How To Fill a Wooden Floor
Depending on your preference you may want to fill your floor. It can prevent drafts coming up from underneath the floor and it can help to make a floor look much more neat and tidy. Some people prefer to keep the gaps, they believe that filling the floor will make it look fake like laminate or lino. Each to their own, personally, I say fill it every time.
When buying your filler, you may want to search on Google for a floor sanding supply shop near you. That way you can get high quality filler, whether water-based or not. Alternatively you can use PVA glue, or better (and cheaper), PVA glue watered down. The reason I recommend using high quality filler is because PVA, even when fully dry, tends to clog up the belts when you are sanding the filler off the surface (I’ll explain in a moment).
Before you start filling you should have completed the edge sanding to a 50 or 60 grit and sanded the main body of the floor with at least 80 grit. I sand the floor to 60 grit, empty the dust bag, then sand the floor with 80 grit. That way you have only fine dust from the 80 grit. But the advice I would give to a novice is also empty the dustbag at 80 as well, then do the 100 grit and use the 100 grit dust to fill the floor (and the 80 grit dust if your run out of 100 grit dust). My reasoning for this is that the dust is finer, it will be easier to mix and to work with. Also the filler must be sanded off the surface of the floor once it has dried and its easier to sand off the filler with 100 grit on a floor that has been sanded with 100 grit, before filling, than a floor that has been sanded with 80grit. I hope that makes sense because now I am confused… and I’m writing it.
If you are sanding pine floorboards you may want to empty the edger bag before the 60/50 grit edge sanding and use that dust to fill the floor. Pine is very fibrous and even the 100 grit dust from the belt sander is not very nice to fill with. Edging dust tends to be a lot finer than belt sander dust.
Once you have your dust (and hoovered the floor). Get a small bucket or a painters kettle and pour some of the dust in. Then add a little filler (or watered down PVA). Stir it with a filling knife or stick of wood or whatever. Keep adding filler until the filler is quite viscous and moves very slowly to find its level after stirring. Then scoop it out and slop it on the floor. Now you can just use a decorators filling knife (I have known people to do this) and use that to fill the whole floor. Trowels like the one I am using can be found in builders merchants and floor sanding supply shops. You can also use a plastering trowel which is what I originally was taught to use. Swipe a bit of filler and fill round the edges if there are gaps or nail holes around the edge. Once you have done this in a small area around you, slight the trowel back and forth, with a fair amount of pressure, almost snow ploughing it back and forth, as shown in the video. Go all the way round the edge and spiral into the middle of the floor. Scoop it up, throw away the excess and wait for it to dry as described on the label of the filler (overnight for PVA).
Once the filler is dry its time to sand it off the surface with either 100 or 120 grit. Use the belt sander first and the edger second. (see: Why you should do the edge sanding last) If you found this helpful please let me know in the comments section below. You can also ask questions there, should you have any. Ben
UPDATE: After 2 years of emails from US readers who cannot find this kind of filler, I have finally been given the name of a filler that is available in the US that serves the same purpose, and it can be found here.