Revisiting The Floating Island Idea

I have never seen the need for mountains, they just get in the way and the only use they serve is for a few people to climb up them and stick a flag in the summit but of course we can't do much about them as they are thousands of miles up it the air which is a lot of rock to find a use for.
I did ponder here if we couldn't chop the tops off some mountains and make some more islands in the 71% of the planet that is water as way of accommodating the 7 billion and growing population of the planet but the UN never returned my phone calls and the owner of the Ben Nevis Mountainside Cafe threatened to sue me so the idea was quietly dropped.
On further reflection we may not need to go sawing mountains in half after all because a new island has appeared in the mid-Pacific made from plastic and other rubbish approximately the size of France caught between the ocean currents.
If we can get our best minds finding a way to somehow secure it together and pour some kind of sealant over it so it's a solid lump and take the top off a mountain somewhere (not Ben Nevis) and we could actually make a floating Island out of it.
Even if it isn't safe for humans, not sure about the toxicity of all that plastic but if people can't use it at least the wildlife could.  
As it seems it isn't going to be cleaned up and is just going to be left there anyway, seems sense to make some use of it even if it's just for nesting birds or homeless Polar bears paddling around looking for an iceberg to cling to.