Floor sanding and varnishing

dl8860 · 18 Feb 2018 at 08:12

Yesterday I sanded my hardwood floorboards using a floor sander and edge sander. I then hoovered thoroughly (after much hoovering during the sanding process), then mopped the floors with a slightly damp mop. Then once dry I applied a layer of water based Varnish.

I went to apply the second coat last night (5 hours later, the Varnish pot said wait 4), and the floor was nowhere near as smooth as I expected. I originally sanded using grade 40 then grade 120 sand paper (I'm in UK, US convention may be different). Do I need to polish or buff the floor somehow to get it smoother to the touch? Maybe just hand sand it with a really fine grade before doing another coat? More sanding isn't really an option as I have another floor to do today before my sander hire ends.

HardwareGeek · 18 Feb 2018 at 08:46

fyi no experience with this but would guess the varnish has raised the grain in the floor and needs sanding back once more before more coats of varnish

Also not sure what grit is normally used but 120 doesn't sound that fine, guess 120 would never give a glass like finish

Abyss · 18 Feb 2018 at 23:32

Both the mopping and the varnish will have caused the nap to raise on the timber. You will need to sand between coats for a smooth finish.

You probably want around 180-220 grit for the first coat then more like 320 to 400 before the final coat

Nikumba · 19 Feb 2018 at 09:43

Also I would image hoovering put decent amount of dust up in the air as well that will have settled on the wet varnish adding to the roughness

Sanding between coats as people advised

dl8860 · 19 Feb 2018 at 11:02

Yep definitely seems like the mopping and the fact that the varnish is water based, has raised the grain, so I have been sanding between coats now. Maddening to have to sand more after having done so much, but got to get that smooth finish! Surely 320 is overboard for a floor though, I'm not looking for an ice rink.

So far I've just been on hands and knees sanding lightly by hand with a 120 grade (since the first coat going on), guess I'll try some 220 tonight before the last coat.