I have an up coming job that has me sanding about a 25 yr old pine floor. Floor is crowned and has larger than average cracks. Some of the cracks are up 1/4" wide. I haven't used laquer and sawdust in many years as we now only use waterbase filler. The floor has little movement but I expect over time filler will fall out. I guess I can go laquer again but wondering if anyone has any other ideas what I can use.
Cheers .

I presume that the pine floor is both the finish floor and the sub-floor so it is only supported every 16 inches by joists. This type of floor will deflect between the joists so filler can get stressed and crack and fall out when it's walked on. I have used epoxy mixed with wood floor, but this can not be used all over the floor, only in the bad spots, because the boards will be glued together and may cause cracking if the wood shrinks. General purpose epoxy in the recommended ratio with about twice the volume of fine edger dust all mixed together at once is what I use to make almost a putty that you knife into the gaps. It takes 4-7 hours to harden so I spread it at the end of the first day after the roughing off. I only use this in two or three rows at a time. What keeps regular wood patch in place is securing the boards so they don't move independently. If there is access from below, you can install blocking between the floor joists which will really make a difference for this type of floor. I charge extra and use strips of one half inch plywood glued and fastened in place with screws or staples so sub-floor adhesive from a caulking gun can hold everything together when it dries.This will prolong the life of the floor, also, because the floor will not crack when it gets sanded thin, at the top of the groove. With a solid floor, I have put wood patch into a caulking gun and filled major gaps between boards that are fastened down so they move in unison.

Thanks for the response, the house was built in 1992 and the pine is installed over 3/4 plywood subfloor.
No humidifier present, we are very dry here in Alberta Canada .
Owners built the house and probably sourced material themselves as they told me they stored pine in basement ( below grade) yikes prior to install.
I remember seeing a product at suppliers some time ago called I think celu set ?
Meant for bonding in large cracks.
This is 1000 sq.ft. Plus so it would be good to be able to flood fill multiple times.
I also need to stain this floor so to much glue could pose a problem.i could tint the filler ?
I have word in at supplier to help me find something and will do some more snooping around this week coming.

If your floor has only shrunk after acclimation, there may be a looseness to it because there are fasteners on only one side of the boards. The groove side is held by the tongue of the next board. If the floor is loose, before filling gaps, top nail with finish nails or powercleats. These are flat "p"nails that blend in with the grain.
Fill the top nails with regular wood patch, even if you use something else for the big gaps, before you stain or finish.