Caulking Confusion

[David McCollum]

The more I read about caulking, the more confused I get. Everyone says do not caulk a dry boat. Yet, when a boat is built new, isn't that a dry boat? The planks are air dried lumber. How is it any different when an old boat sits out of the water and gets air dried?

[Bruce Hooke]

Here's my guess, and it is just a guess...

When a boat is new, the planks are about as close together as they are going to get (if the boat was built well). So, when the planks get wet and swell up most of what happens is the edges of the planks get crushed a bit. When the planks dry out again this crushed area does not fully rebound, so then you have a gap between the planks. However, when the planks get wet again there is now room for them to swell up so if you have not caulked the planks swell up so that they are as close together as they ever were. However, if you do caulk when the planks are dry then the wood crushes more when it swells up, so when you pull the boat out again you have even larger gaps. What is going on here is something called "compression set".

[Bob Cleek]

Bruce is right.

[Bayboat]

A well-built new carvel hull has seams in which the plank edges are together (touching) along the inner two-thirds of their thickness. The outside third of the seam has a slight bevel to accommodate the caulk (cotton or oakum) and the seam compound. When caulking a new hull an experienced caulker will go pretty easy with the mallet and iron, hitting just hard enough to get the stuff into the seam, but not enough to force the caulk hard. With paint (preferably red lead)and seam compound to hold the caulking stuff in, the wood-to-wood part of the seam will close tight, the outer third will also close a bit, but not enough so the wood edge is damaged by caulk that is forced too much. The seam compound will squeeze out somethat, which is why you don't put a nice finish coat of enamel on a new hull. Use semi-gloss or flat the first year.
The above describes the pretty ideal situation. In caulking an older hull that has aready exerienced some shrinking and swelling, a good caulker reads the situation and pounds accordingly. Some factors he takes into account are how long the hull has been drying out; the kind of wood; the width and thickness of the planking; the condition of the seams; the condition of the fastenings; how the iron acts when hit; and how the iron and mallet sound when the caulk is hit.
Good caulking is an art that takes quite a while to learn. There's a lot more to it than just pounding stuff into the seams. It's easy to wreck a hull if it's not done right.

[ 05-13-2005, 06:27 PM: Message edited by: Bayboat ]

[Dave Fleming]

A well-built new carvel hull has seams in which the plank edges are together (touching) along the inner two-thirds of their thickness.

***This is referred to as "outguage".

The outside third of the seam has a slight bevel to accommodate the caulk (cotton or oakum) and the seam compound.

***Bevel depends upon the planking thickness and the wood species used.

***Softer woods need less outguage harder woods need more.

When caulking a new hull an experienced caulker will go pretty easy with the mallet and iron, hitting just hard enough to get the stuff into the seam, but not enough to force the caulk hard.

***This is where the experience and 'touch' come into play. A real heavy hitter can destroy a new build just by not listening/feeling the tightness of the corking material as he/she/it, drives it tight.

With paint (preferably red lead)

***Best to pay the seam as soon as you can after corking.

***I was taught to cork a few seams on one side and then cork the matching seams on the other side.

***When done corking for the day, out comes either the red lead or the 'yard paint' and the seam brush to pay the corking and prevent it from creeping.

***Also, you just don't grab a hank of Mohawk corking cotton and stuff it in the seams.
It must be twisted and 'thinned' before use.

and seam compound to hold the caulking stuff in, the wood-to-wood part of the seam will close tight, the outer third will also close a bit, but not enough so the wood edge is damaged by caulk that is forced too much. The seam compound will squeeze out somethat, which is why you don't put a nice finish coat of enamel on a new hull. Use semi-gloss or flat the first year.

***Then the vessel is hauled out and the seams are 'set back'.
Wood has swelled from a years immersion in the water and the seams can now take a bit harder blow with the mallet.

***NOTE: this once again is a judgement call based on the wood, the tightness of the seam and the skill of the corker.

The above describes the pretty ideal situation. In caulking an older hull that has aready exerienced some shrinking and swelling, a good caulker reads the situation and pounds accordingly. Some factors he takes into account are how long the hull has been drying out; the kind of wood; the width and thickness of the planking; the condition of the seams; the condition of the fastenings; how the iron acts when hit; and how the iron and mallet sound when the caulk is hit.
Good caulking is an art that takes quite a while to learn. There's a lot more to it than just pounding stuff into the seams. It's easy to wreck a hull if it's not done right.

Them *** are my comments added to Clints excellent description.

[paladin]

lessee....cover entire hull with two 1/8th inch mahogany veneers, 3 layers of xynole fabric and wet it with MAS epoxy, prep, paint.....check every other year to insure epoxy corking izzint damaged.....dunno hafta wurree about swellin' planks.

[Bayboat]

Hi Paladin. The process is not quite complete. Next comes the chain saw, then matches.

Dave: Thanks for the additions. Quite apropos.

[ 05-15-2005, 02:57 PM: Message edited by: Bayboat ]

[Ellis Rowe]

On an old boat that has dried considerably I usually try to swell it up before I caulk. If the boat is outside I put a plastic curtain from the waterline down and put a sprinkler or two under it. The owner of an old Elco I take care of insisted on storing it on a windswept hill. Her planks looked like a picket fence, and I swelled her up with this method. When she was swelled up enough that I could no longer throw a cat thru the seams I caulked her up. Then added a little slick seam, OK a couple of cans. She took up and slammed shut a couple of days after launching. On a new hull I generally roll cotton wicking in with a caulking wheel.Depending on the planking material and moisture content you may not want dead fits on the planking. I've seen a tightly fitted Mahogany planked hull bust a seam and crack frames a year after launching. The planking stock was just to dry and Mahogany doesn't give.