How to stabilize wooden knots?

[bikemaniac]

Hi,

This is not 100% boat related, but anyhow: I am building a wooden roof out of Siberian larch. Each board is 120x12x2500mm. Some of the boards have some wooden knots that are a bit loose but they don't penetrate to the other side of the board (they are only present on 1 surface). I would like to "stabilize" these knots so they don't fall out so easily. Since siberian larch has lots of preservatives I will not treat the entire surface, but I would be interested in some localized treatment where the bad knots are located. The roof will be exposed to sun, rain, snow etc.

I could maybe also use a router and carve out the knot and then fill the cavity with some UV resistant caulk.

Any ideas?

Lucas

[skuthorp]

Look up Heimlaga here, he is experienced in restoring historic wooden buildings in Finland. He may be able to help with a solution best for your conditions.
You'll find his posts in the Ukraine thread.

http://forum.woodenboat.com/showthre...-Advice-needed. #10

[Geftb]

Can you pry them out? If yes i would glue them back in.
If no i would leave it.
Or you could always tape them up and pour some epoxy in with a syringe. Don’t fill to the top.

[jpatrick]

If the knots show on only one side of the board, put that side facing up. Then they won't fall out. If you want to glue them, I've used five-minute epoxy to secure knots in furniture wood. That works well.

Jeff

[Garret]

If the knots show on only one side of the board, put that side facing up. Then they won't fall out. If you want to glue them, I've used five-minute epoxy to secure knots in furniture wood. That works well.

Jeff

I have some cherry flooring - now 7 years old - that has knots filled with 5 minute epoxy & they are as solid & smooth as when the floor was installed.

[UCanoe_2]

Unlike furniture, your roof will be exposed to UV from sunlight. That could degrade any epoxy. Maybe you could fill the knots with epoxy and install the boards knotty side down?

Thinking this problem through, epoxy seems pretty expensive to use on a large surface such as a roof. Some messy black roofing cement would be more affordable, and could flex with changes in temperature and humidity.

[heimlaga]

Plenty of pine tar. I said plenty of it. Get another 10 litre can of it before you start thinking.
That is the common reciepe.

If you have completely loose knots you could whittle some bungs to fit the knothole and glue them in with a boatbuilding quality glue. Preferably Aerodux 185 or some equivalent because those glues are UV resistant. The ine tar will privide some UV protection..

12mm is very thin for a wooden board roof. Normal thickness is 22 or freferably 25mm. Thinner boards crack too easily. There also has to be some thickness left after mlilling the water grooves along the edges.