Filling gaps in wooden floors if tongues are showing

[mmflytie]

I've always heard not to fill cracks between floor planking( it will just shrink , crack and fall out). Ours have separated in some places where you can see the tongues. Is there any suitable filler that can be used on these? I'm getting ready to sand off old finish and resurface. Wood is pine.

Thanks
Marc

[HayZee518]

the pine is a tough subject. it is more susceptable to expanding and shrinkage due to its cellulose makeup. A solvent based sealer which is white shellac might do the trick. but here again you'll be using a solvent not moisture [water] there is a paint additive called penetrol which doesn't evaporate. its sort of like a linseed oil or tung oil preparation that is meant for wood. you can try it.

[pushkins]

I think the real question is "why" have the planks shrunk that much ?
Does the gap open and close or is it pretty much that wide open all the time ?