Stacey from St. Martins, New Brunswick, writes: "I have a house that is 150 years old and have just recently refinished the softwood plank floors. They have quite a few cracks and I am wondering what to fill them with. Some are as big as an inch in width due to shrinkage. The planks are directly nailed to the joists with square nails. The cracks are very hard to keep clean and are not very attractive to look at. Can you help?"
Sorry Stacey, I don't think I can help much, but I can explain what you are working with. Many people who have older houses can see the planks that you are talking about if they look up from the basement, as in the photo above.
Those large, often rough planks were never intended as a finished floor but rather, they were considered a sub-floor. Their job was to bridge between the joists proving a strong base upon which you could put a finished floor. So with this function in mind, a one inch crack was large, but not a problem. Many people have fallen in love with the look, when finishing these old wide plank sub-floors with sanding and a clear finish. In theory, you could fill in those cracks with wood, but in reality there are two problems with such a project. Anyone who steps directly on one of these thin filler boards will push it down or break it, especially with a table leg or a high heeled shoe. Also, if there are wide swings in humidity in this old house, the floor boards could change radically in width between summer and winter. If you fill all the cracks and it expands, it will pop some boards upwards.
The best solution to a problem like this would be to install engineered wood floating floors or laminate floors that have the wide old plank look, but none of the cracks over the original sub-floor.