"Dry" delamination from repeated load/flexing?

[HeelBoy]

Is moisture intrusion the only cause of delamination?

There is one spot in the cockpit that emits a loud “CRACK” when I step on it. This spot is were everyone Boarding the boat steps, and everyone entering or leaving the cabin also puts a foot here. It is probably the most frequently trodden spot on the whole boat (Macgregor 25).

The observable symptom says “delamination”, and it’s hard to imagine it being anything else. But, close examination shows no means for water to intrude. Is it possible that this delaminated due to repeated flexing stress rather than moisture intrusion? If this is a the case, would a moisture meter be a viable tool for checking?

I ask because the drives what my fix will be. If the core is dry and intact, I’d like to drill, very carefully, from belowdecks through the plywood core, stopping just as the drill bit touches the cockpit floor’s fiberglass layer. I can inject epoxy from back here without compromising an apparently good cockpit floor (see attached sketch).

 

[dlochner]

Macgregors were not noted for being over built and no one expected these boats to live 30 or more years. With that said, drill a couple of test holes from the bottom to see if the core is in fact dry. If it is dry, the cause of the cracking is probably the light construction and repeated stressing from people stepping on the area. Simply shooting some epoxy in there might not be the best approach. Reinforcing it from below with stiffeners might be a better approach.

If the area is wet, cut the inner skin off to expsose the wet area. Remove the core and replace it with something a little thicker and replace the inner skin with new glass and resin.

 

[HeelBoy]

Simply shooting some epoxy in there might not be the best approach. Reinforcing it from below with stiffeners might be a better approach.

Definitely a lightly built boat, but ease of towing definitely has its perks.

I had considered some "joists" running abeam under the cockpit sole. I have a means of molding fiberglass fins, I think I can do it upside-down. lol

So... that in combination with an epoxy injection? Is there something better than unused/empty calking tubes for injecting the epoxy?

 

[jssailem]

Using the approach from underneath is one alternative.

If it is dry and you want to just stiffen the interior of the shell, here is another idea. After you for the two bottom holes and it is dry, then put 2 or three holes through the top skin of the affected deck area. Apply penetrating epoxy into the top holes. The epoxy will migrate through the space and to the bottom holes. When you are sure it has reached the bottom holes, plug the hole and put gorilla tape over them to keep the epoxy from flowing out. Now go back and continue to fill the top holes till you get epoxy at the surface. Let he epoxy cure for several days. Once cured clean up the holes, add faring compound if needed and then cover with gel coat color matched to your boat. This will give you a solid core and help to reduce the noise. Depending on the amount of air space you may have to add a fair amount of epoxy.

I used this technique to address a similar issue on my Montgomery 15. When finished I had a leak free solid deck that supported my mast step.

 

[jssailem]

injecting the epoxy

I buy syringes in bulk and use them to inject epoxy.

Here is one source.

Epoxy Syringes

Reusable epoxy applicator syringes for injecting epoxy or other adhesives into tight spaces. Available in 12cc and 60cc sizes. Sold in packs of 5 syringes.

www.totalboat.com

 

[Davidasailor26]

Penetrating epoxy travels well in rotten porous wood. If the core is still dry does anyone know if it would spread out as well in solid balsa, plywood or whatever Macgregor used in the core?

 

[Tedd]

"Dry" delamination used to be a problem with fiberglass skis from the era when that boat was built, so it's not out of the question.

As others have said, I'd be inclined to reinforce it from underneath if that's feasible. Remember, the resin essentially contributes nothing to strength, it's just there to hold the glass in place and transmit load to it. If delamination has created a void then just injecting in resin may not make it stiff enough to avoid future delamination. On the other hand, if you get another 30-40 years out of it maybe that's enough!

 

[rgranger]

Do Macs even have a core?

I’d fiberglass a foam stringer from underneath to stiffen it

 

[dlochner]

If the core is plywood, dry delamination is not surprising. Plywood will have large areas of very dense wood which does not adhere well to resins.

Inexpensive cores to supports can be made from blue building insulation foam. In this application the core is not providing the strength, the skin covering the core is providing the strength and rigidity. Cut triangular shapes, glue them to the inner skin and then glass them over with epoxy and several layers of 1708 cloth.

Pay particular attention to the edges of the panel that is delaminating, There is no core in this area and the glass may be too thin, allowing the the horizontal surface to flex which contributes to the delamination.

 

[PaulK]

granger and dlochnerl have the right idea. Injecting epoxy into the deck may create a big "hard" spot that might cause cracks around its edges. (Think of jeans that get paint on them. The paint hardens and then the jeans tear where the fabric bends next to the paint.)

 

[Dalliance]

Dry delamination is certainly possible and you can confirm it with a moisture meter.
A friend on my dock had the same thing happen in the cockpit of his Catalina 30. His solution was to inject epoxy, as you propose, but from the top, then fill the holes flush and repaint the non-skid with Kiwi Grip. Actually I think he may have done the Kiwi Grip the year before and then just touched it up.
Anyway. Injecting from the top allows the epoxy to go in and spread by gravity and capillary attraction. Injection from below is likely to run back out and make a mess.

 

[JBP-PA]

In addition to above ideas, if this is a small spot where people step, you could reinforce it from the top as well and call it a step. Add a few layers of 1708, paint, and one of those black grit nonskid pieces and pretend it's is intentionally a step.

 

[dLj]

Do Macs even have a core?

I’d fiberglass a foam stringer from underneath to stiffen it

That's what I was asking myself. I'm not sure they do.

In any case, easy enough to find out. Support stingers sound like a good addition...

dj

 

[jnorten]

When I bought my '82 Catalina 30, my surveyor used several colors of chalk to mark the deck. One color showed delamination. A second color showed moisture. A given area could have either or both colors of chalk marking it.

My boat had some voids between the outer fiberglass skin and plywood core (cockpit sole and cabintop). Many of these voids occurred when the boat was built. A slurry of resin and sawdust was used to bond these two layers, but the slurry did not always fill 100% of the space.

I had a shoe sized spot in my cockpit sole. It was right where folks tend to step from the seat down onto the sole while boarding. 40 years of this stress and the delamination became obvious. I cut a small square out to inspect. No rotten core, thankfully. But, I could see the missing areas of slurry. Instead of doing a full cockpit sole restoration, I did cut out a slightly larger chunk to verify my observation. After seeing only more of the same, then I replaced the core in that small area. I glassed and faired over the new core to match the existing deck height. For the remaining delaminated area (maybe 2 square feet max), I drilled a grid of holes into the core. I then injected epoxy into the holes. You could kind of tell where the voids were while drilling, and really tell while injecting epoxy. The epoxy would sometimes flow out several holes away from the injection point. I redid the sole with KiwiGrip and it looks awesome. You cannot tell surgery was performed.

 

[dlochner]

That's what I was asking myself. I'm not sure they do.

In any case, easy enough to find out. Support stingers sound like a good addition...

dj

Plywood is cheaper and lighter than glass and resin.

 

[dLj]

Plywood is cheaper and lighter than glass and resin.

I didn't realize it was lighter.

I guess cheaper depends upon what you have laying around...

dj