Selecting Veneer (101)
Types Of Commercially Available
Veneer
Today, there are many different types of
veneer available to both hobbyists and professional. In
general, veneers can be broken down into two categories,
Flexible and Standard. Both are used extensively by pro and
amateur, however there are significant differences in cost
and ease of application. I will briefly describe these two
types of natural wood veneer.
Just as every tree has its own
character, so does every individual sheet of veneer. When
veneer is cut from a log, the manufactures are very careful
to stack each sheet in the same order as it comes off the
log. If this care was not taken, and the sheets were stacked
randomly, you would be unable to select and purchase two or
more sheets almost identical. This is especially important
if you need to joint two or more sheets together to create a
wide matched panel. However, even matching sheets have some
variation in grain and color. Whatever your source of
supply, make sure the supplier offers consecutively sliced
sheets of veneer.
Standard Veneer
Standard veneer is what our fathers and
grandfathers were used to working with. The sheets are cut
from a log, stacked in consecutive order, then sent to a
drier and once again stacked consecutively. Years ago, most
standard veneers were cut to approx. 1/16" to 1/20" thick.
With advances in cutting machinery and technology along with
the need to get more material out of one log, today most
standard veneers are cut to a thickness of about 1/28" to
1/40". However, certain species of veneers like oak, walnut,
maple, cherry, mahogany and some others can still be found
in thicker sheets.
Standard veneer is usually available
in random widths ranging from about 3" to 12". Some species
like oak and mahogany which grow in larger diameters are
available in wider sheets. Veneer distributors usually sell
the sheets in 3 to 10 foot lengths. However, many species
are only available in short 3 foot lengths. If you are
purchasing standard veneer by the square foot and plan to
apply it to a door or kitchen table, make sure you specify
if you need long sheets or you will probably end up with 3
foot lengths.
Standard veneer should not only be
purchased in consecutively sliced sheets, but it also should
be of good quality: relatively flat, with little or no knots
or sapwood, generally uniform in color, with very few or no
checks or splits. There are some exceptions to this. Certain
highly figured veneers like burls and crotches are almost
impossible to find in perfectly flat sheets, free of splits
or some knotholes. This is because highly figured woods are
not as stable as flat or quartered cut veneer and tend to
warp and buckle much more. Therefore, do not be surprised if
you purchase some burl veneer and it is wavy and includes
some checks and knotholes. This is a normal condition for
these types of veneer. Much more preparation has to go into
flattening, filling knotholes, and taping these types of
standard veneers before gluing them down. I will cover this
in detail in a future document. Also, see the document on
flattening veneers.
Standard veneer is usually sold by the
square foot. The price varies depending upon species. Some
species like poplar can be purchased for about 40 cents per
sq. ft. while others like ebony can run $3.50 to $4.00 per
sq. ft. No matter what species you are planning to work
with, when working with standard veneer, make sure you
purchase at least 20 to 30 percent more than what you
actually need. This figure factors in waste and excess for
trimming and jointing.
Flexible Veneer
Over the past 20 years, this new type of
manufactured natural wood veneer product has been gaining
popularity with both professional and amateur alike.
Flexible veneer is manufactured by slicing very thin sheets
of veneer (approx. 1/64" thick) and then treating the veneer
to make it more pliable. Once the cutting and treating is
done, the sheets of veneer are then jointed together to
produce a wide sheet. Finally, a paper type of backing is
permanently mounted to the back to bond it and give more
flexibility.
The two main advantages are: Ease Of
Application Because of its flexibility, it can be cut easily
using a craft knife or razor type blade. It can also be cut
to rough size with a pair of shears. Unlike some standard
veneer, flex veneer can also be easily bent around forms and
contours without the need to wet or steam the veneer.
Available In Large Sheets The manufacture joints narrow
slices together to produce a wide sheet. Most flex veneers
are available in 18". 24". 36" or 48" widths and in lengths
of 8, 10 or 12 feet. This saves the buyer a lot of time,
especially if they would have to joint a number of narrow of
pieces prior to gluing down the sheet.
There are other advantages to using
flex veneer. Some species of burls are also available in
flex. Not only are the smaller pieces pre-jointed to give
you a large sheet, but the burl is perfectly flat, and any
defects such as knotholes and or cracks have been filled and
repaired. Flex veneer is sanded smooth at the factory and
needs little or no sanding prior to finishing. Because the
actual veneer face is so thin, you can not do much sanding
or you will cut through the face. Once the flex is glued to
its surface and the glue has cured, it can be finished like
any other veneer: (stained, filled, sealed, varnished,
lacquered, oiled waxed, etc.). By this time you may be
asking "Then why should I use standard veneer?". The only
consideration is price. Flex veneer is much more expensive
than standard. You are not only paying for the product, but
also all the work the manufacture is saving you. For the
pro, I feel it is still worth the extra cost, but for the
amateur, it's a toss-up. If you have not worked with veneer,
flex will be much easier to handle and apply, but on the
other hand, if you have the time to prep and joint standard
veneer, the price may be too high.
Now, lets talk about
Varnish for your wood
For many amateur woodworkers or
hobbyists who either cannot afford spray equipment or do not
have enough space in their shop to set up a spray booth to
safely spray finishes like lacquers, brushing on an oil
based varnish is one of the best choices for a topcoat
finish. Oil based varnish does not dry very quickly,
therefore it will take longer to complete a finishing
project using varnish as opposed to lacquer, water based or
other faster drying finishes. However, if you are an amateur
or home woodworker, not a pro who has to worry about meeting
a deadline, time should not be top priority, quality should.
Varnish has very good resistance against abrasion, wear,
heat, solvents and water vapor. Other than its slow drying
time, which can also cause problems with dust getting
trapped in the finish before it dries, the only other
disadvantage to oil based varnish is that it tends to yellow
over time. The dust problem can be taken care of by setting
up a dust free finishing area in your shop and sealing it
off with heavy plastic to reduce the amount of dust and
sawdust in that area. The problem of yellowing cannot be
handled as easily. First, most oil based varnishes are amber
(yellowish) in color to begin with. This is because the oils
used to make the varnish are amber. Therefore, oil based
varnishes tend to somewhat change the color of the raw or
stained wood when they are applied. It is not a considerable
change, and unless applied over a very light colored or
white stain, it is satisfactory. In fact, amber varnishes
actually give darker woods like walnut and mahogany a warmer
appearance. Non-amber or what are called water white
finishes like some lacquers and water based finishes can
leave a cold look on darker colored woods. However, if
needed, there are a few water white varnishes available. One
is called water white restoration varnish manufactured by H.
Behlen & Bro. Nothing can really be done about yellowing of
varnish over time and if you think about it, all film
finishes break down in one way or another over time and have
to be removed and replaced with a new finish. Tung oil
yellows less over time than other oils, therefore a varnish
that contains tung oil will have a tendency to yellow less
over time.
Oil based varnish is manufactured by
cooking certain oils that can cure with resins. Once this
blend of cooked oil and resin is complete, solvents are
added to make it thin enough to apply and metallic dryers
are added to help speed up the curing time. Initially,
linseed and tung oil were used by manufactures for the
curing oils and natural resins like pine and gum resins were
used along with solvents like gum turpentine and mineral
spirits (to thin it out) and lead used for the drier. These
ingredients were not only used to make varnish, but also
paint. With the exception of lead, you can sometimes still
find some of these ingredients in today's oil based
varnishes, but modern varnishes usually use synthetic resins
which are superior in strength and longevity and curing oils
that are less expensive to use in the manufacturing process
along with a blend of solvents and metallic dryers like
cobalt and zinc that do not cause health problems such as
lead does.
Types Of Oil Based Varnishes
Phenolic Resin
This varnish is made with phenol (a
plastic) and formaldehyde. The phenol is a solid and is made
into liquid by heating it with oil and then adding in the
other ingredients. When the finish is applied in a thin film
and exposed to to the air, the solvent will evaporate and it
will turn back to its solid form.
Alkyd Resin
Less expensive, this is a type of
polyester resin that is combined with alcohol and acid. It
is also cooked with oil to create a varnish. This is the
most commonly used resin in commercial varnishes today.
Polyurethane
Yes, that's right. Polyurethane is
classified as an oil based varnish, although some purists
will disagree. Initially developed to be used as a
substitute for other plastics, polyurethane has become on of
the most commonly used resins in the manufacturing of many
wood finishes. Polyurethane is a very tough, abrasion
resistant resin. There are many types and forms of
polyurethane, but the kind of polyurethane finish you are
used to seeing in paint and wood finishing supply stores is
not pure polyurethane, but rather an alkyd varnish that has
been modified by adding some polyurethane into it. That is
why polyurethane should be classified as a varnish. Perhaps
a better description would be modified varnish, but
nevertheless, still varnish. It is applied and it cures in
the same manner as other oil based varnishes. Contrary to
what many people say about polyurethane, most modern high
quality polyurethanes do not dry leaving a plastic
appearance. They are available in various sheens from satin
to semi-gloss to gloss and can also be rubbed to a beautiful
smooth luster. Polyurethane's abrasion resistance makes it
on of the most commonly used finishes today.
Satin Vs.Gloss Or Semi-Gloss
Throughout the years, many pieces of
furniture have been finished with varnishes and other
topcoat finishes. Years ago, and on much custom furniture
still today, the varnish was applied and then rubbed down
with steel wool or sandpaper to cut down the shine and give
it a more pleasing look. Today, wood finishing manufactures
make varnishes in different levels of shine so the furniture
does not have to be rubbed down after the finish has been
applied thus saving many hours of hand or machine rubbing.
These varnishes are sold in different sheens. Some will give
the user a high gloss finish, others like a satin will have
a slight gloss. All topcoat finishes start out as high gloss
and if the manufacture wants to make a satin or semi-gloss
finish, they take the gloss finish and add a flattening
paste into the finish along with the oils resins and other
ingredients we now know are used to make varnishes. This
paste is usually some kind of zinc oxide and it settles to
the bottom of the can. This is why you do not have to stir a
gloss varnish before it is applied, but you must stir satin
or semi gloss varnishes to get the paste off the bottom of
the can and mix it into the finish. The flattening paste
makes the finish a little duller and prevents the light from
reflecting off the surface as much as a gloss finish. The
flattening paste also makes the finish less transparent,
thus creating a cloudy look. If you apply too many coats of
satin or semi-gloss varnish, you could actually start to
obscure the grain of the wood. Whenever I elect to use a
satin or semi-gloss varnish, I will use gloss varnish and
then only on the last one or two coats use the satin or
semi-gloss, this way I can keep the clarity and still
achieve the desired sheen. Satin and semi-gloss varnishes
are also softer than gloss varnishes because the flattening
paste or agent used will soften the film finish. If you need
a really hard abrasion resistant finish, but want a satin or
semi-gloss sheen, it's best to use a gloss and after it has
cured, rub it down with steel wool or other fine abrasives.
This will also give you a smoother surface, removing any
dust nibs and leveling the surface.
What Varnish Should I Use
For My Job?
To determine what type of varnish you
should use for a particular job, you must look at what type
of oils and resins are contained within a varnish and what
the ratio of oil to resin is. Varnishes that contain a
larger amount of oil to resin are called long oil varnishes.
Varnishes that contain a lower amount of oil are called
medium oil varnishes. Long oil varnishes are more flexible
than medium oil, but also softer. Medium oil varnishes are
harder, but are more brittle. For exterior use, a long oil
varnish is best. Because it is more flexible, the varnish
will expand and contract with the wood as changes in
temperature and humidity take place. A medium oil varnish
will not move as much and therefore as the wood moves and
the varnish does not, the varnish will soon start to crack
and peel. Medium oil varnishes are best used indoors where a
lot of wood movement does not occur and a harder finish is
desired. The resin contained in a varnish is also important
in determining what type to use for your project. Some
resins are more elastic than others, making them best suited
for exterior uses. Phenolic resin is more elastic than other
resins, therefore it will be able to withstand the extreme
wood movement of exterior projects without quickly breaking
down and cracking. Alkyd and polyurethanes are better suited
for interior use. Not as important, but still a factor is
what type of oil is used. Tung oil is more water resistant
than linseed or other oils, therefore it would be a better
oil for exterior use, but much more expensive.
Putting this all together, we
basically come down to two categories, interior and exterior
use. For exterior use, a modern spar varnish which is long
oil and is made up of tung oil, Phenolic resins, solvents,
dryers an Ultra Violet blockers (to protect the color of the
wood from fading) is probably your best choice if you elect
to use an oil varnish outside. Although Spar varnishes have
a tendency of initially being more amber (yellow) in color
because of the color of the Phenolic resin. For interior
use, my favorite is polyurethane modified varnish. The best
I used is a product called Wood Glo, it is a satin poly that
flows out beautifully and lasts decades. It is sold by
Constantine's in New York (See Sources) back on my homepage.
They also have a gloss version called Super Shield.
Brushing On Varnish
While not very easy to apply by spray
application, oil based varnish is one of the easiest
finishes to apply by brush. Because varnish sets-up slowly
it gives the user plenty of time to brush and spread it out
evenly on to the surface. It's hard to spray because it has
a tendency to run if applied too heavy. I firmly believe
that any film finish can be sprayed successfully if thinned
out enough, but varnish is one of the last finishes I would
want to spray. Over many years of testing, I have come to
realize that brushing is the best way to apply oil based
varnish.
Before applying varnish by brush, you
should know a little more about how long it takes for each
coat to set-up and how long before you can apply the next
coat along with how it reacts to temperature and humidity
and some other facts. Oil based varnish is much higher in
solids than some other film finishes like lacquer.
Therefore, it should only take a few coats of varnish to
build a film significant enough to protect the surface of
what you are finishing. After the surface has been sealed,
it usually only takes about three coats to give you enough
protection.
One very important factor when
applying varnish is how the temperature effects the speed at
which it cures. You should not apply varnish in temperatures
lower than 65 degrees. If you apply varnish in lower
temperatures it may take several days, even weeks for it to
cure. Room Temp. (approx. 70 to 75 degrees) is good for
applying varnish. Hotter temps. will make the varnish cure
quicker, but the solvent in the varnish will evaporate
quicker, making the varnish set-up quickly and you may have
a problem getting the varnish to flow out properly. This
could result in brush marks, bubbles and an uneven film.
When working in temperatures higher than 75 degrees, try not
to work on large surfaces.
Some Tips For Preparation
Try to set aside a room or part of your
work shop to apply your varnish. This room should be as dust
free as possible. Do not do any other woodworking,
(especially sanding) in this area. If you are going to set
aside an area of your shop instead of using a different
room, it would be a good idea to also surround this area
with heavy plastic sheeting. Before applying the varnish,
wet mop the floor, this prevents you from kicking up any
dust when you walk around. I always place clean craft
(brown) paper under the piece I will be varnishing. Once the
surface has been prepared properly you are ready to brush on
your varnish.
Choosing A Brush
There are a number of high quality
brushes that can be used for brushing on clear topcoats. The
best for shellac and lacquers are natural hair (like badger)
or china bristle brushes. While any of these brushes will do
a great job when applying varnish, there is a much less
expensive alternative. A polyfoam brush. That's right, the
disposable type. Oil based varnish is classified as a cold
finish. This means the solvent use is not as strong as
evaporative finishes like shellac and lacquer. Alcohol and
lacquer thinner will melt a foam brush but the mineral
spirits, solvents or turpentine used in most oil based
varnishes will not harm a foam brush. Foam brushes are
especially useful for novices who have a hard time getting
brush marks out when applying a finish. If used properly,
you can get excellent results. I always have a good supply
of 1",2" and 3" foam brushes in my shop. They are very
inexpensive, so I use one for each coat and then throw it
away.
Applying The Varnish
Sealer Coats
You don't need a special sealer to seal
the wood. Special sealers like sanding sealers will not do
any better of a job of sealing the wood than the finish
itself. Sealers only make the first coat easier to sand,
thus speeding up production time. Also, if you use the wrong
type of sealer, you may have adhesion problems. The best
sealer for your first few coats should be the varnish
itself. Take some of the same varnish you are planning to
use as your finish and thin it down 50 percent ( this is a 1
to 1 ratio) with mineral spirits or gum turpentine. This
will be your sealer. It will do a good job of sealing the
wood and you won't have to worry about contamination
problems. Pour some varnish through a paper paint strainer
or stocking into another can or jar, then add the same
amount of mineral spirits into the varnish. Stir well and
strain a second time into a deep dish or bowl. It's best to
work out of an open bowl or dish so you can easily dip your
brush into it. Now, dip the foam brush into the mixture
until the brush has been loaded slightly past the bevel on
the foam brush. Lift the brush up and let the excess drip
back into the dish. Next, brush on the first coat with the
grain making sure not to leave any puddles or drips. Allow
the sealer coat to dry overnight and then sand with 320 grit
paper. Remove the dust with a vacuum, or tack cloth. If you
are working on very porous woods, apply a second sealer coat
following the previous steps.
Varnish Coats
It's a good idea to also thin out your
coats of varnish a little. You can reduce your varnish 20 to
25 percent 4 parts varnish to 1 part mineral spirits or gum
turpentine or 3 parts varnish to 1 mineral spirits or gum
turpentine. This will not effect the strength of the
varnish, it will only make it flow better and allow time for
air bubbles that form when brushing to pop. The only
drawback is that you will have to add a few more coats
because less will remain on the surface once the varnish has
dried. Prepare the varnish by mixing and straining in the
same way you prepared the sealer. Use a foam brush and load
it in the same manner as the sealer. Apply the varnish to
the surface by brushing either with or against the grain
initially. The main idea is to get it on the surface doing
as little brushing as possible. Once on the surface take one
light pass with the tip of the brush moving with the grain.
Overlap each pass slightly, then leave the varnish alone, do
not do a lot of brushing, this will make the solvent
evaporate quicker and the varnish will set up too quickly
and not have enough time to flow out. Let the varnish dry
overnight, and then sand with 320 grit sandpaper and remove
dust using vacuum or tack cloth. When sanding, if the
varnish starts to clog the paper, it has not dried enough.
If the varnish turns to powder, it is dry enough to sand and
apply the next coat. Continue to apply 2 to 3 more coats of
varnish using the same process. If you are going to rub out
the finish (by wet sanding) after it has cured, you may want
to apply at least a total of 6 coats ( not including sealer
coats). This is because if there is not enough varnish left
on the surface, you may cut through the finish into the raw
wood in some spots. Once you have applied the last coat, let
the finish cure for several weeks before you are ready to
use it or rub it out. Varnish does not need much
maintenance. If you wish, you may apply a coat of paste wax
or liquid polish from time to time.
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