Custom Door
Montreux Estates
Reno, Nevada
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The Basics of Hardwood Finishing
Whether you finish on-site or choose a factory application, it's helpful to understand
the basics of hardwood finishing. Finishes enhance or alter the natural beauty of wood,
and protect wood from damage.
Wood Preparation
The most important step in hardwood finishing is wood preparation. Indentations, grease,
oil and other wood defects are removed with multiple grits of sandpaper, scraping, and even
sponging and then sanding. The stain and finish then can be taken into the pores evenly
across the whole surface.
The cellular structure of a wood influences its appearance. Open grain hardwoods, such
as elm, oak, and ash are "ring-porous" species. These species have distinct figure and grain
patterns. Close Grain hardwoods, such as cherry, maple, birch, and yellow poplar, are
"diffuse-porous" species. Most North American diffuse-porous woods have small, dense pores
resulting in less distinct figure and grain.
Certain closed-grain woods such as cherry and maple tend to develop finishing blotches
caused by textured grain. No matter how much sanding is used on these areas, they will never
disappear.
A stain's penetration also depends on the final grit with which the wood was sanded.. For
instance, the large valleys left by 80 grit sandpaper will absorb much more pigment than
will the fine tracks left by 150 grit sandpaper. For this reason it is important to prepare
samples with the actual grits and the actual stains and finishes.
Colorants
After the wood has been well-prepared it is ready for even absorption (Into the wood)
or absorption (onto the wood's surface) of dyes, stains or fillers. In many cases, it is
appropriate to sponge the surface with water, alcohol or solvents to show any areas which
may contain glue marks, oil or uneven sanding. Colorants can be broken into two large groups:
dyes and pigmented stains.
Budget
Pre-finished hardwoods can cost as much as $1.50 per linear foot more than unfinished
products. However, there are several ways to look at the "real cost" question. While
pre-finished material cost more initially, builders can save during installation.
Finishing a hardwood floor to factory standards in the field can tie up a worksite for five
days; even finishing decorative millwork can take three days or more. You'll need a crew of
finishers and extensive site preparation. Other work that could jeopardize the quality of the
finish will have to top, adding time to the construction schedule.
If you finish on-site
Most builders still consider finishing hardwoods on-site the most practical alternative,
especially for major projects like flooring, staircases and paneling. Attaining a high
quality finish on-site is possible, but it requires planning, time and careful attention to
detail. The deep, glossy, pre-finished look takes more than the standard three steps. The
keys are repeated sanding and multiple finish coats.
- Let the wood adjust to the site. Unfinished wood needs protection from moisture and
from extreme fluctuations in temperature and humidity. Before the materials are
delivered, have all windows and exterior doors in place, and brings the house to
occupancy level conditions. Make sure all new drywall and plaster have had at least a
week to dry. Store the unfinished wood in the room where it will be dimensionally
stable when the time comes for installation and finishing.
- Seal it. Solid hardwoods must be sealed on all sides since moisture can pass through
the back, edges or ends as easily as the exposed faces. To avoid shrinking, swelling
and other damages, you should pre-coat surfaces that you won't be able to reach after
installation.
- Smooth it. Sanding is critical to an attractive, durable finish. Items like paneling,
stair rails or cabinetry usually require only light sanding. Hardwood flooring needs
to be sanded at least three time, with successively finer grades of paper. Vacuum the
floor thoroughly after each sanding, and delay spot filling and other minor repairs
until just before the final sanding pass.
- Prepare the room. Once you've installed and sanded your work, the goal is to re-create,
as nearly as possible, the finishing plant's environment. Keep dust to a minimum and
maintain stable levels of temperature and humidity. Seal doorways with plastic film and
schedule other workers away from the jobsite. Mask off any surfaces you wish to protect.
- Clean the wood. Before applying stain, wipe it down with a clean cloth dampened in
mineral spirits to temporarily emphasize defects such as sanding marks. Smooth out any
flaws that appear, then remove all dust with a brush, compressed air or a tack cloth.
- Stain it. Apply stain generously with a brush, rag or lambswool applicator. Allow it to
sink in for five to ten minutes, then wipe off the excess with a clean rag. Let the
stain dry 24 to 48 hours - follow the manufacturer's instructions.
- Seal and finish coats. When the stain is dry, brush on the first finish coat and let
it dry according to the manufacturer's directions. Drying or curing times vary
depending on the type of finish you use. When it's bone-dry, sand the surface lightly
with 280-grit or finer paper. Remove the dust with compressed air or a tack cloth and
brush on the second coat.
- Sand and coat again. The second of third finish coat will usually give you the desired
result.
Dyes
Dyes are a solution of colorants in mineral spirits, oil, alcohol or water. Modern
woodworking dyes are very similar to those used by dyeing cloth, paper or leather. Dyes
change the hue of the wood without hiding its figure or rendering the surface unclear or
muddy. In addition, dyes penetrate both the soft and hard grain, and often enhance or "bring
out the grain".
The molecular size of dye particles is much smaller than that of mineral particles in
stains, and thus dyes appear more transparent. In addition, dyes bind to the wood because of
their chemical molecualr structures and no additional binder is required. With water-based
dyes, as the water evaporates, the wood is left with only the color in its surface.
The four main types of dyes are: water, alcohol, oil and solvent-based. Each has a
particular use in the coloring process. For instance, with maple or birdseye maple, it may
be found that water-soluble dyes penetrate more evenly across the whole surface. On a more
oily wood, oil- or solvent -based dyes may penetrate better.
Oil- and solvent-based dyes may be added to pigments stains to form a combined stain and
dye. This process may be able to yield the same color with only one operation.
Dyes are less light-fast than pigmented stains, and in renovation work this can be used
to an advantage.
Stains
Produced from a variety of synthetic and organic mineral sources, stains are dispersions
of particles of pigment within an oil or solvent base. The pigments are ground into fine
particles and come in a powdered form which maybe added to other stains to increase color
and density.
The depth of a stain and its opaqueness are directly related to the pigment's solubility,
as well as the size and density of particles in the solution.
Stains may be sprayed, brushed or wiped onto the surface. The depth and final color also
are determined by the length of time the stain is allowed to remain on the surface and how
hard the stain is wiped off.
When using very dark colors, it is difficult to reach the saturation of color without also
covering the grain. For this reason, many projects are colored with a dye and then stained to
produce a clear but dark color.
Pigmented stains will fill the grain and leave wood surfaces with less colorant, whereas
dyes will stain the grain, and the areas between the grain, approximately the same color.
Wood Fillers
Woods with open grain structure such as oak and ash have very large pores. In some cases
it may be desirable to fill the pores to allow the surface to appear smoother or the pores to
appear lighter. Oil-based fillers may be mixed with oil-based stains to even the wood's
color and fill, in one step. Fillers are applied in a heavy film or paste form either by
spraying or brushing, and the excess is wiped off with rags, scrapers or burlap, flush with
the top of the wood surface.
Sealers
All finishes require a sealer. The finish can be self-sealing or the sealer can be
different from the top coat.
In many cases, a vinyl sealer is used to lock in the color and protect the grain. Vinyl
sealers even are used under oil-based finishes. The sealer locks in the colorants, seals the
grain, starts the filling process, and provides a sandable coating. In many cases, the
sealer is filled with particles which make the surface easier to sand but can also inhibit
clarity.
Glazes
Glazes are transparent or semi-transparent stains which are applied after the sealer coat.
In some cases, a transparent alcohol dye may be applied as a glaze as well. Glazes are often
used to even out a light and dark area after the staining and sealing process. It is only
after the sealer has been applied and sanded that the true color of the wood can be seen.
This also is typically the time when touch-up of glue marks and unevenness of color can be
corrected.
Toners
Toners are tinted applications of sealer or top coat which are used to build up a color.
Toners tend to cover the grain because they are essentially pigments suspended in the finish.
Check the Moisture Content
Moisture content is the amount of moisture is wood, expressed as a percentage of its
oven-dry weight. The proper moisture content for kiln-dried hardwood products varies in
different regions of the country. When receiving a shipment of hardwood paneling, flooring,
millwork or cabinetry, pull out several sample boards and use a hand-held moisture meter to
measure their moisture content. The figure should closely match the one recommended for your
part of the country, It it doesn't take the following precautions.
Let Hardwoods Adjust to Their Surroundings
Sawmills dry and condition hardwood lumber to the moisture content expected in service.
During transport and storage, hardwoods can accumulate moisture or become too dry. To avoid
problems, let hardwood products adjust to the site before installation. Here's how:
- Have Hardwood products delivered after all windows and doors are installed, and masonry
and plastering are complete.
- With the home's HVAC system operating at a normal level, unbundle and store hardwood
paneling, flooring and millwork for three to five days in the room where it will be
installed. If delivered before the HVAC system is operational, store the material in a
dry environment until you can follow the instructions above.
Plan for Natural Expansion and Contraction
Here are a few important installation tips for minimizing expansion and contraction of
hardwood paneling, flooring and millwork during seasonal changes in relative humidity:
- Install hardwood paneling so it moves across the grain. Use narrow widths when possible.
- For large areas, such as paneling, leave an expansion gap to accommodate the natural
expansion and contraction, based on changes in humidity specific to your region. Conceal
the edge with baseboards or mouldings.
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