Acrylic wood sealants Polyurethane wood sealants

Dominic Wall <dominic_wall [at] yahoo__co__uk> writes

>If anyone can advise on acrylic wood sealants I'd be grateful. The
>joiner wanted to apply a polyurethane varnish initially (more
>hard-wearing than acrylic) but as I knew nothing about this and had
>little time to find little information and advice on its suitability
>I suggested an acrylic instead.

and Zee-Young Chin <zychin14 [at] hotmail__com> writes

>How effective is a polyurethane coating as a barrier for acid
>migration from wood?  I would also like to know how long
>polyurethane has been used for this purpose and if it is stable and
>safe as it ages.

The two inquiries regarding case coatings are related, thus I
thought it would be best to respond to both at the same time.  There
are two recent publications that thoroughly address this issue and
are recommended reading. The CCI published a Technical Bulletin
(#21) in 1999 entitled "Coatings for Display and Storage in
Museums".  It includes discussions of the pollution risks, nature of
coatings, and practical tests and protocols for determining the
correct coating.  Pamela Hatchfield's "Pollutants in the Museum
Environment", 2002, Archetype Publications Ltd., is an excellent
review of current thinking on the subject.  These publications
include comparisons of the different types of sealants and their
long-term performances.

My experience with case materials and coatings has been that
water-borne moisture-curing polyurethane is more effective at
sealing wood board products than acrylic coatings. It has the best
vapor-barrier characteristics and ages well.   We originally used a
cross-linked acrylic coating called Breakthrough by Vanex Corp., and
found that it indeed did allow acetic acid vapors to get through.  I
used A-D strips to test for the presence of acetic acid, and found
an appreciable amount.  I should note that this use of the A-D
strips is not what is intended for them by IPI in terms of
quantitative accuracy, however, museum conservators find them useful
for empirical testing.  They are used as a qualitative indicator of
emissions only.  We switched to Camger 146-1 Polyglase coating,
Camger Chemical Corp., and found that the acetic acid emissions were
negligible after the coating cured properly.  I should also note
that there was some confusion in the conservation field about the
Camger products over the past 5 years or so.  The company was making
Polyglase 1-175 and 1-146-1-175 was the formulation that was
originally developed and tested for conservation use, but 1-146 was
very similar in formulation and cost.  The company kept 1-146 but
discontinued the 1-175.

At that time I contacted the company and was told that the 1-146 was
the same formulation and safe for conservation applications, which I
found in my testing as well.  I just contacted the company again
about the statements in the conservation literature that the 1-146
was not suitable for conservation, and was told that because of this
confusion the sales of 1-146 had dropped off, so they have
re-started the production of the 1-175 and it is now available.  I'm
not endorsing a particular product or company, but we have found the
Camger to be the best product available for conservation
applications in terms of availability, ease of use, effectiveness,
and stability versus the acrylic products.  We use acrylics in
non-case applications such as wall paint in the galleries.

Paul Storch
Senior Objects Conservator
Daniels Objects Conservation Laboratory (DOCL)
B-109.1, Minnesota History Center
345 Kellogg Blvd. West
St. Paul, MN  55102-1906
651-297-5774
Fax: 651-297-2967


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                  Conservation DistList Instance 18:46
                   Distributed: Sunday, April 3, 2005
                       Message Id: cdl-18-46-004
                                  ***