I have a gap between outside wall and pavement.
Could this be the reason for damp smell in the cellar?
If I poured bitumin down said gap, would this help prevent the dampness?
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If you can identify that the basement dampness comes principally from the wall on that side of the house, then you may find dampness abated by creating a water/moisture barrier between the wall and ground; or at ground level, preventing run-off from entering the fissure.
If you have a dirt floor in the basement, chances are that the moisture comes up all-over, and thus sealing the wall (where you mention) will have little effect.
If the moisture is not apparently from any one wall, then all the walls maybe permeated with groundwater — or the floor could be the bigger culprit.
If basement walls show sign of moisture penetrating, then you could use DriLoc to seal them. DriLoc must be applied to dry walls, so if the walls are always moist (not just when it rains) then you would need to bring in a heater + fan + dehumidifier to 'bake' the moisture out of a given section of wall, DriLoc it, and keep moving your 'dryer' setup to prepare and DriLoc all the walls this way.
If the floor is dirt, you will need to cover it with a moisture barrier nd then pour concrete (or similar) to seal the floor.
If you do all this, remember to leave the basement this way for a year or so before doing any further finishing down there — to be sure the fix worked completely, and/or to check for imperfections in the application of the fixes.
To add to the already excellent answer already given... if humidity in your area is exceptionally high, some moisture will always tend to condense on the basement walls (they're cooler than the moisture-laden air).
How wide is that gap? Poured bitumen MAY help, but may also make the situation worse... and you should know that pouring bitumen into the gap will increase the pressure against that basement wall, possibly causing it to crack or collapse.