Question about high gloss finishes

[JIMRPT@aol.com]

"Do you want the wood to breathe? If so, why?

How fast should it breathe? Is fast or slow better?"
Don Mannino RPT
74473.624@compuserve.com
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Don I suppose that each of the questions asked about whether wood should be
able to breathe has a valid point. Perhaps we should agree on what "breathe"
means in this application.  I would consider "breathing" to mean the ability
to react in an unrestrained manner to changes in temperature and humidity.
Wood will collect moisture , as well as release moisture, in a more or less
even manner if left unsealed in any way. When we air dry or kiln dry wood it
needs to have spacers in between layers of wood planks as well as space
between individual planks in the same layer, this to allow airflow evenly on
all sides.  In other words we allow "breathing" space for the wood.  If we do
not allow this "breathing" space we will end up with a much higher percentage
of cupped boards than if we allowed the space for "breathing"
  If we seal one side of a board and leave the other side unsealed  a cupping
effect will take place over time. If the unsealed side is bonded, glued, to
another layer of wood than the effect will be altered tremendously but the
wood will still gain and lose moisture unless the seal is perfect. Wood
swells when it gains moisture and shrinks when it loses moisture and in the
perverse way of things it gains moisture faster than it loses it when
'sealed' with a finish. With most finishes the seal is imperfect enough where
this does not create a problem. This due to the ability of the wood to
"breathe" fairly easily in both directions.  As the finish becomes denser and
forms a more perfect seal, problems are created and they manifest themselves
in many different ways.  'Pressure ridges' in sounding boards are one example
of wood that has collected moisture faster than it can release it. In this
example, because of the relative softness of the wood involved, something has
to give and it is the wood celluar structure that gives way and the ridges
are formed. The board being captive, 'sealed', by the rim on the sides the
ribs underneath and the bridge on top is still going to react to the
absorbption of moisture thus the pressure ridges form as being the path of
least resistance. If you will notice on boards with these pressure ridges it
usually is the panel with the fewest 'growth rings' that has the ridge form
in it rather than the adjacent panel(s) with more 'growth rings'.
   Which brings me back to polyester finishes (poetic license). Since wood
will swell and contract faster than polyester eventually something has to
give way. There will be a certain amount of celluar collapse in the wood
until it reches an equilibrium point and then it will start expanding the
polyester. Once polyester expands it will not contract again without chemical
action and each time this occurs the polyester finish comes closer to
cracking as it reaches its expansion limit. Finally it will crack and once
this crack is started it will not stop. We may be talking about many years in
some cases but this process happens on all types of finishes. Manufactured
substrates may be the answer to this problem,and probably are, we will have
to wait and see.

   So Don I suppose my answer is wood will "breathe" whether we want it to or
not and we need to make allowances for this in our finishing schemes, as well
as in our regulating practice. As to whether fast or slow "breathing" is
better, I don't know.  However if we do not acknowledge this attribute of
wood and work with it, it will surely work against us, i.e. pressure ridges,
cracked finishes, sluggish keys, actions whose regulation is terrific in
December that are terrible in July, etc.
  The manufacturers have acknowledged this by using manmade materials in some
applications in case design with polyester finishes and 'plastic' parts in
some applications in actions. There are many different approaches to dealing
with woods ability to "breathe".  We ignore this "breathing" at our peril.
  I hope this is not too convoluted to follow.
Jim Bryant (FL)