Floor sanding

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It's not hard. You have to be moderately fit, as (for a machine that does all the work for you) it's surprisingly hard work. It will exert a cruel toll on musculo-skeletal wear and tear!

Takes a couple of days to do a room, a week to do four or five. This can multiply enormously if you lift the carpet to discover rot / a mineshaft / a concrete floor / badger sett / a border of 1930s tar-based paint around the rug. The minimum time also depends on things like drying times.

You need to hire a floor sander. You also need a belt sander and a random orbital disc sander. I would hire the belt sander (they're not much use otherwise) and I would buy a Makita or Metabo random orbital sander as a thing worth owning if you have a house to decorate.

You also need a vacuum cleaner (a voracious one, such as a Ron, not a Henry) A Henry might do it, but you will use Many Paper Bags, so a plastic bucket Earlex workshop vac is much better.

Planning

The time taken to sand a floor depends on what needs doing to it, and this is often hidden until the carpet is lifted. Some materials may need to be ordered in advance, although the awkward ones by mail order are usually dependent on simple area, so may be ordered early. The hidden surprises beneath the carpet tend to reveal either woodwork or more time being needed.

Repairs

Rotten timber needs replacement before the sanding. It's not too hard to change floorboards, but often the joists beneath need work too and it can be hard to judge this until the boards are lifted.

Is the floor wooden?

Is the whole floor area wooden? Are there any patches, especially on a downstairs floor, which are concrete? Or concrete that has previously been covered with wood well enough to lay carpet on, but not to sand.

Typical places to find concrete floors are:

  • Hearths and chimney breasts: these are always masonry and if removed or cut back, will need replacement. This may have been done in the past, but has it been done adequately to leave on show? Some tiled hearths, if level with the floor, can be attractive as visible tiles.
  • Walls: where a room has been knocked-through from two rooms, the original wall would often leave masonry behind. However to make this flat it has often been laid-over in timber. Was this done well enough to sand, and was it done with a good-enough damp-proof membrane to not give future trouble?
  • Doorways: as for walls, sometimes a doorway or boundary can be of masonry.
  • Sculleries: these have often been merged with kitchens by now, but the floors have sometimes remained as concrete.

Condition

Electricians and plumbers installing cables or pipework in the past will have damaged some boards in gaining access beneath. The care they took, or didn't, can have an effect. In the worst case, boards may be easier to replace.

Boards will 'cup' as they dry out. Part of the sanding process is to flatten this. It takes time, and extra coarse sanding, so may change the overall time needed to do a difficult floor.

The surface condition of the boards (roughness or ingrained dirt) is usually much less trouble than cupping.

Coatings

Some 1930s houses had a central rug, with the floorboards painted around this. The paint used was tar-based and takes a lot of effort to remove it. Allow extra time and coarse sandpaper.

Preparation

Carpet tacks

Lift the carpet, vacuum, and make the timber beneath smooth and ready for sanding. This involves removing all protruding nails and screws.

Carpet tacks will be around the edges of the room and sometimes in lines across the middle or in high-wear areas. They are best lifted with a variety of prybars, pliers and pincers. If the heads break off and can't be gripped, punch the remains below the surface with a nail set (a blunt steel punch) and hammer.

Nails holding down the floorboards are usually large cut nails and already well sunk. Punch down any that protrude.

Screws are usually found around boards that have been lifted by electricians. These need to be set low enough to be below the surface. Sometimes it's worth replacing all their screws with stainless steel ones.

Gap filling

All floorboards have gaps somewhere in the room, and these vary in width. A filler is needed to block them for appearance, draughtproofing and to avoid the loss of small change. The filler needs to not look out of place, to work for gaps of varying sizes, and to stay in place long-term without falling out.

Gap fillers can also be used over nail holes, knots or other damage to the boards.

Many fillers use a combination of sawdust and glue. The sawdust is collected from the second bagful of dust from the coarse drum sanding step (the first bag is discoloured with the old surface paint and dirt). The glue is simple carpenter's PVA wood glue. They are mixed by hand, then applied with a plastic spatula. It takes an hour or two to dry, ideally overnight, then can be sanded over just like the timber.

A drawback to the sawdust and glue technique is that it needs sawdust, thus can't be applied until halfway through the sanding stage. This is often used to excuse a convenient break - on a large multi-room project it's no delay. A long-term drawback is that this filler shrinks over time as it dries out, and in my experience always falls out of the wider gaps where it's most needed.

I know of no perfect filler for this. A new commercial filler looks as if it's worth trying.[materials 1] This is the same sawdust-and-glue process, but with an improved and flexible glue. Another brand:[materials 2]

Other fillers:

  • Squirty foam. PU expanding foam in a can. Quick and easy to apply, fairly fast curing. It's not hard-wearing on the surface though. This is useful stuff, particularly as a backing underneath wide gaps, but mostly as a support for another filler, not on its own.
  • Mastic. Applied with a squeeze gun. This can be either general builder's mastic, or a specialist one for floors.[materials 3]

Sanding

Most of the work, both effort and time, is done with the large drum sander. Most of this work is done with the first steps and the coarsest sandpaper. Much less of the fine grades are needed, because there is less wood to move, and the sheets last longer (the paper-clogging dirt has gone by now).

Sanding goes in three stages:

  • Flattening the floor
  • Cleaning the floor
  • Smoothing the floor

Flattening

The floor will not be even. There will be steps between floorboards, and some boards will have cupped or twisted as they dried out. Most of the sanding work in doing a floor isn't in sanding the surface, it's in making these steps to be flat.

Begin by sanding a diagonal cross in the centre of the room. The first few passes can often reveal much about the surface, and how long the job is going to take.

Then work outwards, parallel to this. Make strokes that overlap slightly. Work in a boustrophedonic style, going away from the mains lead, to avoid running it over. In a small room it may be easier to work in the same direction, wheeling the machine backwards on its castors.

Cleaning

When changing grits to finer paper, vacuum the floor at the same time to pick up coarse grit and avoid making scratches.

Smoothing

Smoothing the floor involves removing the scratches put in by the earlier coarse grit sandpaper. This needs to be sanded along the grain, going back and forth along the length of the boards.

Edges

Use the belt sander to work alongside the straight edges. This is the fastest and most powerful, but has the risk of digging in by accident.

A random orbital disc sander is a good combination of sanding power and ease of control, but slower than the belt sander.

Oscillating sanders, like sheet sanders and triangular detail sanders, are slow, but fit into corners.

Sealing

The sanded floor should be brushed and vacuumed, then time allowed for the dust to settle and it vacuumed again. Wear clean slippers and avoid walking on it where possible, as the bare wood is prone to collecting dirt and this will be too late to remove easily.

Staining

Once sanded, the floor should usually be stained. This can even up some colour variations (especially if boards have been replaced), but also gives a better colour than the extra-pale colour of freshly sanded softwood, which will darken naturally with time anyway, but may do so unevenly according to sun and shade.

A spirit- or water-based stain is usable. Spirit is usually a bit quicker, but there's not much in it.

If in doubt, 'light oak' is about right.[materials 4]

Apply the stain by hand, working on hands and knees and with either a small brush or a foam brush. Work from the far side, back to the exit door. Working along a few planks at a time avoids visible 'dry edges'.

Varnishing

There are many varnishes available. The only ones I would use are acid-catalysed super-hard floor varnishes.[materials 5][materials 6] Other makes are available.[materials 7] The one I've used myself is Rustin's[materials 5] These are water-clear, extra-hard when down, long-lasting and non-yellowing. To apply them they have a catalyst mixed before use, then cure very fast. They have a foul smell when applied (wear a real mask), but this disappears within a couple of hours and there is no residual smell of solvents. They also set hard very quickly, enough to put furniture on that same day. Two coats are needed, some use three.

No varnishes are cheap, and these aren't. A 4 litre $67 pack of Rustins will do two coats on a typical room (claimed coverage is 24m^2, at two coats).

Mix up enough varnish to apply in one go, not necessarily the whole pack. When applying two coats, only mix one coat worth. Although the 'pot life' of the varnish is claimed to allow enough time to allow both coats from the same mixing, this is optimistic.

Brushes will be destroyed by this varnish. They may be cleaned a little with cellulose thinners, but this is not reliable once it has started to set.

Tools

Machinery

Sanders
Vacuum cleaners
  • Industrial, bucket type
  • Small domestic. Soft brush nozzle for getting corners clean

Hand tools

(Nail preparation)

  • Prybars, pliers, pincers for removing nails
  • Nail set and hammer

(Gap filling)

  • Spatula
  • Bowl

(Staining)

  • Brush or foam brush

(Sealing)

  • disposable mixing bowl
  • paintbrush or two (will be sacrificed)
  • cellulose thinners (not normal thinners) for cleanup
  • wipe cloth for spills

Materials

  • Sandpaper (drum sander)
  • Sandpaper
  • Gap filler
  • PVA wood glue
  • Stain
  • Sealer

PPE

Sanding

  • Dust mask. A cheap disposable 'P2' mask is fine. An exhale filter is more comfortable.
  • Boilersuit, or disposable boilersuit, to keep dust off (optional)
  • Knee pads
  • Foam kneeling pad
  • Clean slippers, or foot bags, to keep dirt off the freshly sanded floor.

Sealing

  • Vapour fume mask, with filters for 'acid vapours'. These are not the same as a simple dust mask.
  • Clean slippers
  • Clean kneeling pad (or cardboard)

Links

Materials

Tools

Personal tools