Deck question- plywood needed for screws?
 

Working on my deck now. I am using 3/8" divinycell, but was planning to use fir plywood in the "fastener" areas, like for the console and leaning post. Basically same as factory, where plywood instead of balsa. Now I am thinking I don't need to do that at all.... If I plan to over drill and fill with cabosil for all of my screws anyways, then why not use all divinycell?

Can you confirm my logic?

[QUOTE=ElBichoMalo;211293]Working on my deck now. I am using 3/8" divinycell, but was planning to use fir plywood in the "fastener" areas, like for the console and leaning post. Basically same as factory, where plywood instead of balsa. Now I am thinking I don't need to do that at all.... If I plan to over drill and fill with cabosil for all of my screws anyways, then why not use all divinycell?

Can you confirm my logic?[/Q


that will work,provided you use an epoxy,versus a polyester resin

personally,i use west system,mixed with 403,for this purpose...

Plywood is good cheap insurance...jmho

done in the method i described - removing the core,filling with epoxy - you can use threaded "machine" screws - example:if you want to use a 1/4 - 20 screw,just drill the epoxy 3/16",the screw will thread the epoxy.that screw will never loosen,nor will it vibrate out - however,need to remove,it will back out and tighten again - doesn't allways work that way with wood...

Why would it only work with epoxy? I was planning polyester...like I have used on everything so far. Is there a reason that that method won't work with polyester?

Island...I get the plywood has worked forever, tried and true...etc. But if I plan to overdrill and fill with resin anyways, the screw would never touch the plywood, so why is it cheap insurance? I don't really like the idea of screwing into the wood, and relying on the bedding or caulk to keep the water out. I get this distinct feeling of unease when I think about ever having to rehab to this extent again.

[QUOTE=ElBichoMalo;211320]Why would it only work with epoxy? I was planning polyester...like I have used on everything so far. Is there a reason that that method won't work with polyester? . . . /QUOTE]

The bond strength of epoxy is about 2000 psi vs. about 700 psi for polyester, so you definitely get what you pay for! For repairs where you're bonding new stuff to old polyester, I think epoxy is the only way to go. The cost of materials is sort of a nit if you figure your labor hours are worth anything at all!

Along the same lines, epoxy is not as brittle as polyester. It will give more before cracking. So a threaded hole in an epoxy plug will not be as likely to strip out as the same approach with polyester. That doesn't mean you have to do your layup with epoxy, just your plugs.

Dave

polyester resin/gel coats - these are brittle,not a good choice for holding screws...follow the method i described...

Makes sense. New plan: all divinycell w epoxy plugs. Thanks guys.