This is how we sand floors

“Always do right. This will surprise some people and astonish the rest.” – Samuel Langhorne Clemens

Table Of Contents

Broad overview of our floor sanding process

PreparationCleaningPunching nails
Fixing floorRough sandingGap filling
Fine sandingStaining and colouringApplying finish

Preparation, preparation, preparation

I worked with my Grandfather for several years part time, mostly weekends and holidays during my studies. There were no powerpoint presentations. I often asked him to explain in detail what he was doing, he often suggested I just watch. He did impart two important points, which impressed as they were the entire spoken syllabus. Preparation, preparation preparation and steady Eddie wins the race.

Cleaning, cleaning, cleaning

I always clean before I start, this avoids existing dust becoming airborne due to the sanding machines or us tramping it around the house as we unload the van. I use Festool industrial dust extractors and custom hoses. Then any gaps are carefully scraped clean and the floor vacuumed again.

If the gaps are to be left natural this looks much better and is cleaner, if the gaps are to be filled later on then any resin, filler or wood slivers can adhere to the sides of the timber and not the dust. This is the most important step in gap filling which most people leave out because it takes time. Any glue or bitumen or heavy paint build up may be scraped off at the same time to save abrasives.

Punching nails, removing screws

All nails that can be are punched down, this not only allows the floor to be sanded smoother, saves abrasives it also has the benefit of retightening the nails. This means the floor is more level, less timber is sanded off, the floor remains thicker, stronger, quieter and moves less, which means less filler falls out over time.

Another job many people leave out, because it takes time. Like a lot of preparation work it requires patience, diligence and is not always particularly pleasant.

You can see the ripples on those finished floors where the nails resist the sanding. Bogus random round wire nails or clout nails are removed where possible as they split the wood as do poor quality screws which are commonly used for sub standard repairs.

Tightening loose boards, glueing loose blocks, floor repairs

Any loose boards or parquet blocks are removed, cleaned, checked for services underneath where appropriate and refixed. Cut floor brad nails, rosehead nails or slim shank high performance torx screws are used. The quality of fixings matter, hugely.

These modern screws have the same or better holding power than two inch flooring nails and avoid the vibrations that nailing entails which can damage lime plaster in older buildings. I use top quality screws and my floors are solid. I also remove any board I need to fix down.

The harder you work the luckier you get, so far I have not gone through a pipe or wire.

Block and parquet floors are cleaned of any old adhesive / bitumen and reglued using high modulus MS polymer adhesive, this costs more but gives a very strong bond and remains flexible. To date I have not learnt of a block I have glued coming loose. If the bitumen is impossible to remove I may use a modern rubber bitumen emulsion adhesive.

On tricky floors where the sub floor has been butchered as in the Queen Anne floor below, glue is used as well as penetrative fixings.

If a fire hearth has been removed and joists reinstated then this is obviously the time when the new boards are ‘stitched’ in and all other floor repairs are carried out.

Rough and intermediate sanding

The aim of expert floor sanding is to remove as little wood as possible. By doing so we can preserve as much patination as possible and leave the floor thicker and stronger. This means the floor moves less, is quieter and any filler applied lasts longer as movement is the enemy of filler.

It is often better to sand extra passes with a finer grit than it is to do less passes with a coarser grit as this normally results in a flatter, thicker floor. The aim of the rough sanding is to level the floor and clean it of any dirt or old finish, glue etc.

On very old, delicate or thin floors or floors where the customer wants to preserve the gentle undulation of the boards, the floor is sanded by hand. The edging machine or smaller finishing sanders are used to clean and sand the floor by hand to retain the three dimensional patination and as much original material as possible.

Many people take the rough ‘wood dust’ from the first sanding pass, which in reality is more like ‘wood wool’ due to it coming off in long fibres. They use this coarse, dirty ‘dust’ to fill the gaps, this method is bound to fail.

I always keep a supply of fine, sieved antique oak and pine dust. If I need to use dust from the job I will use the finer dust from the intermediate passes P80 or greater. This is clean, fine and makes a smooth filling paste when mixed with the resin.

By the time I apply the first coat of filler the floor may have been sanded five, six or seven times already normally to P60 or more often P80.

Gap filling floors

There are three methods for gap filling, I most often use the first method but frequently use a combination of all three plus selective use of two part polyester resin. I self colour the two part filler with fine colouriser pigments to any colour I require.

I also often colour the resin filler with these high quality pigments as normally a slightly darker filler looks better than a lighter filler and floors are usually a range of hues and shades from light to dark. The three methods are:

Resin and sawdust filling

Many people have heard bad things about resin and sawdust due to some of the shortcuts taken described above. If the floor is fixed securely, the gaps are scraped clean and the floor sanded carefully then this method can have very good results.

I use exclusively Lecol 7500 cellulose resin jelly filler, this is the most expensive filler available but I have found it to be the best quality and the solvent is not as strong as some of the cheaper brands.

Some filler will always fall out over time on older period pine floors as they continue to grow and contract. The joists and indeed whole house moves often over time, but by diligent work the amount of filler that falls out can be very little.

The difference between a correctly filled floor and a hastily cheaply filled floor can lead to orders of magnitude differentials in filler fallout over time.

Pine slivers and PVA glue

For larger, more consistent gaps reclaimed wood slivers shaped into fine wedges can be glued in with high performance PVA D3 or D4 glue. These are left overnight to cure are pared, then sanded off.

The main reason not to use them as a first resort is that gaps in old pine floors are rarely consistent or large enough. This does not always allow the slivers to be wedged in far enough for them to adhere correctly.

Very often I will resin fill an old pine floor over the majority of the surface but use pine wood slivers for the larger gaps that are a constant width, this usually gives the best result.

Bona Gap Master mastic filling

Bona AB of Sweden were the first company to introduce water based floor finishes to the market and they make a number of unique products. One of these is their gap master, an acrylic gap filling mastic which comes in fifteen different colours.

Gap master is specially formulated to be compatible with water based floor lacquers. It has excellent flexibility but is relatively expensive to buy and apply. Application is messy and takes a long time to prepare and dry, it is also difficult to sand. The look can appear plastic and artificial and it sinks below the surface of the floor. For these reasons I use it sparingly where there is movement which cannot be ameliorated due to subsidence or a very poor subfloor.

The darker colours like Wenge or Black give the least imposing effect looking like the shadows of the original gaps. On difficult period floors I often use it in tricky areas or around bespoke thresholds. If one wants to avoid drafts but retain the look of the original dark gaps then it is an excellent choice.

Spot filling with two pack filler

There are always larger more irregular gaps in older Edwardian or Victorian pine floors. Old radiator holes for example or other larger gaps that are difficult or time consuming to fill with wood infills. In this case I use a two part polyester resin which I self colour bespoke to each job using my fine pigment colourisers.

Sometimes a client does not want the main gaps filled or even the natural cracks filled in reclaimed timber. Selective cracks nail and screw holes can be filled with two part resin filler. I usually mask off the areas to be filled.

Twice as nice

When using resin and sawdust all my floors are filled at least twice, in reality some areas are filled three or four times, sanding in between fills. Few people do this but the filler sinks and in an irregular manner, if you want a nicely filled floor you have to fill it twice.

I always tell my customers unless they want to pay for the floor to be filled correctly then it is best to leave the gaps open as filler that mostly falls out after a few months often looks worse than no filler at all.

Still cleaning

Cleaning after every pass gives a smoother, scratch free finish and stops dust being tramped into the air and around the house. It is especially important to vacuum during filling otherwise the filler will not adhere properly. The floor will probably have been vacuumed around ten times by the time the second filer coat has been applied.

Fine sanding the floor

After the second filler coat has been applied or the fillets have been shaved off and spot sanded by hand machine the fine sanding commences. This is normally with a P80 grit on either the Hummel belt sander, the four disk Bona power drive or hand held Festool Rotex.

Ordinarily two to four passes are taken at P80 followed by two to four passes with P100 or P120. This is sufficient for most unstained floors, by this time the floor will have often been sanded around ten to fifteen times.

Hand finishing

If the floor is going to be stained then I normally do a final pass with small hand machine with a head torch or powerful LED site light. Even small scratches will show up when stained, the result is rarely perfect, but close enough.

The biggest problem with staining is incorrect sanding. Often I will choose to water wash the floor to raise the grain before sanding by hand machine which helps to swell up any stubborn scratches so they can be cut back more easily.

Staining and colouring the floor

After the final sanding and or final hand sanding the floor is vacuumed again thoroughly and is stained, or left natural. I make my own stains from scratch bespoke to each and every job. This means the customer can choose the exact colour they want. No need for anyone to settle for the closest shop bought choice, which often isn’t very satisfying, or close!

The staining of a wood floor is probably the most difficult aspect of any job. Luckily for me having studied and worked in the professional French polishing and wood finishing industry for many years I can mix pretty much any colour you want. This is the part of my job that normally most impresses my customers. It is also the part of the job that I find most satisfying being both creative and pleasingly challenging.

This also means I can often colour match replaced boards or blocks, because that’s a large part of what polishers do.

Sometimes to get a natural looking colour I will stain the floor two or three times. I use novel French polishing techniques applying transparent light tints in shellac. I am able to get even, very natural looking colours with great clarity and depth.

For deeper colours I will first stain the floor with a transparent dye. This can be either a traditional water stain or a modern solvent stains. These are then sealed in shellac and the colour tweaked with subtle tints to get the precise, even and natural looking colour.

Final finishing, lacquering, shellacking, oiling, waxing the floor

Most floors are finished with one coat of Mylands floor barrier seal (shellac) either transparent or bespoke tinted and two coats of either one pack or two pack water based polyurethane lacquer.

The shellac seals in any impurities embedded in the wood like oils and silicones which sanding cannot remove one hundred percent. Shellac also gives great depth, clarity, chatoyancy and a warmer traditional solvent based looking finish. As shellac is not very durable especially not very water resistant, a high durability water based lacquer is applied over the top.

The floor retains the looks of a traditionally finish but with the advantage of low to no maintenance, indeed most of my floors do not need a recoat for a decade or more.

Some jobs call out for a totally traditional finish. In these cases extra coats of shellac can be applied and the floor simply waxed with beeswax and carnauba.

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