Will expanding foam seal a soil pipe from smell?

The way our extension was built (around 25 years ago) the external downpipe from the gutter was cut above the new roof and re routed. The pipe that went down the external wall which was now the inside of the extension was removed from floor level, literally. I recently lifted a laminate floor to find what looks like the jagged top of an old pipe just below the level of the floorboards. Since then we have been getting a really eggy smell when the shower is on or the hot tap has been running for a while.
I presume the gutter pipe runs into the soil pipe?
The pipe has been filled with a foam type thing (would expanding foam have been out 25 years ago?)
What is the best way I can seal it to prevent the smell coming out? Would loads of expanding foam do the trick? There just seems to be a thin layer of foam type stuff in it just now.
Cheers.
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Can you cut the end of the pipe square, and get a suitable plug or cap from your local builders' merchant?
Cheers Richard
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wrote:

Can you cut the end of the pipe square, and get a suitable plug or cap from your local builders' merchant?
Cheers Richard
No. Unfortunately the bit that goes under the floor is buried into the wall. Also the bit they cut is all jagged so I couldn't even cut more of the floor board to expose it.
Anyone know if cement would cap it and stop the smell?
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Hi, I have used an expanding drain plug in the past for blocking off unused sections of drains. http://www.toolstation.com/shop/Hand+Tools/Plumbers+Tools/Metal+Drain+Testing+Plug+4/d10/sd210/p57702
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wrote:

Hi, I have used an expanding drain plug in the past for blocking off unused sections of drains. http://www.toolstation.com/shop/Hand+Tools/Plumbers+Tools/Metal+Drain+Testing+Plug+4/d10/sd210/p57702
Brilliant. I never knew these existed. Hopefully just what I was looking for. Thanks.
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