we have remodeled our home and discovered when ripping out the ceiling down stairs that they used hardwood for the ceiling, so instead of throwing it away we used it in our dining room it is not tongue and grove its just planks nailed to the floor it looked great when we first did it but now after a year it has shrunk i do not want to get a humidifier or whatever, i need to find out if there is anything that i can use to fill the gaps that wont crack or look crappy, we have just sanded the floor so its bare wood we are going to slightly stain it but it will be light so i need something that you cant really tell that its there, some of the gaps are 1/4 of an inch wide....... please help quickly[/b]

rip it out and put the correct type flooring down.
your playing games

We would use Glitsa Wood Flour Cement mixed with fine dust from the floor we are sanding.

If the planks move when you step on them any filler will eventually pop out. If your flooring is nailed so the planks are not moving much there is a chance the filler may stay in place.

We installed this reclaimed antique heart pine floor (with no tongue and groove) glued directly to the slab. Some of the gaps were ¼” wide and we filled them with wood flour cement and dust from the edger. In this case the filler will stay in place because the flooring is glued and does not move much.

You can see the filler in the gaps between the two planks near the bottom of the photo. This filler takes stain really good and also looks good with a natural finish.

We fill before the last pass with the belt sander.