Mystery Photo: Dark Spots on FRP

Dark Spots on FRP

What in the world?!?

Almost all of the interior of our butcher shop is polyurea on concrete. This is a tough, easily cleaned laboratory grade surface that lends itself well to the sanitation levels I want for our USDA/State inspected butcher shop.

Much more common in butcher shops is Fiberglass Reinforced Plastic (FRP) which is a pebbly wall covering you may also see in commercial bathrooms and kitchens. We have a very small amount of that behind one set of shelves in the initial cutting room (iCutter) which covers the doorway from iCutter to Cave. This provides separation between our first butchering space and the still to be finished of construction zone of the rest of the butcher shop.

Yesterday when I was finishing up some plumbing I noticed four dark round splotches on my pristine white FRP. Eek!

Can you guess how these mysterious dark circles formed? Leave answers in the comments section.


1) It wasn’t space aliens.

2) It has nothing to do with crop circles.

3) It smears away easily.

4) Hover mouse over this text for another clue.

5) Hover mouse here for another clue.

6) Hover for another clue.

7) Hover one last clue.

Well, that’s more than enough clues if you know my penchants for leaving something inside concrete matrices and other hidden places. Oops, that was another clue.

For bonus points, guess why I might have put what I put what I put in there that would form those circles. The clue is also in the photo if you think about how wet that room gets.

Answer #1 Don’t peek until you’ve left an answer in comments!

Magnets are attracting ferrite iron dust from the air. The pattern shows the shape of the field.

Answer #2 Bonus Don’t peek at this either until you’ve left an answer in comments for the bonus question!

We will hang a cover over the air duct grill when doing wash down to keep water from spraying into the duct work. The cover will be ferritic stainless steel and stick to the magnets embedded in the wall.

Outdoors: 64°F/40°F Sunny
Tiny Cottage: 66°F/62°F
Butcher Shop: 53°F

Daily Spark: If life hands you melons, you may be dielectric.

About Walter Jeffries

Tinker, Tailor...
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12 Responses to Mystery Photo: Dark Spots on FRP

  1. AliceDewitt says:

    aaaa….. I dont know what they are caused by but they look like a mans nippls to me…… Weird!

  2. Edmund Brown says:

    Some sort of electrical coil behind the wall inducing a magnet that attracts and grabs dust?

    Either that or you embedded a magnet on purpose to hang signs without hangers…

    I hope you’re wearing dust masks!

  3. Brian Light says:

    They are from the magnets you buried in the wall. Specifically, the iron dust from Will’s project adhering to said magnets, I believe.

  4. David Lloyd Sutton says:

    What Brian said.

  5. Andy Willis says:


  6. David B. says:

    I’m thinking magnets behind the fiberboard that attracted metal particles.

    Or there is something cold behind there and it is causing condensation that is collecting dust.

  7. Bob says:

    I would say that it is mildew, given that the room is so damp. It’s due to condensation, but I have no idea what would be behind that wall that is making those two spots colder, perhaps plumbing? The spacing looks right for a sink on the other side of the wall.

  8. Nance says:

    I was going to say ‘iron filings’

  9. Nance says:

    in fact I did say it. : ) like that old game where you used a magnet to move iron filings around on his head and chin.

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