Replacing core: nidacore question

[JH_B28]

Hi guys,

I'm in the process of replacing the wood core from my b28 cockpit deck and engine lid covers. For the cockpit deck, I will be using 3/4" h-80 divynicell epoxied to existing skin and laminated with 2 layers of 1708 (need it to support a lot of weight). For the engine covers, I have some extra nidacore sheets that I was thinking of using but I have never used it before and have some questions on how to bond them to the existing skin:

1) what is the best way to bond the nidacore sheet to the existing FG skin? Should I prime the scrim with resin, laminate a layer of glass, wait until it dries and then bond with thickened epoxy? Or, just wet the scrim with unthickened epoxy and bond to skin (with weights on top).

2) for both cores, nidacore or divinycell, I know the resin that should be used to bond the core to the existing skin is epoxy. Can I use epoxy for bonding and then use poly resin to laminate the whole assembly? ( thickened epoxy to bond, then 2 layers of 1708 with polyester resin over the core) To reduce resin costs a bit. I was told both cores are compatible with both resins.

Many thanks in advance,

-G

[JH_B28]

Anyone?

Just did one of the floor lids with 1/2" nida core, 2 layers of 1708 on each side and it is very stiff! I didn't think it would work out so well.

Here's a pic of the floor layout I am building with the big fish boxes on each side.

[Kevin]

http://bertram31.com/newbb/viewtopic.php?f=2&t=10129

I don't know anything about that product. Looks like you have a massive project going though.
I might suggest modifying the engine hatches while you are at it. The link to my project is above (with pics) if you had not seen it. One of the best modifications I have ever done to the boat. Not a drop of leaking water........EVER!

[CaptPatrick]

Can I use epoxy for bonding and then use poly resin to laminate the whole assembly? ( thickened epoxy to bond, then 2 layers of 1708 with polyester resin over the core)

JH,

Nope! You can stick epoxy to polyester, but polyester will not stick to epoxy...

[STraenkle]

ask me how I found this out, put west system on the coosa cockpit floor panels, then gelcoated. scraped it off with a putty knife after 2 days of hoping. put marine 3M "bondo" skim coat and tried again. that worked. what a mess and waste of time.

[JH_B28]

http://bertram31.com/newbb/viewtopic.php?f=2&t=10129

I don't know anything about that product. Looks like you have a massive project going though.
I might suggest modifying the engine hatches while you are at it. The link to my project is above (with pics) if you had not seen it. One of the best modifications I have ever done to the boat. Not a drop of leaking water........EVER!

Kevin,

I am actually working with the engine hatches too. I was thinking of doing your modification (one piece hatch). It looks very nice!
Going to use the nidacore for coring. Here are some progress pics:



Found some rotted wood along the way...

Ready for core




Thanks for the link, I couldn't find the thread.

[JH_B28]

[/quote]
JH,

Nope! You can stick epoxy to polyester, but polyester will not stick to epoxy...[/quote]


Hi Capt Pat,

What I was referring to was to use an epoxy putty (epoxy & cabosil/milled fibers) to bond the core material to the existing skin only. Then, on the other side (no epoxy), use polyester resin to laminate the core. There should be no polyester over epoxy in this method but wanted to have a pro's opinion, just in case.

The thing is we don't have access to biaxial 1700 here in PR and wanted to avoid the excess resin (additional weight) when using 1708 with epoxy. I have a roll of 1708 in my shop.

Thanks again!

[CamB25]

I would think that thickened poly would be fine to bond the core to the old skin. I would skip the "milled fibers" as I don't think they serve a purpose in this application. In fact, why not use some construction adhesive and call it a day - West Six 10, or even a poly-based "home depot" adhesive. You'll be laminating glass over the other side of the core to finish the hatch - use poly and fill the weave with gel coat when it kicks.

[CamB25]

As for weight, I don't think there will be a measurable difference between the resins and a minor difference with the 8 oz chop. You could use peel ply and vacuum bag the hatch to pull excess resin out of the lamination. Other than that, I do t know how to dramatically reduce the qty of resin in a hand layup. Your new core is already much lighter than plywood. 2 layers of glass and declare victory!!

[JH_B28]

Cam,

You're right. The difference in weight between resins would be negligible. I think I'm going to go with Poly resin for the lamination, as I can buy the gallon @ $30 vs. $100 + for the gallon of West System.

Thanks for the info!

-G