Fiberglass confusion, I need help?

[DualCore]

I am hoping someone can help clear up some of my confusion about fiberglass layup. I?ve been reading a lot of the posts on here but I can?t quite put the pieces together into a clear picture. There seem to be so many different options and variables that it's a little overwhelming. If I understand correctly, when using Poly resin you need to alternate between layers of mat and cloth right? What I can?t figure out is what weight of mat and cloth and how many layers are needed. I am doing the transom and stringers on a 16? tri-hull.

Would 1.5 oz CSM and 8 oz cloth layers give enough strength or will I need heaver weight? How many layers should I use on the transom and stringers? Would 2 layers of tabbing be enough (csm/cloth then another layer of csm/cloth)? Would the same 1.5 oz CSM and 8 oz cloth be good enough to cover the transom after its tabbed? Will one cover layer of csm/cloth work or should I use 2?

I know this is a lot of questions but I?m having a hard time wrapping my head around all of the options. Any tips that will point me in the right directions would be great.

 

[oops!]

Re: Fiberglass confusion, I need help?

you have it correct as far a s a matt/cloth layup.

i would highly suggest a 1708 bi ax on the transom.....its a total 0f 25 oz of cloth and you will need 2 wraps......it is also a great tabbing materal.

if you choose to use the matt cloth approach.......you will need a minimum 40 oz on the transom.....you can acheive that in what ever combination of matt cloth you wish.

allways remember......resin is weak...thats why the matt is allways next to a cloth.....you can go mat matt.....but never cloth cloth...it wont bond well.

the 1708 bi ax is a matt cloth combination.....so allways lay the mat side down on raw glass or next to the cloth side.....

i know it sounds complicated....but once you understand whats happening it isnt.

read the hull ext thread....the glass discussions on that thread are fantastic....it also includes a step by step transom fabrication and installation.

also the sticky at the top of the forum has a lot of useful information.

cheers
oops

 

[ondarvr]

Re: Fiberglass confusion, I need help?

1.5oz mat is fine, and to be frank, 8oz cloth is almost useless.

Cloth is rarely used in production boats because the cost is very high for the strength it adds, it does get used in the DYI circles mainly because retail outlets sell it due to it's commonly used nickname of "boat cloth".

You were correct in thinking you need a layer of mat between each woven fabric, this helps with the bonding of each layer to the next. The problem is mat is the weakest type of glass and if you use an 8oz cloth very little strength is added for each layer. Using 24oz roving builds strength at almost three times the rate per layer of mat. This makes your final laminate lighter and stronger, plus much lower in cost.

If you move to stitched fabrics like 1708 the strength goes up for the same weight, but the cost goes up too.

 

[DualCore]

Re: Fiberglass confusion, I need help?

Thanks oops! I've been reading your thread, lots of good info! You said that 1708 was good for tabbing, how many layers of tabbing would I need with to include with the 2 wraps? I know that each layer needs to extend further out on the hull, then each of the wraps would extend still further on the hull right?

What about the stringers, should I use 1708 for tabbing them as well? Would it be better to use 2 or 3 layers of tabbing. Would the 1708 also work for capping the stringers or would something else work better? It sounds like a pretty heavy cloth, I'm just wondering how well it would wrap around the outside corners...

I guess I'm just paranoid about not making it strong enough or something...

Thanks again oops!

 

[DualCore]

Re: Fiberglass confusion, I need help?

Thanks ondarvr, I think I'm going to try to work up a plan using 1708 for the tabbing and transom cover. I just need to figure out how many layers. Is there any place that 1708 would not be the best choice? The only place I have thought of so far would be the covering for the sole. After it's tabbed to the hull I was planning on covering it with 1.5 oz csm, does that sound ok?

Can you give me a rough estimate of how much Poly would be needed to do a transom and 3 stringers on a 16' tri? I'll feel a lot better once I get all the details straight in my head. Thanks again for your help.

 

[ondarvr]

Re: Fiberglass confusion, I need help?

1708 is easy to use in most situations, but can be difficult to wrap around tight corners, a little extra mat can help it to lay down sometimes.

The only way to decide on how much glass and resin to buy is to figure out the number of square feet you need to cover, then the total weight of the glass you plan to use to cover each area. If you use mat and roving, double the weight of the glass and that should be about the amount of resin (by weight) you need. With 1708 the amount of resin will be less, almost the same amount by weight as the glass, 1.5 X the glass should work. Just remember as a first timer there'll be some wasted resin, so buy a little extra.

 

[DualCore]

Re: Fiberglass confusion, I need help?

Ok guys, I'm still reading away (there is so much on here...) but I think I'm getting a pretty good idea and just wanted to check if I'm on the right track.

For the transom I'm thinking to use a layer of 1.5oz CSM between the outer skin and the new plywood then 2 layers of tabbing with 1708 (2" then 4" hull contact) then 2 complete covers with 1708 (6" then 8" hull contact). How does this sound so far?

For the stringers I'm thinking 2 layers of tabbing with 1708 (2" then 4" hull contact) then 1 complete wrap with 1708 (6" hull contact).

And lastly for the sole I'm thinking 1 layer complete cover of the bottom side with 3/4oz CSM then 2 layers of tabbing with 1708 (2" then 4" hull contact) then a complete cover with 1.5oz CSM.

How does this sound? Again, thanks for helping me sort through all of this.

 

[ondarvr]

Re: Fiberglass confusion, I need help?

Everything looks fine.

 

[DualCore]

Re: Fiberglass confusion, I need help?

Thanks for all your help ondarvr.

 

[s1120]

Re: Fiberglass confusion, I need help?

Im working on shopping for suplys for my project also, and wondeing...

Can you get away with using just 1708 bi ax for the project?? Stringer, and floor replacement. Will it work well for a layer over the floor? I know its more costly, but realy for one project its not THAT much more, and it would be nice to just have to buy one type of glass.

 

[DualCore]

Re: Fiberglass confusion, I need help?

I hope I'm not getting annoying with all these questions but I was just reading in the completed restorations section and now I have a couple more...

On the project I was reading (Lund Nisswa Restoration ) he glasssed the back of the transom outside the boat then glued it in place with PL, would this work better/worse than using CSM to bond it to the outer skin?

The other thing that looked interesting was that he capped his stringers with glass outside the boat then tabbed them in but he was using Epoxy, would this work with Poly or would it be better to cap them after tabbing?