Hello Wood People -

First time posting. I haven’t been able to find an answer to my question in earlier discussions so I’m hoping someone out there will have some experience or suggestions.

My 1865 house has wide plank pine tongue in groove boards laid directly across the joists. No sub flooring. When I moved in 15 years ago, I pulled up various replacement floors that had been installed over the original fine floors. I repaired, sanded and refinished all of the original pine and all was beautiful for a few years. In the high traffic areas, however, these antique boards began to split along the edges. Due to shrinkage, the tongues and grooves separated long ago and were not supporting each other. Any pressure on the edges caused these areas to split. In many areas, the tops of the grooved edges have completely snapped off leaving 3/4+” gaps.

I know that a new floor would solve the problem, but I want to keep the floors throughout the house uniform. Plus I can’t afford to replace even if I wanted to.

I’m thinking of cutting out just the damaged grooves and patching them with pieces of salvaged antique boards. I’d also double up the joists below and add 3/4 plywood subfloor between the joists to add structural stability.

Anyone out there approached a repair in this way? Any other solutions? What’s the best way to remove the damaged tongues / grooves? Plunge cut w/ circular saw? Thanks in advance for any suggestions.

The old floors that have no sub-floor and are worn thin, mostly from sandings, will have weak top parts of the groove, If you replace with the same material that has not been sanded yet you will be surprised at how thick the original planks were.
When I sand an old floor built like this and the underside is accessible from below I recommend that two inch wide strips of half inch plywood be installed with sub-floor adhesive between the floor joists, with screws/staples/ or nails holding the plywood until the glue sets up. One inch sheetrock screws predrilled through the plywood so they pull the plywood up against the bottom of the planks as the glue is drying will really strengthen the floor and prevent any more grooves from breaking of or cracking to make a splinter. You will feel the difference immediately when walking on a blocked plank floor.
Using the same technique for patching the individual planks using one half or three quarter plywood to support a weak joint where the t&g has been compromised is the only way to make a lasting patch, from underneath. You may be able to successfully patch gaps with thin strips glued to the gap edges and then use a scraper to smooth the surface. It's lots of work, but the old close grained flooring has a different beauty than modern harvested lumber.

Thanks Pete! Those are all great suggestions. I appreciate you taking the time to reply.