My mother's house came with a small concrete pond, kind of like a shallow bathtub or a double-wide washtub. We'd ultimately like to get some plants and maybe a few goldfish going in the pond.

I'd like to stain the glaring white concrete some more natural-looking brown to black color, but both she and I are both very allergic to paints and chemicals.
What would happen if I went to Starbucks, got several bags of their used coffee grounds, filled the pond with them, and watered them into a thick coffee slurry-soup?
I'd leave it there a couple of days, then shovel and scoop it all out, hopefully uncovering newly dark-brownish concrete.

Would this be likely to hurt anything?
Would the concrete take a stain from coffee?
Would this be likely to be a great big hurking waste of time and effort?

I'd appreciate any and all thoughts, opinions, ideas, etc :)

Thanks,
- Evelyn

If this is new concrete, you might want to fill it with water and vinegar (a few percent) to help neutralize the alkali from the cement. This helps provide a surface that things can grow on - like bacteria, moss, algae. They will eventually coat the cement if you make it a pond (get rid of the vinegar before you put any fish in). If you want to change the color NOW, the coffee might do something, but I wouldn't expect instant coffee...color. And the residual caffein might make for very lively fish. How about mud? or inorganic cement colors from HD. The black tends to be plain old carbon black - nothing exotic. And there are plenty of cement paints made for the purpose, but they won't last long under water. If you are really ambitious, do what cement pool companies do when a customer wants a dark pool - they plaster with cement plaster mixed with coloring (like the carbon black). Good Luck

[I know I play fast and loose with staying on topic over at the Japanese Gardening forum, but wasn't sure they'd appreciate this over there - or have much in the way of likely answers :) I may try this over in Ponds, but this forum seems to have the go-to guys for concrete...]

The pond is not new, but had been in place a while when my mother bought the house ten or twelve years ago. During that time she has become less and less capable of caring for her yard, and I'm sometimes able to help fill the gap.

My most recent work on the pond was to bail out a three-or-four year accumulation of very black anerobic plant matter and liquid slime. Two or three good rains later, the concrete was back to not really a truly glaring white, but an annoyingly reflective buff (a slightly defective rain gutter overhead provides easy, if weather-dependent, rainwater filling). Whatever bacteria/algae/slime might grow there seems to be failing on the job.

"inorganic cement colors from HD"
Not sure what you mean here. Would that be like the re-plastering you mentioned? Who/what is "HD"?

"How about mud?"
Now there's an idea. I could pretend that this is a traditional Japanese clay-sealed pond, without the leaks :)
And it'd give me a good excuse/reason to read up on how those work.

But I'd still love to hear from any of these other go-to concrete guys as to what they think of the coffee-staining idea :)

- Evelyn

PS. I promise that, if I do this, I'll give it a couple rainwater changes, and then a couple weeks with just plants before bringing fish in, so as to avoid giving them a coffee buzz :)

The coffee would not be permanent.

I just remembered a mistake I made once that stained some concrete for a long time. I had a place with many black walnut trees, and I collected a drywall bucket full to shell, but I forgot to bring them in and the bucket filled with rain water. When I reached in some weeks later, my hands were stained medium brown instantly, and when I knocked the bucket over, the concrete drive apron was stained brown for a long long time. I'm sure there are ways to control the process, but I think you should have plenty of black walnuts in Oregon and this is the time of year to find them falling. Maybe a walnut cappucino double latte with extra foam would give you the right mix. Hope this helps.

I think the extra-skinny walnut half-caf double cappuccino, with a twist :), could be just the thing I was looking for - I like this idea a lot.

Thanks again,
:) Evelyn