I would like to renovate the oak beam of the living room fireplace. It is split deep enough in several places and along the length of the beam, I was told that I had to re-open the slots because I might cause a fire. What do you recommend?
Slots (or "checks" in the language of the pros) that appear in the lintel beam chimneys are not worrying as long as they remain in reasonable proportions and the beam does not deform. They are part of the natural charm of "tree" wood. If you still want to fill them, you have to insert in it, "by force", a thin slat of the same wood as the beam, then plane on the surface the part that remains projecting, finally reteinter all. No need to put woodpaste because it will not hold. I once saw my father, who was a wood carver, doing this type of repair; he called the piece of wood thus pressed into the slot a "filipot" (spelling not guaranteed).
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