Do you have mystery marks in your wood floors?

Have you been Googling “wood floor problems?”

You just bought a house and pulled up the carpet to get a good look at the hardwood floor the sellers promised, and you find blemishes you don’t even have words for. If you don’t have the words, how can you figure out what is going on?

Let’s start with some photos of known issues.

The pictures below are just a few examples of problems were able to recognize and explain, even if there wasn’t an easy fix. If you have a baffling floor issue, start with this collection. Let’s take advantage of all the sad floor stories we’ve collected and make them work for you, our future customer.

But what if I don’t see my floor problem in these pics?

Sometimes there are just problems that defy all obvious explanations. With all humility, this is where you might want some help from Pete’s consulting service. Figuring out what went wrong on a floor can stymie even the handiest weekend warrior. Heck, it can stump us too.

But until you know what went wrong with your hardwood, you might not want to dive in to solution that you just found on Reddit.

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Discoloration from rug backing or underlayment

We wish it were better known, but material that is most commonly sold as rug underlayment is made from a plastic that is known to interact chemically with the plastic in the polyurethane finish. We aren’t chemists, but you don’t need to be to see the discoloration that results.

In this example, there was a line of plastic glue around the edge of the rug where a fringe had been attached. When the rug was removed, the glue had left a shadow. The answer to this is to use only pure latex rubber rug underlayment. Rug-check plus is guaranteed pure latex – use it!

Why is there a line of lighter-coloured urethane across my floor?

Ignore the three bright reflection spots – that is just bad camera work. The issue here is that band of lighter-colored finish that runs against the grain.

Here’s what happened: this line is right in front of a refrigerator – you can see its foot in the upper left corner of the photo. The refrigerator was dragged forward and then pushed back into place, leaving two deep scratch lines in a brand new floor.

A different flooring contractor was brought out to try to fix the problem. They sanded out the scratches, but then when they recoated the irregular lines, they used a waterborne poly instead of an oil-based poly. This was a problem because the waterborne finish is much lighter and less yellow than the unsanded oil-based poly just adjacent to the repair.

Small repairs are already challenging, but at a bare minimum, use the same finish that is already on the floor you are fixing.

Where did this weird floor shadow come from?

This first-time sanding customer was determined to stain their floor dark. We tried talk them out of it, tried to warn them of the fickle nature of old wood and the challenges of sanding, but they would not be deterred.

Halfway through their stain application, angry phone calls and texts started to arrive. “What is this?  Did you sell us a bad batch of stain? Why is this happening?”  This, my friends, is one of the reasons we hate stain.

We have no idea what happened here. This mark was not visible in the bare wood. It looks someone could have wiped the wood with water, popping the grain before the stain was applied. But it could just be an inherited organic stain, a ghost mark from the floor’s past.

Just because a floor looks good naked doesn’t mean it will look good after staining.

What the heck?

This floor has TWO kinds of mystery marks going on. The black marks are easy to explain. This fir floor is a very tannic wood.

When metal gets wet, it reacts with the tannin, making these recognizable small black marks where the nails are. You will often see this under leaky windows or at bathroom doorways. Much like pet stains, these are deep and don’t sand out. But they are usually minor and every house with any age will have some and prove that your house is authentic and well-loved.

The other marks you see look like narrow pour lines of liquid. As this floor was being coated, the finish was poured in lines and left too long before the finish was spread across the wood.

Sometimes called a “burn pour” we see this especially on dry floors in winter. Caught soon enough, these will emulsify into the next coat that will be applied on top of this. 

Staining makes more mysteries

Can you see that the center of this floor is lighter than the wide ban around the edges? This DIYer did too.

They weren’t a Pete’s customer, but they called for help in the middle of the stain application process. It turned out that they had used a drum sander for the middle of the floor (hence the drum dig marks obvious in the field) but they had been warned not to use an edger around the perimeter.

So they used a bench belt sander. And it looks like they did all the belt sanding without overlapping with the drum, so they kept edging a little deeper into the field each time. And then they wiped up their dusty edges with wet rags. That opened the grain and allowed the stain to take deeper and darker around the edge.

A true mystery

We never did discover the actual cause of these marks. We suspect they are burns from actual heat source, not a solvent or chemical burn as there is no evidence of liquid flow or pooling.

A space heater? Alas, these marks did not lighten significantly with sanding and became a source of vintage character for this floor.

This isn’t a mystery; it’s a feature!

When oak logs are quartersawn, the resulting boards have the tree’s growth rings at at 60-90 degree angle to the growth rings, it reveals this characteristic, beautiful figure in the wood. They are known as medullary rays, and they are only seen when the wood is cut at that angle.

Because it is more wasteful to cut wood this way, quartersawn wood is more expensive and less commonly seen in quantity in a typical red or white oak floor. So, homeowners who are unfamiliar with these odd lines think that there wood is damaged. Quite the opposite – quartersawn wood is prized for this unique patterning.

Be delighted about this mystery mark.

Don’t see your problem here? Check out some other mysteries below.