John:

Yeah, I finally tracked down the info on Kyanoil 021. It seems that this
product (which I have spec'd for years) is no longer manufactured due to the
latest VOC regulations, according to the technical rep at Kyanize
(Baltimore, MD).  C'est les affaires de la conservation. C'est la vie.

I suppose that Acryloid B-67 is now called Paraloid B-67 (Rohm and Haas ). I
assume that it's the same general formulation. It's an acrylic resin and is
described in company literature as a "medium and long-oil modifier, general
purpose thermoplastic." It is apparently sold in pellet form or a 45%
solution in solvents. In a paper entitled "Alkali-Soluble Acrylic
Consolidants for Plaster: Preliminary Investigation" (Studies in
Conservation 32, 1987, p. 145-152), Morgan Phillips described the use of
B-67 in mineral spirits to consolidate plaster. Is there anyone out there
carrying on Mr. Phillips great research?

I refer you to the attached excerpts from some recommendations I wrote back
in '92 to a homeowner who had some serious plaster deterioration. In the
letter, I refer to B-67 as well as Kyanoil (which was eventually used and
worked great...sigh). I'm going to follow up with Rohm and Haas regarding
the current products and their similarities.

Thanks for the info on the vinegar wash. Given the chemical analyis, that's
worth checking out and experimenting with. I'll post any findings on this as
I follow up.

John Horton


----- Original Message -----
From: John Mascaro <[log in to unmask]>
Sent: Wednesday, December 08, 1999 12:32 AM
Subject: Re: Plaster woes


> Found a reference to a Kyanoil as a timber preservative  (a mercury
compound,
> supposedly).  The resin product you refer to must be something else!?  Did
> you ever find your file, John?
>
> What's Acyloid B-67?
>
> Someone mentioned the vinegar wash spec'd on a Sherwin Williams latex
paint
> can.
> Harry Francis - longtime consultant for USG - allows it would probably
work.
> He imagines the reactions would involve Calcium Acetate (lime + acetic
acid)
> and Calcium Sulfate (gypsum), making a glue-like paste that would form a
hard
> surface when dry.  Interesting.....
>
> John Mascaro



(Excerpts from letter to a homeowner regarding the consolidation of deteriorated plaster, dated 1/28/92):

Andrew Ladygo:

Mr. Ladygo assured me that it was not at all uncommon for a building of that construction date (NOTE 12/8/99: HOUSE CONSTRUCTED MID-1870'S) to have had only a two-coat plaster.  Often, the brown coat was trowelled smooth and wallpapered, or simply painted.  In your case, the original coat of calcimine paint may indeed have served as a final finish, the paint filling the pores of the rougher brown coat and acting somewhat as a consolidant.  The subsequent layers of calcimine paint simply built up this surface.  Therefore, when we wash the layers of calcimine off, the original layer is bonded so well that its removal allows the plaster below to abrade easily.  In this respect, we are right in only washing the walls down to that original layer and not damaging the integrity of the surface.

Mr. Ladygo's recommendations calls for consolidating the immediate surface of the plaster and calcimine with a solvent-based sealer.  He recommended two proprietary products.  Pittsburg Paint makes a product called "Rez", which is essentially an exterior type of sealer/primer.  Another product is made by Kyanize of Everett (or Chelsea) Massachusetts, and is called "Kyanoil 021".  These may be available locally. (NOTE 12/8/99: KYANOIL NO LONGER MANUFACTURED DUE TO VOC REGULATIONS).

He also feels that by using a thinned oil-based varnish, we can accomplish similar results.  The theory here is to totally saturate the remaining calcimine paint until the pigment is suspended in the solvent-based varnish, essentially transforming the calcimine from a water-soluable paint to an solvent-based paint.  (This theory seems to be similar to "emulsifying" an existing varnish, as opposed to stripping it).  The thinned varnish will also penetrate into the immediate surface of the plaster, consolidating it to the point where it can be properly painted.

The trick in using any type of sealer is to make sure that it is viscous enough to serve as a consolidant, yet thin enough not to leave a film on the surface of the plaster.  If a shiny film remains, you would have to sand it down before priming.  It will no doubt take some experimentation to find the right formula.

After consolidation is completed and the plaster is completely dry, you would prime the walls with an alkyd primer and then an alkyd or latex finish coat, to your preference.  Any necessary repairs to the plaster itself, such as filling depressions or gouges, should be undertaken after consolidation.  Mr. Ladygo recommends using Durobond, which is to be mixed on site with water instead of using a premixed joint compound.  He does not recommend using bonding agents, as these may not bond to the crumbly plaster.

Morgan Philips:

I then contacted Morgan Philips, an architectural conservator who was also formerly with SPNEA and is now a private consultant near Albany, NY (518/673-8177).  He is theoretically concerned with the potential incompatibility between the consolidated plaster and the non-consolidated material which could lead to delamination.  However, he does concur with Mr. Ladygo's recommendation on "Kyanoil 021", which he has used before with success.  Historically, according to Mr. Philips, shellac was used in the same manner as a sealer/consolidant on old plaster.  However, he is not too sure of the possible problems with incompatibility.

Mr. Philips maintains that "Acryloid B-67", as manufactured by Rohm and Haas is considered the conservator's standard as a proprietary product for plaster consolidation.  Being an acrylic instead of an alkyd, it is not susceptible to attack by any remaining alkalinity within the lime-based plaster which normal varnishes or sealants may be.  He would recommend that we first check the pH level of the existing plaster.  If it is much over a neutral value (pH 7), he would be wary of using a alkyd-based product.  He has seen some old plasters retain a pH value of 12, which is close to that of sodium hydroxide (which in certain concentrations can strip paint, and would attack any alkyd-based product in the same manner).  We could possibly neutralize the plaster to some extent, but this would probably involve further consultation with a chemist.

However, Mr. Philips' biggest concern was that we not get too great a concentration of solvents in the plaster, which would take a long time to dry and could create potential health problems with your family living in the house, especially the children.  It would be critical in this respect to judge the depth of penetration of any application.  He feels that we should aim for just enough depth to bind the remaining calcimine and work slightly into the plaster.  After a test patch is done, we should scrape away the plaster to determine just how far the consolidant has penetrated.  We will simply have to make a judgement on site as to the viscosity of the application versus its penetration.

He is currently contracted to test several water-based plaster consolidants, but unfortunately this work will not be done in time for you to take advantage of new technology, unless you decide to hold off on any further work.  If we proceed, we must make sure that ventilation is adequate at all times.  The hallways will pose the biggest problem as they cannot be closed off.

Derrick Tickle:

To follow up on these recommendations, I spoke with Derrick Tickle, who is the professor for the course on Decorative Painting at Asheville-Buncombe Technical Community College.  Since 90% of any decorative painting work is preparation, I felt he might offer some additional insight.  He has some experience with plaster consolidation, and has had success with using "Penetrol", which is a proprietary formulation used for fortifying alkyd and oil-based paints.  In both our opinions, Penetrol largely consists of linseed oil, spirits, and other resins, and probably is no more effective than thinning out varnish.  In fact, during his apprenticeship in England, he recalls having used normal spar varnish, thinned out as a preparation on plaster, especially to keep stained areas from bleeding through.  He did not recommend shellac, as he felt it would dry so quickly it would not penetrate well enough into the plaster.