wc cast-iron down pipe - concrete/mortar at base is corroded exposing the joint

[dave]

The concrete/mortar (?) around the base of our w.c. waste pipe (cast iron) is crumbling exposing the connection to - well whatever the next section is. I could just fill with new mortar mix but is that what should be done? Is there anything I should/could do to make sure it stays sealed - maybe before cementing over the area? The water in the pic is just from a bucket of water I poured over it to clean out the bits. The joint itself doesn't appear to be leaking although it is corroded. Thanks

[Phil L]

through it when you flush the toilet, and it goes straight down the drain, which is the clay collar that you can see in part of the photograph.

You can just clear out the loose mortar and re-do it with fresh stuff, fairly strong, about 3:1 sand/cement

[dave]

Thanks for the replies. When the silicone is set is it ok to use "readymix" (rather than mix my own mortar)?

[newshound]

Should be fine. If it comes with a separate cement bag you could always strengthen it up a bit by using less sand. But since it seems to be fairly well constrained I wouldn't worry too much about "high strength". To be honest, I wouldn't bother with the silicone either.

[dave]

Really appreciate the advice - the problem has though now "degraded"... the corrosion was pretty bad on that cast pipe so I cleared out the "material" to get at it and then rubbed it down and painted with red oxide.

is (er um) I don't know how to re-seal that joint - and it's an open drain (soddit!). Am pretty clueless as how to do this properly. If I cement the pipe then material is going to fall in that gap and into the drain. Do I "putty" that gap first - or just tape it closed - then cement? (foil hat at the ready)

[grimly4]

Rope.