Deck Coring

[Scott Mather]

Started cutting out what is left of the deck coring. Seems no one properly sealed holes cut in decks for fuel fill fittings tower supports and haws pipes (factory install) or the rod holders (not sure who did these).
The coring is completely gone.The good news is it is not that hard to access from under the decks in the cockpit. Was able to cut out one side in about an hour after removeing all deck hardware.
Any suggestions for what to replace the coring with?

This is on a 1978 37' Hat. sport fish

This also happened on our 1984 32' Hat. express, same areas of deck and also around the cabin port windows.

This has got to be a no brainer when building or modifing a boat. I can under stand a novice boat owner making this mistake, but Hatteras Yachts??????

[captddis]

Scott,
I have done some battles with coring on my 46. My main problem was the dreaded deck rot under the pulpit.I was shocked to find no caulk under the pulpit. And the plywood under the pulpit was never sealed!
My solution was to cut it out from the underside, use marine plywood and West System epoxy and cloth. I also replaced all the wood under the pulpit and soaked it in epoxy. Personally I would use plywood around the areas around the cockpit. I feel it gives something more solid to mount rod holders etc. to. [ this is how Bertram does it and it makes sense to me}
I believe most coring problems could be avoided if people would give thought before making holes and seal the exposed core with epoxy or resin before installing hardware. Dave

[mike]

Another solution is to use a product by Smith & co. called Clear Penetrating Epoxy (CPS). It is a very low viscosity resin system with a slovent that will displace the water in the wood and set up hard after about 2-3 days. I have use this many times (25+ years) on core problems on other boats and it works very well. If you have fungus you can add cupernol to the mix to stop the growth. Smith & co is in richmond, ca. you can purchase it directly from the supplier @ 510-237-6842. It sure beats cutting out all the old core. It also works great as a pre-lay-up treatment for repairs and any end-grain sealing you need done. I always treat all the plywood with CPS before any lay-up work. Mike

[mike]

The following web site covers the science behind the product.
www.woodrestoration.com/w...tion01.pdf (http://www.woodrestoration.com/woodrestoration01.pdf)

[captddis]

Mike, thanks for the info. I have always feared that if the wet core is not removed, the water will migrate. I assume you inject it into the core? Dave

[mike]

You are right, you inject it into the core. There are several ways to do this. The best is to drill a seriers of small holes around the affected area and use a number of small 3/8" dia. funnels and let it wick in. You can order either a slow-set (3-5 days) or fast set mix and continue to pore it in until it is fully saturated. The good news is the CPS will use capallery action and the solvent to transfer the epoxy and displace the moisture. This works well with cores as you can ring the problem area and then make a grid of entry points to cover the entire area. I have a simular problem with the bridge and aft deck area on my 53' MY and I am planning to handle it just as I described. I have recently used this method to fix the transom on my 32' offshore, where the dummies that put in the water pick-ups failed to seal the end grain. The result was a massive failure of the core to above the top of the outdrives. It's now fixed and is as good as new. Mike

[Scott Mather]

Sounds like a good solution, only I did not have any core left. Have all of the inside glass cut out and ready for new wood. Will then glass over the new wood. Going to use 3/4" marine ply that has been sealed. Also had to grind out all of the stress cracks caused by the hardware flexing the decks after the core had deteriorated. Then shoot some new Imron and will be "better" than new in this case.

[34Hatt]

Scott don't worry you did it Right! I have cut too many decks open that I would like to forget I did. I have cut them open after people doing the Injection route they have lot's of air pockets and voids. I have been using Nida Core, www.nida-core.com/ (http://www.nida-core.com/) this is a nice product to work with and less work then the plywood and will never rot. I just would drill the hole for hardware bigger and then refill with epoxy for the hardware area's.
The sheets come different ways you want to use the one with out a skin and make up some resin colloidal and fine chopped glass. If you can vacuum bagging it is the best way. You can do it with plastic, duct tape, bubble wrap packing material "the large size" , plastic thru hull fitting and a shop vac.
Good Luck Dan

[jim rosenthal]

Use Coosa paneling. It is light, rigid, impervious to water and strong. It comes in a variety of thicknesses and strengths. Oceana Ltd in Annapolis sells it, and you can probably find other dealers on the web. It is not the same material as Nidacore, Diviinycell or Airex or Knytex. It glues very well with epoxy and takes primer and paint very well also. Great stuff!!!

[34Hatt]

Well it sounds just like Nida Core and Nida Core glues very well with Epoxy or Poly which is what you want to use since he is working over head. Epoxy is great but not needed for this application take's to long to set up.

[jim rosenthal]

It may be the same stuff after all; the difference is that CP comes if you want with layers of glassfiber already laminated in, which may be helpful to him. It has glass fiber all through it, also some of the varieties have multiple layers of glass cloth in there. I guess in that sense it is somewhat different. I used it on core repairs and some other things when we painted my boat. I have to admit, I use it now because I still have most of a 4x8 sheet left over so I'm trying to use it up.

[ELECTRA VI]

My 34 C has lost the coring around the sampson post forward. I built a new backing plate out of plywood and sealed it with polyester resin. I planned on pulling the sampson post, sealing off the edges of the hole in the deck where the anchor rode passes and plugging the four holes from the sampson post. Then I plan to gravity feed polyester resin into the void. My question is, am I on the right track or do I need to rethink this issue?

[34Hatt]

You are on the right track but I would use epoxy to fill the hole with some high density filler.

[ELECTRA VI]

Thanks, I forgot to mention that I plan on mixing microballoons with the resin. Will that solve the density issue?

[mike]

Polyester shrinks, epoxy desn't. You may need to make a second pass. try to avoid filling too large a cavity with resin and micro baloons, unless it's a non structural, cosmetic repair. The real problem is the interface between the existing deck and the filler, you need both a mechnical and chemical bond inorder to avoid future cracks at the joint. Make certain if you use Polyester to saturate the the core material at the joint interface sufficient to avoid a lean bond. Also make certain to use laminating resin for this part of the job, you want no wax containing material in the joint. Once you are finished with fill part of the job you can then use a wax containing finishing resin on the final surface pass. The seceret to a good seal is to have a good chemical and mechanical surface tooth and to keep all the interfaces clean and dust free when using the resin. good luck, mike

[ELECTRA VI]

Thanks Mike. I appreciate the information. George

[jim rosenthal]

Polyester doesn't bond well to already cured resin areas. You would be better off using either vinylester resin or epoxy, with appropriate thickening agents so it doesn't drip down. Microballoons are a fairing agent; it sounds like a thickening and strengthening agent such as colloidal silica or Cabosil would be better. If you fill large voids with resin mixture, you will end up with bubbles and voids inside from curing heat etc. These areas will be weak and moisture may find its' way in there. The purpose of the foam material is to replace the core that you removed; two fiberglass skins separated by a core are stronger because of the breadth in space braced by the core, sort of like an I beam. You will then need to reconstitute the lowermost skin, with either a preformed fiberglass laminate epoxied into place (probably unnecessarily robust and heavy) or by laminating glass cloth into place in multiple layers, using lam. resin, vinylester, or epoxy. Basically your aim should be to replicate the original structure and strength schedule, minus the defects that caused this problem in the first place.
If you are looking for preformed fiberglass structural elements, search on the web for Strongwell, they make them, and you should be able to find them. A lot of yacht builders are using these. they are not cheap, but they come in all shapes and sizes and strengths, and they are very well made. (sheets, bars, tubes, boxes, etc)

[ELECTRA VI]

Thank you Jim. I will check out Strongwell.

[Scott Mather]

Know one has answered why Hatteras did not seal the coring to prevent this in the first place?