Wetting out fibreglass sheathing

[bloggs68]

Hi all, I am doing some trials with the sheathing material I will be using on a WRC strip planked multi. I am looking at using quite heavy triaxial cloth and am finding that it is a lot more difficult to wet out than say a normal biaxial cloth. Any ideas on wet out that may help?

regards,

Andrew

[kc8pql]

[ 08-15-2005, 04:33 PM: Message edited by: kc8pql ]

[JimD]

Higher tempuratures usually help by making the epoxy less viscose but you probably already knew that. This also means keeping the temp of the wood being sheathed on the warm side, too.

[JimConlin]

Production folk sometimes use machines called impregnators to wet a piece of glass which is then appled to the boat. Lacking an impregnator, i've used a 4x8 table covered with poly film. Pour the resin onto the glass and work it in with squeegees. To move the piece to the boat it could be rolled up on a piece of PVC pipe. By rolling the glass, pieces larger than 4x8 can be handled, but don't dry it out by rolling it tightly and keep an eye on the clock. Another way is to get lots of helpers and wet out on the boat. If each person has only a small area to get right, it'll be OK. On a multihull, especially the outer skin, you might have the opportunity to apply the glass in one piece end-to-end piece with no seams. This'll save a good bit of filling & fairing, so it's worth trying to do it in one piece. Having extra help is always a good idea.

After the glass is applied, apply some peel-ply and squeegee some more to even out the resin mass in the glass.

Of course, temperature helps. See that the shop, victim and materials are warm enough for the resin to be workable. Use slow hardener so you don't have to hurry.

This isn't that hard.

[ssor]

Squeegees work well but the ridged rollers are essential. They help to move the resin around and work out the air. Remember that your gell time shortens as the temperture rises and wraping the cloth around a mandril will serve to confine the heat of curing and set things off faster.

Wetting the hard surface before you lay on the glass gets that side wet at the start.

[ 08-15-2005, 05:26 PM: Message edited by: ssor ]

[George Roberts]

I would use more layers of a lighter cloth.

[JimConlin]

All true. The squeegees are $.30 per and easy to clean and the bubble rollers are $5 up and hard to clean. I have a preference.

[Figment]

The ridged metal rollers are easy to clean. Just fire up the mappgas torch and cook it off!

[ssor]

Originally posted by JimConlin:
All true. The squeegees are $.30 per and easy to clean and the bubble rollers are $5 up and hard to clean. I have a preference.

A little solvent and a bristle brush and a little elbow grease will get the job done; but you must not be lazy. They must be cleaned after every batch of resin.

[ 08-15-2005, 07:59 PM: Message edited by: ssor ]

[mmd]

Sometimes it is not possible to use multiple layers of lighter cloth and one must contend with heavier knit fabrics. Wetting out the surface that the fabric will lay on is a big advantage, as is pre-pregging the fabric on a bench. If doing the pre-preg method, if you wet the fabric out then pick the fabric and the plastic "tablecloth" as a single unit, you will be able to invert the fabric on the hull, thereby placing the wetted side down on the hull. Apply the remaining epoxy to the fabric outer surface, working it into the fabric with squeegees on the broad flat areas and with ridged rollers in the tight spots.

Several helpers make the task much, much easier.

[George Roberts]

mmd ---

It would help if we know what specific fabric he was laying up. bloggs68 says "quite heavy triaxial cloth."

I consider 22oz (0,-45,45) tri-axial lightweight. I would use 3 layers of 7oz uni-axial. I can lay the uni-axial much better than the tri-axial.

[Puka]

consider 22oz (0,-45,45) tri-axial lightweight. I would use 3 layers of 7oz uni-axial. I can lay the uni-axial much better than the tri-axial.
--------------------------------------------------------------------------------

You mean heavy wt right? I am contemplating a 22oz tri project but have never laminated more than 10oz woven! I an kinda nervous about it.
Converting to three layers is considerably more expensive tho.

[mmd]

Would you lay the 7-oz cloths alternatingly on the bias to replicate the triaxial fabric orientation, or lay them in parallel to each other?

[Puka]

For my app. I would alternate to replicate the tri-axial. I guess,there could be the advantage of less fairing with the three layers.
The tri I considered lost its 0 degree 3" from the edge to minimise the overlap build. but I "fear" it may be a b@t#h to "fair".

[Tom Lathrop]

Originally posted by JimConlin:
All true. The squeegees are $.30 per and easy to clean and the bubble rollers are $5 up and hard to clean. I have a preference.

Get a large mouth gallon jar, like a restaurant uses, and pour in a couple inches of acetone. Drop in the roller or brush, replace the cap and just take out and use when needed. The acetone won't last forever but needs to be renewed when sediment builds up in the bottom.

Simple, easy and no contact with mess.

Rubber squeeges from Thalco are expensive but last forever and are far better than the best plastic ones.

[ 08-15-2005, 11:42 PM: Message edited by: Tom Lathrop ]

[Tom Lathrop]

Originally posted by mmd:
Would you lay the 7-oz cloths alternatingly on the bias to replicate the triaxial fabric orientation, or lay them in parallel to each other?

Biaxial and triaxial glass can never be repicated with woven cloth no matter how heavy it is laid up. The non woven straight fibers of axial material makes it far stiffer than woven cloth.

[Puka]

err...I think mmd was referring to uni not a "cloth" so to speak. One at 0, then one at +45, etc.
I guess it gets rid of the need to overlap.
Correct?

I agree that a staight fibre is going to be stiffer than one that bends around another in a woven configuration.

[ 08-16-2005, 12:35 AM: Message edited by: Puka ]

[Stiletto]

themultihull.com has quite a few guys that have done this sort of thing.

[ 08-16-2005, 02:17 AM: Message edited by: Stiletto ]

[Nelson]

The acetone won't last forever but needs to be renewed when sediment builds up in the bottom.

You can also decant the " good" acetone if you have a steady hand. With the current price of acetone I would be saving every drop.

Make sure you are using a thin viscosity "laminating" resin. It will make the job much easier especially if you are working short handed and concerned with gel times.

[mmd]

Puka, Tom; I already know the answer to the "3-layer" question. I was merely trying to gently enquire of George if he had looked into the structural strength differences between stitched triaxial fabric vs. woven cloth, and the importance of fibre orientation in relation to strength.

If the 'glass skin is merely for abrasion resistance and keeping the water out, cloth is fine, but if the sheathing is to provide structural strength as well (and I suspect that this is the case, given the weight specified) it should have some percentage of fibres oriented diagonally ('on the bias') to provide resistance to wracking in the hull.

And yes, though modern knitted fabrics are grand in the strength department, their bulk can be a pain to wet out.

[George Roberts]

mmd ---

The comparision of 3 layers of 7oz uni-axial to 22oz tri-axial was intended to imply that the uni-axial would be laid in the same directions as the tir-axial.

Tom Lathrop ---

Well laid woven cloth is very close (I would like to say better but I will refrain) in stiffness and strength to poorly laid uni-, Bi- or tri-axial cloth.

[ssor]

Originally posted by Nelson:
[QB][.

You can also decant the " good" acetone if you have a steady hand. With the current price of acetone I would be saving every drop.

QUOTE]

I get acetone at less than ten USD per gallon! To Paraphase others "that's a small price compared to the total cost of the boat."

You are right of course but keep in mind that for a final cleaning use fresh solvent and dry off the excess.

[Tom Lathrop]

Originally posted by George Roberts:
---Well laid woven cloth is very close (I would like to say better but I will refrain) in stiffness and strength to poorly laid uni-, Bi- or tri-axial cloth.

Rather than argue the point, I would suggest that individuals lay up both woven cloth and biaxial of equal weight and make their own conclusions. Of course the "poorly laid" statement makes any discussion moot.

[bloggs68]

Thanks for all the responses. For info, the cloth is 1180gsm ( or about 35 oz ) cloth.

regards,

Andrew

[Dan McCosh]

We used a heavy triaxial cloth as a deck surface. There was not much problem wetting it out, as it was horizontal. We poured about a pint of resin at a time on it, spread with a squegee, then a grooved roller. On a vertical surface, it would be much tougher, overhead nearly impossible. A friend who is an engineer in such matters says prepreg is the way to go for several reasons. That's simple a matter of making a kind of shallow tray, wetting it out, the putting it in place. Pretty messy though. The finished surface was remarkably strong. A similar job done 15 years ago on the cabin house top has stood the test of time.

[George Roberts]

mmd ---

I missed your question "if he had looked into the structural strength differences between stitched triaxial fabric vs. woven cloth, and the importance of fibre orientation in relation to strength" the first time.

It is very hard to compare hand lay ups. Some people are skilled enough and have good enough technique to use near the minimum amount of resin. Others do less well.

I think those who ask questions here would do a better job using multiple layers of 3-4z woven cloth than using lightweight (22oz) uni-axial. On a boat hull I would expect those people could lay 27-28oz of woven cloth with the same total weight as 22oz of uni-axial.

I have a graph that shows the effects of orientation for woven cloth over wood strips.

The red line is the stength in bending at various angles for 4 layers of cloth laid with the fibers aligned. The black line is for the same 4 layers with the fibers at equal angles to each other.

You want to look at the minimums of the curves. The 4 layers at equal angles has a minimum strength about 20-25% higher than the 4 layers aligned.

[JimConlin]

34 oz. knitted glass is going to be very hard to wet out on anything but a flat table. I guess you knew this. I'm building a multihull where the basic skin layup (over foam) is one layer each of 12 oz. 0-90 knitted, 12 oz. 45-45 knitted, and 12 oz. cloth. The layers were wet out individually on the boat. Structurally, it accomplishes about the same thing and the finished surface is smoother but the glass cost is somewhat higher. Another plus is that with three separate layers, laps can be staggered, making fairing easier.