I am refininshing 100 year old Fir hardwoods. I have sanded off old dark stain and restained in a lighter color. The boards are beautiful and I would really like to keep them (as opposed to laying new wood), but there are significant gaps due to shrinkage. Over the years it seems people have tried using filler between the gaps. The lighter stain really shows the crusty old filler and I think it looks pretty bad.
So my questions are:
~ Do I dig it out and refill?
~ If so, how do I do it without damaging the boards?
~ What do I do to fill the gaps without it standing out too much? Suggestions for specific products appreciated!

Thanks!

the joints will be dark......... cannot help it.

If you were to clean out those gaps between the boards, that should have been done during the sanding phase, before staining. If you do it now, you may need to resand and restain. They make scrapers of various sizes for refinishing. You'll have to shop around. As far as what filler to use now, if the floor flexes at all, most fillers will just pop out over time. But the brand that many pros prefer these days is called Timbermate. It is not as easy to use as some others but it is supposed to stay put and not shrink. Here's a picture of some scrapers that come with different ends for different surfaces.

Gary,
That old color seems to wick up even after hand scraping.
Are you suggesting he hand scrape out all the joints? Every long and short joint?

Yes, scrape out all that they don't want. If it is all of it, then so be it. You will need to resand to make it look perfect.

Look, there's only three options here. Live with what you got and do nothing,
scrape the grooves/gaps clean of the old dark and crumbly filler (Ray, this is done ALL THE TIME when refinishing bevel edged floors that are being redone from dark to light) and refill the gaps then refinish the floors or lastly, just paint the floors. Then everything will be the same color. You can even use a waterbased poly over latex paint to make it more durable to walk on. Oh yeah, fourth option, put new floors in over the old ones.

Well, I guess I'm soured by the number of Re-Finish jobs inspected where the dark stain was visible in the joints..
I guess Gary is saying (and Floorguy) that I've been inspecting jobs re-finished by LAZY installers...
But Gary does re-finish, so he would know ..........

Yeah Ray, It's true that when refinishing a bevel edged plank floor, you need to deal with those bevels. Now I try to tell the customers that they will be better off if they keep the new stain color close to what they already have because you just cannot get all the old stain color out of those grooves. I've tried many times. But some folks want to go way lighter and then I explain that I'll make every effort to get most of that old stain out but not to expect it to be perfect and that some old stain color will remain. It's a very laborious job, to say the least and many people just don't want to pay for it. My position is; if you have a dark, beveled edged plank floor, try to stay close to that old color. You can go a bit lighter but not much. If one goes from Antique Brown to a natural, you will see some of that old stain in the bevels and sometimes, in the open grain of the wood. If you're refinishing a 3/4" thick plank that's been blind nailed and it has shallow bevels, then you can consider grinding it down to remove all those bevels but it often requires a lot of extra sanding. In the case of 5/16" face nailed plank, this is not an option because you'll be running into the nail heads before the bevels are gone. Plus the bevels on Lebanon Oak are quite deep.

Gary,
I don't see where the original post had anything stated about eased or beveled edges.
NWFA has a statement concerning square edge color change.......... going to lighter color will result in the joints visible..
Now I gotta find the NWFA or NOFMA statement concerning this..
Your explanation tends to make the statement that the darker edges will be visible after going to a lighter color...
I'm so confused...

Sorry Ray, I'll try to explain better. For me, when refinishing a floor, it's irrelevant whether the floor has bevels or is an older floor with big gaps filled with an old dark filler. The end result is the same; there will be dark "lines" between the boards. This is unavoidable but can be minimized by scraping the bevels or removing the old filler. Now in the case of a square edged floor that was dark and now is going lighter, if there has been any gaps filled, the filler in those gaps will have taken the stain dark, as it should have. But when you resand, often times, the wood will return to it's raw, natural state but that dark filler will remain dark. Not always but most of the time. So you get those dark lines between the boards. It's just the nature of wood floors.

I don't think your too confused. You agree it was explained, just like the NWFA has it documented.

This is common sense.

Oh Good Gary,
For awhile there I thought I was losing my mind...