Any ideas on the greenest solution to tanking a new build basement? Many thanks in advance, Mike

I didnt tank mine and it isnt damp yet

Do it on the outside before you backfill. I watched a German "kellerbau" company do one some years ago. The memory is a bit hazy but I seem to think the outside was first spray primed with tar/bitumen, then a layer of bitumenised metal or plastic foil was applied all round, I haven't seen it in the UK but it was in 1 mtr wide rolls, a bit like the small rolls of flashing, only bigger. Next a thick layer of insulation, sort of a tar impregnated polystyrene, and then backfilled, with a drain inserted around the bottom.

Mike

Have you already built the basement?

Paul: ordinary concrete is not waterproof. Permeability improves with density. (Waterproof concrete can be produced by special additives and manufacturing techniques - usually at local ready-mix plants under direction of specialist hired-in technicians)

good quality concrete is waterproof - most of the problem is at the joints. additives do help in reducing the permeability right down. also you get a guarantee from the manufacturer.
the outside tanking system is grace bituthene (i dare say there are other brand names). again it's the joints that are the problem. personally i would do the concrete top quality through supervision, joint strips and additives.

Mike,

Do you want the greenest solution or the cheapest solution, and what soil type are you in?

Not sure on the greenest but we have looked into all sorts of solutions and I will happily offload - bit boring though!

Mike, I have sent you some info via e-mail

C

Crofty,

We used Grace Bithuthene 8000 with a drainage sheet ( which also acts as a protection barrier )but we got quotes from others. We never did get the quotes through from Visqueen for the torch on stuff.

The Grace product is like Blue Peter sticky-back plastic !

You brush on the bithumen, then peel of the backing of the membrane and stick it onto the bithumen, add the drainage sheet ( which is like mini plastic egg cartons) and backfill.

Sounds easy but the sticky membrane is very very sticky and it you get it in the wrong place, or catch something against it then is sticks instantly and you cannot peel it off and have another go.

I've got lots of info sheets etc so if you whisper your e-mail address I will send you some over.

Here's a photo so you can see what I mean

Tony,

On the other side of the concrete wall you can see, there is a cavity ( insulated ) and then internal skin. Then its my living space with MVHR and normal air movement caused by general living, doors and windows opening etc, passive solar and then woodburners, so all in all should dry out quickly and remain that way.

I will let you know if there are problems after being in there for a winter!

The tanking is to stop a potentialy large amout of water getting through that concrete wall, we are in heavy clay here, and there is no way on this earth I would have got mortgage funding without it.

Property care association - structural waterproofing
http://www.property-care.org/about-us/structural-waterproofing

(turn speakers down before clicking on 'online guide')

This is the method we went for. http://www.bbacerts.co.uk/PDF/2278i2_web.pdf See page 5 detail for external tanking

We've used visqueen torch on for the soil side of our basement, although the technique was slightly different to what Cassie had to do, our experience was similar. It was a horrible job. First you prime the wall, then peel off the backing paper, stick the visqueen on and then blow torch it.
The visqueen is very sticky and once you've peeled off the paper backing and let it touch something, there's no going back. It is a two coat application which provides a homogenous coating.
Once we'd applied the visqueen it was then covered with a protection board to stop damage from things like stones etc.

On the inside of our wall we have used vandex BB75, which is great to put on, even for a couple of DIYers. It's permeable, and we will go on to vandex our foundation slab.
Our building inspector has been very keen for us to use this method of tanking.

Edit: We've also put in a top perforated drainage pipe along the bottom of the basement wall, and also one at approximately 400mm deep.

or against moisture in the air inside being drawn through the concrete in vapour form and condensing on the back of it when it is very cold outside. Even waterproof concrete is not impermeable to water vapour.