# .053 thick glass. How much oz??

Discussion in 'Fiberglass and Composite Boat Building' started by jrork, Nov 26, 2011.

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### OFFSHORE GINGERJunior Member

John , not much fabric there at all , and are you sure you want to go with that same layup again ?

2. ### CatBuilderPrevious Member

I'm sorry if I'm a little dense here, but I can't understand. There are examples for chopped glass, mat, etc... I have none of this.

I have only biaxial (no mat) and triaxial (no mat) on my boat.

How do I figure the *thickness* of the layup from the weight of the cloth?

My designer dictates thickness, made from a certain type of glass, but not weight sometimes.

I have Fiberglass Boat Building for Amateurs, but it's too out dated. It doesn't have the modern materials.

As an example, how thick would 3 layers of 23oz (700g) biaxial be?

How about 3 layers of 34oz (1150g) triaxial?

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### waikikinSenior Member

Use your target resin to glass ratio by weight say 1:1 & the weight to volume for epoxy say 1.15 & glass say 2.54 & metric units, From a quick calc comes out about 0.7mm per 1000 grams per meter squared resin & glass combined- do your own maths, I'm hav'n breaky so not too sharp right now, with metric 1liter water = 1kg, 1000 liters = 1 Cubic meter, also for resin various substrates take extra to "prime" .

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### AndrewKSenior Member

CatBuilder, you can only generalize when calculating thickness from aerial weight as it is cloth specific.
For most brands of stitched glass fabric multiply the gsm x 1.2 to get laminate thickness in mm for hand laminating.
Multiply by 0.8 for infusion at full vacuum.

5. ### CatBuilderPrevious Member

Ah, so the original post I made was correct, for stitched fabrics. I used 1 instead of .8 or 1.2.

Thanks for confirming this. I had worried seeing so many different answers here.

Thanks!

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### YellowjacketSenior Member

I agree. Depends on what you are attaching to the stringers and where. Up near the front and where the seats are you can try to match the old layup. But of you are sitting an engine on these things you are going to need more beef than this little bit of glass. Also depends on how you are attaching things like the seats and engine, but the original stringers didn't do much other than provide a place to bolt things. If you are putting something heavy on them you need some more cloth on them, and/or, I'd be thinking about more material (like a bulkhead) to spread the loads to the tunnels.

7. ### tunnelsPrevious Member

Take a piece of the original glass and burn the resin out of it then very carefully you can check the layers of glass .
I usually burn with metholated spirits and use a pair of tweezers to gently lift off the glass layers
Its what is done in the laboritory

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### rxcompositeSenior Member

“Modern fabrics” such as biax or triax or “stitched” fabrics are made by bunching together the rovings (a group of fibers) and stitched to form a flat sheet and laid up on top of another at an angle to get 2 two or three layers. It is basically a uni, held together by stitching so it does not separate during handling. You can basically work with uni and lay the subsequent layer(s) at an angle to form a biax or a triax except that the factory has done it for you. Being fairly flat, the fabric nest together well and less resin is needed to saturate it. For all practical purposes, the glass content achievable in hand layup is between 0.5 to 0.53. Biax or triax have more “packing efficiency” compared to wovens. Something like more beer cans in a carton if packed right.

In Woven Rovings, the fibers are twisted together to form yarns so that it can be woven into a fabric. Because it is woven, the yarns have undulations or “peaks and valleys” if viewed from the edge. The hollows tend to be filled by resin even when the cloth is saturated so it tends to have more resin content than biax or triax no matter how hard you try to squeegee out the resin. So 0.5 Gc or 1:1 ratio is probably the best you can do in hand layup.

Special fabrics such as biax with mat also have good packing density. The cross ply naturally nest together well and nest to the CSM well because it is laminated at the same time. The cross ply tends to sink into the CSM. Try laminating a WR over a CSM “wet on wet” and you will find that you need less resin than you would normally do when laminating separately each layer. Because there are two variables, and the density of mat varies, it is hard to estimate. Better do a small test piece. Measure and weigh the fabric, apply enough resin to saturate it, then weigh it while still wet. Total weight minus fabric weight is the resin content per area. It is important to weigh while still wet because when it cures, the volatiles has evaporated and your measurement will be off.

To estimate the volume of resin you need for a project, find the surface area (in English or Metric) multiply it by a factor posted, to get the resin weight (mass) and simply divide the result by the density of the resin. The formula is V=m/p, where V is volume, m is mass, p (rho) is density. Just keep the units constant. That is; yd2 for area, ounces for weight, oz/yd2 for density in the US system and m2 for area, grams for weight, and grams/m2 for density in the Metric system then convert the resulting volume units to liters or (fluid ounce to) gallons. Just substitute the specific gravity for the density of resin. The result is the same, just a different way of expressing things.

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### michael pierzgaSenior Member

Actually the original question is easy to answer. You will tab your longitudinal stringers in with 12 or 17 ox bi axial fabric. 12oz is much easier to use...perhaps 2 offset tapes of 12oz set in epoxy.

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### OFFSHORE GINGERJunior Member

personally in my opinion 2 layers of 17 oz S or E glass with a staggered layup bagged , should be more then enough to do the job using epoxy considering he wants to do is lay up using epoxy .

11. ### tunnelsPrevious Member

Have known this since stitched fabrics first came on the market but trying to convince people of these principles its almost impossible so going to copy and print it in big letters and hang it on the wall .
To add to this its important to remember its the quality of the resin that is holding all this together that is important so a switch to Vinylester resin is an addtion to the strength and to getting lighter stronger laminates .
.

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### rxcompositeSenior Member

Tunnels, I take that as a compliment. Thank you.

Now we have something to agree on.

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