Need advice on rotten wood repair!

[jim binnings]

I have an all wood thistle sailboat I race down in Birmingham Al. The hull is made of 3 laminated sheets cold pressed together. The total thickness of the hull might be 3/8 of an inch. In the past year a rot spot has appeared on the starboard side. The area is probably 4 by 6 inches and the wood is soft on the outside of the hull but hard on the inside of the boat. Water came through a crack in the awlgrip paint(which I have sanded all off).

Everyone has told me to cut out the rot and get to good wood. Rot spreads I am told. However West Marine sell "GET ROT" which I have been told is an epoxy which I pour onto the rotten area. The wood is supposed to absorb the epoxy and bring the wood back to full strength. I was also told to drill tiny holes around the rotten area in good wood and pour the epoxy into the holes. The idea is that the epoxy will keep the rot from spreading.

I need to mention that the rot spot happens to be on a load bearing spot. On the inside of the boat the starboard seat attaches to a vertical board. the vertical board is glued and screwed to the hull. One of the screws is right in the middle of the rot spot.

I have a beautiful boat and a fast boat and want to do a good job on this repair. I would love some advice on whether "GET ROT" has worked for others. I would also like some opinions on how some of you seasoned craftsman would approach the patch job. thx for your help!

[The Bigfella]

Jim

It sounds like that screw you mentioned may be the reason the rot got a hold.

Can you post a photo of the rotted area? It would help forum members give an appropriate answer.

[paladin]

You don't patch rotten wood....you get it all out and replace it with good wood, then you refinish the boat......

[Woxbox]

What Chuck says -- plus when you start digging, it's usually worse than you thought.

And while you're working on it, check similar spots around the boat very carefully -- pull the fasteners, etc. and rebed anything questionable. The good thing is you're getting at this stuff when it's relatively easy to repair.

[Todd Bradshaw]

And make no mistake about it - saturating rotten wood with epoxy (Git-Rot, CPES, regular resin, etc.) may stop the rot in that area and return the wood to a solid, hard state while filling missing areas, but that is a totally different thing from "bringing it back to full strength". It's not even wood any more after that process and anybody who thinks it will have similar characteristics to the piece of wood that used to be there is either dreaming or badly misinformed.

If you tried to make your own planking with a mixture of epoxy resin and sawdust, it would generate a plank that was heavy, stiff, brittle and fairly easy to break by simply bending it because it has no long fibers to resist that type of stress. This is essentially the very product you are producing with rotten wood and resin-based quick-fixes like Git-Rot.

[Ian McColgin]

It's made of five layers and metric but close enough to SAE that you can call it 1/4" total. The three inner plys are 1/16" each and the innermost and outermost are 1/32" each. Repairs are most easily made with doorskin or any other available mahogony vaneer that's 1/16" thick. You need to get or borrow a router and buy the collette system that laminate installers use to make both the cut-out and the inlay from one jig. It ends up as a step scarf.

The Thistle I've been rather lethargically resorting had some repairs by a variety of inferior methods including attempts at solid wood scarfs, GitRot injection, fiberglass, and something like Bondo. All were disasters leading to more work. The step scarf works even on all the difficult compound curves.

G'luck

[J. Dillon]

Jim , Weclome aboard.

It appears I have the same problem on my 18' sprit sail skiff Carrianne. A crack in the paint on the transom and water rotted away a golf ball sized area. Maybe more . What I intend to do is cut out the rot till I get to sound plywood then mount a carbide bitt in my Dremmel tool and scarf out an oval shape. As Ian said the steeper the better. Then make a series of veneers on my table saw and oval shape them each a little smaller to fit in the oval hole. Each layer will be edge tapered with sand paper. and be successively smaller. After a suitable backing is a fixed to the hull ( some ingenuity here ) I plan to epoxy in place each at 45o to each other to resemble the British flag ( no disparity intended) and in effect a kind of home made plywood If the final layer is cut and matched carefully the scarf should not be to offensive to the eye resulting in a well executed repair if you plan to finish bright. If painted no one will know the difference.
As the extent of the damage is determined I may make the taper from both sides, kind of locking in the repair from both edges.
When the weather breaks temp wise Ill post images of the repair as I go.

JD

[Nicholas Scheuer]

I've never heard the term "step scarf", Ian. I assume each layer of the sound plywood surrounding the rot is exposed as a "step". But what would be the recommended breadth for each step?

My first impulse when reading the above was to consider a fibergalss repair, as I have a lot of experience there. But the step scarf method doesn't seem difficult at all, and certainly would preserve the integrity of the "all wooden" hull.

Moby Nick

[Ian McColgin]

On a flat surface the standard beveled scarf is the thing but it's not on for compound curved hot-molded plywood. And look at plywood - the way the vaneers work are often not continuous anyway. On Il Pipi (the Thistle, short for Il Pipistrello Fuori di Inferno) I just just treat it as 1/4" ply made of four layers. Some of the repairs go all the way through and some don't. Where it goes through I have to make a temporary batting inside to give shape.

Anyway, there's this supercool gizmo that laminate types (counter tops and such) use and can be had at any good woodworking place. It's essentially a pair of collets that fit on your router. The directions tell you what size of bit to use.

You make a female jig and use one collet to be the guide against the jig when cutting out the insert. Move the jig to the boat, tack it in place, switch colletts, and rout out the outline of the place the insert goes.

I'm working entirely from the outside and the inner-most new layer is the smallest. Depth control of the router is very fussy but with practice you can make perfect cuts 3/16" in, 1/8" and 1/16". Where I've had to go all the way down, the inner and second layer go down together but after that it's one layer at a time just stapled down, then clean the staples and smooth the surface before cutting the space for the next layer.

I make each layer about 3/4" longer and wider than the one under.

Especially for the compound shapes, I've had great luck making the jigs out of "wiggle-board" sometimes four pieces tacked together with gussets to take the curves and move to a flat surface for cutting the insert. On the curvy bits, I sometimes have to slit the vaneer along the grain to get it to lie down on the compound shape.

I allign the inner and outer vaneers with the finish vaneers on the hull as some parts will be finished bright.

In this approach the steps do NOT line up with the original plys. At least on Il Pipi the building schedule was 1/32 - 1/16 - 1/16 - 1/16 - 1/32. I'm placing in 1/16 - 1/16 - 1/16 - 1/16. Depth control is by router rather than by an eye on the old glue lines which is more reliable for getting flat depth.

I'm generally better with hand tools and do all my normal scarfing with a plane and chisel. In plywood, the glue lines help see that you have a nice flat bevel. But going to a flat depth is really different and a good router is the way to go. The collett system is ultra frosting on the cake. You can make about any shape. I experimented with ovals and such but actually rectangles end up looking best and fitting most readily, besides which they are a more efficient use of your vaneer wood.

G'luck