Coosa board

[makomike1]

Hello, I have a Bertram 28 replacing partially rotten bulkhead behind and in front of motors close to bottom of bilge.I am going to use coosa board. But I have never worked with this material before. Do I have to prep the coosa board before I fiberglass it to the good wood remaining?. Does the coosa board need a layer of glass to it before I attach it to good wood? Can I use fiberglass resein or west system ? Also what type of fiberglass would you recommend using, Matt or roving to tie into good wood? Thanks MakoMike

[Navatech]

Can I use fiberglass resein or west system ?

West System is essentially an epoxy (two part) glue… Fiberglas resin isn't… In fact, unless you attach something to fiberglass resin that hasn't fully cured yet (i.e. it's still "green") you don't get good adhesion… For that reason alone I would recommend using the West System (or any of the other marine epoxies: System Three Epoxy, Silver Tip, Marinepoxy a.k.a. E-Poxy)…

[CamB25]

Sounds like you are planning to lap the coosa over the existing "good" wood? My approach: Use epoxy for the bond between the wood and coosa. Sand the interfaces with 80 grit. No need to glass the coosa at the bond. If you want to finish the visible surfaces, I would glass the coosa before installation using epoxy or poly, then tab the coosa panel to the hull and the remnants of the bulkheads. Pull a generous filet at the lap joints with thickened resin first and let it harden up for a few hours before you tab over with fiberglass. You probably do not need a heavy weight glass...it is not a structural joint?

Do you have pictures?

[makomike1]

Actually I have cut out the rotted wood, it was worse than thought, went from one side of engine bed stringer to other side of other engine bed stringet down at bilge. I want to put the coosa board where the rotten wood was. Its about 8inches high and goes agross bilge. So actually im replacing the rotted wood.Dont know if i needed to put glass cloth on the coosa board. I plan on using filets at each corner where it meets engine bed. Than glass the corners over top of the filets to tie in with engine bed stringer. Any other suggestions. Thanks Mike

[Raybo Marine NY]

I think the question is do you have to glass the coosa?
Yes you should, i would suggest glassing it after you have it cut and fitted but prior to glassing it into the boat. Use poly or vinyl for that.
You can then epoxy it into the boat

[makomike1]

Thank you Raybo marine, that was exactly what I was asking. You answered my question.It may have been confusing the way I was explaining what I wanted to know.Thanks alot Michael Weiss

[Marlin]

Used 20 plus sheets of coos a on my 31 rebuild, words of caution,u ain't cutting plywood, when u start to make the pieces to fit were protective garb, a big fan blowing the dust particles downwind, the captain has a saying ,fiberglass ain't your friend, coosa will become your worst enemy, when cutting it creates a sand like particle that's very tough on soft skin tissue, I literally locked up the bearings on a hand circular saw after a few cuts, found some special blades for my scroll saw at Lewis Marine that really held up well, regular blades were dull after several minutes, coosa has a layer of cloth embedded into the foam on each side slightly below the surface in addition to shards of glass mixed into the sheet of material, wash the areas to be bonded with lots of alcohol, prime these areas with a diluted epoxy,maybe 20% alcohol! my internal bulkheads and aft bulkhead were all finished off with a troweled coat of thickened epoxy! sanded primed and painted! I tabbed all attached hull areas with several layers of 1708 and worked the epoxy in with a bubble breaker, several years of use in some heavy seas and the bonds have held well as well as the painted finish,no need to cover the entire area with cloth