What is the best carpet underlayment that will not hold water and cause the floors to rust? still working out some leak issues in my D1 Mike

 

same boat here - they rubber backed padding has hardened and is breaking apart everytime I touch it - debating on duct taping the crap out of it or replacing.

on a side note - check your A/C drain tubes are clear and connected, use sealant adhesive around the wire pass thru grommet behind the kick panels (pull wires in a bit and add some in between the wires too) - - then scrap off the rust on the floor plan, wire brush, clean and apply POR-15 rust sealant. You should also pull off the fenders, clean and re apply seam sealer on the A- pillars

 

Never tried in a rover but ive used Dynamat and similar self adhesive sound deadning in other cars. Dynamat and most others wont hold water at all. Get an aluminized one and it will also improve thermal insulation. Fairly easy to cut to size and then throw carpet over all said and done.

 

I understand you're not primarily concerned with sound-damping, but with water-holding. Because a reply mentioned dynamat, I will go a bit off-topic.

Ideally, on the painted metal, there would be a constrained layer damper (Dynamat). Then there would be an air gap, and the practical way to achieve that is with closed-cell (won't absorb water) foam (neoprene rubber). Then there would be a layer of mass-loaded vinyl. Anything on top of that (carpet) is mostly cosmetic. To review, the CLD is to dampen panel-borne vibrations. The MLV absorbs sound waves and works best when it is not coupled to a rigid surface (hence air-gap foam).

What I actually did: I stripped the interior and laid down Kno Knoise (a little better than Dynamat but basically the same thing as Dynamat Xtreme, I have Xtreme in another truck). Then I used 1/8" closed cell foam. Then I put down mass loaded vinyl. Then the OE carpet. I made it all fit. It was many, many hours of work. It's still loud. I have replaced all door seals with D2 door seals. It's still loud. I don't have that much tire noise (had M-55 and recently changed to KM3), and I have minimal engine noise (two large mufflers in series). I get wind noise and gear noise. The other truck I treated similarly is like a library inside, but not the Land Rover.

Now, if I could, I would redesign the interior with roto-molded polyethylene panels. With a foam-backing, they could take the place of the foam, MLV, and carpet. They'd be chemical resistant (compared to PVC or ABS), easy to wipe-clean, could be pressure-washed, and would last the life of the vehicle. With the right molds, there would be minimal seams. I would have expected this or at least could have wished for this on the 2nd generation defender, but I'm not surprised at all that JLR's rhetoric about ruggedness was a total sham and they just introduced another 'luxury' vehicle for middle-class surburbanites rather than something that would compete with 4-seat SxS for ruggedness and off-road utility.

To get back on-topic, to prevent rust, the water has to either be prevented from going under the carpet or it has to be removed somehow (drained or evaporated). The carpet is not permeable except where it is cracked or has holes in it. So if water gets under there, it will be trapped. Maintaining the integrity of the paint on the sheet metal will prevent it from rusting. The only place I had any rust was by the driver's side door sill in the footwell. I had to remove the rust with a wire brush, naval jelly, rust-converter and then re-prime and paint it. That area is still going to get wet from wet boots going in and out and water seeping in by the door sill, but it won't rust as long as the paint has integrity.

To underlay the carpet, closed cell foam and MLV are both impermeable. The foam is much lighter and easier to install, but is somewhat fragile. The MLV is heavy, tough to install, but very rugged.

 

Thanks for the great reply. This is exactly what I was hoping to find. Mike