Seal the pump sump

A pump sump always runs to a certain level with water, which is then pumped out by a submersible pump. While modern pump sump systems are closed and therefore leak-proof, this is not the case with concrete shafts as pump sumps. Below you will find information on how to seal such a pump sump.

The pump sump as required

There are different systems and also different requirements for a sump:

  • Pump sump to drain the basement
  • Pump sump to connect sanitary facilities below the backflow level (greywater)
  • Pump sump to connect sanitary facilities below the backflow level (black water)

Dump pump sump to basement

The sump for draining the basement is an open system. From below (special pump sump layer, cleanliness layer of gravel, etc.) the water pushes up and is sucked off. This type of pump sump is mostly a concrete shaft.

The pump sump of a lifting plant

The pump sump for receiving waste water, which accumulates below the backflow level of the channel (if the basement is lower than the road channel), absorbs the wastewater and pumps it above the backwater level at a certain level and directs it to the channel.

While modern systems are all closed, in existing buildings especially in lifting systems for gray water (wastewater without fecal matter and solids) are pump sumps, which are also just a concrete shaft and have only a steel plate as a lid. The pump sump for black water (sewage with faeces), however, is always in a closed system.

Seals to be made on the pump sump

So it's the pump sumps made from a concrete shaft that needs to be sealed. Different seals have to be considered:

  • Sealing of the entire surface of the inner walls of the concrete shaft (seal)
  • Sealing between base plate and screed

Between screed and floor slab

Just the lack of sealing between screed plate and floor slab of a building quickly leads to an expensive refurbishment case in case of pump failure. Not infrequently, even the insulation under the screed was drawn to the shaft and is then also affected by a trampling of the sewage.

Sealing slurry and bitumen

There are sealing slurries that can be applied here. However, the problem with a floating screed is that the sealing slurry is not flexible enough. So far, bitumen or tar is out of the question because the service life of tar and bitumen is considerably reduced by contact with water - the bitumen dissolves much faster, so it does not provide a good remedy in the long term.

Alternative solutions

Now there are still a few - let's call it unorthodox approaches. Polyester mats, which are glued in this area (overlapping over the cross-section of the floor and screed slab), at least seal off the layer between screed and floor slab. Instead, however, a plastic container can be used, which exceeds this level (from the bottom plate to the screed).

Sealing and renovation of the concrete walls of the shaft

Then there would be the sealing of the concrete shaft walls. Even waterproof concrete (WU concrete) is not really impermeable to water. Therefore, the concrete must be repeatedly coated and waterproofed. Even the Romans knew an excellent remedy that builds up an effective barrier - water glass. In addition, there are also numerous impregnations and sealants for concrete.

Tips & Tricks

It is usually necessary to seal the pump sump between the screed and the floor slab if the submersible pump fails its service and overflows the water. All of the suggestions made here are only so effective, the basement floor is also tight from above. Often in the basement graduation work is neglected - for example, the expansion joints between screed and wall. So you also have to seal the basement floor down. Because when the water comes out of the pump sump, it eventually spreads over the basement floor and then runs in the absence of sealing at the expansion joints between screed and base plate.

The most efficient are either two submerged pumps, which are alternately switched on and off via a pump control. In addition, there are also systems that trigger a visual or audible alarm when a certain water level is exceeded.

Video Board: How to Unseal and Reseal Your Ground Water Sump Pit