Old Crusty Black Varnish

[Gregory Messier]

As many of you know I just completed a rework of a 1910 OT Charles River. One of my most controversial decisions on this hull was to attempt to retain the original blackened varnish inside the hull. I did this for aesthetic reasons (because I loved the way it looked) and also to attempt to retain some of the “story” of this old boat.

One of the major challenges I knew I would face is adhesion of the new varnish. I improvised a process that so far is working well so I thought I would document it here:

1. I patiently hand sanded the inside of the hull with used (dull) 80 grit sand paper in order to knock down high spots, debris in the old varnish, and provide tooth for the new varnish. I completed this step with great care not to cut through the original varnish. The 80 grit worked by far the best as new pieces of 120 or 220 would cut too aggressively and were not equal to the task of knocking down years of accumulated gunk.

2. I thoroughly wiped the inside of the hull multiple times with a rag charged with mineral spirits to remove any oils or contaminants from the surface.

3. In order to hydrate the old dry varnish I then treated the inside of the hull with Tung Oil which did a great job of softening the original varnish. I let the tung oil cure for several weeks as I worked on the outside of the hull.

4. Applied 2 coats of System Three gloss spar varnish 12 hours apart as to avoid sanding between coats. The gloss varnish of course didn’t look great over the original finish but I intended to apply the final coat in satin

5. After the two coats of gloss dried for 48 hours I lightly hand sanded the inside with 220 and wiped with mineral spirits.

6. Applied the show coat of System Three satin spar varnish

So far the finish is holding up nicely with no bubbles. I will update this post with changes if any.

 

[Worth Gretter]

I think your concept works nicely. The black varnish is a great contrast to the mahogany trim and the light cane.
But a lot of work to sand all that old finish! Of course, removing it is also a lot of work.

 

[Howie]

I'm curious about the wood treatment on/in the top of the inner rails above the thwarts and seats. What's going on there? I'm guessing you carved out the two 90deg bevels in the rail, drilled c-sink hole(s) for flat-head screws, then glued/epoxied in wood to match the wood you carved out so that the bolt head is hidden. Wow. Nicely done.

 

[Gregory Messier]

I'm curious about the wood treatment on/in the top of the inner rails above the thwarts and seats. What's going on there? I'm guessing you carved out the two 90deg bevels in the rail, drilled c-sink hole(s) for flat-head screws, then glued/epoxied in wood to match the wood you carved out so that the bolt head is hidden. Wow. Nicely done.

Hi Howie,
When I got the canoe several of the original seat and thwart bolts had been replaced with large carriage bolts and washers that were surface mounted which wore into and iron stained the inwales to the point that I couldn’t just countersink and plug the new bolts. I came up with a solution to use a diamond shaped “plug” about 1 1/2” long that spanned the inwale and cover up the unsightly black gouges from the old carriage bolts.

The bevels were actually already there on the inside edges of the inwales. In my ignorance I assumed that was the profile from the factory and put it back the same way. Either way it was handy because the top inside edge of the inwale was quite marred and it was easy to sand down to good wood using those bevels.

 

[Howie]

Are you worried that the strength of the rails have been compromised? After all, if a rail breaks it's often at the bolt holes where the wood is slightly weaker, and removing this much wood just makes the area weaker still. Sorry - I don't mean to rain on your parade. But better to answer & address concerns now while the rails are still intact. Maybe epoxying some wood to the inner side of the rail might be called for - like maybe a 5"x3/16"x5/8" chunk? Maybe other guys will chime in with their opinions...

 

[Gregory Messier]

I guess we’ll find out. The wood in and around the bolt holes was compromised by the iron rot so I drilled and plugged it before doing the chisel work. It was the only solution I could think of without scarfing in new pieces which I didn’t want to do. In any case it’s done so I’ll let you know if I have any regrets later.

 

[Michael Grace]

Re "bevels", I think Howie was referring to your inlays, but the chamfers on your inwales are interesting. Early AA-grade Old Town canoes with open gunwales have a very neat, consistent chamfer all along the top inside edge of each inwale. This was done at the factory through at least 1916. It is a very nice detail, one that didn't have to be done but that further dressed up their best canoes.

 

[Gregory Messier]

Howie,
The more I think about it, I think you are right. I will laminate an additional strip of mahogany under the rails where the seats connect just to be sure.

 

[Howie]

Re "I think you are right". Wish my wife would read this.

 

[Worth Gretter]

Thanks for the "before" picture. What a difference!

 

[Gregory Messier]

Thanks for the "before" picture. What a difference!

It’s amazing what a man can do with about 200 sheets of sandpaper

 

[NedL]

Be aware that the "System Three Spar Varnish" is a urathane. That might not be the most desirable in the long term on top of an old traditional varnish.

Very nice work!, she looks great.

 

[Dave Osborn]

As a word of caution, be careful in sunshine.
I experienced a problem when I varnished over old varnish because I loved the old patina. I thought my prep was good, but the heat of the sun caused the original varnish to blister under the new. With the dark color the heat will intensify.
Not saying it will do this, but wanted to share.

 

[Gregory Messier]

Howie,
Based on your insight I strengthened the rails by epoxying a 1/2” x 13” strip of mahogany under the rails. If my fat butt breaks them now it’s a sign from the universe to cut back on the twinkies. I know it’s not correct to the canoe but it does carry the benefit of lowering center of gravity a touch.

 

[Howie]

It's certainly stronger than it was, and it lowers your center of gravity as well thereby I creasing stability.

 

[Gregory Messier]

Be aware that the "System Three Spar Varnish" is a urathane. That might not be the most desirable in the long term on top of an old traditional varnish.

Very nice work!, she looks great.

I believe what you are saying but am curious why?

 

[MGC]

We use spar for exterior finishes. It remains (relatively) soft and handles weathering/flexing better than the harder urethane products that are typically used only indoors. It also provides a degree of UV protection.
Bonding the two can work if the surface of the softer (spar) finish is structurally good and very well prepared (sanded and cleaned).
From personal experience, I would expect to see bubbling or separation between the spar and urethane if the boat gets some continuous use and is left out in the sun.
The rule of thumb most of us follow is to use only good quality spar varnish on hulls and trim.