Finishing

Preparation for Finishing
and
Various Finishes Explained

by Tom Paley

Preparation for finishing
Back to the future! A brief overview
by Tom Paley

The problem
Surface imperfections - if left - become emphasised, to a larger or lesser extent, by the finish chosen. In general, the higher the gloss the more the imperfection show.
A trap for the inexperienced: Do NOT over-rely on power sanders & the like to produce an acceptable raw-finished surface.
Although these methods provide a precursor to the finishing process, total reliance thereon might lead to more complications than might be thought. In essence, while valuable in initial preparation, such tools have limitations and these must be known.
Usually, there are ripples left by the rotating cutters, or fine scratches from various machine sanding operations.
Traditionally, the final smoothing of the surface is accomplished using smoothing planes & cabinet scrapers to remove the small imperfections left by the machinists. Until this is done the surface might not be truly smooth.
Method 1: Smoothing by sanding
Contemporary finishers have been encouraged to remove imperfections with abrasive papers, commencing with 80 - 100 grit and continuing through progressively finer papers in increments of 30 - 50 grit. For a super, ultimate, finish the process can be carried through 400 - 600 - 1000 - 1200 grit. Very fine grits cut very slowly & tend to clog quickly, so surface remediation should be accomplished before moving beyond 200 grit.
The effect of sanding - always with the grain - is to remove coarse scratches, replacing them with ever-finer ones!
The surface should begin to take on a sheen at about 300 grit and this improves marginally as the process continues.
It is important to realise that this process - which has become ingrained in the methodology of finishing - is geared to the continuing use of abrasive papers - to the general profit of their manufacturers.
Method 2: Diminishing the reliance on abrasive papers
It is assumed that the raw-machined surface is at the stage of sanding with 80 - 100 grit paper.
If less reliance is to be placed on abrasive papers, older tool-skills must be relearned:
(a) Planing with finely set well-sharpened planes; and
(b) Scraping with well-sharpened cabinet scrapers.
There is much written about these skills in almost any text book on wood working; it is worth spending a little time learning & relearning the techniques, as these skills can really pay-off in terms of money & time.
Essentially, much depends on the ability to properly sharpen these tools as opposed to merely making an edge. It is the inability to master these techniques & overcome frustration that leads to over-reliance on abrasive papers.
Small ripples & scratches left by initial machining operations are first removed a little at a time by planing at about 45 E to the grain one way and completed by planing at about 45 E the opposite way. Note that shavings as such are not produced by this process - the idea is to remove only the tops of the ripples, the board having already been made flat by the machining process. [This is NOT easy.]
The cabinet scraper is then used to complete the smoothing process, also at 45 E each way, finishing with the grain. When the process has been completed, the outcome can be improved greatly by resharpening the scraper and repeating the final scraping with the grain.
If well done, the scraper finish will be clean & ready for the application of the chosen finish. However, some improvement can be made using a last sanding with very fine abrasive paper to burnish the surface before finishing.
This re-education process should reduce -
(a) the cost & reliance on abrasive papers by at least 70%; and
(b) the time taken in preparation for finishing by at least 50%.
Summary
The effort expended is the same, or less - You just use different tool processes to the same end, & save money! Simple!

Oil-finishing
(for inside-use)

by Tom Paley

The product

The oil-finish is a simple finish to use on timber (for inside use only). The principal advantages are:
* Its simplicity
* The use of readily available materials
* Cheapness
* Repairability
* General robustness.

There are, however, some disadvantages:

* It is not entirely proof against the accumulation of dust and grime.

* If more than a 30 - 40% level of gloss is desired, a great deal of labour & effort is needed.

* If the oil is not fully polymerised and the item is used in a damp atmosphere, a fungus (sooty mould) can grow on the surface. This is unsightly, but not self-damaging.

Almost any vegetable oil, salad or cooking oil can be used, with varying effects.
Professionally, the choice is largely dictated by cost and, to some extent, by its colour or darkening effect on the timber.
The most-commonly used oils are Tung Oil & Linseed Oil. Both may be cooked, or raw.
Cooked oil dries (polymerises) faster and this is an advantage. It tends to build a higher gloss more easily, but it has a shorter shelf-life.

WARNING
Cooking raw oil is a simple process, but this is inadvisable because of the inherent danger of its catching fire.

Application
This finish, perhaps more than any other, is subject to many individual secret mixes and methodologies!

Basically, coats of oil, applied sequentially, soak into the timber and, over time, build up a surface. [This is a type of finish that is never finished!]
To start: Brush or wipe a generous amount of oil onto the surface and let it remain for about 15 - 30 mins and thus penetrate the timber. Then, wipe off the surplus before it starts to go gummy.
With a fresh cloth, wipe the surface hard, removing the surface oil and generating friction heat to initiate the setting process (polymerisation).
Make sure no residue is left on the surface - because that eventually would become tacky and attract dust & dirt.
Put the item in a dust-free environment for about 48 hr to let the 1^st coat dry.

Second coat: Repeat the process with a thin coat of oil and allow to stand for 10 - 15 mins.
Then, using the last grade of fine abrasive paper used in sanding, commence to sand with the grain.
This will produce a small amount of gunk (a mixture of oil and sanding dust) which will become incorporated into the finish, filling the pores.
A little heat from sanding pressure will help build the surface finish. Wipe off the surplus oil & gunk to leave a smooth surface free of oil (any residue will become gummy).

Thereafter: Successive coats of oil are applied at longer intervals until the surface builds up to an acceptable level; Typically: 48 hr; 48 hr; 60 hr; weekly; till patina develops.
Note that friction heat is important as a precursor to the polymerisation process.

Ageing: Oil finish improves with age. It is said that a fine patina is only achieved by a combination of the original maker and a little-old-lady dusting & polishing daily for 100 years.

Speeding-up ageing : To quicken the appearance of the aged patina it has become customary to apply furniture or floor wax after the oiling process, thus imparting a soft glow.
That, however, is another story.

OCCUPATIONAL HEALTH & SAFETY:
Oily Rags & Cloths
In a workshop environment there is a real danger of fire (spontaneous combustion) from screwed-up oil cloths being left lying around. After use, EITHER spread out used cloths to dry; OR place used rags & cloths in a bucket of water.

Wax-finishing

by Tom Paley

The product
Wax is one of the oldest finish mediums (media) for finishing timber items. Its application makes it almost impervious to water & moisture. It is easy to apply and can provide an acceptable-looking finish that requires little maintenance.

Due to the thinness of the finish standing water will penetrate eventually, however spills can be wiped-up without causing damage.

The main disadvantage of a wax finish is that (depending on the type of wax), dirt & dust & grime can become embedded into the surface, gradually darkening it and obscuring the grain.
Soft waxes are very prone to darkening; whereas hard waxes are more serviceable but harder to apply.

There are many waxes in common use:

Bees’ wax : Fairly soft; can be polished to a high sheen.

Carnauba wax : One of the hardest waxes

Bees’ wax + Carnuba + various oils: Form the basis of most commercial wax polishes.

Japan : Is extracted from the berries of the tree which produces lacquer resin.

Lac : Is one of the components of natural "shellac" and a by-product of the industrial process of de-waxing shellac resin. The addition of lac-wax provides a hard glossy surface that is desirable in some blends.

Parafine : Is distilled from crude mineral oil. For woodwork (polishing) it can be brought to a high gloss - but this is variable, depending on the source of the mineral oil.

Microcrystalline Parafine : Is basically parafine with a very fine crystalline structure that tends to impart a higher gloss than parafine.
Its main use (Museum Quality) is in the overfinishing of very valuable antiques, as it does not react with the original finish and can be removed without damaging the original finish.

Blends : Most of the waxes can be and are blended with various oils to accentuate particular properties and assist in the method of application.

Summary :
Softer waxes are easy to apply whereas harder waxes are more difficult. The harder the wax the higher the gloss that might be achieved.

DIY :
A simple soft wax can be made from Bees’ wax & genuine Art-turpentine. [NOT mineral turpentine]

Application of wax finish
Wax can be applied to bare wood and a finish built-up from there.
However, it is usual to apply a seal-coat of thin shellac (approx.1 to 1-1/2 lb cut) which is allowed to dry - say 2 hr; then lightly sand and dust-off.
A soft wax blend is applied with a clean cloth in a circular motion; alternatively with a fairly stiff brush. In the same manner as with shoe polish and cleaning, a cloth is used vigorously to rub in the wax, producing a degree of surface heat which helps with its spread and also to remove the excess. Finish with the grain.
Allow the wax to dry and soak-in in a warm dust-free environment, for several hours. Buff the surface to the desired level of gloss.
The process of wax-application & buffing can be continued indefinitely. However it is important not to build the wax too thickly (it needs more buffing).
The wax coating may be stripped-off when it is desired by dissolving it - usually with "Art-turpentine", & wiping the dissolved wax away. Then the whole process can be repeated.

Wax over other finishes
Wax can be & often is applied over almost any of the traditional finishes: varnish; laquer; oil; shellac (French polish); usually as a secondary finish, or an everyday maintenance/cleaning medium.
These are usually special mixtures with a few more additives, in the form of wax emulsions (liquid furniture polish).

Shellac Finish
also known as
French Polish (FP)

by Tom Paley

The product
As with most old systems of finish, there are almost as many variations of FP as there are polishing practitioners.
Shellac (the basic component) can be worked-up to a glossy smooth surface - the finish of antique furniture (the years 1750 - 1900).
There are many "secret ingredients" that are added to FP to help overcome some of the major drawbacks of this fine medium.
It is not very forgiving of imperfections in the timber surface beneath; it is not particularly robust; it is not proof against water, heat, or anything containing alcohol (which is its solvent).

Shellac recipe:
500 g in 1 Litre methylated spirits
( = 4 lb cut)
250 g in 1 Litre methylated spirits
( = 2 lb cut)
Ready-mixed shellac
(usually 3 - 4 lb cut)

Refinishing, with a warning :
The saving-grace of FP is the ability to refinish. Refinishing a valuable antique, although obviously "improving" its appearance, will almost certainly lower its value.

Application (see next column)

Note : Strictly speaking, the process involves four steps; however, the steps can be run together, one after the other.

Secret : The secret is to pack down the layers of polish, one upon the other as the process proceeds (as many as 30 - 50 coats)!

Uh-oh : The major mistake is to coat the FP too thickly. This can make the item look like a toffee apple!

Repair :If things start to go wrong, don’t despair. Just stop; allow the polish to harden for 24 hr or more; then cut-back the surface with wet & dry fine abrasive; wipe-off; dry; and proceed.
Application of FP - Steps (1 - 4)

1 Filling:
The pores of the timber need to be filled. This is usually done with some form of fine powder (e.g. pumice, whiting, fire-clay, brick dust). There are commercially prepared grain fillers.

2 Bodying-up:
This is the 1^st application of the FP
(usually 1-1/2 lb cut).

3 Stiffing:
This tends to flatten & smooth the surface without adding greatly to the thickness of the finish (2 - 3 lb cut)

4 Spiriting-off:
This is the finishing process that provides the rich warm gloss (with straight spirits).

Housekeeping :

Particular stress is given to the need to keep the polishing pads, the equipment, and the work area CLEAN and FREE of DUST.

Dust & dirt are easily incorporated into the finish, making it very cloudy.

End Note:

Traditional French Polishing

In the past,
Traditional FP
was a 5-year Trade course!