Deck core repair: balsa or divinicel?

[Bill Root]

We have ended six wonderful weeks in St. Augustine; two at the downtown municipal marina and four at the Conch House marina. Had a great tome, but tomorrow we have to depart for Lamb's in Jacksonville to address the coring problem in the flybridge deck.

I removed and re-bedded all the screws in the flybridge seating area. The 54 doesn't have screws holding down the fly bridge helm like the earlier boats do, but it does have a large molded seating area behind the fly bridge helm that is screwed down. Apparently I didn't get to it soon enough, because when I took core samples I found the balsa core to be rotted all along the outside edge of the fly bridge deck back about eight inches. The rest of the core seems to be sound, so apparently the water leaked through the seating area screw holes, ran to the outside edge and collected there, rotting the balsa.

I've done quite bit of research on core repair, including Vincent's excellent narrative of the aft deck repair on his 43. I am getting conflicting opinions on which core material would be best to use in this application. The marina is recommending Divinicel (sp?) because it won't absorb water if leaks should occur again. However, I do understand that it will disintegrate if it stays saturated long enough and that it can have problems sticking to the epoxy used to glue it in place. Others are recommending to go back with balsa because it's linear fibers make it stronger and also better at soaking up the epoxy for a strong bond.

I would much appreciate hearing back from anyone who has experience with either or both of these products, or any other core materials I may not be considering. If I'm going to do this job I want to do it right the first time.

Thanks much

 

[Boatsb]

There is literally more choices than you think. What are you familiar with is a good place to start.

I usually work with products Im familiar with to get better results. Trying new stuff can be a problem

 

[sandspur1966]

http://www.fiberglasssupply.com/Product_Catalog/Core_Materials/core_materials.html

This site has a good description of the three most popular core materials.

 

[mdshore]

use vinylester. easier to work with and good properties

 

[Vincentc]

Bill,
If you are going to epoxy the coring I would not worry about future rot since you will be encapsulating the core and know better than to create future penetrations. I agree with the suggestion to use material you are familiar with. For me that is plywood and epoxy. Depending on the volume of the coring you will be replacing, the weight difference between plywood and balsa may be insignificant and the plywood will be stronger. epoxy with a light weight filler did fine filling the gaps for me. All of these options should weigh less than water soaked balsa.

Regarding the question of what material you are familiar with, that would apply to to the person ding the job. If you are hiring someone, that would mean the material he is familiar with.

Whether you have problems with wet core in the future will depend more on how you handle penetration than the coring material used.

Regards,
Vincent

 

[bobk]

Bill,

Sorry we are going to miss you in St Augustine. We arrive Hidden Harbor Marina on the San Sebastion River tomorrow for a few days.

If your repair is limited in size, and you do not need to remove the entire top skin, there may be two simpler options for you. The first step is use a moisture meter to identify the area with wet core. Then use a 1" or 1 1/2" hole saw and cut holes 5-6" apart and dig/vacuum out the bad balsa. Let it dry and then fill with micro balloon thickened epoxy, or easier yet, gun in a high density urethane foam. Let it cure, fair and skin it over with a layer of glass. My sundeck was repaired with the foam six years ago and is doing well. My foredeck was done with the filled epoxy and it too is doing well after about two years.

Bobk
1981 48MY

 

[SeaEric]

If this is along the edge of the deck, is it really necessary to fix it? I can't imagine that it's structural. Wet deck core on a Hatteras is a fact of life. You'll never fix all of it. Stop the source of the water intrusion and consider leaving it alone.

I've been shopping for a moisture meter to have in my arsenal. A Google search turned up this interesting piece: http://www.marinesurveyor.com/meters.html

 

[Pascal]

I agree, if the rotten core is along the edges it s not structural and may not need to be fixed, although the problem with balsa core is that it will suck up whatever moisture is in there and the damage may expand

I totally disagree about divinycel disintegrating if it stays wait... I don't dont know where you read that but it s total BS. I kept a piece of divinycel with glass on the each side but the edges open in water for months to check water absorption, it never soaked water and never disintegrated. I d use Divinycel anytime over balsa. I know hatteras cores hillside with D, I not sure about decks but I doubt they still use balsa

 

[mdshore]

tramex makes the industry standard moisture meter .

imho if the wet core sustains a load and is not cracking or causing further damage , leave it . when you do repair , use coosaboard or the like as to not have possible rot in the future . dont bother trying to save the old skin on a large repair , lay out the coosa and laminate, then fair sand and finish.strike a clean line and remove old to that point. very difficult to work an odd shape.dont ever think you will air out balsa to dry it to reglass. if its wet its wet. before you drop in the core material apply thickened filler mixture to perimeter creating a block /damming effect to prevent any travel of moisture.you can also embed a 1/2 pvc drain pipe as a relief .

if you have a small area and you need to mount something and dont want to go through the extent of removing wet core , use pettit a788 epoxy repair filler.
http://www.jamestowndistributors.com/userportal/show_product.do?pid=6766

you can apply this to wet and even underwater substrates, its a great emergency product to keep on board. repairs steel , impervious to fuel and heat up to 250 .

 

[34Hatt]

No reason to use Balsa again it should be the last thing to use these days!

Coosa or Nida core but coosa works out better when doing a repair then cored materials for height reasons. Divincel is great stuff but over priced for that Job if you were making a hard top or building a race boat yes but a bridge of a hatt? If any one says something is stonger just think how long have you been cruising with a wet core! Most hatts have so much glass on top of the core its hard to know it is shot!

 

[GJH]

I recently re-did the boat deck around where the davit pole went through; whoever installed it many moons ago did not seal the hole, eventualy the caulk let water in and voila:

The flange of the davit pole was attached to the deck with a bunch of short screws into the fiberglass:

So Bruce Morrison and helper scraped all the rotted core out, fortunately it was fairly limited in part because the hole is on the down slope of the deck, and because there are reinforcing dams. Then filled the area with reinforced epoxy. Note the fiberglass is 1/2" thick on each side of the core!

We then through-bolted the flange through the epoxy.

I've used good marine plywood in some other more trafficked areas with "so far, so good" results over the past 5 years. But honestly unless the deck was cracking, I'm not sure I would bother.

 

[Bill Root]

We just got tied up at Lamb's in Jacksonvile and opened the website. Great feedback from everyone. Thank you very much.

I seriously considered just leaving everything alone, but the coring all along the outside edge of the fly bridge deck has actually dissolved and turned into dark brown water, so a small repair is not going to be possible. The top skin is spongy and cracked in a couple of areas. It is necessary to walk on that area to clean and polish the outside of the seating area, so I'm going to have to fix it.

An on interesting thing about the moisture meter. We used it to try to identify the wet areas and the readings were not bad, but when we drilled the 4" holes in the fiberglass skin to take core samples, we found that in some of the areas that showed low to moderate moisture, the core was actually completely gone. Seems these moisture meters can be fooled.

I'll be working on this repair along with the marina guy. I'll take photos and post them as we go along.

 

[GJH]

Good luck Bill, hope it goes well. I wonder what a moisture meter would have shown in my case, since like you there was just air there. Tapping the deck with a screwdriver handle gave us a pretty accurate idea of the extent of the problem beyond what we could see.

 

[jim rosenthal]

I've been there and done that, and probably will be there again. I would use Coosa panel, as it's what I am familiar with, but Divinycell or Airex are fine, too. Not balsa, no way. As for marine plywood, it's probably stronger, but you do have the "what-if" issue of water getting in there. And sooner or later, water seems to get into everywhere.

If you decide to use plywood, use the best marine ply you can get, and follow Vincent's visual manual. He's described it very well indeed.

 

[bigbill]

bill, i just did the back half of the bridge of my 58yf, i use corecell. very easy to work with, doesn't weigh much, and wont absorb water.