Wet Core Repair

paulk · #1 (**permalink**) 03-26-2005

Am in the midst of removing wet (but not rotted, thankfully) balsacore from about a 2'' dia. section of the hull where it has delaminated. We''re working from the inside, so we don''t have to worry about fairing the hull afterwards. In my earlier efforts, we''ve used polyesther (fiberglass) resin with new balsacore and cloth for repairs under the impression that the repair would have the same characteristics as the surrounding structure, which would help to maintain its integrity better. Using epoxy instead of polyester resin it was suggested, would create a "hard spot" in the hull that would end up causing problems later, as the hull flexed and worked around its stiff edges.
I am now hearing suggestions that since epoxy is actually more flexible than polyester, and (as I knew before) is a much better adhesive, expoxy would be the way to go with this new repair. What''s the latest word on this issue?

Billpjr · #2 (**permalink**) 03-26-2005

Boats aren''t built light enough to make that argument valid...not even close. Maybe on a composite aircraft skin it could be argued that way but not on a boat. Use whatever resin you want and don''t worry about it.

CJV · #3 (**permalink**) 03-27-2005

I''m in the same ''boat'' regarding inside delam repairs, but have a twist:
In the worst sections the core is soaked with a disgusting, smelly oil/fuel/water mixture. It appears that the oil/fuel has seeped into the fiber of the outer skin. Outside the hull skin is barrier coated and painted with a teflon paint (VC Offshore).

I''m concerned that de-greasing the inside surface of the outer skin will be next to impossible and am considering laying up an additional skin on top of the oil-affected area. Then I would bond coring material, then the new inner skin.

This would add perhaps another 1/8 in to the starboard side under the engine bed, which could be balanced on the port side.

Can anyone suggest other ideas?

Thanks in advance.
Cesar Vallejos
Huntington, NY

CJV · #4 (**permalink**) 03-29-2005

From the good people at West System: Use a laundry detergent or bilge degreaser, reapplying until all oil has broken down. Then follow up with acetone or lacquer thinner and finish by grinding/sanding.

FalconEddie · #5 (**permalink**) 03-29-2005

I have had to deal with all of these problems and one, a 42'' centercockpit ketch, had only 3 square feet of balsa core that was NOT wet. Obviously, the job was done from above, as working from below would have meant dismantling far to much interior and it simply wasn''t an option. This is what we did:

We removed all deck hardware and equipment, then cut the entire non-skid area of the deck with a 1/2 exposed blade circular saw, leaving a 1" lip all around the edges both outboard and against the center cockpit. Then we carefully tore of the outer layer of glass and disposed of it. The core had maybe as many as 10,000 1/4" diameter West ''rods'' in it where previous attempts at repair had been made by laying pegboard on the deck and drilling holes through every hole in the pegboard into the deck, then injecting West and squeegeeing flush.

Good Lord. When the first thousand provide no improvement, why do people keep going? Anyway, you can''t saturate with West what is already saturated with water, and I mean saturated. We used standup barnacle scrapers (five feet long) to scrape off the basla and got soaked head to foot by how much water gushed out.

We had to be very careful no to step in the wrong places and cause damage to the inner liner. Next, detergent and scrub, again. Then big body grinders with 80Grit to smooth the surface, then begin the buildup.

Wipe down with acetone, then apply a mixture of West and colloidal silica with squeegees and set in place the first diagonal layer of 1/4" Luan cut into 2" strips and weighted down with many small weights to apply pressure and hold the right shape. By the time we made it to the back, start the second layer from the front, opposite diagonal with thinner West and now using Monel staples. Third layer went of side to side, then fair and grind.

Next, three layers of 1808 Biaxial fabmat with West, smooth and fair, seal with Interlux 1000 then 2000 barrier coat, Awlgrip White, then light gray with non-skid.

25,000 and a bargain, considering all the work and materials. The deck is solid as a rock and the owner is delighted, though sincerely wishing he hadn''t spent the first ten grand having people drill holes and fill.

I know this was long-winded, but the method works well. You can substitute door-skin to come up with a thinner laminate, but the beauty of those materials is that they are virtually flawless, inexpensive, far superior as a deck core to balsa, which DOES NOT deter water migration which was once thought, and it is as easy to fit as anyone with a sheetrock knife can tell you. Score and pop as you go.

paulk · #6 (**permalink**) 03-29-2005

Thanks for input & interesting approaches. Am still interested in hearing more about the compatibility /flex issues between polyester resin and epoxy resin in the same hull. It was presented to me as an important item by a professional several years ago, and I don''t want to dismiss it based on a single response to the effect that it''s not rocket science. (It''s MY BOAT, after all!) On a wooden boat, a builder wouldn''t repair a douglas fir hull with a teak plank; the stiffer teak would make the other parts flex around it, and lead to more leaks and problems in the long run. Is this comparison valid with different resins?

paulk · #7 (**permalink**) 03-29-2005

Thanks for input & interesting approaches. Am still interested in hearing more about the compatibility /flex issues between polyester resin and epoxy resin in the same hull. It was presented to me as an important item by a professional several years ago, and I don''t want to dismiss it based on a single response to the effect that it''s not rocket science. (It''s MY BOAT, after all!) On a wooden boat, a builder wouldn''t repair a douglas fir hull with a teak plank; the stiffer teak would make the other parts flex around it, and lead to more leaks and problems in the long run. Is this comparison valid with different resins?

CJV · #8 (**permalink**) 03-29-2005

I''d suggest giving the folks at West System a call or an email. They were very informative and, as yachtsmen tend to be, truly interested in helping out.

From a practical perspective, though: You really need to consider what conditions you will be sailing in, and what strain might be present under those conditions in the hull area under repair.

If you are able to sail the boat now and go below under way, preferrably close hauled to windward, take some measurements around the affected area between hull and fixed points in the overhead. If you see changes in those readings as the boat moves thru the water, you might have something to be worried about. However, if you don''t see indications of hull flex, then the boat, in its currently delam''d condition, will not be any worse off after you repair her even if using epoxy resin.

Also, an experienced hand with Tartan Tens (my boat) has told me that when he re-cores he goes for West System epoxy and does not look back.

Hope this helps.

arjan · #9 (**permalink**) 03-30-2005

I am building a 43'' catamaran using both vinylester and epoxy. I don''t believe that there are any problems using them side by side but the problems arise from adhesion. If you apply Polyester or vinylester on top of epoxy the styrene in it will soften the cured epoxy making for a very poor bond at best. putting epoxy on fully cured polyester is problem free.
One of the advantages of using epoxy is its superior adhesion as compared to the esters, so i would use epoxy for the job.
Arjan Bok
www.rotkat.com