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We have recently bought a new house, well a new old house. It dates from 1900, we have taken the carpet up ad are now looking to sand back the exposed original floorboards.

We plan on giving the floor a light sanding, as it smooth just somewhat dirty/cosmetic imperfections. Is the correct process to use a fine sandpaper, and then possibly an intermediate if necessary ? We will be using a large commercial floor sander.

After sanding we envisage the wood being a lot lighter, and therefore we will need to stain it. What stains are best oil/water/spirit based ?

How many coats of stain are required ?

After staining it is necessary to apply a varnish ? We intended to apply two coats of clear varnish. The first coat can be watered down, as it is used to seal the wood ?

Does our plan look like a good one ?

Edit

Just in case anyone is interested, the floor is all done.

We used 3 coats of ronseal diamond hard floor varnish. Before the final coat of clear varnish we sandpapered with fine grain by hand, and wiped with wet cloth/let dry for couple of hours. This got rid of a number of cloudy marks that were present and caused, I think, by our slightly imperfect sanding.
So one thing I learn't - don't be afraid of the rough paper and really giving the floorboards a good going over. We got them smooth, but there is substantial variation in colour where different amounts of wood were taken off by the sanding/levelling process,however we quite like this the distressed/aged look; They are over 100yrs old after all.

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2 Answers 2

up vote 6 down vote accepted

First, a quick note on technique - start with a coarse grade sandpaper on the floor sander and work down to the the finer grade.

The coarse grade removes the old finish and levels out the imperfections, then the fine grade makes it nice and smooth. If you go the other way around, you'll definitely curse every time you see the grooves in the sunlight. Fixing this means stripping off the nice new finish, not fun.

In passing, an obvious-in-hindsight but sometimes-missed point is to go with the grain, i.e. sand along the boards, not across them. In any case your sander will complain bitterly if you don't.

Also, give the boards an incredibly good wash before you start with e.g. Sugar Soap - you want to try and strip off everything gungy to stop the sandpaper clogging too often. Leave for at least 24 hours to dry nicely.

Be sure to hire an "edge sander" too, this will help you get to the edges that a drum sander won't get to. If you can, remove the skirting boards (baseboards) as then you can get right underneath; only do this if you know you're redecorating the walls too and don't mind patching up the woodwork. You'll inevitably end up doing the fiddly bits around the door frame and right in the corners yourself by hand with a scraper or sandpaper, which takes longer than you could possibly imagine.

While doing the sanding, remove everything from the room (obviously) and get heavyweight dust sheets to tape around the door. Wear airtight goggles as this is an insanely dusty process. You'll also need ear defenders as this is an insanely loud process too.

Regarding stain, it's a matter of personal preference. I've done both and prefer the more uniform result that stain gives.

Regarding finish, I've used both oil-based and water-based finishes. Both are OK, but the oil-based one looked richer (can't say why, can't say how) -- and took about three days to dry. Somewhat inconvenient for a hall, and our puppy left nice pawprints.

Follow the instructions on the tin; in general thinning probably isn't worth it, as you'll find the second and subsequent coats will go further anyway. I applied three coats of the oil-based finish, and five of the water-based finish, but this depends on the state of your boards. It's handy to rent good bright work lights so you can see where you've been, especially for the second and subsequent coats.

What is important is that you get flooring-grade varnish, regular varnish won't stand up to the first party, and yacht varnish will cost so much you won't have the first party...

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It might be better if you didn't stain the wood.

We have varnished the floors in nearly all the rooms in our circa 1900 house and in each case we used clear Ronseal Diamond Hard varnish - it's quick drying and "does what it says on the tin" * - and with three coats it still darkens the wood quite nicely.

It isn't necessary to stain before varnishing and most varnishes don't need diluting.

In a couple of rooms we stained the boards, but only because we had to replace some and the new ones were the wrong colour. In those rooms is was a case of two coats of stain on the new boards and one on the old. Any more and the wood becomes too dark.

The best thing to do is to stain a piece of board in areas with one, two and three coats plus leave an area plain, then varnish. This will give you an idea of what the final effect will be and you can compare the different levels of stain against each other.

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Agree with the testing plan: helps to use the same kind of wood, too. Most houses have either pine or oak boards. –  Jeremy McGee Sep 12 '10 at 21:07
    
+1 for the star -- I never knew that was the origin of that phrase! –  Mike Powell Sep 13 '10 at 2:15

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