Fixing delamination

[brainiac]

I'm new to sailing, and last fall I bought a low price 1978 Mac 2-22. I've been doing minor cosmetic repairs and cleaning. Today's project was to replace the original ceiling carpet.

Once I got the old carpet out, I noticed delamination in two places. One area is significant, about 1 to 2 square feet, and the other is just starting to fail. Both problems are caused by water seeping through the hardware penetrations.

http://cid-ae3d190ae1637b35.skydrive.live.com/self.aspx/Delamination%20area/IMG^_6246%20-%20Copy.jpg

From my inspection, I think there is mold filling the separation void. Both top and underside surfaces are fine.

It appears some previous owner knew about it and re-enforced the plywood in the dinet area. After removing the reenforcements, the area is soft and crunchy.

I would like to repair this properly before putting the ceiling carpet back on. I'm not sure the best way to proceed and am looking for advice. Thanks!

[paulk]

To repair delamination properly, you have to know how the structure was put together in the first place. Is there (was there) balsa core, foam, or plywood used between the layers of fiberglass? There are a number of ways to fix delaminations. They depend upon how big the areas are and how much work you want to do. Sometimes you can just inject epoxy in between the delaminated layers and (with a bit of convincing; clamps, pressure, weights, sticks, etc) get them to stick back together. Other times the core material has rotted and needs to be replaced. You have to remove one side of the delaminated area to get at the rotted core. We had a large area of our hull delaminate, and we approached it from the inside, so as not to mess up the awlgripped outer hull. Rotted core material needs to be removed and replaced - generally with the same stuff. If you change the material, it can create hard spots that will cause problems. Wet core material can also be replaced, or if it's in good shape, it can be dried out and re-glassed. Drying out can take a LONG TIME. After fixing the core, new fiberglass needs to be layed up over the patch, hopefully following the same schedule as the original layup. (When you create the opening, at a fine angle, you should be able to uncover the different layers that were used in the original layup.) When you're done you can sand it smooth and paint or gelcoat over it: good (or better!) than new. This is only a rough idea of how to approach this problem. There are books (long ones) that go into more detail and cover various nuances that you may encounter. Most things are fixable. Good luck!

[brainiac]

It appears the core is a marine plywood about 3/8" thick, making the total thickness about 1/2". I have full access from the underside, and was on my way to covering it again following the original plywood/carpet design.

If I were to cut out the bad portions of the plywood, how do I ensure the replacement edges have an adequate connection to the existing good plywood?

[sailingdog]

scarfing the edges at a 8:1 bevel is the typical way to scarf in a repair, but may be both overkill and almost impossible to do in this case. However, cutting it at a 45˚ bevel and bedding the replacement piece in thickened epoxy would probably be a good start, making sure the edges are well coated with thickened epoxy.

[brainiac]

OK - I put another hour into the project and have some discoveries. First, the inner layer where the majority of the problem lies is just a single layer of fiberglass mat. Fiberglass gets much thicker at the edges.

I decided to cut away the entire thin area that was easy to peel away. Now I have edges toward bow and stern where the ceiling fiberglass and inner plywood are as-one, a laminated assembly.

The next discovery was a seam in the plywood. The bad piece is the one on the outside edge of the boat (since water drains that way). The piece toward the center has not rotted and is just slightly damp on the edge.

Now, I've got the wet wood removed, and have a fairly sloppy shape to fit, with one edge that is straight.

I am wondering how I should fill the core. If I use plywood, which I have enough from the original ceiling carpet backing, I'll have a difficult time getting all the edges to fit well. The surface is curved in multiple ways.

Alternatively, I have a bunch of scrap red oak that I can shape to size, in strips. Red oak is not a good boating wood, but it seems to me if any wood gets wet in this way, it is done; the water is trapped, so penetrations must be sealed well.

I was thinking the oak would perform best because of its stiffness. And if I made two layers of 3/16" thick each, I could run grain perpendicular. This would allow me to tuck some of the pieces into a few voids where wood was removed but inner fiberglass is still in place.

I have an epoxy adhesive to apply as a bedding to bond to the top fiberglass, and clamp. Then I was thinking liquid nails between oak. Then re-glass bottom fiberglass.

Too McGuyver? I'm open to suggestions.

[tommays]

I found balsa core to best and done in 6" X 24" sections to insure you have good contact with the outer skin

If you try for to much in one shot you will get voids that let it flex

[sailingdog]

I'd recommend going with Baltek ContourCore end-grain balsa. This is a far better core material than plywood. Plywood is a lousy core material for several reasons—first, it is heavy compared to end-grain balsa or foam; second, it has the worst characteristics of both balsa and foam—it rots like balsa, and allows water to quickly migrate and delaminate large areas of the hull like foam can.

Use a thickened epoxy to bed the new core material and then layup a proper lower skin of laminate using epoxy resin.