General recoring questions

[crufone]

Hello all,
I have several recoring projects ahead of me and will start with the smallest, the foredeck of a CD Typhoon Weekender. Why not just remove the coring and replace with a hand layed up fibreglass matt/cloth layering system? This can't be more than 30sq ft. so how much more can a solid build up weigh? I also have a 1/4" thick felted material which would make the build up go faster? What do folks think of using that?
Another major question is which resin to use? Epoxy of some sort or Polyester or Vinylester? I know that more modern dinghies are made of Vinylester but have not seen this material available for sale.
Thanks for your ideas,
Michael #161 Typhoon

[Ryan]

Use the core material (foam, balsa, etc). Assuming that you properly prep all deck penetrations, I cannot think of one single advantage to a solid layup in the deck areas. It is heavier, costs more, is slower to complete and is not any stronger than a properly cored lamination. As far as resins go, I think you'll find the consensus here is overwhemingly in favor of epoxy. It is superior to the other choices in every way except for price, and with the type of work in your future, cost shouldn't be the primary concern. Good luck!!

[Jason K]

In addition to everything Ryan said, a cored structure will also be more rigid than solid glass. It is the better way to go: cheaper, easier, and a better end result. It's not too often those three things go together in boating; so celebrate that by ordering some balsa core. :)

Balsa - and other cores - work exceptionally well so long as owners make the effort to ensure they stay dry through proper isolation of the core from fasteners and occasional rebedding of hardware.

Also, the primary negative to poly- or vinylester resins is poor secondary bonding. In other words, while it may be sufficient for initial layups in many cases, it is not sufficient for repairs.

Good luck on the project.

[crufone]

Thanks for your thoughtfully replys. I am slowly formulating a plan for the recoring. First I will build framing inside to support the deck when the outer skin and core are removed. This should not be too tough because the Typhoon is small and there is not much in the way of the needed framing. Since I will be doing this work while she is in the water I assume that I will need some athwartships support as well. Some have suggested that I remove the entire outer skin in one piece so that it can be reused/replaced after the coring is renewed. I wonder about reusing the original outer skin. Would it not be better to lay up the new outer skin layer by layer instead of trying to get the original to adhere to the new core without any voids? All comments appreciated. What have others done?
Thanks,
Michael #161 Typhoon

[Rachel]

I'm in complete agreement with the earlier respondents about the use of core and epoxy. I would say use them! Way more rigid, lighter, and good secondary bonding.

I do have one question about Vinylester: I don't tend to use it because I despise the smell, but is it in the same poor-secondary-bonding category as polyester? I tend to think of it as one of the "good guys," but now I realize that may be wrong.

(Not that I'm suggesting Vinylester.)

Rachel

[Tim]

Vinylester resin is a type of modified polyester. Draw your own conclusions from there.

That said, vinylester has better adhesive properties than polyester. But not in the same league as epoxy.

[Rachel]

Thanks for clarifying on the Vinylester, Tim.

[Quetzalsailor]

I don't think that Vinylester is sold for small users. I understand it's no tougher to use. It's supposed to be more water and thus blister resistant than Polyester. It's also supposed to be more tolerant to being applied over damp layups. It was the repair resin of choice in our boatyard for boats being reconstructed due to excessive blistering, and for barrier laminations over a peel job.

I'm sold on Epoxy for repairs but really, plenty of repair is done in ordinary Polyester. I'm just less used to it, particularly the way it goes off at it's appointed time rather than more slowly like epoxy.

Don't ya' love Wikipedia? <<<<Vinyl Ester, or Vinylester, is a resin produced by the esterification of an epoxy resin with an unsaturated monocarboxylic acid. The reaction product is then dissolved in a reactive solvent, such as styrene, to a 35 - 45 percent content by weight.

It can be used as an alternative to polyester and epoxy materials in matrix or composite materials, where its characteristics, strengths, and bulk cost intermediate between polyester and epoxy. Vinyl ester has low resin viscosity(approx 200 cps), than polyester(approx 500cps) and epoxy(approx 900cps)

In homebuilt airplanes, the Glasair and Glastar kit planes made extensive use of vinylester-reinforced fiberglass structures. It is a common resin in the marine industry due to its increased corrosion resistance and ability to withstand water absorption. Vinyl ester resin is extensively used to manufacture FRP tanks and vessels as per BS4994>>>

[Rachel]

I'll agree that plenty of repair is done with polyester, but I still would not recommend it. (I just wanted to reiterate in case the original poster got the idea that "plenty use it" meant it was the way to go.)

I think a lot of boatyards use Vinylester because it has some better-than-polyester characteristics, and it cures very quickly (like polyester does). That makes a difference when a worker can either get the job done in an hour, in one sitting; vs. working on it a half hour per day for three days (because there is the time/cost of setting up, gathering tools, going out to the boat, etc.).

But for my own boat, where 20 minutes here or there is a drop in the bucket... I prefer epoxy. (And that's not to say that epoxy can't be used efficiently in boatyards, either; I was just addressing one reason why Vinylester might be attractive).

Rachel

PS: Years ago, I built some kayaks and then did later patching with Vinylester, and I don't remember it being particularly hard to work with. I did hate the smell though.

[stone]

I actually find polyester/vinylester alot easier to work than epoxy. Controllable work times much easier to wet out ability to make whatever size batch you want , no hot pots,etc. When I redid the core on my Chris Craft(balsa)there was nothing wrong with the polyester skins of the deck or with delamination issues with the balsa. In fact I was actually surprised how even the wet core was still tenaciously bonded. Because balsa has an exposed end grain the wood cells suck up the resin and by simply pre wetting the balsa letting it kick then procedding with the glassing you can get an excellent bond.No special adhesives are needed.In my experience I see very few delam problems with balsa core and old boats. I reglassed with three layers of 1708 and finished with a 10oz cloth all within a couple of hours working by myself.(Iso polyester).All of the fairing was microballons in polyester which btw was nice to deal with no pinholes after it dries. I am positive my hand lay up was better than the original and I expect no problems. In the past couple of years I have also started to use Vinylester more and more and have never had a problem. In my garage at any one time I have several different resins (epoxy,poly, vinlyester) and I believe they all have an appropriate use depending on the situation.