Which type of mix should I use for sealing outdoor pipe?

anonymous12124

I noticed that some of the sealing is coming apart on the outside main drain pipe. It looks and feels like a cement mix but I am looking for advice/recommendation on what I should use to completely reseal it again. 

Please refer to the image below:

https://imgur.com/a/yQxQ2N7

Mr.Generous

A bit of sand/cement mortar with a waterproofer additive.

ButterCheese

I would use builders sand (not sharp sand) to make a mortar mix with standrad cement.  Ratio 4 parts sand to 1 part cement.  +1 for a waterproofing additive.  You can get pre-mixes in a bucket or tube but it's obviously more expensive, but if you don't have use for a full bag of dement and sand it might be better to buy a dedicated off the shelf pre-mix in a tub (usually about 14 quid)

stuart45

I'd say it's breaking up because it looks like a cast iron soil pipe with a cast to plastic, plastic connector, something like an SP140.
These connectors shouldn't need sealing at the top. However, a sand/cement fillet won't stick properly to those materials without  priming with a bonding agent. If you mix SBR and cement into a paste and prime the area, a sand/cement fillet will bond to it much better. A bit of SBR in the mix helps waterproof it as well. Wickes sell SBR in small tubs.

anonymous12124

stuart45 said:

These connectors shouldn't need sealing at the top.

Is there a way to confirm this?

stuart45

anonymous12124 said:

stuart45 said:

These connectors shouldn't need sealing at the top.

Is there a way to confirm this?

Does any water leak through the top of the connector? If it does, the connector is faulty.

grumpy_codger

I'd remove the mortar and try blue/white tack (or similar, but more expensive rope caulk).
Or black silicone for a nicer result.

Section62

grumpy_codger said:

I'd remove the mortar and try blue/white tack (or similar, but more expensive rope caulk).
Or black silicone for a nice result.

+1 for getting rid of the mortar and using black silicone instead.

Silicone isn't necessarily the correct way of doing the job and may be frowned on by some, but the reason the mortar has failed is likely to be related to differential movement between the three different materials.  Fixing the joint with standard mortar means ensuring the strength of the mix is relatively weak - if something is going to crack then you don't want it to be the cast iron pipe or plastic fitting.  Adding waterproofer to the mix isn't really necessary.  (I wouldn't advise the same if this was a below-ground joint)

The key advantage of silicone is it retains some flexibility, so should accommodate any movement in the pipes.  And is cheap.

sheenas

Normally as another poster said these iron pipes don’t normally need sealant. You could simply use no nonsense roof and gutter sealant if you want to be sure.

anonymous12124

Given the consensus here is that it's more cosmetic than functional, I will grab some brown or black silicone and apply that.