Opinion Needed - Wood Options for Cabin Roof Replacement

woodster · Oct 11, 2011

ASH, WHITE OAK, MAHOGANY, SAPILIE,and or ANDAROBA..

arswann77 said:
Hello all,

This is a follow up to a post I did last month "A Little Off the Top" - I have a 1972 Oday DS II and the PO cut the roof off the cuddy cabin. I want to replace using wood ribs, marine ply and a bit of fiberglass. I am an amateur, so I'm taking my time this winter using the trial and error method of construction.

I was going to make the ribs out of marine ply with small nailing blocks to attach the roof to, but when making rib templates this weekend out of a spare 1" x 6" pine - I really liked how light and sturdy the ribs were when cut to shape.

My question/s: if I were to use untreated pine for the ribs what is the best way to treat it to avoid rot? Is several coats of paint enough? Is there a specific product out there?

The ribs will be covered with at least a 1/4" of marine ply and a coat or two of fiber. Is this doable or a horrible idea?

Any input is greatly aprreciated...
AR

....but not pine...in your part of the country you should have very good sources for ash ......i dont like pine for much of anything other than when doing anything other than framing a house or barn too soft and will rot very quickly ........

regards

woody

kendall · Oct 11, 2011

If you've ever worked in reconstruction of Victorian and colonial era homes, you'd find that it was pretty standard practice to faint each piece before assembly, that way every surface is covered and protected. Modern cut/install/paint when finished practice leaves everything dependent on a hair thin layer of paint/varnish to span the joint and keep moisture out of laps etc.

It's a habit I developed for nearly any project. dry assemble, tear down then paint/varnish, do the final assembly, then final finishing with whatever paint or varnish I intend to use.

You can buy the same 'potion' they use for pressure treating wood from various suppliers, it goes a long way towards extending the lifespan of wood, but bear in mind you will most likely be painting it on, so the penetration won't be that deep, and most steps taken to extend the life of pine would increase the cost and time required enough that there's no advantage to using it.

From experience of replacing a few bulkheads and braces, I've found that a lot of 'rot' is started when braces and bulkheads etc are left with no way for accumulated moisture to drain out, the moisture normally accumulates at the lowest point and starts rotting out the wood. So typically, I paint the edges with resin, then when I tab them in I leave the edge on the lowest point un-tabbed, that way any moisture that gets in, has a way out. No matter what you do water will get in, so always provide a way for it to get out.

mitiempo · Oct 11, 2011

You shouldn't need large beams. I would look at cutting temporary beams to the proper curve and then temporarily installing them. Cover the areas adjacent with plastic so the epoxy doesn't stick and mess things up. The top could be made of several layers of thin ply, 1/8" being a good choice. The first layer is cut to fit and attached to the frames with finishing nails. Each successive layer is epoxied to the preceding layer and weighed down until the epoxy sets and/or stapled. Remove the staples after the epoxy sets. 3 or 4 layers should be enough. After all layers are finished remove the assembly and pull the frames off - the finishing nails should pull through or can be removed with pliers. A light layer of fiberglass cloth and epoxy will finish the interior and possibly a heavier layer for the exterior. The assembly can be attached to the boat at the edges and will hold its shape without beams.

higgs · Oct 11, 2011

I am out my league here, but wonder why pressure treated wood would not be a good choice.

kendall · Oct 12, 2011

higgs said:
I am out my league here, but wonder why pressure treated wood would not be a good choice.

Most often, pressure treated wood is pretty much trash wood, full of knots and bad grain issues, and it's typically soft pine. It's also softer, not as strong, and far more absorbent than natural untreated wood. Take a treated stud or sheet of ply, and put it outside along with it's untreated counterpart for a while, and the treated wood will absorb water and warp at least twice as fast as the other. The chemicals used to treat the wood are also caustic, and tend to eat fasteners

mitiempo · Oct 12, 2011

Whatever wood is used it's future depends on it staying dry. Epoxy should be used on any joints and it should be totally epoxy and glass covered. I agree that pressure treated wood may not bond well, and is not great wood either. If using ply use exterior grade which is made with waterproof glue. Marine ply will not be required as it will be glassed over.

Pressure treated is good for patio decks and fences though.

higgs · Oct 12, 2011

Thanks for the info on pressure treaed wood.

kloudie1 · Oct 12, 2011

If ya really want to make the wood not rot, first ya have to not get in a hurry and use 4-5 coats of copper naphtenate, put on after all the finishing work (sanding, shaping, drilling, etc) is complete .. it really stinks for a few months so after you soak the wood in it, the parts should be left to dry for a couple of weeks before working them.. Nasty stuff so you'll want to wear gloves. Ya can find it in places like Home Depot in spray cans.

mitiempo · Oct 12, 2011

Agreed, but it would not be necessary or wanted with epoxy/glass coating. Often used on carvel planked wooden boats.