coffin cover recore adhesion/bonding?

[aquaprouts]

I know this topic is well covered but have a few questions on the best approach.  I have removed the 1/2" wet coring from my 196 coffin cover and prepared/sanded the molded glass panel to accept my newly cut plywood insert.  From what I have read, I should poly resin the virgin plywood, let dry,  then adhere this panel to the molded coffin cover using poly and or epoxy using heavy weights on a flat surface.  Should I lay 1/2  oz fiber matting on the molded cover before brushing out the poly( or epoxy) and setting the plywood insert.  Should I use epoxy or poly to set the plywood panel to the molded cover? I am worried about the working time of poly here.   Will epoxy bond to the poly coated plywood if I choose epoxy as the bonding agent? To finish the encapsulation, I was planning on using poly and biaxial cloth(what oz here please?...6?) matting to entirely seal in the plywood and further strengthen.  I could also use epoxy in this step if necessary and if any benefit.    Would a combination of epoxy and poly make sense in my application(it seems perhaps better adhesion using epoxy as the first step?)?  How many quarts total would you think necessary to accomplish this task?  I live up in Massachusetts so cold temps here now.... a benefit using epoxy of poly given the winter now?Thanks for your sharing your knowledge!

[gran398]

Would go all epoxy. Wet out both the rear of the coffin with epoxy, and one side of the DRY plywood you're affixing. Then slather on adhesive-thickened epoxy as the sandwich.




Let that set up with the weights you've mentioned. Then come back over it with cloth and epoxy. Then some bilge paint, etc. to finish. Done deal.

Doesn't have to be real pretty. No one will see it since it faces the tank.

 

[GoneFission]

You might be making this tooooo complicated.  It can be pretty simple:

1.  Tape over any holes on the outside of the shell now that you have the old core out.
2.  Cut the new core to fit the shell - if you going to keep the deck plate - cut it later.  
3.  Drill 1/8" holes on a 2" x 2" grid in the new core to allow air and resin to escape
4.  Put the shell face down on a flat surface with plastic sheet under
5.  Mix up about a quart of the resin (I don't think it matters between epoxy and poly) and pour/spread out inside the shell to about an even thickness
6.  Fit the core into the shell - put some cinder blocks, bricks, or something else heavy on top
7.  Use a putty knife or other blade to spread the resin as it oozes out of the holes
8.  Let it sit overnight or until the resin sets - you don't need a complete set - tacky is OK
9.  Cut your glass cloth or mat to fit the inside of the shell
10. Mix up another quart or so of resin and spread it evenly on the new core
11. Lay the cloth/mat on the resin and wet it out with more resin
12. Use any excess resin with some chop or glass pieces to fill any gaps around the edges between the shell and the core
13. Put another layer of cloth/mat down if you want (I recommend) and wet it out with resin
14. Let the whole thing set overnight or until the resin sets
15. Use a grinder to trim excess cloth from the edges of the newly-cored panel
16. Turn the panel over, take the tape off, and clean up any resin that seeped through the holes with a scraper  
17. If you are keeping the access/deck plate, use a hole saw or saber saw to cut the hole using the old hole as a template
18. Test fit the pie plate/deck hatch to make sure it fits
19. Drill 1/4" holes through the core where the hold-down screws go
19. Seal the edges of the hole cutout and screw holes with resin to prevent water intrusion/rot
20. Caulk and install the pie plate/deck hatch
21. Clean the edges of the coffin where the cover goes in and squirt a good amount of caulk around the edges for bedding
22. Install the newly-cored cover and screw down - squirt a little caulk in each hole before putting the screw in
23. Caulk the seam between the deck and the cover
24. Have a cold one, sit back, and admire your work!      

Hope this helps - good luck!

[RickK]

Capt John has a good description/plan and I agree that it doesn't matter what resin you use in this application.  I would add that if you're using poly I would lay a layer of 3/4 or 1.5oz matte under your wood, that will help it adhere to the old substrate.  If you go epoxy you don't want to use matte but can use a light cloth to help.  Gran's approach also will work with a thickened resin (I would still put a light cloth under the wood to help the bond and then finish up with the cloth on top all wet on wet.
I would make sure to bevel the top edge of your wood so that the cloth or matte transitions to the base substrate easily.  For the outer/top layer of cloth/matte I would roll it up the inside of the lid lip if you can and if you can do all of this wet on wet you'll get a better bond.  Just lay plastic under the hatch and on top of your last layer before you put the blocks on top to weigh it down and make sure that whatever you lay the lid on is flat so the product ends up flat and the wood doesn't slide down where you weren't expecting it to.
My $0.02

[wingtime]

I used poly on my coffin cover recore.  But I used a high quality poly resin and i made sure I had roughed up the inside of the cover so the poly would have some good tooth to bite into.  I used Akume plywood.  I don't have that boat anymore but I'm sure it is holding up fine.    Here is a link to my coffin cover rebuild:  viewtopic.php?p=27958#p27958

[slvrlng]

I used epoxy and divinycell for my coffin cover re-core. It now weighs about 35 lbs. here is the link to my thread about the repair.

http://classicaquasport.com/smf/index.php?topic=6907.0

I did lam a layer of mat down first as I had quite a lot of resin starvation in the original layup.