Zero MDF

Victoria Gill <victoria.gill [at] endangeredheritage__com> writes

>I am seeking advice from anyone who has done research on the zero
>MDF. I am trying to discuss options for showcases which have had
>Zero MDF placed in the floor and the back of the showcase. The
>showcase fabric has already been used, *before* consulting a
>conservator. I now have the impossible job of mitigating the off
>gassing effects.
>
>Unfortunately the showcases are intended for Asian silk cloths with
>metal threads and silver jewelry. Yes the entire exhibition is of
>highly sensitive material. The showcases are entirely sealed and
>they have a closed humidity controlled system (Munters MG 50
>Desiccant gel dehumidifiers). I must convince the bean counters that
>it is worth the cost to remove the cloth and barrier seal the MDF or
>replace it. I am considering the barrier recommendation be wrapping
>boards in "Intercept" plastic. However drilling for furniture mounts
>will perforate the "Intercept" in places and a total seal will not
>be entirely possible. Any experience with the dehumidifiers would
>also be helpful, this exhibition is in Asia and they have spent a
>fortune on products with no prior conservation advice. I can't see
>how gels will be practical in the tropics.  Any supporting sources
>to convince the project managers will be greatly appreciated.

In my posting of June 21, 2003 on the Distlist (Conservation
DistList Instance: 17:4 Monday, June 23, 2003) I discussed what I
had learned about MDF board's permeability. I also did some research
on its transference of moisture, but as I mention below, none of
this is likely of any real importance in this application.

"Intercept" technology comes in a number of forms. One common form
of Intercept is as a sheet of copper "doped" polyethylene. This is
NOT a good moisture barrier, although one formulation of Intercept
film does come integrated with an aluminum barrier film. If you
needed to cover the MDF, the important thing would be to get a good
barrier film, such as Mitsubushi's Escal, their aluminum foil-based
barrier film, Marvelseal, or any other foil-based film.

Also note that the MDF board does not need to be "wrapped"; to seal
out pollutants and moisture you need only cover the interior surface
of the MDF. Most barrier films can be heat sealed directly to the
MDF with a regular clothes iron set on low. If the drilling of the
mounts perforates the sealing material, this should not be a problem
unless air leaks through the holes (they can be sealed with
acceptable caulking or covered with foil tape).

However, when one steps back and looks at the big picture, you may
be over reacting, and no sealing may be necessary!

The Munters units use silica gel, but not in the same formulation,
or in the same way that a conservator would (as a buffering tool).
In the Munters units silica gel in a rotating wheel is dried using
hot air. The wheel turns, and a stream of air is then passed through
the dried gel and sent to the display case; the now damp silica gel
rotates to be dried again, and the generation of dehumidified air
proceeds continuously until the unit is turned off.

The questions you need to ask are:

    How much air will be generated and fed into the cases?
    What is the volume of the display cases?
    How many cases are there? how many humidity control machines?
    What is the air exchange rate of the display cases?
    What is the ambient humidity?
    How dry will the supplied air be?
    What is your target humidity?
    How much humidity variation can you allow?
    Will the unit turn off if target humidity is reached or keep
    going?
    Can you filter the incoming air, etc.?

These are standard questions about the microclimate control of a
sealed enclosure, and these aspects will affect the build up of
pollutants as well.

I suspect that you may actually have too much supply air. When all
is considered and calculated, it may actually be a good idea to keep
moisture moving into the case through the MDF to keep the unit
running! As for pollution control, air from the microclimate control
units will likely flush pollutants out of the case much faster than
they can be generated or transmitted by the MDF.

I would suggest discussing this with someone who has some experience
with display case climate control before making demands on the bean
counters--you might even be able to save them some money.


                                  ***
                  Conservation DistList Instance 22:65
                    Distributed: Friday, May 8, 2009
                       Message Id: cdl-22-65-003
                                  ***