Impregnant C120 require a retainment home to perform. It cannot create a home for itself as it is too fluid. A vertical gap can therefore only be successfully impregnated providing there is a means of retaining it whilst it cures. This could be existing weathered silicone rubber or putty; in-place substances that have become dysfunctional. The cracks and loss of adhesion of aged sealing products can provide useful capillary attraction and retainment for the impregnant and can actually refresh the existing seal joint. This is why we do not advocate removal of spent products.
For example; if a window surround has gaps greater than their ability to cause retainment of the impregnant it will drain away. This can simply be remedied by rubbing chalk/cotton-wool or similar into a voids prior to impregnation; they combine to make a permanent seal. Whilst the impregnant has a short pot life, it is possible to premix chalk filler with the impregnant before adding the catalyst and then apply to the cavity. The availability of a thixotropic filler will turn the impregnant into a jelly that would allow the filling of a vertical cavity. The advantage over silicone rubber is that whilst the impregnant has become a jelly, it is still very mobile (like Swarfega) and can be simply finger massaged into the cavity.