What level for paving?

[AndyF]

Hi,
thanks for a great website. I've made a start at leveling the sub-grade for a new patio, but have a dilema over what the paved level should be. The house is circa 1890 and does not appear to have a DPC, is fully rendered on the rear walls, and seems to suffer from rising damp around the kitchen walls.
The ground level has been lowered by some 10-12 inches, exposing the top level of the stepped foundations, which coincides with the top edge of the salt-glazed gully (or p-trap?).
While the lowest 12 inches of render is missing pending a tidyup, I am contemplating injecting a DPC. If I do this below the suspended floor level, it will be around the level of the top of the foundation. Obviously this does not make it 150mm above what is my lowest paving level (i.e.. the top of the drain.) I don't think the gully/p-trap can be lowered. The connection is directly underthe foundation, heading off somewhere under the kitchen.

As the side of the kitchen was once rendered down to a long narrow concrete slab that drained into the gully and no DPC has ever existed, is it not my best solution to install a DPC, continue the render to the foundation and install my paving sufficiently high to facilitate adequate drainage (linear drain?) away from the walls, ensuring that render and paving together make a watertight seal?

Would also appreciate advice on the drain, which sits as low as the base of the foundation on what I believe to be chalk. There's no concrete bed or haunching, just a surround of sodden clay. I think the clay is so wet because the orginal concrete slab leaked around the top of the drain and allowed the water to soak down. The brick mortar is in poor condition in this vacinity and the floor joists are damp. Should/can I get an old salt-glazed drain tested, and should I create a more stable bed?


Just to make this post a little longer...We intend to lay 12-15mm ish slate. One of your listed suppliers suggest that a concrete base be laid over hardcore, then a full mortar bed laid down as the slate goes down. I read in your archives that you suggest laying a 75mm concrete base as the slate goes down (or have I misunderstood?) I know which I'd rather do, but need to be confident that it's of sufficient strength for such thin paving. We're terraced, so all agregates have to be carried through the house.

Any advice welcome.

[Tony McC]

It's difficult to say what would be best regarding the DPC because the changes in levels complicate matters and it's one of those jobs that really needs to be seen, but using a linear channel against the property is a good all-round compromise.

Testing old s/g pipework? No problem...or at least, there shouldn't be! It's tested in exactly the same way as 'modern' drainage.

Laying slate: at only 12-15mm thick, it would be better to have a solid concrete substrate onto which the mortar bedding could be placed (as described in another post today). Direct bedding is fine, but with such thin slate, you need a good eye and an accurate hand.

[AndyF]

Thanks for the reply.
Today I discovered that the flange on the pipe at the joint to the drain is cracked, and there's some movement in the drain. Even if it isn't leaking, I assume it would be foolish not to rectify the problem before laying the paving?
The end of the pipe is right under the foundation and access is difficult. Will the flange have to be removed from the pipe to facilitate e.g. an adaptive coupling? How is SG piping normally cut? Any chance of an in-situ repair?
Thanks again.

[Tony McC]

Flange? Do you mean collar? Damage to the collar can be critical or it can be completely immaterial: it all depends on the extent and the position. A cracked collar at the top of the pipe is often ignored.

However, if you want to replace it, the simplest way for a DIYer is to use a cut-off saw to slice through the barrel of the pipe, thereby removing the collar, and then use a couple of adjustable couplings to insert a new short length of pipe to replace the damaged section.

[Tony McC]

Forgot to mention: if the damage is minimal, encasing the damaged pipe/collar in concrete or a strong mortar will often effect an adequate repair.