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FINISHING TIPS (PRINTABLE
PDF)
 These
finishing tips are the key to successfully working with our line of polymerized tung
oil based products. The tips are a
combination of our own experiences with our products and those you have sent our
way. If you would like to submit your suggestions just mention your "tip" on one
of our response forms!
- The higher the oil content the longer it takes for the coat to dry and
cure.
- Best climatic conditions: temperature range 55-75 degrees F. and humidity
less than 65%.
12- 24 hours is median dry time.
- The higher the oil content the faster the coat will tack up. Reduction in
surface area coated at one time maybe required. If coat tacks up before it can
be wiped off, add more finish to the already tacky surface and wipe off
immediately.
- Drying and curing of the finish. If bad things are going to happen
finishing with Polymerized Tung Oil this is where 99.999% of disasters are
created.
Drying and curing are a function of the temperature and
humidity in the finishing area, the percentage of oil in the coating, the
application technique, elapsed time between coats, the wood species
(veneers,
some exotics need to be coated with an oil/resin system), thickness of the
coating applied, number of coats previously applied. Drying occurs on the
surface of the finish and is the result of the solvents evaporating into the
ambient air. Drying occurs fairly rapidly. The second stage, or curing, takes
longer and involves the ambient oxygen reacting with the finish in an
oxidation process which results in the surface becoming hard and smooth. When
two or more of the above stated variables begin to interact the cure becomes
significantly longer (exponentially longer). It is imperative that the cure
test that follows be used religiously to avoid creating a disaster. The
above stated problem is associated with our Polymerized Tung Oil because the
solid content of each coat is high, which is a good. Most “over-the-counter”
finishing products don’t present with this problem because their solvent
content is so high, each coat you apply is more solvent than solid. What
protects wood and provides a beautiful lustre is Polymerized Tung Oil (solid)
not solvent! You have purchased the best Polymerized Tung Oil produced - but
it has specific tolerances for application that need to be respected for
success with our finishes.
- CURE TEST:
Push your fingers perpendicular to the grain of the wood
over various locations on the surface you previously finished.
Your fingers should slip over the surface easily. If there is any drag
or grab, the surface is not cured . Additional time is required before
re-coating with oil and/or color.
- Disaster Remedy
- You will know that you have re-coated to quickly when
flat areas in the finish emerge. Moisture is trapped between coats of oil.
There are two ways to deal with the situation. The first is to remove the coat
that flashed. If it is an oil-only coating, stripping off the flashed coat is
the only solution. The sooner that is done the easier the process is. The
second solution is to allow the coat to harden as much as possible and then
topcoat the flashed coating with either Wiping Varnish or Murdoch’s Table Top.
The second solution is a viable solution only if using a resin coating is
acceptable. Removal Procedure: If the flashed coating was recently
applied (within the last 24 hours) and you notice these flat areas you can
scrub the surface with Sutherland Welles Ltd.® Di-citrusol™ or Xylene and
#0000 steel wool and attempt to remove the coat. The uncured Tung Oil will gum
up the steel wool. Keep using clean pads and fresh solvent until the surface
is smooth. Dispose of the waste properly - this is very flammable as well as
combustible. Allow the surface to cure for 24 hours. Test the surface for
readiness to re-coat with the cure test described above. If it has been awhile
since you re-coated and you find these flat areas in the finish, the surface
will have to be sanded to remove the layer where the moisture is trapped. When
you hit the layer that is uncured, the paper will start to fill with gummy
finish. You may have to use a coarser grit to remove the uncured oil. After
the uncured oil is removed, sand the surface to the finish grade recommended
prior to applying finish. Once the flashed coating is removed and the surface
restored, begin applying your topcoats of finish per the instructions on the
label. Topcoat Procedure: Utilizing this procedure, locks in the
uncured coat and masks the surface with a uniform sheen which is why you need
to be using a resin system for coating as you will be applying the topcoat
with a brush and leaving that surface to cure without wiping. A
Polymerized Tung Oil coating without any resin is to be used
as a penetrating, wiped coat only. It does not have a drier schedule that will
support an oil-only coating to cure as a surface coating. The only
exception is when you are applying the Exterior Polymerized Tung Oil and
you are coating in the outdoors where there is adequate air movement to
facilitate both fast dry (surface closure) and curing.
- To expedite the curing process
. After the finish is applied and wiped
off, you can run a fan in the room where the project resides. The movement of
air will speed the drying and curing process. You can also increase the air
temperature but only with topcoats of higher concentrations of oil doing this
with sealer coats will precipitate bleedback NOTE: Don’t run the fan while
you are applying the finish as this speeds evaporation of the solvents
allowing the surface to tack up very quickly making finishing a difficult
process! NOTE: Do not run a fan in the room if you are using any of our
products as a surface finish, that is a coat that is brushed out and
not wiped off.
- Speckling or bleed-back.
Bleed-back or speckling on the surface of the
coating will be noted after you wiped the surface dry and you come back later
and find shiny speckles over the surface. This usually happens when you are
using a low concentration of oil in the coating such as Sealer or Low Lustre.
The typical reasons why this occurs is; the finishing area is too warm,
the wood pore has been closed by sanding to a high grit(
woodturners take note), you are using a wood species or substrate with
very limited absorption capacity such as exotic woods or veneers
or the opposite - very open grain woods such as oak. In general, the
evaporation process is so rapid and the oil so fluid (due to heat in the room)
that the oil is brought to the surface with the evaporation of the solvent. If
sanding is the reason, apply your Sealer coats when you are sanding to 180/220
grit and then move to a higher grit after the Sealer is applied. If you
observe this soon after you applied the finish, adjust the room temperature
and just keep wiping the surface with a clean rag or #0000 steel wool.
Continue wiping off all the oil that comes to the surface until the bleed-back
stops. If you should find the bleed-back after the oil has dried and cured on
the surface, scrub the surface with some Sutherland Welles Ltd.® DiCitrusol™
and #0000 steel wool or lightly sand with the finest grit
possible to remove the speckles and then proceed with your next coat.
- Curing a color coat.
Adding any Sutherland Welles Ltd.® Concentrated
Stain to the surface you are finishing can extend the curing time because the
colors are formulated with a very high oil content. The prolongation of the
curing time is directly related to the concentration of the color coat you
apply. The stain as it is packaged, is very concentrated. It is formulated to
be diluted and added to your second sealer coat and to each finishing coat to
facilitate layering of the color, which gives added depth and
intensifies the color value. There are times that using the color straight out
of the can gives the best results. Undiluted stain and the thickness of the
coat you apply as well as the climatic conditions can really extend the cure
time. Always use the cure test before applying a new coat of oil/color to a
previously coated surface.
- Wiping Cloths -
Scott paper makes a “paper shop towel” that is a
wonderful wiping cloth. It is very absorbent and lint free. It is
especially useful with resin finishes where lint in the towel can be deadly.
For Polymerized Tung Oil and Wiping Varnish, wiping the surface using a
circular motion with a high quality cheesecloth polishes the sheen to create a
beautiful hand-rubbed look
- Preventing the finish from gelling in the can-
as you use the finish
from the can and oxygen remains in the available space, the finish will begin
to oxidize as evidenced by gelling. A simple, effective method for preserving
the finish is to add water to the can! The oil will rise to the surface. You
will need a basting syringe to draw off the finish from the can for future
applications. You will not be able to pour from the can after adding water
as the water will co-mingle with the oil as it exits the can. Clean stones
or marbles are effective as well. The best method is to decant the finish to
smaller glass jars filled to the brim with a secure lid and then inverted(
canning jars and lids are perfect). Make sure you properly labeled
the contents. This method allows visual inspection of remaining quantity
(a downside of water in the can- you never really know how much remains unless
you record all withdrawals - a lot of work). Another factor that speeds
gelling (oxidation) of the oil in the can is repeatedly working out of the can
where the lid is off for the entire time you are finishing. It is best to pour
a small amount into a bowl and work out of that container. Any unused
portion can be returned to the container.
- Finishing Veneer and some Exotic Wood Species-
For veneers use
a straight Tung Oil finish with caution as pores
are too compressed to absorb much oil. The oil remains on the surface and the
drier schedule in the Polymerized Penetrating Oil is inadequate to cure
multiple coats of surface applied oil. Also, when using a
combination of veneer and hardwoods in a piece we recommend using a
product from either the Murdoch's line or the Wiping Varnish as the different
oil absorption capacities of the two wood surface produce an uneven sheen when
using an oil-only finish. Exotics - can be a challenge getting an
oil-only coating to cure readily. You will want to consider either a very low
solid in oil-only( Sealer or Low Lustre) or a Wiping Varnish product or
Murdoch's Hard Sealer or Hard Oil - both are wiping finishes..
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