Confused about my floors being grounded

[Naphtali]

I am a complete novice when it comes to electrics but I have recently bought a grounding mat and so I've been doing some measurements and I'm totally confused by something.

Upstairs I get a reading from my body of 5 (ish) volts (bare foot). When I touch the earthing mat this goes down to 0.2. Great. The mat clearly works. My body measurement is consistent throughout the upstairs with some minor expected variation depending on where I'm standing.

The confusion comes when I go downstairs. Using the same equipment and the same method my body measurement is between 0.5 and 0.8 and this is consistent throughout the downstairs of the house regardless of the floor type (sandstone tiles, wood flooring, ceramic tiles and carpet). This is without using a grounding mat obviously. Thinking that the floors must somehow be grounded throughout the downstairs of the house, I decided to test that by intentionally ungrounding myself by putting rubber-soled shoes on. There was no change. Still getting measurements similar to those I got when touching a grounding mat upstairs. I've tried everything I can think of to distance myself from the allegedly grounded floor. Wellie boots, plastic, sofas, wooden tables, several pairs of shoes and the measurement hardly changes at all no matter how much I try. How can this be? What am I missing?
I'd be happy if the floors were grounded - saves me some money on grounding mats, but the fact that I can't unground myself is making me think I'm doing something wrong.

 

[James]

Draw a picture of what you are measuring between.

be very cautious, introducing an independent and isolated source of ground could be fatal if your body is wet and connects between 2 different Earth potentials

 

[Naphtali]

Draw a picture of what you are measuring between.

be very cautious, introducing an independent and isolated source of ground could be fatal if your body is wet and connects between 2 different Earth potentials

Thanks for the reply. So, I have a grounding mat which is plugged into the wall socket and only attached to the earthing port. The other prongs are plastic and the socket isn't 'on'. I then attach the black lead from the multimeter to the grounding mat and I hold onto the red prong. Multimeter is set to V~. This is how I get the readings both upstairs and downstairs of what I assume is the voltage I carry with me in my body. The grounding mat is small - the size of a mouse mat so I keep away from that and only touch it to see what difference it makes when I'm in contact with what I'm assuming is the grounding of the house (through the sockets). I'm confused as to why the readings are so different between upstairs and downstairs and why the surfaces or objects I'm standing on seem to have no impact on the readings downstairs at all.

 

[DPG]

Measuring voltages like that with a high impedance multimeter will always give varying results. You could hold one lead in mid air and still get a reading.

Do the mats have a resistor in series with them? ie. between the earth connection in the plug and the mat. This is important for safety reasons, and is the reason why antistatic products typically use a 1M resistor in them.

To be honest I'd recommend going outside in the fresh air rather than standing on a mat, but each to their own. Being of an engineering background I am always very sceptical of this sort of thing.