[chelmostef]

I was raised on a boat as a child. The boat had a wooden hull which was sheathed in concrete pushed into a wire matrix. Thus effectivly a very big faraday cage, we could not pick up radio in the hull or "downbelow" as we used to say. We had to run the arial up and out to get a signal.
It does depend what fequency you are trying to block as this depends on the size of the holes in the matrix. For instance the holes on the front of a microwave are very small, which stops the waves escaping out of the microwave.