Karen Potje

Canadian Centre for Architecture

A Comparison of Three Test Methods Used to Determine the Effectiveness of Epoxy and Latex Paints as Vapour Barriers

ABSTRACT

At the Canadian Centre for Architecture, several combinations of wood products and paints were evaluated as potential exhibition case materials. The tested boards were Panfibre, a medium density fibreboard (MDF) manufactured by Uniboard Canada, which contains formaldehyde in the binder, and Medite® II, a low formaldehyde medium density fibreboard manufactured by the Medite® Division of Sierra Pine Ltd. The paints were Accolade® Interior Satin Enamel SOCW, an acrylic latex paint manufactured by Pratt and Lambert, and Tile-Clad® II Epoxy, a solvent-based two-component epoxy paints from Sherwin Williams®. In order to determine the effectiveness of the two paints as vapour barriers on the MDF boards, passive sampling of organic carbonyl pollutant concentrations in mock-up cases was carried out (using GMD Formaldehyde Dosimeter Badges and passive sampler tubes provided by the Getty Conservation Institute). The Oddy test and the Image Permanence Institute's A-D test strips were also used to evaluate test samples of the materials.

The latex paint proved to be ineffective in blocking organic acids but did reduce formaldehyde emissions. The epoxy paint also reduced formaldehyde emissions significantly, and cut organic acid emissions from both MDF products by about 80%. The epoxy-painted Medite® and Panfibre samples showed similar total organic acid concentrations but different concentrations of acetic and formic acid. The Medite® case, with lower acetic acid levels, was considered to be the safer option; however, during the evaluation of the data and following the presentation of this paper in Amsterdam there was some discussion about whether the environment of this epoxy-painted Medite® case should be considered suitable for paper-based collections. Not enough is known about the effects of internal pollutants on paper to state that, even with the reduced pollutant concentrations, this case is good enough for the display of the CCA's collections of prints, drawings, documents, architectural duplicates, books and photographs.

It was hoped that a comparison of the quantitative data supplied by the sampler tubes and formaldehyde badges with the qualitative data provided by the Oddy test and A-D strips would permit a better understanding and interpretation of the results of these more accessible tests. The A-D test strips are intended by IPI to be used for the evaluation of vinegar syndrome in acetate film, and give no indication of the presence of formaldehyde or any other non-acidic vapours. They are not sensitive enough to detect acidic vapours at the concentrations generated by the epoxy-painted samples. The strips could be useful as a screening tool before the Oddy test: a sample that does not pass the A-D test (i.e. causes a colour change in the pH indicator dye) could be rejected without further testing. But a sample that DOES pass the A-D strip test does not necessarily provide an environment free from organic carbonyl pollutants, and would require more rigorous testing.

The results of the Oddy test using lead coupons corresponded more consistently with the quantitative results. In the mock-up cases the unpainted and latex-painted samples produced the highest concentrations of organic acid vapours, as measured by the samplers. In the Oddy test these materials caused a degree of lead corrosion indicative of materials that are unsuitable for use. The epoxy-painted samples, where the sampler tubes detected lower amounts of pollutants, were rated as acceptable for temporary use according to the Oddy test. Unfortunately, these results are only directly applicable to lead specimens. Again, it remains unclear whether-epoxy-painted Medite® cases could safely be used for the temporary exhibition of paper objects. The Oddy test did not pick up any distinction between epoxy-painted Medite® and epoxy-painted Panfibre, where the samplers found similar total organic acid concentrations but different concentration of acetic and formic acid.

Until more in known about the effects of internal pollutants on paper, the conservation department of the CCA is recommending against the use of paint films to seal the interiors of our exhibition cases. Pre-formed films such as aluminised polyethylene will be preferred. Exceptions may be considered for short exhibitions that include no objects with their own chemical peculiarities, such as some photographs and architectural duplicates.