How to waterproof a brick built manhole

[jfb]

So I have a brick built manhole (engineering bricks on a concrete pad base) where the water supply is split into three and when it rains heavily it fills with water (very high water table). I presume water is getting in through the joints in the brickwork. Water is then getting into the duct and reappearing where it comes up in a barn (which is lower than the manhole level) causing a minor spillage.

 

two questions:

1. Best way to waterproof the manhole itself ?

2. Best way to waterproof where the duct starts (as in the blue pipe and the blue duct in the picture)?

 

any suggestions?

I do see some blocks where the ducts exit so don’t suppose those are waterproof but I presume some water is getting in through the joints.

Edited November 25, 2024 by jfb

[joe90]

More than likely the water is entering where the pipes enter the manhole.

[Cliffpope]

We have recently had a borehole installed, and the wellhead is in a manhole looking very like yours. The installers included a length of ducting from one corner of the hole and we were advised to dig a trench to lead the duct away downhill to somewhere it could soak away, obviously at a lower level,

 just in case any water got in.

[Conor]

You cant. It needs to be drained to a lower level. Even then it'll eventually silt up. Just the way it goes. Just block up the ducts properly. 

[jfb]

18 hours ago, Conor said:

You cant. It needs to be drained to a lower level. Even then it'll eventually silt up. Just the way it goes. Just block up the ducts properly. 

Fair enough.

whats the best way to waterproof the duct?  A bit of expanding foam as a backing and then a bunch of bathroom sealant ? Any advice on the best type?

 

[Cliffpope]

What do you mean "waterproof the duct"?  The duct is a convoluted plastic pipe about 2" diameter. Do you mean seal the join where it connects to the manhole? Just knock a hole and seal it with mortar .

[Gone West]

Back in 2010 I had a problem with a high water table and the sewage treatment plant at my last place. The hydrostatic pressure was forcing water around the inlet and outlet pipe seals. When the water table dropped in the summer I sealed around the inlet and outlet by packing bentonite around the pipes about 150mm thick. It seemed to do the trick. You could uncover where all the pipes enter the manhole and do the same.

[Kelvin]

The product to use to seal the end of the duct is this stuff: 

 

https://www.millsltd.com/default/cable-ducting-fttx-products/duct-sealing/filoform-duct-sealing.html

 

It’s not cheap but it’s what I’ve used in all my ducts. Some folk will say just use silicone sealer but it doesn’t work. I had to redo the sealing the ASHP installers did. 
 

SEPA have a best practice guide for borehole headworks chambers which I followed. 
 

https://www.sepa.org.uk/media/34501/an-applicant-s-guide-to-water-supply-boreholes.pdf
 

We don’t have a high water table so haven’t had any problems. Heavy rainfalls has allowed water to get in but the drain to lower ground deals with it. 

 

 

The only way to stop water getting in would have been to tank it properly.

 

 

[SteamyTea]

11 hours ago, Kelvin said:

The only way to stop water getting in would have been to tank it properly.

Would one of those polyurethane roofing solutions work.

Something like this:

 

https://www.topseal.co.uk/polyurethane-roofing-system/