure if that is what Scott actually used. On Peter's Princess 28R, he mentioned using 12 oz biaxial cloth only. If 1208 IS what is being used, it would account for a lot of the problems in working with it. One reason why I decided to start this thread. Education for us amateur builders.

On my test samples, I didn't have much trouble getting the biaxial tape to wet out, but it did still take a lot of epoxy, compared to normal woven tape. But that is to be expected.

On using it as actual tape, I glued up a number of 6 inch planks of 3/4 inch plywood, set at 90 degrees. Each got a 3/4" fillet and the test was for break strength for 2", 3", 4" woven tape and this 6" biaxial. I anchored down the base and used a hydraulic jack to break them apart, and measured the pounds of effort to get them to come apart. Was surprised to find very little difference in them. In most cases, what gave out first was the plywood right at the fillet. The fillet alone provided an incredible amount of strength. A longer piece of tape only meant more plywood was peeled off.

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Graham's PS26 plans called state:

"Because the centerboard is buried inside the trunk, it is a good idea to glass it. Use at least 12 oz - suggested it 1208 biaxial."

He also states that "The chine joints are taped using 1208 biaxial cloth, cut on the 45 degree bias. Use a single layer, each strip being 7.5 inches wide, on the inside and out. Bulkhead tabbing and transom are attached the same way."

He doesn't say anything about covering the hull, deck, inside or out, with 1208. It's strictly for those structural points, and then the centerboard. And I think the centerboard use is a special case.

The 1208 biaxial I used is just what Howard described: 12 oz biaxial fibres over a 8 oz. mat. Wicked itchy, very thirsty. I will handle with care in the future... I imagine that for hull and deck covering, I'll use the standard 8 oz weave.

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Scott:

As I recall from some of the searches I have done, there are two types of 1208 biaxial. Some have a binder in the mat that is broken down by the polyester resins and these are strictly used for fiberglass layups. (For a demonstration of this, try using Boat Yard poly on a block of styrofoam sometime.....if the project matters, you won't make that mistake twice). Others claim their mat is compatible with epoxy. Curious to know which you wound up with. My guess is as Paul suggests, the mat is not needed or desirable for this use. Probably be a good idea to double check on this.

I have a dated version of the Princess 26 materials list and it mentions the quantity of tape (but not which one.....those are on the plans which I don't have) but also goes on to mention using 10 oz fiberglass cloth or comparable poly synthetic (I would assume Xynole or Dynel) for the hull and other exteriors. Peter did his P28 in biaxial cloth..inside and out. It looked bomb proof to me. But again, I'd want clarification and direction on this. One thing on the bottom of the hull below the waterline. Another thing adding that much weight up high on the deck and cabin top. Might be fine, but again, that is something I would check on first.

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Inside a center or daggerboard case, a combo fabric like 1208 (heavier preferred) makes some sense, as the high resin content will benefit the abrasion aspect of the part. It would be better if Xynole was used instead, as it's far superior to 'glass in this regard. This said, Xynole or Dynel have no strength value, so these materials can't be substituted for tabbing, tape or other structural laminates and are only used in addition to the prerequisite laminate schedule.

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Biax cloth is generally chosen for the mass and orie3ntation of the fibers for strength.

A thin 4 oz xynole might soak up a lot of epoxy and build film thickness but likely will not have the strength of 12 0z of fiberglass roving.

The mat is added to biax to provide better adherence between the roving and the next layer of cloth or substrate, or in the case of applying to say gelcoat in a full glass layup works to prevent post cure shrinkage print through..

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I would agree.....when you see something that seems unusual or out of place, ask. I treat it like measuring twice or three times and only cutting once. Better to ask and get it right from the start than fix it later.

Beyond that, this makes for interesting discussion and education. So much of boat building seems contradictory. Truths, half-truths, outright wrong information gets circulated and for the novice builder trying to sort through it all can be frustrating. Glassing for example. I found a series of videos on YouTube in which the obviously experienced builder did a number things that I've been led to believe were totally out of whack. Glassing over a boat and letting the epoxy fill coat totally cure (days) before going back to fill the weave. No sanding between. etc. Seemingly violating everything that is holy.

This circles back to what I had in mind when I started this thread, which is how to work with biaxial or 1208 if you wanted to. Again, the contradictions. Example: To pre-coat or not to pre-coat.....that is the question?

A "how to" article from the MAS website:

http://www.masepoxies.com//How_To/Glassing_with_Knitted_Reinforcing_Materials.html

Talks about working with the fabrics, but no mention of pre-coating. There is a short video on the MAS site that mentions a cotton ball test. One item it mentions is if the cure is beyond the point where a cotton ball sticks, it should be scuff sanded. This on a no-blush premium epoxy coating?

By comparison, the System 3 materials flat out state it's better to pre-coat and epoxy will chemically bond within 72 hours, tacky or not.

And these are for the premium sites with literature that explains what to do with their products. Once a builder swerves into using any of the generic epoxies (must be dozens of those), they are on their own.

My guess is that while there are no absolutes, there are certain "fail safe" procedures to follow. Pre-coating before application of heavy fabrics and knits, for example. A guy could probably be pretty safe to pre-coat, let it cure to a green stage beyond tacky, rinse it with water to remove any chance of blush, give it a quick scuff sand and lay on the fabric. The sooner the better for the glass to get a chemical bond. Essential tools being rollers, squeegee and bubble chasing rollers. All tempered by using the right epoxy and hardener for the job. Certainly an experience based combination of art and science.

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The mat is added to biax to provide better adherence between the roving and the next layer of cloth or substrate, or in the case of applying to say gelcoat in a full glass layup works to prevent post cure shrinkage print through..

This is my understanding of using 1208 biaxial. It is for bulk and to lay the mat side on a mold to eliminate print through of the coarser biaxial fabric. (Implication here is the glass piece will be pulled from a mold and thus the mat side leaves a smooth surface). Again, for those of us using epoxy, it should be compatible with epoxy, meaning none of the binders holding the mat together that are "melted" by polyester resin.

Which brings us back to the intent of using the fabric in the first place. Is it structural to the piece beneath it or is it structural to the substrate to the epoxy?

Again, these comments are not intended to be applicable to any one use (such as Scott's project), only education and information.

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When I apply biax to plywood I put it mat side down to the plywood under the assumption that the mat is providing a better interface between roving and ply in order to get better more intimate adhesion of fibers.

Maybe I am all wet on that, but that is my rational.

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Again, mat, what ever incarnation is a bulking fabric and required on relatively low modulus of elongation resin systems, such as polyester or vinylester. Epoxy doesn't need, nor is it desirable to to use a bulking fabric. The only time mat is useful in an epoxy layup is to prevent print through and in these cases you only need a "veil" product, which uses a minimum amount of resin, so you're not wasting it or using more then a fair compound would need to remove it (the print through). Mat can be useful on rough surfaces in hand laminates, but not necessary with better bonding techniques.

The binder used on some fabrics, that's designed to work with polyester resin systems, is perfectly fine for use with epoxy. The binder chemistry just remains in suspension if you use epoxy, becoming part of the matrix once cured.

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