how to fill gaps in wood floors with oakum
colonial farmhouse,  DIY

How to Fill Gaps in Wood Floors with Oakum

For the small percentage of you living in really old houses (bless you!), let me share one of the more historically accurate ways to fill gaps in wood floors with oakum.

This is the information I needed when we bought our Colonial Farmhouse and didn’t know what to do about the gaps between the original wood floorboards. I had to comb through the internet to find bits and pieces of information, so I’m combining what I learned all in one place with links out to the information that helped me.

If the gaps in your wood floors don’t bother you, leave them. But if your kids can push things through the cracks like it’s their very own slot machine, if a cup of juice can spill through the gap in the floors and land on the basement floor below, or if bugs (so many bugs) can crawl through the cracks, you may want to consider filling the gaps between the wood floors.

Why Are There Gaps Between Old Wood Floors?

There could be a variety of reasons, but many wood floors from the 1700s and 1800s (or earlier) were nailed to the floor joists with a bit of a gap between the planks to allow for expansion and contraction of the wood between seasons.

Some of the oldest floors in our house (circa 1780s) have wider than expected gaps because edges of the boards have worn or broke off.

In some areas of our home where there’s not a ceiling below those floorboards, the gap in the floor allows you to see right through it to the room below.

music room wood chandelier

How Were Gaps in Wood Floors Filled in These Old Houses? 

The short answer is they shoved something in-between the gaps in the wood floors.

This was likely done with either oakum, natural fiber rope, or cotton cloth. I’ve even heard of people finding newspaper shoved between the gaps in their wood floors.

People sure do find a way to fix a problem, don’t they?

What is Oakum?

Oakum is what was used to caulk wood ships.

How did oakum come to be? Sailors used to oil the natural fiber ropes for rigging to make them last longer. When the ropes finally wore out, someone would untwist the rope (it was a terrible job) and the remaining oil-soaked fibers were called oakum.

Oakum was widely used for all manner of applications before the invention of chemical caulking. It can be used to seal plumbing pipes, to caulk cracks in concrete, to seal wooden ships, or for hoof packing for horses.

Nothing was wasted back in the day, so oakum was also sometimes used to fill the gaps between wood floors.

Oakum is still used today, especially in the construction of log homes. However, oakum is now manufactured, as opposed to being reused from marine rigging, so you can expect a consistent result from the oakum you purchase.

Oakum appears to be manufactured by a few different companies, or at least, sold under a few different brand names.

Brown oakum is made from natural fibers (could be a combination of jute, hemp, and/or burlap), oil, and often bentonite.

White oakum is made from jute, Bentonite, and water.

Bentonite is a clay that expands when it encounters water.

What Do You Need to Fill Gaps in Wood Floors With Oakum?

You need oakum. It is usually sold in 1 pound or 5 pound increments and at the time I’m writing this I found it to be extremely affordable.

(If you don’t want to use oakum to fill the gaps in your wood floors, you could also use a natural fiber rope either as is or stained to match your floor. The same installation techniques detailed below will apply.)

You’ll also need a tool to shove the oakum into the floor gaps. I used a multipurpose paint tool, but a putty knife would work in a pinch.

I wore gloves because I didn’t like how the brown oakum I ordered felt on my hands.(I learned about the white oakum later.) It feels a bit like touching really oily human hair. Aren’t you glad you have that visual? Ha!

how to fill gaps in wood floors with oakum

Installation Technique to Fill Gaps in Wood Floors With Oakum

The oakum comes in twisted strands that are super easy to pull apart.

Separate the strands of oakum into a size slightly larger than your gap. Then tightly re-twist the oakum so it resembles a rope strand. You need your oakum strand to fit very snug when you push it into the gap, but not so tight that you accidentally break off the sides of your wood planks to insert it. I learned that the hard way.

The oakum can be trimmed to the length you need with sharp scissors.

how to fill gaps in wood floors with oakum

Then using your paint tool or putty knife, press the oakum into the gap between the wood planks. You want to push it down below the planks slightly – at least 1/8 to 1/4-inch. However, I’ve found the farther you can push the oakum into the crack without pushing it all the way through, the better it will be later for cleaning purposes.

If there are a lot of “flyaways” from the fibers, try twisting the oakum strand tightly before pushing it into the gap. If there are any random flyaways when you are finished, you can trim them with scissors.

Learn from my mistakes! In the below picture, I should have twisted the oakum tight. I ended up re-doing this section later to eliminate all the flyaways.

how to fill gaps in wood floors with oakum

The paint tool worked great because one of the ends had a rounded point that was good at working the oakum into a slightly tight area.

It was easy to accidentally push the oakum all the way through the larger gaps. If this happens, just pull it back out with your paint tool and try again.

how to fill gaps in wood floors with oakum

I also used the oakum to fill or pack other random holes in the wood floors like gaps left by nails, breakage around a wood knot, or space around a wood plug.

The gaps between our floorboards were not uniform because why would this old house make it easy? The benefit I found with the brown oakum is that the fibers are super flexible, I think, partly because of the oil. That meant that I could form and reform strands to a custom width.

I could also wrap the start of one strand of oakum around the end of another so that there wasn’t any break in the strand as I was filling a long gap. I found this tip to be especially important later when I was mopping the floor. In the places where I had a small, random “tail” of the oakum lying too near the top of the gap, it was easy for it to catch on my mop strands.

I was able to repositioned the oakum when I figured out what was happening and now know how to install it better to avoid this problem. This is the mop I was using with just a bit of water.

how to fill gaps in wood floors with oakum

Update July 2021: After living with the oakum for 2 months, I had some sections that needed to be redone because I didn’t take my own advice. Ha! Figures! There were areas of oakum that were pulling up because I didn’t have either enough oakum in the gap to make it tight or I didn’t twist two sections together tightly enough to avoid a tail sticking up. Basically, it took some trial and error to get good at the installation technique. But, overall, I’m happy with how it has performed in regard to cleaning. As long as oakum is in the gaps tight and slightly below the surface, I haven’t had a problem with vacuuming with a wand or taking a damp rag over it.

Downside of Filling Gaps in Wood Floors With Oakum

I’m sure the internet will help me out with this (ha!), but I did think of two downsides to using brown oakum to fill the gaps in our wood floors.

(Remember, I’m figuring things out as I go and didn’t learn about the white oakum until later. You can learn from my experience, but be kind with your comments!)

First, the brown oakum has oil in it and for a variety of reasons, you might not want that in your home. Natural fiber rope or white oakum might be a better choice in this case, but I don’t know if either will match or blend in with your floors.

Second and related to the first downside, after inserting the brown oakum in one particularly large gap (1/2-inch) where it left a lot of the oakum visible and closer to the wood surface than I would have preferred, I did pause and think that maybe if I had babies crawling around on the floor I would have used a natural fiber rope or white oakum in that gap instead of the brown oakum that had the oil on it.

On the other hand, I chose the brown oakum over rope because I was going for maximum protection against water since this particular floor was in a wet area. If it could seal a wooden ship, it should be able to to protect my home.

Update July 2021: The oakum exposed to the surface did dry out and become less oily over time, which addressed some of the above concerns.

Final Thoughts on How to Fill Gaps in Wood Floors With Oakum

I’m writing this tutorial a month after we used the oakum to fill the gaps in our wood floors.

There are definitely pros and cons to using oakum to fill gaps in wood floors. So far, I’m happy with the result in terms of how the oakum blends into the floors and how it is performing, but the bottom line is I’ll need to watch the oakum over time and report back on how well it holds up to daily use, cleaning, if that top layer remains oily, etc.

If I decide I don’t like it, it’s super easy to pop it out and start over. I have about $25 of oakum and an hour’s worth of time into this experiment, so I’m not out much if I decide to try another solution to fill the gaps in our wood floors.

There are sections of our wood floors where the gaps have been filled, I’m assuming 150 – 200 years ago, and the filler that was used has hardened. I’m assuming they used oakum maybe with some tar on top, but I’m not certain. That’s another reason why I’m curious to see what happens with the oakum I installed. There’s just not a lot of information available about the longterm viability of this solution. I’m hoping that together, as old house owners, we can change that!

Our original wood floors are one of the absolute best parts of this Colonial Farmhouse. If those floors could talk! I am so happy we get to live here and it is important to me, as a caretaker of this home, to respect its historical nature while balancing the needs of a modern family.

If you try filling the gaps in your wood floors with oakum or a natural fiber rope, let me know about your experience in the comments. Your insight might be able to help someone else who wants to tackle this project.

Project Resources:

Painter’s Tool: (similar)

Brown Oakum: Amazon has a 1 lb. bag. Remember that you will be separating the strands into smaller pieces, so 1 lb. is a lot more than it seems. I’m not sure how many gaps it will fill though. If you need A LOT of it, I ordered a 5 lb. box Nupak Oakum from Schroeder Log Home Supply. I haven’t finished using my box, but I can probably tackle most of the rooms in our house with that one box.

*affiliate links are used in this post*

Website Resources: 

The following websites helped me tremendously in learning about oakum and its uses and I think they will help you too.

The American Institute of Architects Historic Resources Committee

Sage Restoration

Nupak Oakum

This Old House

Old House Web

If you have information to add about this topic, please leave it in the comments section so others can learn as well. Thank you!

Thank you for being here today! Here are some other blog posts you might enjoy.

All About Rim Locks (Vintage Door Hardware)

Turning a Tub/Shower Into a Closet Without Doing Damage

All About Our 240-Year-Old Pumpkin Pine Floors

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One Comment

  • annisa

    Hi Annisa,

    I came across your blog post about how to install oakum to fill the gaps in your 1880s hardwood flooring. I tried to ask a question in the comments and I kept getting an error message, so I apologize if it went through a bunch of times and I didn’t know it ha!

    It was a great article and I’ll definitely be using those directions! We also have an 1880s pine floor with “see through” gaps in many places. We plan to sand and polyurethane the floors as well. In your opinion, would you suggest that we sand and poly first, and then do the oakum? Or would it be helpful to sand, then oakum, and then polyurethane on top to “seal in” the oakum? Just wanted to get your two cents since you’ve worked with the stuff 🙂 Thank you!


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