Deal with defects

Furniture finishing Dealing with defects
DEALING WITH DEFECTS
In my cabinet-making and finishing business, we always allow 20% stock
overage in our quotes for furniture. This is to accommodate various defective
areas in the rough stock that most customers object to: knots, internal checks
and splits, worm holes and sapwood. While it can be argued among
woodworkers that these areas are what gives wood a special type of beauty, the
public usually regards them as defects, so I err on the side of caution and try to
design around them.
The last commissioned piece I built was a cherry settle and my wood supplier
said that he had approximately 70 bd. ft. of cherry that he would give me a
discount on since it had more that the usual amount of sapwood, knots and end
checks. After extracting the clear stock for my customer,
I figured there was just enough stock left to build a smaller version for myself.
The only problem was how to deal with all the splits, knots, sapwood and worm
holes. In this article I'll show you how I turned 30 bd. ft. of stock normally
destined for the scrap box into a cherry settle.
Before starting with the various techniques I use, I would like to impress upon
readers the value of having a clear, detailed scale drawing of the piece you are
building as well as a detailed cutting list. This will help you to visualize how the
different parts of the project relate to each other and which parts show the most.
A detailed drawing is also essential for the first method of dealing with defects,
which is to simply design around them.
Designing Defects Out
Probably the easiest way of handling defects is to incorporate them into a part of
the design so that they are hidden. This is what I did with the knots on the back
of the settle. Many knots that seem large on one side disappear almost entirely
on the other side of a 3/4" board, so putting defects on a back or non-show side
works nicely. However, be sure to take into account that furniture gets moved
around frequently, so what may be a side facing a wall one year may be a show
side later on. The large knots on the oak legs in the photo of another
commissioned piece were dealt with in a similar manner, I designed them so that
they faced to the inside of the side table. Once the piece is completed with the
drawer, they will never be noticed. Because this weak area is near the location of
a mortise, I filled the large knot hole with a polyester filler (like Bondo) to give it
strength, then touched it up with pigments and shellac. (This will be discussed
later.)
zaini@selectvest.com Wisdom Management Services (M) Sdn. Bhd. 1

Another way to handle large defective areas is to place them in the initial layout
so that they fall on an area that will be cut out. This is what I did with a large
worm-holed area on the right side of the settle. Most of the holes fell in the area
that I cut out for the arm. A few holes were left, but they were filled and touched
up later.
For the back panel below the seat, I saved all the sapwood cut offs and small
width pieces and glued them up to make a large 8" wide piece. This panel is
never seen when the seat is down so I wasn't really worried about the
appearance of this piece. However, because it is a structural part that supports
the weight of the person sitting in the settle, I avoided wood with splits, checks,
and large knots. (This is an important point to remember, any part that is a load-
bearing piece should be as defect free as possible. Sapwood does not affect
structural integrity.)
Dealing With Sapwood
I don't always regard sapwood as objectionable, rather, I really like the sharp
contrast between light and dark, especially on dark woods like walnut and
rosewood. But you have to be careful that it doesn't interrupt the natural flow and
form of the piece, like the sapwood on the front panel of the settle. I didn't notice
this when I was building the piece, because in freshly cut cherry, the distinction
between sapwood and heartwood is not that obvious. After a month however, the
contrast became very obvious when the heartwood darkened. It's wise to wait
anyway before correcting this problem, so that you can match the sapwood to the
color of the heartwood after it's darkened.
I handled this problem by darkening the sapwood using alcohol soluble dyes.
Using a fine pointed red-sable artist's brush, I mixed several dye colors together
until I got the sapwood to blend in with the heartwood. I find that working with
several layers of slightly different thinned colors gives a much better final color
match than trying to hit the color all in one shot. Once I padded on several more
coats of shellac, the sapwood was hardly noticeable.
This technique can also be used on pieces that are unfinished. Here I use water-
soluble dyes, because they are easier to handle and do not dry so fast. I find
spraying the dye with a small touch-up gun works best. The trick with this
technique is to anticipate what the wood will look like when it's finished, so I find
wetting down the wood with water first will give a close approximation of what the
wood will look like finished. This technique also works if you're planning on
staining the wood with a pigmented wiping stain like Minwax. The sapwood will
literally disappear after staining.

Knots
I really like knots, and particularly, the area around knots. As mentioned above,
areas that will be subjected to stress should be free of knots but other areas, like
the upper right top of the settle are open ground for incorporating knots. The area
around a knot usually has very swirly dense grain, so care should be taken when
finishing, and the use of hand scrapers is suggested. Knots that have large
cracks or are loose need to be consolidated so that they do not fall out or chip
later. I use several techniques for this depending on how bad the knot is.
Where large cracks have developed, or where large pieces of the knot are
missing, small pieces of wood should be glued in with epoxy tinted with
pigments. This is especially true of knots in walnut. Mix some dry pigment
powders into five minute epoxy and glue in small pieces of wood cut into small
enough pieces to jam in the cracks. (Tip -- rather than mixing the epoxy in the
suggested 1-1 ratio, I mixed the epoxy in a 1.5 resin to 1 hardener. This results in
a much harder glue that scrapes better when fully cured). When completely
cured (24 hours) cut down the wood slivers with a flush cutting saw. Notice my
homemade one in the photo. It's nothing more that an old hacksaw blade with the
set banged out on an anvil. I wrap tape around one end to act as a handle. Then
I finish the surface with a hand scraper.
With smaller cracks, or just to consolidate a loose knot, cyanoacrylate glue can
be used. I use the water-thin viscosity because it actually wicks into the cracks by
capillary action, but I usually put tape on the other side to keep the glue from
seeping through. If you use the accelerator sold with these glues, the area can
be scraped and sanded immediately. Don't sand before the glue is completely
cured, because the sawdust will mix with glue and form a light filler that doesn't
look appropriate with the dark knot
With large knots that are missing or are powdery and brittle, I usually scrape out
the loose pieces and fill the area with a catalyzed polyester filler, such as those
sold in auto-body stores. If you buy these type ask for white hardener since red
hardener is too strong a color when dry. These fillers also dry quickly, and I sand
the area flush after about an hour. They also have the advantage of not
shrinking, which is what will happen with water-based fillers. When dry, I rub
some pigmented wax sticks over the area to fill in the small imperfection and
bubbles on the surface of the filler and then blend the area into the rest of the
wood area using shellac and dry dyes and pigments. As mentioned above I try to
hide these large knots as much as possible in the design.

Cracks and Splits
During its life, trees may be subjected to growing stresses which cause internal
cracks and splits in the structure of the wood. This is known as reaction wood.
This is different from end checks and cracks at the end of the board which form
as the board dries. These should always be cut out. On the other hand, cracks
and splits in the center of an otherwise good board can be filled with dark tinted
glue which has a nice aesthetic look. Very small cracks can be filled with water-
thin super glue like "Hot Stuff" sold by Satellite City. Simply hold the tip of the
dispenser against the and the glue will wick into the crack. Tape the other side of
the board if the crack goes all the way through. When the glue dries it will look
just like a grain line and blend in perfectly. If you don't want it to appear dark,
start sanding with 100 grit sandpaper before the glues dries. Doing this kicks up
some sawdust and push it into the crack along with the glue and dry to almost
the same color as the wood.
For large cracks, I use the same technique as the epoxy technique describe
above for knots. Using the dry colored pigments, you can tint the epoxy light or
dark to create the effect that you want. Several applications may be in order,
because the epoxy will shrink slightly as it dries. The gap-filling advantage of
epoxy is that it also strengthens the weakness in the board caused by the crack.
This is what I did on the left side of the settle, where long cracks went right into
the wedged through tenons. The tenons were a tight fit and the glue-filled crack
stayed put when I drove the tenon home during glue-up.
Worm-Holes
I can't say that I like worm holes so I usually like to place them on areas that will
be hidden or cut out entirely. The other disadvantage is that they severely
weaken the wood, so care should be used when using boards that are badly
worm-ridden. Several techniques can be used, but I like to fill them with tinted
epoxy and then touch them up with shellac and dry powders to blend them into
the rest of the piece. You can also use a water-based filler and then tint them
with the dry colors. They dry lighter than the color when wet, so you may need to
experiment a bit to get the feel of this technique. The filler I made dried too dark,
so I had to lighten the dried filler up with shellac mixed with dry pigments.
Another quick and easy technique for worm holes are pigmented wax sticks sold
by several suppliers like Behlen or Mohawk. Simply push the wax into the hole
and then scrape off the excess with a wooden chisel like in the photo. Then
smooth it level with the paper back of some lightweight sandpaper. Contrary to
what you might think, most finishes can be applied over the wax, as long as the
area isn't too large.

The extra time I put into fixing up the left over stock for the settle was worth it. I
figured that I saved over 100.00. That's a good enough reason for me to try and
save it from the kindling bin. It may take a little extra work, but my wallet sure felt
the better for it.

Preventing Warping and Splitting of Hollow Wooden
Furniture
Almost everyone is familiar with a piece of wooden furniture that, in use, lasts
many many years, even centuries. As soon as that piece becomes dis-used --
emptied, and put into storage -- it suddenly undergoes some dramatic changes,
including warping and splitting. An understanding of why this is so can be applied
to prevent damage to pieces of wooden furniture, particularly those stored in
conditions with little or no environmental controls.
Splitting and warping in wooden objects is often attributed to an incorrect (too
low), or fluctuating relative humidity (relative humidity is an expression of how
much moisture the air is holding, compared to how much it could hold at a given
temperature). This sounds reasonable, until we consider furniture -- we know,
from experience, that even furniture in use may be exposed to long periods of
very dry conditions (i.e. during a Canadian winter), followed by very moist
conditions (i.e. in the summer). The shifts between these extremes can, in some
climates, occur fairly quickly -- and yet, many armoires, dressers, and other
hollow furniture exhibit no ill effects.
Studies done by researchers at the Canadian Conservation Institue in Ottawa
indicate that the key is not in the fluctuating relative humitidy, but rather in how
quickly it affects the furniture. Wood has some "plastic" or "visco-elastic"
properties, meaning that it can "give" in response to stresses, provided that those
stresses are gradual (imagine bending a stick; if done with a slow and gradual
application of force, the stick will bend a fair bit before breaking. If bent suddenly,
the stick will break sooner). In general, splitting of rigid, constrained organic
materials (such as wood) becomes probable when the relative humidity drops
25% to 50%. Note, however, that if the drop occurs over several months, a piece
of furniture may be able to survive a 40% drop without damage; if the drop in
relative humidity occurs over one week, then damage may occur after only a
25% drop.
The response time of the wood to changes in relative humidity can be lengthened
to help minimize damage. For a closed chest of drawers (in the test case, 5' high,
40" wide, 20" deep; wood thickness 3/8" average), response time is lengthened
from 6 days for unfinished wood, to 8 days for wood coated with a light varnish.
Most furniture, however, has already been finished; as well, a difference in
response time of a mere 2 days is not sufficient to prevent damage.
The most dramatic difference in response time occurs when the furniture is kept
full of textiles. The response time of the chest of drawers with a light coat of
varnish is 8 days when empty, and 60 days full of textiles. Thus, the textiles act

as a "buffer" to the changes in the relative humidity, allowing the wood to react
over a longer period of time. This, as already stated, will prevent damages.
It is important that the textiles used be made of natural, absorbant fibres (such as
cotton), and not be coloured (there is always the danger of colour transferring
from the coth to the wood). Old, white terry-cloth towels are excellent for this. Do
not put the textiles in plastic bags before storing them inside the furniture, as the
plastic will prevent the "buffering" that you are after! As well, do not store the
furniture with doors or drawers open, as this also decreases the effectiveness of
the textile "buffering".
Simply storing your furniture full of textiles will help prevent splitting and warping
-- damages caused by too-rapid changes in relative humidity.

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