It's not nylon, it is fibreglass mesh that gets embedded with thin coat renders. It is alkaline resistant, with approx 4x4mm grid. The mesh itself does next to nothing by itself, but once it is embedded in the render it makes a huge difference to the performance of the material with regards to attack from outside. As far as any rodents are concerned it is the same as a concrete wall - if they eat through the approx 4mm cement based render then they can reach the polystrene but I doubt that any rodent will be aware that it isn't a much thicker layer of hard material.

I don't really understand how you did it with dabs. The easy way of doing this well that I did is to;
1) Sand the E/XPS boards and get rid of any surface dusting
2) Use a hawk and trowel, apply appropriate adhesive over the boards - getting good coverage but not too worried about depth (I used Parex Maite - would recommended)
3) Use a 10mm square notch trowel to get even 10mm beads over area you are meshing
4) Cut mesh to size, use trowel to embed mesh. This will show up any low spots which need further Maite.
5) Finish as appropriate. Topcoat/Dash/Paint - but whatever, this layer you have completed will completely change the way the EPS behaves, give it a good kick and you will hurt your toe.....

The Maite by itself does little spread straight onto polystrene - it would crack easily and allow beasts to start tunnelling easily via cracks. The addition of the mesh completely transforms it and it gives a solid finish. Parex just describe their mesh as glass fibre reinforcement, don't know what the treatment is for enabling it to resist the alkalinity. Lots of suppliers of suitable mesh very cheap on ebay.

useful thermal image Gravelld
we are hoping to have deterred the gnawing beasties with cement board and some rather fetching galvanised sheeting. it also had the benefit of creating a level plinth for the above ground EPS.
it's all a bit too new to be able to report back on its effectiveness though.
Ps. all credit for this to an02ew

and another

All seems a bit paranoid, expensive

Much good it's done em!

Here's an image of isotherms showing the temperatures in the ground below a floor slab (top left) with some perimeter insulation. (Steady state, 2D ie.cross section of a long narrow building. LH side is centre of floor slab)

Each band of colour indicates a drop of 1C from 20C inside to 10C ambient.

...and here's the two together:-

See what I meant about the lines crossing at right-angles, and the pattern being made up of curvy squares - OK mine are a bit rectangular, and some angles are a bit off right, but it was a struggle to get them that good.

Thanks Mike. I've never read one of those diagrams but it still looks like an enormous improvement; the external wall with skirt appears to contact that first dark red line, yet without it's the blue or get line, a further 3-4° drop.

10°C ambient means ground temp right?

I do this , seems to work ok , though wouldn't bother with the XPS now , just use EPS

I know we've had this discussion several times, but what (James) has caused you to change your mind about EPS rather than XPS underground?

yes djh . as in photo. Shingle to the bottom of the slab
Wookie. well mainly Tom comments on here and ive no concerns regarding eps degrading or taking up any problematic amount of moisture