Refinishing Old Floors - How to fill gaps?

I'm working on stripping and refinishing the wood floors in one of our spare bedrooms. It's 160+ year old heart pine that had previously been hiding under some hideous brown carpet. While I'm no expert, I've installed new hardwood flooring with my dad before, both prefinished and unfinished, and refinished newish hardwood with my uncle, but working with stuff this old is new to me. I've got relatively large and fairly irregular gaps between the boards, and SWMBO wants a reasonably smooth floor when this is finished. This room is also kind of a trial run before we eventually tackle the downstairs flooring, which is in somewhat worse shape.

What's the best way to fill the gaps? Google suggests everything from rope, to wood fillers, to various concoctions of beeswax, pine tar, epoxy, sawdust...What would the hive recommend?

Here's what I'm working with, that's roughly .125" or more gap in most spots:

I've used Durham's Water Putty in the past with mixed results.  I live in an old house with similar gaps in the floors, so I would love to hear other peoples suggestions. 

In reply to Furious_E :

Stop!!!!!! 

Wood shrinks and expands based on humidity planks that wide will easily move that much. 

If you stuff something between the boards what will happen is this summer during really humid periods  the boards will cup up!!! 

Wide plank boards like that are to be chairished  and apprecIated  for their heritage. 

Don’t try to make this a big piece of plastic.   If you refinish it use shellack. Not a typical plastic based finish.  If scratched plastic must be removed (sanded off) it cannot be repaired.  

Shellack on the other  hand, repairs easily and completely invisible.  Plus it is so easy to apply you can do it yourself easily. Ask I’ll walk you through it.  

Tom Silva used rope on one episode of "Ask This Old House".  It looked pretty cool.

I agree with frenchyd. Wood floors should have character. I just finished my oak floors myself although I don’t have the large gaps you have, the floor is not perfect and it shouldn’t be especially in an old house but it looks great. 

In reply to Streetwiseguy :

Lots of ways to fill gaps but don’t!!!! Wood shrinks and swells with humidity. Tight flooring in the winter will cup in the summer. Maybe enough to pull the nails loose. 

I was just looking at my floor's with the same issues. Might wait till summer and see what they look like.

frenchyd said:

In reply to Streetwiseguy :

Lots of ways to fill gaps but don’t!!!! Wood shrinks and swells with humidity. Tight flooring in the winter will cup in the summer. Maybe enough to pull the nails loose. 

The rope is compressible.

In reply to frenchyd :

Right, which is my concern with just jamming them full of putty or similar, won't have enough give to allow for the natural expansion and contraction. I don't want to ruin the classic look and I don't want a perfectly flat slab of poly, but I also don't like picking up splinters from the edges of the boards every time I walk across it and don't like the way some of the massive gaps looks (this is more of an issue downstairs than in this particular room.) I know there is a proper and period correct looking way of doing this because I've seen it done before. My parents have a rental property of similar vintage that has very similar flooring which was refinished by the PO and is a perfect example, but unfortunately I don't have any pictures handy.

Haven't decided on a finish yet, that was gonna be my next inquiry. Want to give me a quick lesson on shellacking? 

Streetwiseguy said:

Tom Silva used rope on one episode of "Ask This Old House".  It looked pretty cool.

Found that video on Youtube yesterday and it's a neat way of doing it. 

In reply to rustybugkiller :

Got any pictures? Would love some inspiration. 

Furious_E said:

In reply to frenchyd :

Right, which is my concern with just jamming them full of putty or similar, won't have enough give to allow for the natural expansion and contraction. I don't want to ruin the classic look and I don't want a perfectly flat slab of poly, but I also don't like picking up splinters from the edges of the boards every time I walk across it and don't like the way some of the massive gaps looks (this is more of an issue downstairs than in this particular room.) I know there is a proper and period correct looking way of doing this because I've seen it done before. My parents have a rental property of similar vintage that has very similar flooring which was refinished by the PO and is a perfect example, but unfortunately I don't have any pictures handy.

Haven't decided on a finish yet, that was gonna be my next inquiry. Want to give me a quick lesson on shellacking? 

 Pine tends to splinter easily unlike hardwoods like oak or maple.  It also could be a sign the floor has been sanded too much. See if you can estimate how thick the wood is above the spline.  Less than an 1/8 inch you are in the splinter territory. Time for a new floor. 

Shellac is  really easy to apply. I’ve used a big wide brush or roller.  Just mix 2 gallons of denatured alcohol  with one gallon of Shellac. Slop ‘er on. Gotta do it fast because it dries really fast.  Just paint everything.  Tape around the edges if you’re a really bad painter like me or pull up the trim.  Don’t worry about brush marks etc shellac flows nice and smooth better than water!!!! 

The first coat dries in 15 minutes. Then feel the floor. Feel those little nibs that are raised?   Gotta sand them off. I use a little 5” DA sander.  Mikita is the best Royobi the worst. And 220 grit sand paper the kind that just velcro’s on. Figure one disk per 100  sq ft. 

Its a light fast sanding. All you are doing is removing the nibs.   Now wipe off the white dust you made. I use towels because the shellac dust comes off in the wash easily. However a T shirt or even wear cotton Sox’s and slide your feet.  

 After that put on a second coat.  Just cover the floor as quickly as you can. It’s not a race but don’t dawdle.  The second coat will melt into the first coat so it takes twice as long to dry. 

Again feel the floor checking for nibs. You can sand locally if there are only a few.  

The third coat goes on like the first two. Melting into the first two. That means the third coat will take an hour to dry.  You double the previous drying time with each coat  15 min 1/2 hour 1hour 2 hours 4 hours  ~ 

Now here comes judgement  time.  Do you want more coats?  My personal taste is no but you may differ. 

On certain things I’ve used more coats but I also switch to one gallon of shellac to one gallon of denatured alcohol.  Now I really have to paint carefully because it doesn’t do as good a job melting into the previous layers.  So you can see missed spots and overlapping areas. 

Its ok if you screw up though, just use pure denatured alcohol and wash over the whole area.  That does a nice job of fixing a mistake 

In reply to frenchyd : Smell, you are smelling alcohol so it might get you legally drunk so don’t drive for a while after doing this or if the weather allows open windows. 

The smell doesn’t linger long  even hyper sensitive women can’t smell anything a few hours after it dries. 

That’s one of the great things about shellac 

it comes from the Lac bug in India. It’s natural and been in use for about 5000 years!!!  denatured alcohol  is corn whiskey that has been turned into poison by adding 2% of something so you can’t drink it.  That something varies, it could be methanol or gasoline etc. 

 As far as a paint goes shellac is about as safe a thing as there is. 

Shellac is the coating on pills  ( except medical grade alcohol is used)  and some foods. 

In reply to frenchyd :

Shellac is really really hard!!! Tough!  Much harder and tougher than normal floor finishes which are basically plastic and pretty toxic. 

 Pills are coated with shellac . (Except they don’t denature the alcohol they use medical grade). 

However shellac does not like water left on it for long periods of time.  It will produce a white ring if you leave a wet glass on it overnight. 

No problem. 

Take a rag soaked in denatured alcohol and  rub it off!   The shellac will melt and the white ring will disappear with the shellac usually spread nicely to make an invisible repair. Remember alcohol will melt shellac even 100 years later.  

Scratch?  rub with denatured alcohol - invisible repair.  

If the finish wears off just apply more shellac. The same way you did to start. No need to sand off the old plastic  finish. 

Cleanup is easy. Just wash your hand and hair and anyplace you get it on you. ( see I told you I was a bad painter).  When I get it on my glasses I use glass cleaner to remove it. Because most glass cleaner is alcohol based. 

Toss your clothes in the washing machine same as usual use hot water instead of cold though.  

Your clothes come out shellac free. 

Furious_E said:

In reply to rustybugkiller :

Got any pictures? Would love some inspiration. 

Imagine yuckie blue carpeting here! First pic is what I had after pulling up the carpet. I was lucky that after 65 years the wood was not damaged and it was never finished. A couple passes with a pad sander and it was ready for finish. 

I also would avoid the fillers. If the floor has any ancient finish on it , it might be shellac.  If it has character, don't sand it with a floor sander.

Shellac is a good suggestion. I would put two or three coats on before sanding the nibs, then one final.

Another way to go is OSMO hardwax, which is similar in ease of application and touchup later, and has a nicer tactile feel. Can also be tinted. I used it here on an old farmhouse we renovated.  

I've done many floors.

I agree to not fill the gaps.  Anything you put in there will pull and crack apart eventually and look like a botched repair.  Even if it doesn't pull apart it will scream "look at me, I'm a repaired spot."

I'm also a bit surprised at the recommendations for shellac.  I'm not a fan.  It is 800-year-old technology that is literally bug poop dissolved in vodka.  If you try to refinish it, you can't sand it (it melts instead of sands) and is not nearly as durable as poly.  It also comes in colors ranging from fecal brown to pumpkin orange.  I've probably done 50 floors and used to teach classes on it for Home Depot.  4 coats of a properly-prepared poly finish will last you 20 years on even the highest traffic areas.  Even if you cared about scratches, they're super simple to repair, and if you don't like it or want to change it 10 years from now you just sand it off.

If I'm refinishing a floor with Shellac on it, my quote instantly goes up by 50%.  It must be stripped chemically.  Spill a gin and tonic on it, it is stained for life.  Water spills have to be cleaned up right away.  Wife's nail polish remover will bubble it up like paint stripper.  Poly is remarkably durable and so much less succeptible to damage from liquids.  It is also less hard which is good for a wood floor that expands and contracts.

To me, recommending Shellac for a wood floor is like recommending a donkey for a work commuter vehicle.  Poly is infinitely better in so many ways.

In reply to frenchyd :

I don't have any shellac worthy projects at the moment, but I have really enjoyed the mini education here. It sounds like awesome stuff, I'm sure I'll put it to use at some point!

Curtis said:

I've done many floors.

I agree to not fill the gaps.  Anything you put in there will pull and crack apart eventually and look like a botched repair.  Even if it doesn't pull apart it will scream "look at me, I'm a repaired spot."

I'm also a bit surprised at the recommendations for shellac.  I'm not a fan.  It is 800-year-old technology that is literally bug poop dissolved in vodka.  If you try to refinish it, you can't sand it (it melts instead of sands) and is not nearly as durable as poly.  It also comes in colors ranging from fecal brown to pumpkin orange.  I've probably done 50 floors and used to teach classes on it for Home Depot.  4 coats of a properly-prepared poly finish will last you 20 years on even the highest traffic areas.  Even if you cared about scratches, they're super simple to repair, and if you don't like it or want to change it 10 years from now you just sand it off.

If I'm refinishing a floor with Shellac on it, my quote instantly goes up by 50%.  It must be stripped chemically.  Spill a gin and tonic on it, it is stained for life.  Water spills have to be cleaned up right away.  Wife's nail polish remover will bubble it up like paint stripper.  Poly is remarkably durable and so much less succeptible to damage from liquids.  It is also less hard which is good for a wood floor that expands and contracts.

To me, recommending Shellac for a wood floor is like recommending a donkey for a work commuter vehicle.  Poly is infinitely better in so many ways.

I’m sorry but you really don’t know what you are talking about 

First shellac is thousands of years old. Not 800.  Second shellac is harder and much more durable than poly  (plastic)  it’s only weakness compared to poly is it’s resistance to water damage.  Long term water damage. If you leave water on a wood finish for 5-8 hours the shellac will turn white. But unlike poly you don’t have to sand it off  to repair!!! 

Stripping shellac is done with the same stuff you apply it with Denatured  alcohol.  But it will sand off just fine!   

Unlike poly it’s not toxic 

pills are coated with shellac.  Let’s see you eat a poly coated aspirin.- no wait, don’t. Poly is toxic.  

Spill gin and tonic on it you’d wipe it up same as any spilt drink. Spill  a dark red wine and leave it you will get a stain. But bleach will remove it pretty well ( nope not perfectly but what kind of drunk leaves split wine on the floor)?   

I don’t know what nail polish remover will do to shellac probably not much but it will ruin plastic, er,  poly. 

Fire repair damage specialists use it to coat wood to keep the burn smell trapped in the wood to avoid tearing down the whole house because of fire damage. Kilz is shellac with paint to eliminate stain from previously leaking roofs showing .  

I understand why floor refinishers use plastic on floors. Like you said it is softer which means it will scratch  and mark easier,   ensuring future work.  And as you said require sanding. Which means that you will soon need to replace the floor. 

Over a decade ago I helped a friend refinish the dance floors in his old house. The floor was over 100 years old.  And hadn’t been used since the 1950’s  although kept clean by the housekeepers  the room still had a coat of dust which we wiped off with water. 

Then we cleaned the shellac with denatured  alcohol  and gave it a top coat  of shellac and it looked great.   Total time for about a 35’X80’ ball room floor was about 3 hours  

Shellac is used on fine musical instruments like a Stradivarius Violin and pianos. Because of its rich yet not plastic appearance. It’s also used in all collector pieces of furniture  again because it’s ability to be invisibly repaired without the need for sanding.  

The clear is the most commonly used color of shellac. But yes it has a light clear Yellow color to it that still beautifully shows all the grain and color of the wood beneath it.  It goes from there to Amber and then a reddish hue and finally to black.  

FWIW I used water based poly. No complaints. Note: I think that last pic of mine is after staining before the ploy

In reply to coexist :

I’ve never used beeswax on a floor but I’ve heard of it. Heard it’s nice too.  Is that the same stuff you suggest?  

frenchyd said:

Curtis said:

I've done many floors.

I agree to not fill the gaps.  Anything you put in there will pull and crack apart eventually and look like a botched repair.  Even if it doesn't pull apart it will scream "look at me, I'm a repaired spot."

I'm also a bit surprised at the recommendations for shellac.  I'm not a fan.  It is 800-year-old technology that is literally bug poop dissolved in vodka.  If you try to refinish it, you can't sand it (it melts instead of sands) and is not nearly as durable as poly.  It also comes in colors ranging from fecal brown to pumpkin orange.  I've probably done 50 floors and used to teach classes on it for Home Depot.  4 coats of a properly-prepared poly finish will last you 20 years on even the highest traffic areas.  Even if you cared about scratches, they're super simple to repair, and if you don't like it or want to change it 10 years from now you just sand it off.

If I'm refinishing a floor with Shellac on it, my quote instantly goes up by 50%.  It must be stripped chemically.  Spill a gin and tonic on it, it is stained for life.  Water spills have to be cleaned up right away.  Wife's nail polish remover will bubble it up like paint stripper.  Poly is remarkably durable and so much less succeptible to damage from liquids.  It is also less hard which is good for a wood floor that expands and contracts.

To me, recommending Shellac for a wood floor is like recommending a donkey for a work commuter vehicle.  Poly is infinitely better in so many ways.

I’m sorry but you really don’t know what you are talking about 

First shellac is thousands of years old. Not 800.  Second shellac is harder and much more durable than poly  (plastic)  it’s only weakness compared to poly is it’s resistance to water damage.  Long term water damage. If you leave water on a wood finish for 5-8 hours the shellac will turn white. But unlike poly you don’t have to sand it off  to repair!!! 

Stripping shellac is done with the same stuff you apply it with Denatured  alcohol.  But it will sand off just fine!   

Unlike poly it’s not toxic 

pills are coated with shellac.  Let’s see you eat a poly coated aspirin.- no wait, don’t. Poly is toxic.  

Spill gin and tonic on it you’d wipe it up same as any spilt drink. Spill  a dark red wine and leave it you will get a stain. But bleach will remove it pretty well ( nope not perfectly but what kind of drunk leaves split wine on the floor)?   

I don’t know what nail polish remover will do to shellac probably not much but it will ruin plastic, er,  poly. 

Fire repair damage specialists use it to coat wood to keep the burn smell trapped in the wood to avoid tearing down the whole house because of fire damage. Kilz is shellac with paint to eliminate stain from previously leaking roofs showing .  

I understand why floor refinishers use plastic on floors. Like you said it is softer which means it will scratch  and mark easier,   ensuring future work.  And as you said require sanding. Which means that you will soon need to replace the floor. 

Over a decade ago I helped a friend refinish the dance floors in his old house. The floor was over 100 years old.  And hadn’t been used since the 1950’s  although kept clean by the housekeepers  the room still had a coat of dust which we wiped off with water. 

Then we cleaned the shellac with denatured  alcohol  and gave it a top coat  of shellac and it looked great.   Total time for about a 35’X80’ ball room floor was about 3 hours  

Shellac is used on fine musical instruments like a Stradivarius Violin and pianos. Because of its rich yet not plastic appearance. It’s also used in all collector pieces of furniture  again because it’s ability to be invisibly repaired without the need for sanding.  

The clear is the most commonly used color of shellac. But yes it has a light clear Yellow color to it that still beautifully shows all the grain and color of the wood beneath it.  It goes from there to Amber and then a reddish hue and finally to black.  

You just gave me a bunch of reasons that would make sense if I were eating my floor or selecting a coating for a sonically-tuned instrument.  Putting poly on a violin would make it sound like its made of styrofoam.  Eating polyurethane is not something I think we're entertaining here.

Shellac is old-school.  It is not durable to spills, chemicals, or abrasion like Poly is.

I have put acetone (nail polish remover) on floors many times.  It is the standard way to test for shellac.  If you put it on and nothing happens, its varnish or poly.  Varnish often will be hazy for a day or so, poly does nothing, and shellac will look wrinkly like aircraft stripper on a valve cover.

Just because shellac was the choice of Stradivarius (actually, Antonio Stradivari used a mixture of acacia gum, honey, and egg whites) in the 1600s doesn't mean it is the best thing for a floor today.

We'll just have to agree to disagree.

frenchyd said:

In reply to coexist :

I’ve never used beeswax on a floor but I’ve heard of it. Heard it’s nice too.  Is that the same stuff you suggest?  

I personally don't prefer it.  You will be limited to a matte finish, and you will never be able to put anything else on it.  Once it is waxed, it will only ever be waxed (or replaced or covered).  You'll never be able to get the wax off since it soaks in.

Waxing a wood floor was a way to add durability and life to a floor in something like a thatched-roof hut.  It prevented water intrusion/rot and bugs eating it.  It was a way to use existing raw materials to help, but as a durable wood coating it will be disappointing.

In reply to rustybugkiller :

Looks fantastic! 

The flooring has all been refinished at least once in the past, probably more times than that. Plenty of material left on the boards upstairs, but downstairs there probably isn't much more than 1/8" left above the tongue and groove. Plan will be to rent a large orbital sander when the time comes, as I think a drum sander will be too aggressive and I haven't had good experience with those in the past, just skim enough to take the existing finish off and smooth it out a bit.

I have no idea what's on it now for finish, but perhaps I'll try Curtis's acetone trick this evening. Whatever it is, it sands off easily enough. My original inclination for the new finish was water based poly, but I'm certainly not dead set on anything yet. Looks like I've got a lot more research to do.