A system for sealing one end of an existing conduit through which a number of cables extend and in which a number of elements are placed for holding each of the number of cables in a position in the conduit, the system comprising: a sealant for applying a first layer of sealant at an end of the existing conduit against the number of elements so that the first layer of sealant completely covers that end of the conduit as far as not occupied by any of the number of cables; a number of flexible elements which each have a first end for positioning that first end into the first layer of sealant when the first layer is still uncured, each of the number of flexible elements further having a second end at such a distance from the respective first end when the first ends are positioned in the first layer of sealant, that the second ends form together a structure against which a second layer of the sealant can be applied, a single-part or multiple part subsystem for constructing a rigid second conduit around the flexible elements from their respective first end up to and including their respective second end when these first ends are positioned in the first layer of sealant, so that the number of cables also extend through the second conduit and a first end of the second conduit is sealed off by the first layer of sealant and a second end of the second conduit can be sealed off by applying a second layer of sealant against the structure formed by the second ends of the number of flexible elements.