What would you change in this plan? (fiberglass part of a rotten core job)

[Rabe]

Last weekend I finished getting the rotten plywood core out of the section I am working on. While there is more to remove forward of this work area, I am limiting this job to just the area 2 foot forward and 2 foot aft of the port chain plates. This area is an "A" issue on my survey.

The existing fiberglass top and bottom will be used again in this project, while the water rotten plywood core with be replaced with small (5" x 5" max) pieces of plywood. The area is about 5 feet long by about 8-10 inches wide.

I have West Systems epoxy and extra slow hardener. I want as long of a working time as I can get. With the temperatures above 70F the extra slow seems to be correct. I also have 6 ounce cloth, although I don't think I'm going to use much if any. I have 6 ounce 2" cloth tape. The fillers I have are 406 and 407.

What I don't want do is get caught with too much to be done when the epoxy starts kicking off. This is why I'm thinking about my procedure so much.

Cut and dry fit every piece and making sure that chain plate holes line up correctly. (Chain plate holes should be a bit oversized so that I can epoxy fill the gap. Mark the pieces so I know where each goes.

4-6 Piece Batch

1. Start with enough pieces to go maybe a foot or less along the length of the work area, about 4-6 pieces.
2. I think I should wet these 6 pieces along the edges and the bottom face until it stops soaking up the epoxy. I want to leave the top uncoated until later.
3. After the plywood is soak enough epoxy, I will wet out the bottom fiberglass of the deck sandwich
4. Judiciously spread thickened epoxy (mayonnaise consistency with 406) over the bottom of plywood pieces
5. Position the pieces in their appropriate spot and weight them down with say bricks
6. Fill edge gaps with thickened epoxy

Repeat the 4-6 batch process until I get the entire 5 foot section done this far. This will leave the entire top area of plywood pieces without any epoxy on them.

Cover the area one cut out piece at a time

The deck sandwich top was taken off in 5 pieces, ranging from about 8 inches to a foot in length. Working with a single piece

1. Wet out the top of the plywood until it wont take any more epoxy
2. Wet out the sandwich top piece
3. Judiciously spread thickened epoxy (mayonnaise to peanut butter consistency with 406) over the top of plywood pieces
4. Position the sandwich top piece and weight it down.

Repeat for the remaining top pieces

Join the edges

Once the sandwich has cured I'll bevel the edges an inch on each side and cover it with 2" tape. That should be a big enough bevel for the 1/8" cut. It should be simple enough, maybe a one inch wide piece covered by a two inch wide piece. Covered with nylon fabric (Ripstop Nylon Fabric from Joann Fabric) as peel ply. That should work right? It's 1/2 to 1/10 the price of "peel ply / release film" and 100% nylon.

I'm sure some people may be able to finish this in 4-6 hours. But I think I am going to do one stage per day. Saturday, the plywood. Sunday the lids, Monday (holiday) the edges.

After that I think I'm going to take a couple weeks to see how things look and decide how to gelcoat it. Is there problem with waiting a while (weeks... a month... till spring?) without a gelcoat on it?


Thanks everyone!

-Rick

 

[sandpiper10471]

Bevels should be about 12 - 14 times skin thickness. Top skin is likely about 1/4 inch. Therefore bevels should be about 3 - 3 1/2 each side of the kerf. That doesn't leave a lot of original skin. Why I prefer to discard original top skin and use all fresh glass. I far prefer polyester resin for a repair like this. Faster, cheaper and plenty strong. Also compatible with a gelcoat surface. My 2 cents, having recored a lot of decks.

 

[Rabe]

Bevels should be about 12 - 14 times skin thickness. Top skin is likely about 1/4 inch. Therefore bevels should be about 3 - 3 1/2 each side of the kerf. That doesn't leave a lot of original skin. Why I prefer to discard original top skin and use all fresh glass. I far prefer polyester resin for a repair like this. Faster, cheaper and plenty strong. Also compatible with a gelcoat surface. My 2 cents, having recored a lot of decks.

Thanks Sandpiper,

Core is in and epoxied. Tomorrow I am going to grind off the squeeze out.

I'll post pictures tomorrow. I didn't get any today.

I thought the bevel had to 12 times the hole or in this case - kerf width. I'll have to figure something out. At 1/4 inch, how many layers of 6 ounce is needed?

 

[sandpiper10471]

I use 1708 stitchmat. About 1/16" per, or four pieces to a 1/4". I would guess you would need at least three times that many. Best of luck!

 

[Rabe]

Got the new core installed, epoxied and old skin put on. Still have to bevel and glass the kerfs this coming weekend. I was surprised at how easy it was to work with epoxy. I thought that given a 15-20 minute pot time I'd have to rush the whole job. But to my surprise it didn't really matter. The working time was long enough to work at a good clip.

Saturday, I got all the plywood pieces cut to size and dry fitted. The first piece with a chain plate through it I cut to much. The next two chain plate pieces I tried a different technique to only cut out enough for the chain plate. It worked pretty good. Was able to get everything leveled and dry fit with a little looseness to to all, in order to not have any fitment issues and to allow some squeeze-out to come up through.

Sunday, it took me about about 3 hours to install the plywood. 22 pieces totally about 6 feet by 10-11 inches. I wet each plywood piece with straight epoxy and I wet the area it was to occupy. I mixed up some thickened epoxy to a mayonnaise consistency and liberally applied it to the bottom of the plywood, enough to squeeze out of all sides. Repeating this for each piece and once all were in I went through and filled any edges that needed it with thickened epoxy. Weighted down, I left it to cure overnight.

Monday, I came back and ground down the high areas, roughed up and cleaned the chain plate pockets, and cleaned everything with some acetone. I made up a slide off sleeve out of painters tape by putting one layer down sticky side out, and then a second layer over top of that. Installed the chain plates with the sleeve positioned so the epoxy wouldn't stick to the chain plates. I filled the pockets with thickened epoxy and then set out to put down the 5 top skin pieces. Once everything was down, I again set bricks and cinderblocks to weight it down while it cured.

I went back today to prepare the area for some rain. After removing the bricks I had to make sure I didn't screw up the chain plates. That little tape trick I did worked like a charm. They pulled right out. Doing some soundings it appears that there is a 2 inch square that sounds like it's got a pocket. I don't know what I'm going to do about that.

This coming weekend I'll go back and bevel the edges, fill the holes and do something about that 2 inch area.

 

[kappykaplan]

Looks good, @Rabe !

 

[SamLust]

If I understand what you said you're looking to leave the holes large so you can glass in the chain plates? Sorry, but wrong approach . As it sails the boat as a system, works and flexes. That bond will very quickly break, leaving you with some pretty serious leaks. The approach is to leave room for sealant with enough leeway to flex without pulling apart. If I somehow misunderstood, just ignore me.

 

[Rabe]

If I understand what you said you're looking to leave the holes large so you can glass in the chain plates?

Not glass them in. But waterproof them by epoxy-ing the holes so that if a leak occurs water doesn't wick into the wood.

Kind of the same idea as the drill fill and drill again method for waterproofing drilled holes.

 

[DianaOfBurlington]

I’m sorry; but you are both overthinking and under-thinking this.

You lost me with your too-small pieces of plywood. What supports them? - the thin layer of ‘glass on the underside? Is that going to support the full load of the deck above? Why do you think they used plywood core at all? If you cut open the heavier upper layer and just patch it back together, what resists the flex loads? - the epoxy? Epoxy DOESN'T flex. It just cracks. And then what?

I have written about how to fix rotten deck core in these bulletin boards so many times that anyone doing a cursory search will find my answers. If you still don’t get it, please ask me and I’ll explain it. I started in this business in 1972. I started using Gougeon WEST epoxy when it was a new thing (c.1975). I've built and rebuilt plenty of composite/cored decks and fixed/improved all of the decks on my own boat. If you want to know, please just ask me.

In short:

• A thorough understanding on both technical and experiential levels is vital before altering any major structural component on a composite-materials sailboat (deck around chainplates being a prime example).
• WEST-system slow hardener was designed in Michigan for Florida whose users complained standard ‘205’ hardener was ‘too fast’. ‘205’ is NOT ‘fast’ hardener; it is normal for working temps between 60 and 90 degrees. I NEVER use ‘206’ hardener here in New Jersey. It’s meant for temps consistently over about 85 degrees - and even then there are ways to use ‘205’ if that’s what you have.
• Your concern about working time stems from a belief that you will have huge buckets of epoxy to work with. Using plywood, you won’t. It simply won’t soak up that much, owing to its internal glue, which is plywood’s great detriment with epoxy, and why I do not recommend your idea.
• Using epoxy in your core will inhibit anything but the most tentative bond between it and polyester-resin fiberglass on top; so, if you want to use gelcoat to finish it off, this is a compromised mend.
• Any cutting-out of plywood core in such small sections should be mended with fiberglass, not plywood. Chip out all the core you can reach from inside your hole and lay up the glass with thickened vinylester. If it’s a deep space you might stuff in a thin sheet of Coosa.

So in answer to your initial question, my answer is:

You should consider changing everything as about your plan after you cut out the deck from the top.

 

[Rabe]

I’m sorry; but you are both overthinking and under-thinking this.

You lost me with your too-small pieces of plywood.

I made them the same size as what they were originally.

• WEST-system slow hardener was designed in Michigan for Florida whose users complained standard ‘205’ hardener was ‘too fast’. ‘205’ is NOT ‘fast’ hardener; it is normal for working temps between 60 and 90 degrees. I NEVER use ‘206’ hardener here in New Jersey. It’s meant for temps consistently over about 85 degrees - and even then there are ways to use ‘205’ if that’s what you have.

I used the slow and it worked out perfectly. The time was exactly what I needed. Even though I bought the extra slow, I didn't use it. The temps was over 85.

• Using epoxy in your core will inhibit anything but the most tentative bond between it and polyester-resin fiberglass on top; so, if you want to use gelcoat to finish it off, this is a compromised mend.

So in answer to your initial question, my answer is:

You should consider changing everything as about your plan after you cut out the deck from the top.

I appreciate the comments. The job was finished 6 weeks ago. If I observe any problems I'll look into polyester-resin.