Filling void in deck

[Shark]

I found this group while checking Tim's site the othe day. Hi from Canada Tim.

I own a 1986 Shark 24. Check out our website www.shark24.org
and I'd like to ask the group's opinion on the following.

When I was buying my boat in 2001, I sounded the decks and discovered a void or hollow in the bow area of the deck, forward of the hatch. It is in the center of the deck and covers an area of about one square foot, plus or minus. There are no fractures in this area of the deck and the core is dry, confirmed by moisture meter. It appears that the builder didn’t “wet out” the area enough when laying in the balsa core and the top of the deck never fully bonded with the core. There is a very slight hump to this area and the top flexes a bit. There is clear access to the underside of the deck from the forepeak and no sign of other problems from below.

I would like to fill the void with polyester resin so that the deck skin does not keep flexing and possibly fracturing. I want to do this from below so as not to damage the look of the deck itself. I definitely do not want to put holes in the top surface of my deck.

It has been suggested that I should drill a series of holes 1/8” diameter in an all over pattern from underneath into the void but NOT through the deck. I would then have to “pump” the resin into the void through the holes using a syringe. As resin appears in the adjoining holes, I am to plug the hole being used with dowelling. I am to continue till the whole area is done. I have done very little fiberglass work except to patch my old car body.


Questions:

Is this the best way to do this?

How big, diameter, should the holes be?

How closely should I place the holes? I’d like to make as few as possible.

How long i.e. working time will I have on a typical summer day before it “goes off”?

Where would I find the proper syringe or other pumping device?

Would it be better to use duct tape to temporarily seal the holes rather than dowelling?

Any other words of wisdom or suggestions?

Lyman (Shark)

[Shark]

Sorry about the codes &#8220. I typed the text in Word and then pasted it into the forum. The codes are for quotation marks.

Lyman

[dasein668]

Hi Lyman,

I'll offer a couple of suggestions.

First, I think this is a case wher you'll be happier using epoxy resin, rather than polyester. What you really need in this case is a good adhesive, and epoxy excels in this regard. Polyester is great for fiberglass layup, but for gluing cured FRP to the core material, epoxy is likely to give you a better bond.

The other thing I would suggest is really thinking hard before attempting this repair from the bottom. I understand not wanting to drill holes in a perfectly good deck, but....

My thinking on this is two-fold. First, Since there is a bulge on deck, it would seem that the TOP skin is not bonded. The bottom skin may well be bonded to the core. If you drill up through the bottom skin and the core, it will be much more difficult to get the resin to fill the space between the top skin and the core material. Gravity will be working against you. If you attack the problem from the top, gravity will be on your side, and you won't have to drill through the core--just the skin. This means that resin that you flow into one hole will spread out over the core more evenly. Then just apply weight to hold the top skin down, and you'll be set.

The other problem with working from below is that epoxy will go everywhere. It's hard to envision just how messy this sort of thing can be until you try it. I would suggest that you'll be much happier if you never have to find out! ;-P

Of course, that's not to say it can't be done from underneath. It certainly can. I would suggest, however, not drilling a series of holes, but rather just a couple, or a few. As few as you think you can get away with, then force the resin up with a syringe until it starts to come out the other holes. Then seal the holes up and weigh down the deck. The fewer holes you have, the more surface area will be able to bond between the deck and core, and the less resin is likely to ooze out onto your head.

Either top or bottom, you should make the holes only large enough to accept the nozzle of the syringe, in my opinion. No need to make them any bigger for this purpose.

Working time for epoxy resin will vary, depending on your hardener, but with a typical resin/hardener combination, you can expect 8-10 minutes of working time. Check with your epoxy dealer for longer cure time options.

Duct tape might work, but I think you'll find that once the resin starts oozing out, you'll have a hard time getting things to stick well. I think you'd do better with a dowel sized to the holes that you drilled.

The only other thing I would say is make sure that you apply weight to the bulged area after you get the resin in place. You don't want to fill the void with a solid blob of resin, but rather you want to get enough resin in there to adhere the core to the skin, so pile a load of bricks, or a cinder block, or something else heavy to hold the top skin in contact with the core while it cures.

Good luck, and let us know how things turn out!

[Tim]

Lyman,

Nathan's response is pretty much right on the mark, and has therefore saved me a lot of typing!

What you are describing is top-skin delamination, or top-skin debonding. This is a frequent manufacturing defect, or damage that occurs shortly after initial construction, and is caused by improper bonding of the core to the deck skin. With the layup techniques used when your boat was built, cores were often improperly bonded in some areas, since only hand pressure was used to secure it, often only in a bed of polyester resin-soaked mat. (Or sometimes a core adhesive like Core Bond, but mat was very common). This common construction error has been responsible, along with other common coring deficiencies, for much of the heartache and expense involved with older boats.

Injecting the area with a thickened epoxy mixture will certainly extend the longevity of the deck, and will be successful in rebonding the area in question. Do not use polyester resin here--it lacks the adhesive qualities that you require in a repair like this. The two-hole technique can be successfully used for smaller areas, but gets wasteful and time consuming as damaged areas become larger. It sounds like you're describing a fairly small, contained area, so the injection process should do what you want.

I would encourage you to consider attacking the problem from the top, mainly for the reasons Nathan already indicated. Since you seem to have solid, dry, sound core, the problem exists only in the space between core and top skin, and you want to direct your repairs to this precise area as much as possible. You'll have better luck with this from the top.

If the area is fairly small, say something that would fit inside a 10 or 12" circle, you would probably be OK with as few as two holes--one to inject into, the other as a telltale "relief" hole. The holes can be quite small--probably 3/16", depending upon the syringe or loadable caulking tube you choose. I don't see any reason why you'd need anything larger than 1/4", max. You can use duct tape to seal the holes, but you'll probably end up with a slightly raised disc of epoxy afterwards--the tape will flex as the epoxy pushes against it, and you'll get a small hump. This is why dowels are recommended in the technique you read or otherwise heard about. At the end, you'll end up with two small plugs of epoxy in your deck, which can be easily touched up to match, probably. They'll look the same as the discarded boltholes that are probably so common on many of those heavily-raced Sharks. If the holes are in the nonskid area, you can probably even more successfully hide the repair, since you can create your own texture to match, and it will stand out less than it would on a smooth area.

You can certainly attempt this repair from beneath, if you absolutely had to. But given the nature of the problem to begin with, I think you'll have more success from above.

Most syringes will work. West System, among others, sells these two to a pack at retailers. You can also purchase empty 10-oz. caulking tubes that you can fill with your own mixture, for larger quantities or better control using a caulking gun.

Note that this technique is only acceptable for small areas, where you are just filling a small void. If your core is damp or otherwise damaged, or if the area is more extensive, then other types of repair make more sense. When you drill your syringe holes, you should be able to get a good visual on the core condition. Moisture meters are not infallible by any stretch.

Good luck, and let us know how you make out.

I guess I lied...I still had to type a lot!

So, is the ice out of the lake up there yet?

Tim

[Shark]

Thanks for the replies and good advice. I just need to work up the courage to do it. It's been this way for 16 years so a few more weeks shouldn't be a problem.

Tim, I think you hit the nail on the head regarding how it happened. The slight hump leads me to believe that the debonding took place when the deck was mated to the hull and was further constricted by the extruded aluminum toe rails. I guess I should have hired you to survey the boat. On balance, I did OK finding this boat. I went through 6 or 7 boats of various vintages and this one was in by far the best shape overall. I found boats with oil canned hulls, wet decks, fractured decks, bad deck hardware etc etc. This class of boat was manufactured by 4 different builders and quality control from the mid 60's to the 80's varied a lot!! Above all I am always amazed at how little some owners seem to care about their boats.

Yes, the ice has gone but you wouldn't know it by the temperature of the air coming off the water. I hope to take the cover off my boat this weekend and start the "spring ritual." My scheduled launch day is May 12th.

Lyman

PS Nathan's site is also terrific. My favourite boat, other than the Shark, is the Alberg 30 so I am in general agreement with you fellows about what constitutes a great looking sailboat.

[Figment]

Hey guys,

I'm curious about why you'd want to use thickened epoxy in this application? Wouldn't you want the resin to be as "watery" as possible so it can flow easily into all the various voids?

Or is it more a concern of adding some kind of aggregate to hold the resin together, and less a matter of actually making the resin "thick"?

-MH

[dasein668]

I'm not sure how "thick" Tim meant. For bonding, the best technique is to wet out the area with unthickened epoxy, and then bond with a thickened mixture which will help fill and slight gaps or unevenness between the surfaces, and it helps to prevent resin starvation.

In this case, since Lyman will be injecting, I'd say in a sense that you are right, but I'd still go ahead and thicken the epoxy somewhat. Obviously, you'd still want a pretty loose mixture, but at the same time, you'll definately want the "gap filling" of a thickened epoxy. After all, the core and especially the underside of the deck skin are pretty likely to be somewhat rough.

The trick is getting the epoxy thick enough to fill the gaps between the skin and the core, while still being loose enough to "flow."

Oh, and Lyman: thanks for the kind words about my site!

[Tim]

This is a case where you want the "ketchup" texture--slightly thickened with cabosil in order to give it some structural integrity and to provide better adhesive qualities and strength, but still thin enough to flow.

He's not talking about trying to saturate core with thin epoxy; rather, this repair is all about filling an existing void while at the same time providing new adhesive qualities.

So, "thickened" epoxy covers a wide variety of options. I should have been a little more specific.

Tim