----------------------------Original message----------------------------
From Stefan Michalski, Canadian Conservation Institute, Ottawa.
In response to the query below about concrete floors, forwarded to me
by the CCI librarian, Vicki Davis:
Fresh concrete is most often a problem of moisture desorption, i.e,
release, not absorption. I have seen new archive buildings of heavy
concrete construction that released enough moisture for two years to
cause a problem of damp and a need for dehumidification, even in a
Canadian winter. The source is simply the excess of water added to the
concrete mix, an excess beyond what is needed for curing (hydration).
I don't know of any coined term, so I'll call it "fresh concrete"
damp. In massive walls and pillars, it can take years to release the
hundreds of gallons of water involved. A floor slab, however, is
usually only a few inches thick, and should reach equilibrium with its
surroundings in a few months. That leaves just the long-term problems
of rising damp and damp due to cold. Rising damp from the earth below
is not a problem in high quality new construction because the slab
sits on a vapour barrier, and in turn on a gravel bed, so that the
earth is not in moisture contact with the concrete. If you think you
have rising damp, or "fresh concrete" damp, you can test easily by
just laying down a few square yards of polyethylene on the concrete,
and waiting a week or two. Any condensation or fogging of the
polyethylene UNDERNEATH indicates moisture emission from the concrete.
If you get fogging ABOVE the polyethylene, this is quite different: it
is damp due to warm humid air striking the cold floor.
In any event, the lowest shelf should always be at least 4inches
(10cm) off the floor to avoid water damage during minor floods, and to
allow complete floor cleaning as part of integrated pest management
(cleaning and inspection, avoidance of habitats, placement for sticky
traps). Given such a gap, and some forced ventilation, damp should not
occur. Ceiling fans in large warehouses, placed over aisles, not
stacks, help enormously in preventing stagnant damp areas. Bottom
line, place little cobalt blue humidity indicators at the bottom shelf
to make sure you don't get damp. If you find a modest degree of rising
damp or "curing" damp by the polyethylene test, you may want to
consider sealing the concrete, which will also help reduce the
alkaline emissions which can be a threat to unwrapped oil paintings
(yellowing of oil media, Japanes studies). The problem of damp due to
cold floors only arises if you overzealously humidify in winter, or
experience humid summer conditions without dehumidification equipment.
P.S. Since this often gets lost in the deliberations over damp, and
since I've seen a lot of warehouses full to the brim with cardboard
boxes of stuff, I would like to remind everyone of fire risk. A few
firewalls or bulkheads every few shelves, such as 1/2 in. drywall,
will help stop fire spread. Detectors right up at a high ceiling often
don't work because the air in a warehouse may form an inversion layer.
Have a smoke test done to see if smoke actually reaches your
detectors. Some may have to be placed on drop mounts to reach below
the inversion layer. A revised version of the NFPA 911 Protection of
Museums and Museum Collections is in the works (National Fire
Protection Association), and will cover much of this and more. Many of
you will already know NFPA 910 Libraries and Library Collections, NFPA
232AM Archives and Records Centers.
Hope this helps. Stefan Michalski, CCI, Ottawa
______________________________ Forward Header
__________________________________ Subject: Advice & Help Needed:
Storage space with concrete floors
Author: ART LIBRARIES SOCIETY DISCUSSION LIST <[log in to unmask]>
at INTERNET Date: 6/24/96 5:59 PM
----------------------------Original
message---------------------------- Advice on this storage problem,
from fellow list members, would be greatly appreciated:
We are going to be leasing newly-built storage space while the
building we are acquiring for our new library and museum is under
renovation. The storage space is on the ground floor. The flooring is
concrete. We plan to store our art library (approx. 20,000 vols of art
reference), paintings and works on paper there. For this purpose, we
plan to set-up (raised off the floor) shelving units to store all of
the items which for the most part will be packed in crates, boxes,
etc.
A colleague just informed me that the concrete floors will tend to
absorb large amounts of moisture, and that nothing sensitive should be
placed/stored *directly* on the floor. This remark raised a concern
that the moisture might even affect the items stored up on the
shelving units--especially books and works on paper.
My question to the members of the list is: Will concrete floors (the
supposed moisture they absorb) pose a threat to books, works on paper
or even paintings if those items are stored up on the shelves? Are
there any special steps that would need to be taken? Do we need to
cover the floors?-- Again, I want to mention that the space is all on
the ground floor, i.e. above grade, but the concrete floor is (I
assume) laid over the ground. Is the moisture absorbed from the ground
below, or the air above the concrete floor? Or have I been altogether
misinformed about concrete floors absorbing moisture?
Mark
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Mark Ast, Ph.D.
Curator
Museum & Library of Barbizon
& Pre-Impressionist Art
The Schlesinger Foundation
email: Mark Ast <[log in to unmask]>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
