Matt or cloth

[great white]

A book... "Covering Wooden Boats With Fiberglass", by Allan H. Vaitses, makes what I think is an interesting point regarding using fiberglass cloth or fiberglass matt to reinforce and waterproofsa wooden hull.
He says... "Examine a piece of glass cloth closely, and you will see that it is constructed just like a strainer. It is a mass of holes neatly arranged by woven threads. Lay it up on your deck and you have a deck covered with a strainer that happend to be clogged with resin. Crack the resin and any of those holes or rows of holes will crack right through, top to bottom. As far as water is concerned, a crack from top to bottom in any material is a place to seep through."
Most of the information I have see here, and around the 'Net, talks about FG cloth, biax or triax. Vaitses, in his book, tells of finishing more than fifty boats, at all stages of repair, with matt, and he follows many of them through their lives, some, twenty five years after he covered them.
My question is this.
Is Viatses right? Should we be using matt rather than cloth to strengthen and waterproof our wooden hulls?

[Tom Lathrop]

Originally posted by great white:

My question is this.
Is Viatses right? Should we be using matt rather than cloth to strengthen and waterproof our wooden hulls?I think not. First, it's the resin and not the glass that provides the waterproofness. Second, mat makes a far weaker layup than cloth. That is, unless vacuum or pressure layup is used.

If what is wanted is a tough, abrasion resistant, waterproof sheath, the synthetics like xynole or propylene are superior to glass of any type.

If what is wanted is additional strength, the case gets complicated with literally hundreds of layup schedule choices to make but mat is near the bottom of my list for hand layups. It is used mostly as a binder layer between layers of other materials to aid adhesion.

[Corso]

Matt its just a bunch of pieces of glass fiber pressed together, if you put it beside a comparable sized cloth all those little fibers catch (and require) more resin than a cloth would, offering little strenght since the fibers arent continuos but rather "glued" together.
To see the difference of strenght just pull apart a piece of matt and then a piece of cloth, the first just rips, that is what you can think about as the "basic" strenght of the material you are working with.
As someone else in the forum can explain better than me eventually with numbers at hand, 'strenght' doesnt mean everything: if, for example, you work with an unidirectional cloth and you lay it down in the wrong way (direction) the stress it can stand to is greatly reduced, the matt virtually covers any direction, so a good matt would be better than a cloth badly applied. The fact is that rarely you would work with just unidirectional cloth, youd go at least with the biaxial (strenght in "two directions") and that reduces the chances of a bad sheating.
Now think about the undulated fiberglass used to cover some porches or sheds roofs, if you bend it it just cracks and breaks, thats matt, if you used cloth for that you would see a crack but the runs of glass wouldnt let it break as easily.
Another point is in the quantity of resin the matt absorbs: if you let the resin cure with no fiberglass in it you have basically a delicate piece of plastic prone to develop cracks and openings even just by the curing process, the thicker the easier it will happen. The resin itself, without a substrate to apply it to, its not worth much, its just bonding material. A cloth maximize the quantity of fiberglass and minimize the resin, while the matt is the opposite. But being the matt thicker and having more resin its more resistant to puncture than the cloth, but thats it, use other materials other than glass cloth (kevlar & c.) and you can get rid of the puncture problem.
A well studied and executed application of fiberglass cloth simply shouldnt happen to crack right throught, if it does then you must be in a situation where your major concerns are others.
Belt and suspenders would be one or more layers of matt followed by one or more layers of cloth, that would give you the advantages of both, a lot of weight and...a fiberglass boat.

[ 07-26-2004, 11:57 PM: Message edited by: Corso ]

[Todd Bradshaw]

The binder in fiberglass mat is designed for polyester resin, not epoxy. For the mat to conform to shapes properly, the binder needs to soften substantially, which it won't do when saturated with epoxy. This leaves you a choice between polyester or vinylester resins, neither of which are formulated to stick well to or properly seal wood. A good example of this would be the thousands and thousands of old fiberglass boats with a currently rotting sheet of plywood glassed into their transoms and theoretically "protected" by being covered with a layer of polyester resin-soaked fiberglass mat.

I have no problem with using fiberglass sheathing as part of the hull if it's designed that way and the glass offers something to the mix, but if slathering a layer of glass mat on an old hull is this guy's idea of a proper repair for a leaking wooden boat which originally had no fiberglass on it, he certainly wouldn't get any of my business. The people who are successfully using that technique on old workboats end up putting on almost enough glass to be a stand-alone hull.

[George Roberts]

great white ---

Vaitses is completely right and completely wrong.

Ignoring the fact that epoxy is not suitable for use with mat ...

On the plus side: Mat is cheap and has a random pattern of fibers. The random pattern tends to stop cracks.

On the minus side: Mat requires more of the expensive plastic. When measuring strength per pound, it ranks at the bottom.

Many people use 1 layer of glass on small boats. That is rather foolish as Vaitses claims.

I use 4-5 layers of much lighter woven cloth (as equally spaced radially as possible). This performs better than mat or a single layer of cloth.

[ 08-11-2004, 01:51 PM: Message edited by: George Roberts ]

[ion barnes]

Vaitses' thinking is dated. He started,I think,in the sixties with glass and those were the ideas of the day. Unfortunately, those ideas die hard and still send people in the wrong direction. If you read enough, you begin to separate the misconceptions and the truths. Ken Hankson is a good author to follow.

[great white]

Did some more research. Is the concensus that stitched mat has the same drawbacks as CSM? I am still concerned about his point that cloth is a collection of holes filled with brittle resin. It makes sense to me that fracturing the resin would leave an open channel to the wood.

[NormMessinger]

Ease your mind. The wings on my Long EZ airplane have been flexing for about a thousand hours over a period of 20 years. No hairline fractures. Other such aircraft have a lot more hours than mine.

[Cuyahoga Chuck]

Fiberglass cloth is used because it has high tensile strength and very low weight. It's strength is the greatest in the direction of the yarns. When it is bonded to wood it imparts it's strength to the laminate. It can give max benefit when the resin 'glass ratio is 50/50. 6 oz./yd. cloth only needs 6 oz. of resin/yd.
Today they have denser weaves of 'glass that have less voids but soak up more resin. The coarser weaves still predominate. It's your choice.
Mat has no yarns so it's tensile strength is meager and it soaks up resin like a sponge. In fact, it's primerily a matrix for whatever resin is applied. Since most commercial resin based hulls are made with the cheapest resin available mat fits right in.
Whether it's for high performance boats or high performance cars, if strength is important, the 'glass, Kevlar or carbon fiber that's used is all cloth.
Charlie