Expanding insulation foam. Available in a spray can at your hardware store.

Mask the skirting board and floor with tape and squirt into the gap with the tube/nozzle supplied with the can. Then trim excess after it has expanded and set with a knife and remove tape.

Edited By Paul Lousick on 12/07/2023 06:35:36

Sikaflex for sure it also sticks very well if the surface is clean, contact the local supplier. Never silicone, it is not nearly as durable, and forget expanding foam for detail work.

For a nice job mask both sides with tape. apply the Sikaflex to the slot then spray on a little soapy water (if needed) then smooth with a wet finger. finally remove the masking tape straight away while the Sikaflex is still wet. Finally! try not to improve and fiddle with it unless really necessary.

That's how the professional Caulkers do it.  

Oh! Sikaflex is available in colours.

Edited By John McNamara on 12/07/2023 08:48:12

Selleys butyl mastic skins but remains flexible for years,.