Diy background - colored cement rubbing off

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Registered Member
Original poster
May 3, 2019
Hi everyone.
So I did a stone wall aquarium background for my 30 gallon community tank.
Background is made from styrofoam, coated with 1St layer of cement mix, second and third layer added color to it and coated it.

Now after I had the initial first layer on I siliconed the tank and fastened the background inside. It looked cool bit after several days running the water still looked cloudy and the fish colors seemed to get lost on the light grey background.
So I decided to empty the tank again, let it dry and then I coated it with the colored cement. It's been 24 hours since the last coat and I'm noticing that the cement still looks wet in certain spots which could be due to not good enough ventilation since the background is already siliconed in the tank.
But my concern is that the spots that are dry, when I touch them the color just rubs right off.
Has anybody done a did background with colored cement and had this issue? Is this something that's gonna be OK once the tank is filled and drained a few times to rinse everything off or does this mean the color is just gonna wash right off?

I'm really at a loss why it's doing this, any help/ advice would be appreciated