[bryson]

Question for you fiberglass gurus out there -- is there any disadvantage to using multiple layers of lighter cloth rather than one layer of thicker cloth?

For example, say the plans call for 3 layers of 10 oz cloth. What about using 2 layers of 12 oz and a final layer of 6 oz? Or just using 5 layers of 6 oz?

The reason I ask is because I have a good bit of cloth of unknown weight that was given to me. I measured the thickness at around 0.0085", so I'm guessing (according to the below chart) that it's 6 oz cloth. It actually is measuring closer to their value for S-glass rather than E-glass, but I would rather assume it's the weaker of the two. It was used for race car bodies where weight is a concern though, so it may actually be S-glass.

http://www.uscomposites.com/cloth.html

Any advice would be great, as this would potentially save me a significant amount of cash, and it would make the guy who gave it to me really happy to see it get used on a cool project. Also, the lighter cloth should lay out a little nicer, and would (in theory) require less compound to fill the weave. It would also be a nice bonus if it were S-glass, but I don't know if I'll ever figure that out.

Thanks guys -- also, I'll be using epoxy resin in case anyone is wondering.

 

[Guest]

Follow what Chris says on your build! You can probably use what you have for hatches, bulkheads, cap, and floor provided you get the thickness needed for the finished parts. I wouldn’t trust the unknown for the hull layup though!

 

[Sethsawyer]

I have used 4oz sglass and 6oz eglass and I like using them a lot more than 10oz. Usually cost and time are the reasons you use heavier cloth. Technically multiple layers of lighter cloth will be just as strong, wet out easier, are easier to get really good resin to glass ratios, and will conform better to chines and the edges of the hull.
Just make sure you don't under or overbuild your hull.

 

[bryson]

@Boatbrains I definitely wouldn't consider the cloth unknown; I'm not worried about identifying it. I'm about 99% sure it's 6oz, and that shouldn't be hard to verify.

@Sethsawyer, I was thinking kind of the same thing. If anything, I'd assume it would be beneficial to use the lighter cloth, although more expensive if you were to plan it out that way from the beginning.

I can't imagine the end result would be very different, especially if I can lay everything up wet on wet. I can see additional layers increasing the risk of a poor secondary bond -- the more area you have to prep, the more potential for error. I just wanted to make sure there wasn't another aspect of this that I was missing.

 

[Dutch]

Are you going to be laying wet-on-wet or letting it cure in between coats? If you sand in between layers be sure to not sand through that thinner fiberglass. It is very easy to do. Then after you have all of your layers you would end up with less than was originally planned for in the plans.
Another is you risk a bad batch if you haven't done it much before. I'd rather peal up a heavier layer of fiberglass than a thin layer on top of other thin layers.

I agree with the others, save the lighter stuff for some of the other work. The hull fiberglass is for structural strength.