Mister Green

Fixing Draughty Floors

We found a floor that had been sanded and varnished, but with the gaps between the boards left unfilled. In most UK houses with timber ground floors, the space under the floor is (or should be) ventilated to the cold outside air. It is surprising how the area of the narrow gaps between the boards adds up. In a typical room of say 25 square metres, each gap of 2mm between boards would be equivalent to an open letter box!

Unfilled joint on the left.Filled joint on the right

Ideally, gaps should be filled when the floor is sanded, using a binder mixed with the left-over sanding dust, but it can be done later after the floor has been varnished, although it is very time consuming. Go to a local joinery shop and ask for some sanding dust. You will need about a supermarket plastic bag full for a 25m2 room. You might get the dust for nothing or for a small charge. We used Bona Kemi Mix and Fill for the binder, because it is water based and easy to work with. Mix a small quantity (put the liquid in first and add the dust) and mix to the consistency of porridge. Work it into the joints with a paint scraper.



When put in during initial floor sanding the joints are usually over-filled and sanded back level. When doing it later, the gap filler will shrink back slightly, but this maintains the definition of the board joints and gives a pleasing effect. If there is a significant gap between the skirting and the floorboards, this can be covered with a timber quadrant bead or scotia moulding, either painted to match the skirting or stained to match the floor - tip: paint or stain it first before fixing.



The whole floor then needs a light sanding and re-varnishing. An easy DIY job for autumn and a very cost effective energy saving home improvement.