Telltale Water Stains

Removing, fading them can be a DIY project

By Laura Kourajian, Certified NDSU Extension Master Gardener,

I doubt I am the only plant lover with water-stained woodwork – dark stains that perfectly mimic the round bottom of a plant pot, the wedges of a plastic protective tray and the white-rimmed spatters of ancient dried water droplets. Not only are these stains unslightly, but they taunt me about my penchant for overwatering plants. 

Fig. 1 This area in front of the window shows evidence of black water stains from potted plants. The stain on the left shows the wedge outlines of a plastic protective tray.

Hunkering down during the pandemic gave me the opportunity to figure out if I could remedy this situation, get rid of the stains and live happily ever after in our family room. There is an oak ledge that rims three outside walls, marking the top of the foundation, in this garden-level room. There are two windows, one east-facing and one north-facing, and the oak ledge makes a perfect spot to set plants where they’ll get natural light. 

Google, Pinterest, the local hardware store and lots of elbow (and shoulder) grease gave me the resources I needed to get rid of or fade these stains. 

Fig. 2 The materials needed to remove or diminish the water stains included a stainless steel scrubber, Bar Keepers Friend cleanser, and oxalic acid.

To start, I sanded the finish from the ledge, all the way around the room. Sanding at near-shoulder height was physically taxing, but the results were encouraging. I wasn’t concerned about removing the stain, only the finish, exposing the water stains so the oxalic acid would be able to go to work doing its bleaching work. 

Oxalic acid is very strong chemical available in granular form at most hardware stores. It is mixed with hot water and spread over the stained area. In my case, I mixed only a small amount and used a foam brush to apply it liberally to the stained area. The instructions on the oxalic acid are adamant about wearing gloves, safety goggles and protective clothing to avoid skin burns. 

Fig. 3 Oxalic acid solution was applied to the stain with a foam brush.  The solution was applied twice and resulted in lighter, but still visible, stains.

After wiping and rinsing three times, per instructions, the acid had lightened the stains but they were still noticeable and ugly. The instructions indicated a second application might be necessary, so I went with Round 2. Again, the stains were lightened, but except for the light droplet stains, they didn’t disappear. 

So, I did more reading. On Pinterest, I found several champions of using Bar Keepers Friend,  that gritty cleaning powder kept on standby in the dark recesses under many kitchen sinks. Apparently Bar Keepers Friend contains a small amount of oxalic acid, so works to lighten and remove stains. 

I bought a can of Bar Keepers Friend (found it at my nearby Runnings after striking out at the grocery store), mixed up a paste and used a wooden craft stick to spread it on the darkest parts of the stains. Once it had dried, which took several hours, I used a plastic putty knife to scrape it from the wood.

Fig. 4 In a second attempt to remove the stains, a paste of water and Bar Keepers Friend was spread over the stains and left to dry.

There were traces of the white paste embedded in the grain of the woodwork. Pinterest offered several suggestions for getting rid of these, including sanding with ordinary sand paper, scrubbing with steel wool and scrubbing with a stainless steel scrubber. (One site warned of using steel wool, noting the shavings from the steel wool are hard to clean away and if left on the surface and sealed into the wood, they would eventually oxidize and create the black stains like the ones I am trying to remove.) 

I used the stainless steel scrubber, and it worked beautifully. It quite literally scrubbed the embedded paste from the wood grain and, in a wonderfully surprising bonus, it scrubbed much of the remaining dark stains from the woodwork. (I threw away the scrubber when I was finished; it should not be used for cleaning pots and pans after being used for removing stains from wood.)

Once I had removed as much of the stains as I felt I was going to get, I restained the wood and coated it with three coats of water-based polycrylic, following the instructions on the cans. Polyurethane also would have worked well as a finishing coat, but it is oil based and has a much stronger odor, which I was trying to avoid in the closed house in the winter. 

Fig. 5 The finished results show the wedge stains from the plastic tray are almost invisible, while the adjacent black stain has been diminished significantly.

The pictures tell the story. The stained wedges shaped to the bottom of the plastic protective tray are nearly unnoticeable. If you didn’t know they were there, you’d never be able to tell. The round pot-shaped dark stain next to it proved a little more formidable and while the traces of the stain are still visible, I’m happy with how much of the stain disappeared. 

I’ve removed all the potted plants from the ledge, and while I anticipate I’ll have to use the ledge again in the future, since the window is a good source of natural light, I will place them on a small rack on top of the ledge to keep them from sitting directly on my newly refinished woodwork. 

By worddirt2020

Dr. McGinnis is the Director of the NDSU Extension Master Gardener Program.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s