I have made an earthern floor on my yurt platform.
It is build op in various layers.
First layer is crushed rock en then a layer of siky sand. On thop of that I have put the cob in two layers.
Since it has been a very wet summer here, the cob doesn't seem to dry, I guess my crushed rock layer doesn't stop the moisture from the ground level to rise upto the cob.
I didn't wan't to use plastic as a moisture barrier.
Now I wonder if the cob floor dries this summer in good weather, and I finish it of with lineseed oil. Will it keep hard in the winter? Even if it becomes wet again outside?
The problem you have is very common, but very difficult to remediate. I recommend not using sand, just stones and gravel. You start with larger cobbles and reduce the stone size with each layer until you have gravel on top. This ensures that you don't wick water up out of the soil while providing a solid base. It sounds to me like the sand has infiltrated the gravel layer and is wicking moisture up through the floor.
To remediate I would; dig up the entire floor and save the clay. Remove the sand and gravel. Dig the undisturbed soil so that it is draining away from the structure. Find lots of cobble rocks and install the floor all over again. I would also add lime to the clay mix to help the floor withstand the occasional wetting from below without turning to mud.
I'm trying to visualize this floor. Is your yurt platform raised? I wouldn't think that much moisture would wick up the gravel and sand to permeate your floor if there is air under your yurt platform. If it is really humid your floor may just be taking a long time to dry. How deep is the gravel layer, sand layer, cob layers? If the earthen floor is really thick it may take a bit of time. How long has it been drying for, my earthen floor is on six inches of drain rock, 3 inches of road base, followed by 4-6 inches of cob.
Whatever you do, don't try oiling until the floor is dry. You will trap moisture in the floor and definitely have to redo the entire thing. Put some fans in there if possible and get air circulating.