2002 Mk II Hatch

[Dale Stone]

Hi Robert
Let us know how that goes, I was thinking digging it out would be a first good attempt.

[hwd]

Robert,
Thanks for the update - I'm still interested to learn how extensive your damage is, and how you decide to fix it.
Harry

[Robert Mann]

Today I removed the rotted core.  The affected area was wedge shaped from the front left corner of the hatch heading towards the port bow, it extended approximately 11".

The first photo shows the extent of the rotten area around the hatch and the use of a heat gun to dry it out. 
The second photo shows the pile of crap I pulled out.
The third photo shows the weapons of mass destruction, a kebab skewer and the longest sawzall blade I could find, in a handle
The last shot shows the trim ring and how the water pooled in the rim.

On looking at the damage I believe it had been leaking for a long time, either under the hatch or down the screws which showed no signs of sealant, remember the hatch is sealed with Butyl tape.  The water soaked the core and when it final got so wet it filled the rim of the trim ring and ran over the edge.

Next step, after further drying out, West 105, 206 and 406 filler and pump it in with a caulking tube, I think.  Then re-seal the hatch, after potting the screw holes, I am not doing this again!

[KWKloeber]

Robert

I did a similar core damage repair.  Suggest you use poly tubing to extend the tip of the caulking tube to get unthickened resin deep into the void, or use a long (artist's) brush to thoroughly saturate/wet out all edges of the void before pumping in the mix.
I used to nearly always use 406 but once I tried 403, I universally use that for everything.  It has better adhesive properties, and is nearly as strong in compression as 406 (the repair isn't that large.)  It wets out SO MUCH easier than trying to mix in 406 (which I equate to trying to mix dandelion wisps into peanut butter.)  Microfibers mixes in so much more easily and quickly.

How deep does it go in the corner? Could you cut a wedge of marine plywood, butter it up and slip it into place?  Or alternately roll up a bunch of pieces of wetted-out fiberglass cloth or mat, and poke them into the hole using a dowel the height of the void?

[Robert Mann]

Thanks Ken, the deepest point of the vee is about 10". I really can't tell the shape of the cavity accurately,  so putting wood in might leave a potential void.  I think adding unthickened resin first is a great idea to shore up the core, followed by a mix. I will take a look at 403.  I was debating between 406 and micro balloons, or a mix of both.  Colloidal silica and micro balloons was the mix recommendation from Fibreglass Coatings.

[Breakin Away]

I did a similar, but much smaller, repair around a chainplate on my C250. I taped the bottom and filled the core from the top. Even for a small repair, I was concerned about overheating from the exotherm, so I decided to do it in a few thinner layers, waiting for the exotherm to kick off before doing the next layer. However, this led to concerns over amine blush, which would interfere with adhesion between the layers. Normal procedure is to grind and clean the amine blush between layers, but this is impossible inside the fiberglass sandwich, which required a blush-free epoxy chemistry. From prior work that I had done using West Systems epoxy, I knew that they have very severe, slick, slippery blush as part of their chemistry.

With that said, I'm just wondering what you guys think about these guys as an epoxy supplier. They're the guys that I used:

https://www.epoxyusa.com/category_s/3.htm

[hwd]

Robert,
I pulled my hatch this weekend and found that there was a minor leak with the water collecting in the trim similar to the situation on your boat.  There was not much water damage to the core, however - only a small area located around one of the longer screws of the hatch hinge.  I cleaned it out and filled with a small amount of thickened epoxy from WEST Systems.  It appears the deck on my Mk11 2005 is cored with balsa.  I really appreciate your post - if I had let it go, I think there would have been much more substantial damage to the core.
Thank you!
Harry

[KWKloeber]

Robert,

Actually getting a good pattern to replace the core is fairly simple, just a tad tedious.  Not that you'll decide that path but I'll describe it here for posterity:

IIWMB, I would rip some strips out of scrap pine to just thin enough so it's snug but not tight in the slot.  Like 1/2" x slot thickness.

Slip a strip in place, w/a slight hammer tap to set it into the punky core.
Mark the strip at the edge of the opening. 
Repeat along the slot until you get one side done.
Pull the strips, lay one on stiff cardboard, mark the "embedded" tip, draw a line down the length of the strip.
Repeat, laying the next one next to your mark, repeat the process.
Repeat in the other direction(s) of the void/hatch opening.
Connect the dots, you'll have a very accurate template of the void.

Another way is to use THICK (1/4"?) bamboo kabob skewers w/the pointy tip to embed it into the punky core.  Using them about every 1/2 to 1" to get the depth.  The trick with those is to keep them square to the opening.



To repair, cut the replacement about 1/4 to 3/8" shallower than the template.
Wet out/saturate the punky core and slot as described. 
Pump in peanut butter mix (NOT MUCH!) to the punky back edge.
Wet out the replacement top/bottom w/ a little poxy (not drastically buttered up.) 
Tap the replacement into place, the leading edge being forced into the thickened mix so there's no void between the punky core and the replacement.


Now to your filling method:

That's too deep to do in one fill.  No matter how you think the thickened mix will butter in there, there will be sag somewhat before kicking and it will be more difficult than you think to do a large void.  Doing a void in multiple fills, the trailing edge of each fill will slough off, not remain square.  You have to make sure you get that void filled w/ the next fill.

There are many ways to skin a cat, but if I were doing this on someone else's boat, I would choose the replace the core method ("just because.")  And because it's not standard practice to fill LARGE voids w/ just poxy.  It's expensive, difficult, and a waste.  That said, IIWMB, I would use one of two methods -- this is one of those need to "have eyes and hands-on" to decide.

M1):
Make a strip(s) (about 1/2" thick) out of treated lumber to fill the edge of the opening.  Once fitted and tight, set aside.
Wet out/saturate the bad core as described.
Butter up and set the edge strips in place. 
Once cured, drill a few holes, large enough to insert poly tubing to pump in the mix (prob 3/8" hole.)  One in center, one near each end the strip(s). 
Pump in a little mix in each hole using tubing; deep into the void first. 
Repeat filling a little more. 
Repeat and final pump until the mix oozes out each hole -- which demonstrates that the void is filled.   
Tap a dowel plug in each hole (so it doesn't ooze before kicking.)

M2):
Get a bag of cheap open-cell foam sponges from the dollar store. Or open cell foam if you have that available (like the black foam often used to pack around electronics.)
The foam doesn't really matter, you just use it as the VEHICLE to carry the thickened mix.
Wet out the core/slot as described.
Wet out a sponge, fold in half long ways, w/ a paint stirrer stuff it deep into the slot.
You want to use a thinner mix (so the foam gets fully saturated) than if pumping in the mix.
Repeat as needed until the void is filled. Do it in stages.
The thickened web of epoxy in the foam cells will be like steel, and the pressure of the folded foam will assure that there are no voids top and bottom of the slot.

Microfibers being the best for void filling (adhering better to top/bottom and keeping the void filled.)

As for blush, you want to use a NON BLUSH (you need to if filling in stages.)

I've done a fair amount of poxying over 25 years, from waterproofing, to damage repairs, to tabbing, to dropping/refairing my keel joint, to attaching cleats for drawers and storage. Initially, I used West, but have switched to Mas Epoxy exclusively. 
https://masepoxies.com/
* It was a family business ((Mas ie, mother's Epoxy)** 
* I prefer it, Flag resin has a TAD more body but has surfactants so it flows as well as West. 
* Mas hardeners are NON BLUSH** (wax in the hardeners, not the resin, is what causes the blush -- I even used up my remaining West resin using Mas hardeners.)
* The mix ratios are more forgiving than West.
* Mas has a penetrating resin (you can use it for both penetrating and filling.)

** Mas got gobbled up, and now markets other than the original epoxies, so choose the Mas non-blush.

West Marine used to carry both brands (ordered in) dunno about now.  Defender carries Mas.

West does have one non-blush ("Special") hardener.

-ken

[Robert Mann]

Thanks for the input Ken.am heading towards trying to make a pattern and then filling a majority of the void with wood and then using epoxy to fill the smaller gaps.  Due to the irregular shape i will probably need to put at least 3 pieces of wood.

[KWKloeber]

Sounds good. Keep us in the loop.

[Dale Stone]

Hi Robert,
Good description of your find and work. I agree that using a wood filler for most of the repair is better than filled resin. I am now concerned I will have the same problem with a second  C34 II owner confirming it. I'll be taking off the inner trim this weekend. So you think the butyl tape had a minor leak?
Another spot to look at is the piano hinged seat cover in the cockpit. I had several loose wood screws that penetrated right into the core and had to replace a large section underneath the port winch and 12" aft. I used a plywood filler with filled resin and attacked it from the underside which is not usually recommended. But is is now fixed and better than new and will never leak again.

[Robert Mann]

Dale,
I have not pulled the hatch yet, I will after I fix the core, (currently the boat is tarped and I have run poly-sulphide around the hatch and down the screw holes).  I did find most of the hatch screws could take a half to three-quarter turn.  The hatch is bedded on Butyl tape and the screws that were in the rotten wood show no signs of ever being sealed, but of course they are 17 years into the program.  Its either the screws or the hatch having slightly loosened as the Butyl tape aged that has caused the issue.   

[Dale Stone]

Hi Robert
I'll report back after this weekend. I love the boat but have some issues with details like yours and mine of last year. When I fixed the piano hinged locker, I made sure no water would ever again get in that area. I would hope Catalina would have thought to seal exposed balsa around hatches. Thanks to this site and others, our experiences can warn others and we get great information in return. Thanks for sharing.

[Dale Stone]

Hi Robert
Tried a reply earlier but didn't go through. Maybe due to an attachment.

Anyway, I am not a victim of hatch related sougey core. Both forward and main hatch trims removed. Exposed core and interior plywood are sealed with I believe poly resin. Not sure by whom. PO didn't do that type of improvement but the trim kits were cracked before removing them. Maybe he did but maybe Catalina did that prior to 2002. My boat is a 2001.

I need a couple of trim kits now, hope Lewmar has them.

I can sleep better with knowledge of not needing to do a core repair again.

Thanks
Dale

[Robert Mann]

So after finally getting kid 2 graduated, Go Dawgs, and a deck built on kid 1's house I finally finished the repair to the boat!

Following Ken K's suggestion we made a pattern of the cavity, using thin wooden stirrers.  We transferred the shape onto foam cored poster board and got as close as possible. We finally figured out we were trying to be too exact with this and ended up with the most 3/8" balsa core crammed in the cavity we could manage, shaped to fit.  I then pumped in un-thickened West epoxy to coat the back of the cavity to as great a degree as possible, buttered the wood with epoxy thickened with colloidal silica and went at it.  Drop cloths all over the interior and cabin sole, its a messy job!  When the epoxy cured I used a coping saw and a half round rasp to finish the job off. 

In the meantime I removed the hatch, which came out easily as it was almost sealed with butyl tape.  Now here are my bitches about the way the hatch is installed.  Firstly, the cut out in the deck missed the outline of the hatch in the leaking corner, which I have read about from someone else here.  Secondly the hatch is screwed to the deck with self tappers, through the butyl tape into the core.  That must have saved Catalina at least a couple of bucks per boat!  Got into a losing discussion with she who must be obeyed about a ring of bolts in the cabin head liner, so I re-screwed the hatch down.  In a perfect world potting the fasteners and through bolting would have been the preferred way to go.

Without getting into a long argument about tapes and sealants, the hatch went back with 3M 4000UV.  I love butyl tape when it's through bolted, but not with screws.  I am leaving the interior trim ring off, to check for leaks after the sealant/adhesive cures, and then I will seal the end of the balsa with epoxy. 

The end of that project, I hope.