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Old 21-05-2019, 10:44   #1
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Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

I need to rebuild the forward most bulkhead in my Tayana 37. It is the same bulkhead the Samson posts bolt to so I need to make it strong. I was just going to use 1708 biaxial for the entire project. As I read more I realize that this may not be the best option.

So, you more experienced boat guys... What cloth is best for this type of work? I will be using epoxy, not vinylester or polyester resin. I mention this because I was told to finish the project off with chop strand matting. However, CSM does not properly "wet out" with epoxy because one of the binders are not compatible with it.

Thanks
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Old 21-05-2019, 11:27   #2
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

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Originally Posted by CharmCityBoater View Post
I need to rebuild the forward most bulkhead in my Tayana 37. It is the same bulkhead the Samson posts bolt to so I need to make it strong. I was just going to use 1708 biaxial for the entire project. As I read more I realize that this may not be the best option.

So, you more experienced boat guys... What cloth is best for this type of work? I will be using epoxy, not vinylester or polyester resin. I mention this because I was told to finish the project off with chop strand matting. However, CSM does not properly "wet out" with epoxy because one of the binders are not compatible with it.

Thanks
FWIW I have a lot of experience with epoxy and woven fiberglass in making airplane parts (including bulkheads). In the aviation world the use of mat is practically unheard of (at least to me) as it is anathematic to concerns of cost, weight, strength which I sort of assume are shared with boat owners.

Nonetheless, in the boating world there is an often-repeated idea that mat, when used between woven layers, helps bind layers of woven fabric together. This latter point makes absolutely no mechanical sense to me with respect to understanding of composite construction after ~1970 or so, but it's what you'll read/hear. Perhaps I'm missing something. My assumption is that mat does indeed help the wetting out process, but this is a labor-saving measure, such that people...with mat...end up using a lot more material because it's easier. Sort of a "if you can't tie knots, tie lots" type deal.

I would point out that glass hulls made in the 1960s are routinely observed to be "built super strong but really too thick...more material that is what is required." People will say this, then, when doing repair jobs, will specifically employ the practices of the 1960s (including heavy laminates with low glass to resin ratios...which mat specifically causes).

FWIW I'd use (for ease of use) biaxial without mat throughout; if the superficial layer is of cosmetic concern, then top-off with a layer or three of a lighter-weight fabric (e.g. 4oz) You can off course experiment with a couple coupon sample layups to determine what your surface finish will look like, and can use plastic dropcloth (e.g. visqueen) to get a ~glassy smooth (if wavy) surface.

At any rate, endeavor as much as possible to get excess resin out without leaving the layup dry. To me this is as much about increasing strength as it is about weight savings. That you use less resin (and save money) is sort of besides the point.
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Old 21-05-2019, 11:50   #3
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

Excellent feedback! Thanks. I think I will stick with 1708 biaxial. I may drop down to some 1208 in certain areas where 1708 may be a bit stiff. I will make sure to focus on properly wetting out Matt, removing air bubbles and not over doing it with the resin.

Thanks
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Old 21-05-2019, 14:20   #4
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

I do believe that there are CSM materials that are specifically made to use with Epoxies. They employ a different binder w hich is compatible.

But I agree that there are better materials to use in your application.

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Old 21-05-2019, 15:02   #5
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

1708 is 17oz biax stitched to csm. csm is just an epoxy sponge and a waste of expensive resin. the same material w/o the csm is 1700 biax and is perfectly fine for tabbing (multiple layers offset seams and edges). make pealply your new best friend and youll have no need for csm ever again.
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Old 21-05-2019, 16:18   #6
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

Most of these responses are dead wrong. You do not want to use mat with epoxy. It is a complete waste of epoxy and doesn’t provide any real strength.

1708 is not the right choice of material. 1708 with mat was created for polyester laminations.. The purpose of the mat it was to bulk up the lamination.

You just want a stitched fiberglass cloth. Depending on the exact placement of the material, you could use uni, biaxial, or triaxial cloth.

If you are unsure of the vectors of the stress, one of the best things to use is just biaxial. So what you need is a biaxial cloth. You can get this in 17 ounce. Or in many various thicknesses. Depending on the loads you are looking to carry with it.

If you can provide a picture of the bulkhead, we are you need to fix it, including all of the loads that are on it, I can help you determine the weight of the cloth to use as well as the direction of the weave when you lay the cloth down.
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Old 21-05-2019, 19:04   #7
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

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Originally Posted by CharmCityBoater View Post
Excellent feedback! Thanks. I think I will stick with 1708 biaxial. I may drop down to some 1208 in certain areas where 1708 may be a bit stiff. I will make sure to focus on properly wetting out Matt, removing air bubbles and not over doing it with the resin.
Please review what everyone has said about avoiding mat. Just to emphasize...1700 biaxial is stiched without mat.

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Most of these responses are dead wrong.
I can only assume that you're referring to posts made by the OP and that you didn't read the other responders to the OP whom you effectively parroted but called dead wrong.
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Old 21-05-2019, 20:45   #8
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

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I can only assume that you're referring to posts made by the OP and that you didn't read the other responders to the OP whom you effectively parroted but called dead wrong.
Yes. That is probably it. Someone was coming to my door at the moment I was making the post. So I rushed a bit.
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Old 21-05-2019, 22:10   #9
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

Surely three layers of 17oz double bias both sides of the bulkhead will be enough. Maybe 150mm, 200mm, 250mm wide tapes, then peel ply with the centreline of each tape marked so they can lay exactly in hull/bulkhead cove? All done in epoxy resin with slow hardner. With the tapes wetted out on a peice of ply on the workshop bench then the tapes rolled up and carried back into the yacht on a plastic paint tray. Hardest part of the job is going to be not touching anything when you have epoxy resin on your gloves.
I remember glassing the bottom of an anchor locker bulkhead on a 50 foot yacht while being held by my feet so I could reach and glass right down the bottom.
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Old 22-05-2019, 14:01   #10
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

One of the main issues with CSM is that it uses a silane treatment as a binder and it is therefor very, very difficult to wet out with epoxy. Polyester is OK though.
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Old 22-05-2019, 15:29   #11
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

I NEVER finish off with chopped strand matting, and always use a woven mat, and on top of that, peel ply. The sanding of uneven glass surfaces, even if fasiring compound has been used, in a confined space would be one of the terrors of hell for me.

Personally, I would be inclined to replace this bulkhead with what was used originally, and I suspect this may have been layers of epoxy-sealed plywood.
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Old 22-05-2019, 17:22   #12
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

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Originally Posted by sand6000 View Post
One of the main issues with CSM is that it uses a silane treatment as a binder and it is therefor very, very difficult to wet out with epoxy. Polyester is OK though.
I have never had trouble with silane or volan treated cloths with epoxy, 4 and 6 oz plain weave. I do seem to have more trouble with a batch of cloth from Ebay that is 7.5oz and may be direct-sized or some other odd construction. It was gotten on a steep discount from a coworker. If I wanted something to be 'pretty' as-glassed I would get official 'surfboard' grade glass cloth.


I do not use CSM and stitched bi-axial...yet. This vendor cites the CSM binder as a Polyester that needs the styrene from Polyester or Vinylester resin to dissolve:


https://s3.amazonaws.com/cdn.fibregl...oads/00348.pdf
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Old 22-05-2019, 18:24   #13
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

Quote:
Originally Posted by CharmCityBoater View Post
I need to rebuild the forward most bulkhead in my Tayana 37. .
I was just going to use 1708 biaxial for the entire project. As I read more I realize that this may not be the best option.

So, you more experienced boat guys... What cloth is best for this type of work? I will be using epoxy, not vinylester or polyester resin. .
Thanks
I used 17 oz bi-axial cloth for our deck and no problems. On the deck I used 5 to 7 layers, which gives nearly a hull-strength deck. This was with West Systems epoxy, mixing just 6-7 ounces at a time. Sanded between layers.

You might want several layers. Finish and fair with a light epoxy paste that is not structural but is very easy to sand and fair. Much easier than chopped matt or structural paste.
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Old 23-05-2019, 02:15   #14
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

Though you didn't ask, at least as important is the material you're using as a bulkhead, as it will (or should) designate the layup schedule.

3/4" plywood or 26 lb coosa? Single layer of heavy or double layer of less-heavy cloth with triple staggered tabbing seems about right.

3/4" 5 Lb PVC foam? Double layers of heavy or triple layers of less-heavy cloth with the same triple layers of staggered (4", 6", 8") tabbing seems about minimum, to reach the 'strong' qualification at any rate.

This is of course just a generalization; the real decision needs to take all the idiosyncrasies of the application into account.

Keep in mind this is a boat, heavy, slow, long-lived and potentially subject to repeated loads imposed by a medium almost 800 times denser than air. Whilst some of the properties of construction overlap from other industries, boat building or repair has a much different scope of necessities--and responsibilities, peculiar to it. For instance, weight for a bulkhead on an 11 ton monohull has a different relevance to say, weight for an engine bulkhead in an aircraft. A little resin-richness in a layup is preferable, perhaps even desirable, to resin starvation on a boat (at least a cruising boat); I presume the reinforcement/resin ratio in aircraft construction is more important and tightly controlled for, for a variety of reasons, but which can be summed up as it having to meet a very different set of operating and environmental conditions...
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Old 23-05-2019, 10:26   #15
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Re: Fiberglass Matt / Cloth to use for structural bulkhead rebuild?

Thanks to everyone for the feedback...

1. Stay away from CSM
2. Use a biaxial cloth without a matt layer (maybe 1700)
3. Proper layup technique and use of resin is critical
4. use proper tabbing and stagger the glass

One question. Does the first piece of glass going down need to be the largest piece, then moving to smaller pieces, or the other way around?

Thanks
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