GETTING a surface ready for finishing is work which should be done with the utmost care when the finish is to be the finest possible and even for ordinary jobs. Unfortunately, the price received for many jobs of finishing: is so low that it is quite impossible to do more than the most rapid cleaning and sandpapering, so that is where the responsibility must be placed for many muddy, cloudy natural and stained finishes.
Wood to be finished in natural or stained colour is especially deserving of most thorough work in preparing it for the finishing process. It should first be dusted off with a duster brush or a broom in the case of floors. Then all spots of plaster, dirt or grease ought to be removed.
Usually, such spots will come off with a washing over with benzine, using a putty knife to scrape off as much as possible. If the wood is oak, walnut or other open-grain variety, be particular to remove dirt, lime and grease from the pores of the wood. When such spots are not properly cleaned, stain does not take hold and penetrate and the finish is thus spotty in appearance.
New surfaces which are to be finished with paint and enamel ought to be cleaned well, but there is no need to be so particular about light stains. All loose particles on the surface should, however, be removed.
New surfaces which show dark stains from rust or other substances should be bleached out in such spots before being finished in natural or stained colours. The bleaching methods will be found later on in this chapter.
New surfaces after cleaning should next be sandpapered if the finish is to be natural or stain colours. This is not necessary for paint or enamel finishes. If water stain is to be used many finishers prefer to brush or sponge on a water coating before sandpapering. The water stain will raise the grain of the wood, making little wood fibres stick up all over. If the surface is wet in this way before staining, the water stain does not raise the grain so much and the second sandpapering is very light.
If the water wetting is not done before staining with water stain the sandpapering operation on some woods must be done so heavily that some of the stain colour will be cut off the wood. This sandpapering operation on new wood before or after wetting should be done with No. 0 and No. 00 paper, depending upon the roughness of the wood. Sometimes it is well to go over the wood first with a No. 1 paper and finish up with a finer grade.
The cleaning necessary after sandpapering should be well done with a duster brush on ordinary jobs. On fine furniture and cabinets, more effort should be spent to remove every particle of dust. In furniture factories, the dust from sanding is blown out of the pores with compressed air.
Woods to be finished in natural colour as light as possible, maple, birch, etc., are often bleached before any finishing coats of filler, varnish or shellac are put on. The bleaching raises the grain of the wood and a thorough job of sandpapering must be done after that process. The bleaching methods will be found later in this chapter.
New surfaces to be finished in natural or stain colours and which show cracks and holes should be filled to remedy these defects. Plaster of Paris soaked in water is preferred by many finishers for this filling because it will absorb stain and also will take on the colouring given by filler. Other putty does not absorb colour. On stained finishes, as a rule, the putty is put into the cracks and holes after the stain is dry.
After putty is dry it should be sandpapered down smooth and clean. Then the surface should be cleaned up around the repairs.
Preparing an old painted surface for repainting or for an enamel finish simply calls for sandpapering to remove dirt, grease and roughness, assuming that the old paint is firmly attached to the surface. If it shows any tendency to crack and scale or alligator it should be removed entirely from the surface with sandpaper or liquid paint remover.
Old enamel surfaces which are to be refinished call for sandpapering just enough to cut the old glass and clean up the surface. Defects such as holes, bruises and cracks should, of course, be filled with good putty.
Old varnish to be refinished with varnish, paint or enamel should be rubbed down clean and smooth with No. 1 sandpaper just enough to remove the gloss, dirt and grease, assuming that the old varnish has not crazed or alligatored. If it shows indications of an infirm hold on the wood, better take off all of the varnishes with liquid or paste varnish remover. After sandpapering to remove high gloss some finishers prefer to wash down a varnished surface with benzole or with warm water and soda to make it absolutely safe to paint or enamel. The soda bites into the varnish a little.
Old varnished surfaces which are to be refinished with stain call for stripping off all of the varnish, using liquid or paste varnish remover. A thorough job must be done. If any of the varnish is allowed to remain on the surface, even in a very thin coat, it will prevent new stain from penetrating into the wood. A penetrating stain is then needed to do an even colouring of the wood. After stripping off the varnish a most thorough washing should be done to remove any wax left on the surface by the remover. Wash up with benzole, preferably. Benzine, naphtha or turpentine will also do this clean-up work.
On low-priced work, restaining is sometimes done without removing the old varnish. The old varnish is rubbed down with No. 1 sandpaper to remove the gloss and clean up any dirt or grease on it. Then it is washed down with benzole brushed on to cut the old varnish a little, or is washed down with hot water in which soda has been dissolved to do the cutting of the old varnish. The stain used for such work is an oil stain which must be brushed on very deftly with as few strokes of the brush as possible to avoid raising or lifting the old varnish. Brush this stain only in one direction. For very cheap work a good brush hand can coat the surface with shellac to which a little pigment has been added to make a stain. These processes simply colour the wood and supply a gloss. They do not pretend to enhance the beauty of the wood. In this sort of work, it is sometimes necessary to touch-up bare, worn-through spots with a coat of thin oil stain before staining the whole surface, this is to make the worn places match the whole surface in colour.
Old stained or natural varnished surfaces from which the old finish has been stripped off with varnish remover are often too dark in color to produce a nice finish with the new stain. Then it is necessary to bleach out the old colour before restaining. The bleaching methods are presented later in this chapter.
Putty Mixing and Use.
Plaster of Paris Putty is used by some finishers on new wood to be finished in the natural colour or stained. This putty will absorb stain and the colour given by fillers. The plaster of Paris putty is made by simply submerging a handful of dry plaster of Paris in water. As long as it remains below the surface of the water it will not set, A small amount should be lifted with the putty knife and kneaded with the fingers.
Press it into place and clean off the surface around it. Be sure to fill the cracks and holes full and level with the surrounding surface.
Cabinet Makers’ Putty is made of fine wood sawdust from the kind of wood to be filled. The dry sawdust is mixed with a glue made from 1 ounce of good quality glue and 16 ounces of water. A little watercolour or dry pigment tinting colour is added if needed to make the putty match the surface. When this putty is well made and used it is practically impossible to detect the fillings, even in fine woods like mahogany and walnut
The wood finishes has occasion to use bleaching solutions for the purpose of removing stains from woods to be finished or refinished, such as rust stains, water and weather stains. He also needs a bleaching solution occasionally to bleach large surfaces of maple, birch, oak, walnut and other woods which are to be finished in as light a color as possible, for instance, oak, which is to be finished with one of the popular light gray, two-tone finishes with white filler, and walnut or gum, which are to be finished with the very light brown French walnut color. Then again when old stained and varnished surfaces are stripped off, removing all the old finish possible the wood is sometimes found to be too dark to take the new stain of light colour and make a nice job. The bleaching is resorted to.
The bleaching processes use water solutions and they raise the grain of the wood. So after the bleaching and neutralizing washes, the surface is permitted to dry and is then sandpapered to cut off the raised wood fibers. Sometimes a very thin coat of white shellac is brushed on to make the wood fibers stiff so they can be clipped off easily with the sandpaper.
After bleaching the surface may contain a bit of the chemical and it is well, therefore, to wash up immediately with clean water, using a sponge. Then a coat of ordinary table vinegar without dilution will neutralize any alkaline traces left on the surface and make it safe for finishing coats. The surface should be allowed to dry at least twelve hours before the finishing coats are put on.
There are many chemical solutions used for bleaching. Some are most effective on one wood while others succeed best for other woods. The oxalic acid solutions are probably used most by wood finishers in the house building industry.
Before using any bleaching solution it is best to thoroughly clean and scrubs a surface, using hot water to which soap and a little sal soda have been added. Use a wad of No. 2 or No. 3 steel wool for the scrubbing, then wash up well with clean water, using a sponge for the purpose.
Oxalic Acid Bleach. Oxalic acid can be secured from any drug store and from paint store stocks in dry crystal form. Usually, a saturated solution is made by dissolving as much of the acid crystals in a gallon of water as the water will take up. Hot water is best and the solution is more effective when put on to the surface to be bleached while it is very hot. Use an old flat wall brush to apply the solution and let it dry on the surface. For bleaching weather stains and also dark sap streaks in wood, 8 ounces of oxalic acid in two quarts of water is about right.
If the first application of bleach does not remove the discolourations or make the whole surface as light as you want it, apply the same solution hot a second time or repeat several times.
When sap streaks or whole surfaces to be bleached are greasy, wipe them off by rubbing with denatured alcohol and let dry before the bleaching solution is put on.
Chlorine Bleach makes an effective bleach, especially if followed by a solution of hydrogen peroxide.
Use this bleaching solution hot and brush on with an old flat wall brush; let dry; wash up with clear water.
Hydrogen Peroxide Bleach. This chemical is a positive acting bleach when freshly made. It is a little expensive when large quantities are needed for large areas of the surface. For small stains on patches and spots, it is entirely practical. Brush on and allow to dry. Wash up with clear water.
PAINT AND VARNISH REMOVERS
There are certain liquids which a finisher can use to remove paint and varnish, such liquids as benzole, wood alcohol, caustic soda and water
solutions, ammonia, etc., but as a general proposition, it will be found that it is most economical to use the factory prepared patented liquid and paste removers. The cost may seem high, but it also costs money to fuss around with mixing solutions with which you are not entirely familiar and which seldom work as effectively as the patented removers. In these days of high-wage scales, time must be reckoned as money.
There are two or more grades of patented removers on the market. They are made in a thin liquid form for flat surfaces and in thin paste form for vertical surfaces. The cheaper grades of removers depend upon wood alcohol and benzole largely as the solvents for action, while the more expensive and better removers use acetone as the principal solvent. Most of the removers sold now are made under the same license patents which cover the use of wax in the removers to prevent the very volatile solvents from evaporating too rapidly and before they have dissolved the old varnish or paint.
It pays to buy the best quality of patented removers as a rule. When they work too fast on large surfaces to permit scraping off the old varnish before it gets hard again, add more wax to the remover. Place the can of remover in a pail of boiling hot water and when the liquid is hot shave into it a few ounces of paraffin wax. Then it will remain wet longer and permit you to do a cleaner job. Also, it is well to coat not so large a surface at a time when the remover permits the varnish to get hard again.
Removing Shellac. To remove shellac from floors and other wood brush on denatured or wood alcohol and scrape up the soft gum as rapidly as possible. Then wash over the whole surface with the alcohol as a final clean up. The denatured alcohol is cheaper than wood alcohol as a rule. Benzine will not do for the final wash-up. Turpentine does not dissolve shellac. Repeated applications of the alcohol may be necessary to remove all of the shellac. When the patented varnish removers are used to remove shellac be sure to wash up well with benzine or benzole later to remove any wax left on the surface from the remover.
Removing Wax from Varnish. Before a waxed surface can be successfully revarnished or painted the wax must be removed. The new coats do not dry when spread on over wax. The wax must all be removed including what has lodged in the seams, cracks and pores of the wood.
The waxes usually used on floors and trim are soluble in benzine, benzole, turpentine and denatured alcohol. If you want to remove wax without injury to the varnish or shellac under it do not use alcohol; the benzine used freely will probably take off all of the wax if you scrub hard enough with it and sandpaper the surface well.