Backbone checks: new construction

[Seth Wood]

I've read (and dug up) various thoughts on this over the years, here and elsewhere, but I could use a "check" on my thinking.

I'm building a 30' traditional plank-on-frame sailboat. The backbone and stems are boxed-heart white oak, appx. 10" square. Big, I know. Boxed-heart, I know.

Okay. The trees were felled in winter here in VA, sat at the mill for a year, and then cut into my timbers. I slathered them with linseed/turps, let them sit for another 6-12 months, then shaped and assembled them.

Then they got CPES and 2 coats of thinned red lead. When the checking began, I dribbled red lead into the checks and then squished in Dolphinite. Except the Dolphinite dries out and pulls back from the sides of the check -- I'm guessing this is because the wood is pulling the oil out from the putty.

My new plan, and here's where I need the advice: mix up a warm witches' brew of beeswax, linseed oil, pine tar, and turps and pour/brush/squeeze it into the checks. Then once it cools, either dolphinite or more beeswax/tar mixture.

Then maybe some more red lead to seal it against future drying?

This is an unheated, dirt-floor shop in VA, so the ground's pretty damp. But I'm beginning to worry about these checks weakening the timber and I need them to stop long enough for me to get the boat in the water, 2-3 years.

Thanks for any advice.

[Bob Smalser]

Leaving the logs lay for a year before milling and boxing hearts are both practices that make significant checking the cost of doing business.

I'd keep them laying on the ground on stickers covered in sawdust before I used them. Remember they only dry at the rate of one inch of thickness a year, and the time spent in the log doesn't count, so they are still drying and you want that to be slow or you'll get even more checking.

And I'd use a poly sealant like 5200 or plumber's Vulkem to fill them....those checks move seasonally a good bit and what you stuff in there to prevent water ingress has to expand and contract with the movement. And never stuff anything hard in there or it may crack all the way through next season.

Keep your eye on them....any checks that weaken the timber structurally have to be reinforced by bolts/plates if the timber can't be replaced.

[ 09-30-2005, 10:25 AM: Message edited by: Bob Smalser ]

[Ken Hutchins]

What bob said, also EVERY time you remove any material from those parts, cover they immediately with paint or varnish to slow the drying and subsequent cracking. I personally use thinned varnish.

[Seth Wood]

Guys,

Yes, I'm familiar with treating freshly cut lumber to slow checking. What I'm asking about now is:

What is the best method of filling my existing checks to prevent them from spreading?

Bob mentioned 5200 or plumber's Vulkem. I'd prefer not to use 5200, as its tenacity worries me. And I'm not familiar with Vulkem.

The beeswax-pine tar-linseed oil mix I mentioned has been brought up here and in a number of books I've checked. Mainly I need to know if that's the best treatment for my checks.

Anyone? Surely deadwood checking is not so rare a problem that people haven't been able to find the best solution, or at least a workable one.

[Bob Smalser]

There's nothing you can do to prevent further checking in boxed hearts short of slow drying. Yards that used them built fast so as to get the vessels in the water where they'd season slowly. A one-man operation can't do that.

http://pic3.picturetrail.com/VOL12/1104763/7534648/98698786.jpg

This is where you want something that:

1) Stays stuck forever.

2) Stays flexible forever.

3) Remains watertight forever, expanding and contracting with wood movement.

Nothing does all of those perfectly...you will be monitoring those cracks for the life of the boat...but adhesive poly sealants come the closest, from my experience. Beeswax and pine tar don't even come close.

When the 5200 does deteriorate, just pump in more....it sticks to itself very well:

http://www.woodenboat-ubb.com/ubb/ultim atebb.php?ubb=get_topic;f=1;t=011982 (http://www.woodenboat-ubb.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=011982)

Vulkem is merely a 3-dollar-a-tube version of 5200 that isn't quite as adhesive but seems to take paint better.

[ 10-01-2005, 08:17 PM: Message edited by: Bob Smalser ]

[Don Kurylko]

I have read that automotive antifreeze does a very good job of slowing and even reversing checking in timbers. It apparently also replaces (expels?) moisture and acts as a rot inhibitor. The main ingredient in antifreeze is glycol, which is what is used in preserving wooden artifacts that have been recovered from underwater archeological digs. It is also compatible, when dry, with most Marine finishes, including Epoxy. It’s supposed to work wonders on old, dried out wooden decks - the trick is to lay it on pretty heavy. But keep your pets away from it. They love the taste of the stuff and it will kill them!

[Adamant]

I've packed white oak in sawdust kept moist to slow drying to good efect. Bob S."s methods of repair of checks is excelent. If the piece is totaly dry and final cut I would red lead it.

[Seth Wood]

OK, thanks for the replies, everybody.

[Thorne]

Rather than start a new topic, I thought I'd ask here since I think the answer is Bob's just above.

I'm removing several coats of paint from my 18 year old Chamberlain dory skiff built of fir over oak, and finding some gaps in between the gunwales, the curved board laid on top of them (capping?) to raise up the oarlock blocks (or whatever they are called) and the blocks -- not to mention the odd gap elsewhere.

http://www.luckhardt.com/gunwale.jpg

Since I want to finish the gunwales bright, as well as the outside of the transom, what should I use to fill these gaps? The previous fellow used epoxy in some, putty of some kind in others, and various unknown substances that are all somewhat decayed.

I can live with the filler being a different color than the oak and fir, but would like it to stay put, swell and shrink with the wood, and take varnish (and maybe stain??) well.

Any suggestions?

[ 10-05-2005, 12:05 AM: Message edited by: Thorne ]

[Bob Smalser]

Those pieces don't move seasonally anywhere near as much as checks in a heart timber.

I use dyed epoxy for cosmetic fills under varnish. Unlike putties and wood fillers, it stays put forever.

http://www.woodcentral.com/cgi-bin/readarticle.pl?dir=smalser&file=articles_403.shtml

But I'm not sure I'd varnish anything on your skiff. Besides all the work...and damage...of getting all that paint out of recesses, your dory is a heavily-built work boat that wouldn't have originally had varnish on anything.

[ 10-05-2005, 09:44 AM: Message edited by: Bob Smalser ]

[Thorne]

Bob - Thanks for the prompt reply.

I really am paying attention, even if it seems otherwise - honest!

;- )

I guess I'm going for varnish cause its a wooden boat which is rare out here, and also to flaunt the solid wood construction -- much rarer, but will still leave a lot of her painted.

I'll use epoxy with glass microbaloons for the gaps -- any suggestion on dyes? I prefer to use the local products from Smith & Co. - http://www.smithandcompany.org/

This weekend I'll take your advice and pull off the false plywood bottom and sand off the red lead bedding between that and the plank bottom. Then I'll attach the replacements for two semi-rotted cleats I removed - starting the screws from underneath.

Don't know if red lead can still be bought here in the SF Bay area, but I'll check some of the Marine consignment/flea market stores in Sausalito and see what I can find. Otherwise I'll use copper bottom compound/paint to bed the cleats as well as the replacement false bottom, then paint over them.

And I've ordered the plans from Mystic Seaport, so I'll know where to place the centerboard case, how to build the rudder, place the mast, etc.

Thanks again!

[ 10-05-2005, 01:42 PM: Message edited by: Thorne ]

[Dave Fleming]

Thorne, email Gary Bergman at this address:

orcaboat@sbcglobal.net

He is an old Sausalito hand and he should know all the good places over there.

[Bob Smalser]

Ask Smith's what dyes they have available.

West sells epoxy dyes, as does Brownell's....and any aniline dye in powder or alcohol-based paste will probably work.