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Current Replies for deck core thickness
  deck core thickness (Anna69)
Posted: 4:51:53 pm on 6/12/2012 Modified: Never
Hi Folks,

I've got a moist core issue on the bow of my CC27 mark III (1976).  Anyone know the core thickness if I decide to recore that area?  And of course this leads to the inevitable question of...remove the old core or drill holes and fill with epoxy? Anyone done this before...I haven't.  

  Re: deck core thickness (sony2000)
Posted: 8:11:48 pm on 6/12/2012 Modified: Never
I have some softness near the aft stanchon of the bow pulpit. From underneath I will cut a 4-6" hole around the aft bolt pattern, then clean out the core around the hole, and open up an internal passage going to the the forward 4 bolt holes if possible.
Refiberglass the bottom of the 4-6" hole, so when I pour in an epoxy resin and filler mix, it will be from the eight holes in the deck.
  Re: deck core thickness (Scott)
Posted: 10:13:15 am on 6/13/2012 Modified: 1:17:01 pm on 6/13/2012
I’m not certain where on deck you’re referring but in most cases, most of the deck is cored with ½” end-grained balsa.  And I’m not sure exactly what you mean by “moist core issue”.  Usually when someone is talking about re-coring, it is far beyond “moist”.  Regarding repair, there are as many differing opinions as there are owners & repairers.  Again generally, if the area is relatively large, it’s best to open it from the top, remove the bad, prep, replace and finish, permitting gravity to aid you in the repair.  The Black Arts section of this site has excellent examples and this is by far the most established method and has proven the test of time.  Repairing from the underside is a constant argument with gravity, but in certain conditions it is potentially a good solution such as posted by sony2000.  I know I’ll get comments for this but in my opinion, drilling holes in the deck, filling with epoxy, etc., is a disrespectful thing to do to a boat.  If you properly repair the boat, it will last you for your entire boating life and well into another’s.  If you've got a deck core problem, fix it right the first time.  There's an old saying; "If you want your boat to care for you at sea, see you care for her the same way at shore." I realize you're probably not "going to sea" but the point is still one of the best statements I've heard when it comes to maintenance.

Scott Schoeler, Hull 858, "Scot-Free"

[Scott neglected to mention that he is an accredited marine surveyor . He's probably seen more soggy decks and deck repairs, good and bad, than the rest of us combined. His advice is worthy of serious consideration. - Admin]
  Re: deck core thickness (wrapper)
Posted: 11:31:56 am on 6/13/2012 Modified: Never
My 1975 boat measured 10-12 mm ... about 1/2 inch.

My starboard deck was done about 3 years ago.  See pictures.

C&C 27 Hull 518

  Re: deck core thickness (Anna69)
Posted: 2:22:28 pm on 6/13/2012 Modified: Never
Thanks Scott. The area in question is the if I order new balsa I should get 1/2?  You're right in the differing opinions...right now it is all very daunting but I tend to agree on your approach. I have read about CPES and it sounds like an interesting approach...if I made a series of holes and put a heater blowing down to dry the balsa this stuff might just work. (fingers crossed as I type this!!)
  Re: deck core thickness (davidww1)
Posted: 12:36:46 pm on 6/14/2012 Modified: Never
I feel like you're still toying in your mind with the short-cut of CPES and would like to give it a shot. I think Scott is saying, "Don't go there, do it right the first time", and I agree with him.

CPES is just a fancy way of saying "GitRot", which was a popular product in the seventies for "rescuing" wooden boats that were past their discard date. The problem with the concept is that epoxy saturation may stop rot progressing if it's done properly, but it doesn't restore the strength in the area - in fact, the drill, dry and fill process you describe robs the area of the fibreglass strands that are the source of the deck's strength. It's sorta-kinda okay for small parts like a hatch cover, but I would not employ such a method for a large structural panel like your deck, where a lack of strength in one area has the potential to reverberate through the entire structure.

At the risk of prosing on about something you already know, let me explain that the balsa core is like the vertical part of a steel "I" beam - the flat sections on the top and bottom of the beam have considerable strength, but what gives the beam _real_ strength and resistance to bending is that the vertical part resists movement between the top and bottom panels. Since they can't move in relation to one another, the beam won't bend. You can model this by clamping or taping two long battens together with a spacer of styrofoam - your once-bendy battens become a very stiff beam.

When balsa core gets wet, the bond between the balsa and the fibreglass layers quickly breaks down. so instead of acting like the stiff composite batten-styrofoam-batten beam described above, the panel (in your case, the soggy deck) becomes just two very flexible battens again, with little bending resistance or strength. Moreover, most fibreglass doesn't like bending repeatedly, so the breakdown of the fibreglass layers is accelerated.

None of this would matter if CPES restored the bond between the upper and lower glass surfaces and the balsa core, but in many - probably most - cases it can't. Moreover, you've turned one source of your deck's strength into Swiss cheese, drilling away the glass that provides 90% of the deck's strength (and filling those holes does not restore strength). You end up with a compromised deck panel whose undue working may cause problems in adjacent areas.

Dealing with your damp balsa in the way described in Black Arts will make your wet deck as good as new; CPES will give you a half-measure that may come back and bite you.

David Weatherston
Towser, Toronto
C&C 27 Mk IV

  Re: deck core thickness (Anna69)
Posted: 1:48:26 pm on 6/14/2012 Modified: Never
Hi Dave,

Last night I made an executive type decision...I'm going to enjoy the boat this summer and then pull her this fall and do it right. I plan on keeping this boat for quite a while and she is a real beauty; I think I owe it to her to do it right.  

  Re: deck core thickness (Scott)
Posted: 7:57:41 pm on 6/15/2012 Modified: Never
Good plan and yes, order the 1/2" balsa.

Scott Schoeler, Hull 858, "Scot-Free"

  Re: deck core thickness (Anna69)
Posted: 11:27:04 am on 6/15/2012 Modified: Never
Hey Scott,

Thanks for the good advice. I have read about some type of synthetic core to use...a plastic product. Have you heard of such a thing?

  Re: deck core thickness (Scott)
Posted: 8:20:58 pm on 6/16/2012 Modified: Never
Foam core material has been used for nearly as many years as end-grained balsa but it has not been as widely used as balsa primarily due to cost and the success of balsa.  J/Boats among many other builders are still using balsa in their deck and hull construction. When asked about it, Johnstone replied; “…we use balsa because it’s still the best material.  When correctly applied its stronger and offers better sheer resistance than any of the foams.  If foam was better, we’d use it.”  Manufacturers using foam core material will disagree and provide their side of the argument.  I feel it’s not worth debating Foam Vs. Balsa as there are many examples of successful, long-lasting, well-constructed builds of each.  In the case of re-coring, the proven method has been to use like-kind material, i.e. use what the original builders used: end-grained balsa and polyester resin.  However, many repair facilities are using West Systems Epoxy resin due to its low VOC, better adhesion and low shrink properties.  But it’s much more expensive and the application must precisely follow the manufacturer’s instructions.  The key successes in re-coring is providing a clean connection to the existing material, correctly filling all the “channels” between the blocks and properly saturating both the balsa and the fiberglass.  Don’t be overwhelmed.  It’s not rocket science.  It’s simply paying attention to the detail of application.  Practice on rebuilding a couple hatch covers like the anchor locker or cockpit hatch covers.  Visit some repair shops who’ve done this and ask questions.  Also, ask some of the folks on this site who’ve done it like Allan of “Cygnus” above and others.  There is great wisdom to be gained from the experience of others and these people are amazingly willing to share their experience with another C&C owner

Scott Schoeler, Hull 858, "Scot-Free"

  Re: deck core thickness (Kilroy)
Posted: 11:49:52 am on 6/18/2012 Modified: Never
Well Scott.
You have inspired me too finally get off my #$@#% and get these pictures on the web. Seeing how Allan did it showed me the way. I hope this works. Four years ago we bought our C&C 27 with a rotting out deck(knew it when we bought it). So that winter we hired a gentleman to redo the deck. I assisted in the project and spent some three hundred hours myself on this. As you will see from the photos it was a big project. We used a moisture meter to determine the bad spots and found that we replaced about 25-30 square feet of core. The sole in the cockpit was so bad, I installed a wood floor to get me to the winter. As you will also notice we used the foam core. I found it easy to use, but I have never worked with balsa, so I can not compare.
In my second set of photos, you will notice that I had too redo the deck surface again. When the primer and paint were spayed on, the temperature was not right and we believe there was moisture on the surface. The paint peeled and for the second time in three years, ALL hardware was removed(including windows and pedestal). Not fun.

Tim ,Windsor On.
"Oui R One"
C&C 27 MK III  511
  Re: deck core thickness (Scott)
Posted: 6:31:02 pm on 6/20/2012 Modified: Never
Nice job on the repair Tim. It's nice to see the salvation of another 27. I've seen several deck recores with foam in the last few years and probably a few more with balsa, either is fine, it's all in the application.  Sorry about your paint woes. Painting certainly seems to be so much tougher. The slightest little contaminate will affect the outcome.  Hopefully your current paint job will be a lasting one.  Thanks for the pics & story!

Scott Schoeler, Hull 858, "Scot-Free"