Radon Proof Sump Cover

When we demoed the slab floor we saw that drain pipes were connected from the outside perimeter foundation of the house into the sump tank.

Exterior pipes into sump tank

Exterior pipes into sump tank

We seldom saw water in the sump tank so we were not sure the system worked, but we left it as originally designed as we think it supplements the drainage around the foundation perimeter. But the sump cover was loosely laid and the holes in it were raggedly cut and open.

Sump cover and Boiler drainage

Sump cover and Boiler drainage

Having that hole in the utility room is not good for Radon infiltration. I knew we needed sealed radon cover but the covers made for radon were too large for the space. So I ordered a sealed cover with a few extra fittings for our existing pipes.

Structural Foam Sump Cover

Structural Foam Sump Cover

Unlike the photo, the holes in the cover I received were both sized for 2″ pipe with a third hole for the sump pump wire plug. Our sump pump had a one inch pipe but unfortunately when I was working on the system, I discovered that the pump is clogged or broken and does not pump water anymore.
In order to fit the cover over the sump hole, I had to cut the plastic corregated pipe down to the concrete level. I was reluctant to try to bolt the cover directly to the concrete because the cover was so close to the edge of the hole that the concrete would just crumble. So I got the idea of attaching a ring around the tank. I cut the ring from 1/2″ plywood.

Plywood set up to cut round hole

Plywood set up to cut round hole

I marked the hole with a nail and a piece of wood and cut both an inside and outside circle.

Inside and outside circle cut with jigsaw

Inside and outside circle cut with jigsaw

Unfortunately I had cut the inner circle exactly the size of the tank so of course it didn’t fit. Luckily I had cut it wide enough that I could take out a second circle and end up with a ring of the right size.

Second circle cut to fit

Second circle cut to fit

I used Liquid Nails again to glue the circle of wood to the concrete around the sump tank. Then I weighted it down with some boxes at hand and waited for the glue to dry.

Plywood ring glued around tank

Plywood ring glued around tank

Then I used concrete caulk to seal the inside and outside of the plywood ring to the concrete.

Tank caulked inside and outside plywood ring

Tank caulked inside and outside plywood ring

Next I had to prepare the cover. To seal up the larger openings, I ordered a sample kit of neoprene materials in 4″x 4″ size and a couple of plugs for the pipes I have running into the sump. One is the 3/4″ overflow for the boiler, and the other is the 1/2″ condensate drain. Ideally we would have a pump in the hole but I vacuumed out the water that was in the tank and noticed enough silt on the bottom that it may have clogged the sump pump which I bought for clear water only. I just put a neoprene patch between the bolted on hole gasket and the cover.

Neoprene patch over one of the 2" holes

Neoprene patch over one of the 2″ holes

I decided to try to mount a smaller gasket inside the second 2″ hole. I ordered some 3″ plastic covers and drilled a hole in one to pop in the 3/4″ rubber gasket. I used the adhesive neoprene sample to seal the plastic cover to the hole.

Adhesive neoprene

Adhesive neoprene

I used a spade hole bit to cut a hole in the cover and neoprene layer to make a hole for the gasket and then I used extra flat neoprene tape to reinforce the gasket in the hole.

Gasket in plastic lid

Gasket in plastic lid

The rubber gasket material that came with the cover was stretched around the outside
edge of the bottom of the cover to make a seal when it is screwed on. I also made an extra 1/2″ hole in the cord plug and temporarily plugged the cord hole.

Cover prepared with rubber gaskets

Cover prepared with rubber gaskets

The cover was ready to be fitted to the sump tank. To fit the cover, I made sure the pipes could be inserted before I screwed it down. Without the pump piping, I only had the boiler overflow and the condensate drain to fit into gaskets.

Cover screwed on with condensate and overflow pipes

Cover screwed on with condensate and overflow pipes


Until I replace or fix the pump for the tank the tank cover is finished. It is sealed so that any radon gas that gathers in the tank will not be released into the house.

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