How do I repair the Benching in an Inspection Chamber?

[Michael D]

When I rodded my drains recently I found that the benching needs to be patched in a couple of places in one of the inspection chambers. The inspection chambers appear to be original, installed around 1914. The places that need repair are just above the main flow so get wet at times. I=92m got some questions:

- Do I just use a normal mortar mix, or is it more likely it be some kind of render?

- Anything I can do to help it dry more quickly?

- Anything I should do to make sure the new mortar sticks to the old bricks succesfully?

Any other tips?

Michael

[js.b1]

Benching is usually 3:2:1.

Blue Circle Rapid cement may be ok - Extra Rapid will not be (and is too fast anyway).

SBR considering this is a wet application. I think B&Q do a 1L bottle relatively cheaply, check online and check the solids contents.

[Rick Hughes]

When I rodded my drains recently I found that the benching needs to be patched in a couple of places in one of the inspection chambers. The inspection chambers appear to be original, installed around 1914. The places that need repair are just above the main flow so get wet at times. I?m got some questions:

- Do I just use a normal mortar mix, or is it more likely it be some kind of render?

You could use a lime mix ... but I have benched many inspection chambers (even in days when it was Ok to call them Manholes) never needed to use lime.

... wire brush well at the joint to old benching. Liberally coat with diluted PVA ( for adhesion, nothing to do with drying)

Mix up a stiff mix of 3:1 with OPC, with some plasticizer in water if you have it ... if not a quirt of washing up liquid will do.

Apply with loads of pressure to get it into every crack, trowel with plastic or wood float to avoid drawing out the cement. When close to set, smooth off with a sponge for finish.

If you need it to set quicker use some rapid set in with water ... but unless you are due to overflow channel, I wouldn't bother.

[Andrew Gabriel]

I wouldn't use lime in this application. (Neither did the Victorians, and the Victorian benching in my drains is still in perfect condition. Only the more recent ones have needed redoing.)

For this, I would use EVA (sold as waterproof or exterior PVA) mixed up with cement into a slurry. It will tell you how to do this tin - it's a standard waterproof bonding method. Note that waterproof PVA is only waterproof when used with cement. Ordinary PVA is water soluable.

I'd use a metal trowel, as that gives you the best waterproof finish.