Sanding a floor

January 26, 2006 7:51 AM

It's time to sand and varnish the floor in the front room, ground floor. We'll be replacing a few worn out floorboards but we're not totally confident about the best way to fill the gaps between boards. Some people say use resin, some say use a sawdust/pva mix, some say use filler, some say use wood fillets. The floorboards are 1" thick tongue and groove, solid pine. Any good suggestions? (Based in the UK)

I know we need to punch down any sticking out nails, and we're going to remove the skirting boards and replace them, so we can get tight up to the edges. The radiator will be coming off as well so we can do the whole thing.

Some people say that using filler is not rigid enough and that it will crack and eventually get hoovered out of the gaps, and that the resin can be quite expensive, but provides a really good finish. I've also read of horror stories about some fillers not taking up the varnish on the final layer, so you have pale strips where the filler is, in comparison to the nicely varnished boards.

Can you calm my nerves about this? Perhaps there's something we've not thought about...

posted by gaby to Home & Garden (9 answers total)

Couple things:
Are you trying to get an absolutely tight fit on the boards? If so, the best way is to reseat them all so that they're tighter. At that point it'd be easier to just replace the floor (or lay a new one on top).

If the gaps are smallish, I'd be inclined to live with them.

Here's a little photo set of similar work I did and the refinished floor.

If you're intent on using a filler between boards - yes, many glues or fillers will not accept stain when they're dry--you can fake it a little bit. What I did was save a bag of some sawdust from the floor sander after fine sanding. I mixed that with wood filler to get a closer color match and used that on face nailed boards. You can also mix your stain or varnish into some glues or fillers or into the sawdust that you mix into the filler to help match the color, but save some scrap boards to experiment with color mixes.

I chose not to fill gaps, primarily because I think they match the character and secondarily because the boards shrink and expand dramatically during seasonal changes. Filler would likely drop out at that point.

In the working pictures, you'll see that I used a repeating "big to small" pattern. I did this so that the patches wouldn't stand out screaming "I'M A PATCH". I only had to face nail the smallest board in each section.
posted by plinth at 8:16 AM on January 26, 2006

I second everything plinth says (although I don't have any nifty photos of my work). I can't imagine why you'd want to fill the gaps, unless they're really, really huge (as in, big enough go get the foot of a piece of furniture stuck in). And, if they're that huge, then you'll probably need to refit the floor in any case.

The floors at my mothers (circa 1810) house have gaps up to 1/2 inch wide in some places, and its never, ever been a problem. We sanded 4-6 layers of paint off these floors (an awful, backbreaking job), then triple-varnished them, and use area rugs, and they look great.
posted by anastasiav at 8:39 AM on January 26, 2006

Nice work plinth! I agree about learning to love the gaps, which are part of the character of your house. But if you do insist on a filler, experiment first on some scrap wood, filling, sanding, and finishing. A friend had his old floor cracks filled and the floor refinished, and the filler was much brighter than the wood (despite using sawdust from the floors themselves.) Looked awful.
posted by LarryC at 9:09 AM on January 26, 2006

One thing to bear in mind if you're thinking of leaving the gaps unfilled: we did this in our front room, and now the room is effectively connected to the outside, and it is absolutely fugging freezing in winter.
posted by chrismear at 9:58 AM on January 26, 2006

You may find some good tips here. Although 4easypayments never followed up.
posted by togdon at 10:04 AM on January 26, 2006

Response by poster: I hadn't considered completely replacing the floor. Floorboard is reasonably cheap over here so it would only cost a couple hundred quid. The actual gaps that we have aren't that big at all, ranging from 1mm-8mm, and the boards are T+G as well, so there's something there. I reckon that the varnish would sink into the gaps and fill up most of the gaps anyway.

What might be an option is to make up some filler from sawdust and varnish, and shove a bit of that in the holes before doing the final smooth sanding. Am I going to have problems sanding off the excess varnish? I figure that it would just clog up a sanding belt. Which is better for this, a resin-based varnish or polyeurathane?

There's one or two large gaps where work has clearly been done, but they're not the end of the world, and would be covered by furniture anyway.

chrismear has a valid point, we live in the north of england, up a hilly area. I, like most others, like to be able to feel my toes and fingers whilst watching tv :)
posted by gaby at 11:22 AM on January 26, 2006

gaby, I'm really curious -- why (other than heat) do you want to fill in these gaps? Filling in a 1 or 2 mm gap is going to have a high cost to the benefit you see IMHO.

re: heat: Is it possible to insulate the floor from underneath (i.e. insulate the 'ceiling' of the basement or crawlspace underneath the house?) or are you on a slab?
posted by anastasiav at 11:45 AM on January 26, 2006

Also, are the gaps seasonal--ie, do they close up in the summer? Wood expands and contracts across (perpendicular to) the grain in response to changes in temperature and especially humidity. In our old house, noticeable gaps develop between the floorboards in the dry winter, but close again in the humid summer. If we filled the gaps in the winter, when summer came the floor would either 1) force the filler back out through the pressure of expansion, 2) buckle upwards ot relieve the force, or 3) nothing at all. Me, I'm not the betting type.
posted by LarryC at 2:25 PM on January 26, 2006

With regards to what to finish the floor with, I think polyurethane is the way to go. I used water-based poly that I put on with rollers. In dry weather (like the winter), you can realistically put down 8 or more very thin coats in a day since it will dry very quickly. You will need many, many coats in a high traffic area. I like the water based poly because it isn't nearly as stinky, it doesn't add a lot of color and the cleanup is fairly good. I don't like it because it isn't durable and I don't think it's acceptable for high traffice areas and it raises the grain of the wood on the first few coats.

Oil based poly reeks to high heaven, takes longer to dry, is harder to clean up, and adds a slight yellow tone to the wood (this can be a good thing too--it adds some warmth) but lasts much longer and can be more friendly to stained wood (you might have some issues putting a water-based poly on top of an oil-based stain).

I do not have experience with varnish.
posted by plinth at 7:12 AM on January 27, 2006