The rope or twine has been used by high-end professionals (in this situation) for generations. It is an art form. Good luck. If you attempt it, you will need to have someone beside you helping you with the technique.

Yes, thanks. I need something flexible as the joists under the floor are not 100% solid and there is always some bounce as one walks across the floor.

Apple Pie, the bad cracks are variously a few feet to maybe 10 feet long, and range between 1/4 and 1/2 inch wide. There are plenty of 1/8 inch cracks but those don't bother me so much.

Rope/twine sounds like a good solution. Also some fill-in wood would be good in the worst of the cracks. What about pouring a solution of linseed oil, turpentine, and beeswax over the twine instead of glue and varnish? I am planning to use the linseed oil, turpentine, and beeswax mix on the rest of the floor, which needs to be stripped and re-varnished, but again I don't have time for that.

The benefit of the ltb mix is that it will stick to the areas of wood that need a new surface...I used this mix in another house and it worked well. However that house had uniformly unvarnished floors, whereas the cabin has some varnish and some bare spots.

I suppose it would be possible to rout a rabbet and insert matching material to extend the groove side to cover the gap. I'd only glue one side and the bottom in place though.

Yes, that it would, Joseph, if I had the skills or a carpenter. It is completely impossible to find a qualified carpenter for small jobs, and I certainly can't do it. Sorry to be grumpy but I have had nothing but trouble on any kind of repair job. Skilled crafts people do not want to work on small projects in my area...they just want to build McMansions from pre-fabricated panels or do extensive custom remodeling for big bucks.

Polyurethane is a vast improvement over linseed oil, beeswax and turpentine. No comparison on ease of upkeep in both short and long term for floors.

northface99:

I would not call what I've suggested a "small job". I don't know the dimensions of the room, but if you didn't have 7K for a budget, I wouldn't take a look.

Thanks, Joseph and Apple Pie. I'll post an "after" pic if I can find this thread when I'm finished.

What about the wood being able to shrink and expand with the weather? My log cabin isn't exactly perfectly climate controlled and I worry that if I fill the gaps in the boards with something rigid like timbermate filler that the boards themselves will crack. Granted, the boards are old heart pine and very strong, but I have a walnut corner cabinet whose cabinet doors cracked because someone painted the cabinet doors front and back, which prevented the panels from moving within the doors.

northface99:

Your fears are well founded. It's always about tradeoffs.