<%@LANGUAGE="JAVASCRIPT" CODEPAGE="1252"%> Paper-Hangings - Quality Products for the Professional Paperhanger

P-H Wheat Paste

By Robert M. Kelly
(www.paper-hangings.com)

More wallcoverings are made of synthetic materials than ever before. But, many are still paper-based. Most of these are in the high end of the market (blockprints, European machine prints, and screenprints, both table and rotary). This essay gives a closer look at the most traditional product for hanging such papers, namely: wheat paste. The type Paper-Hangings sells is called "P-H Wheat Paste".

In the recent past, high-moisture pastes such as wheat and cellulose have not fared well in the market. Partially, this is a result of improved prepasted technology. Also, premixed clear, once a poor cousin to clay, has improved in many ways. These factors have pushed paste nearly off the map, and helped to elevate adhesive (especially clear premixed vinyl adhesive) to nearly "universal" status.

And yet, I think there is still a place for wheat. The simplicity of it, the ease of cleaning it from wallpaper surfaces, and the way it works with naturally porous paper to create good slip and grab, especially with a liner, are all important features for hanging high end goods. Many wallpapers are highly porous, and nothing quenches their thirst quite like wheat paste.

Not too many years ago, wheat and cellulose were often recommended for paper. But many papers that used to hang perfectly well are now so heavily inked that an attempt with paste is likely to disappoint. And yet there it still is, on the “instruction” sheet: “Use ONLY wheat or cellulose paste”.

You sometimes wonder if there is a living human being at the factory, or whether the whole place is run by robots, because somewhere, sometime, surely, there must have been a call back to the factory to alert them of the idiocy of attempting to use a high-moisture paste with some of the non-breathables that are coming out of the factory.

Wheat paste is a good and even a great paste, provided it's used on the right product. But, if used on the wrong product, for example, on a heavily-inked screenprint, it's more likely to be a disaster looking for a place to happen. That's why I like to carry stronger adhesives, just in case, because it is definitely easy to get fooled by a paper. But, when I have a "real" paper (wood pulp), I like to start with wheat.

Most paperhangers are familiar with the type of powdered wheat that's mixed by hand with a cooking whisk. This is how P-H Wheat Paste is usually mixed, although NGPP member Jeff Evans of Venice, California has made a good case for using a squirrel cage with P-H Wheat and then straining with a bag-type 5-gallon nylon strainer.

Before I get into the basics I want to give a little back-story about wheat paste, and why we started selling this type.

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Common wheat flour Triticum vulgare (sativum), readily available in temperate climates, is the most frequently recommended flour in old paperhanging manuals for making wallpaper paste. Though it's been challenged since World War II by the introduction of methyl cellulose, and by the transformation of 'wallpaper' into 'wallcovering', it remains in use to a limited extent.

For the type sold in decorating centers, the user simply adds the powder, while stirring, to water. This powder performs well for most residential use but it's been altered. After processing, it's cooked in a factory, then dried and re-combined with biocides and other ingredients; when we mix "wheat paste" from a bag we're really adding water and reconstituting it. It's impossible to know how pure it is. Grades can range from "food grade" all the way down to "feed grade". At the lower grades, the product may be brownish and gritty and may lack the adhesive strength of the more refined types.

For reasons like these paper conservators and others with a fine arts background reject commercial wheat starch – they prefer to cook their own. When I began to work more in historic houses and handle more expensive wallcoverings, including antique wallpaper, I began to wonder if I should try cooking wheat paste, and one fine day I decided to "roll my own".

When cooking pure wheat starch a typical formula uses one cup wheat starch to four cups lukewarm water, heated at 300 degrees for 45 minutes in a double boiler, stirring constantly. This makes a very thick, translucent paste which can be thinned at 50/50 proportions with pure methyl cellulose to make a great all-around paste.

The gelatinization temperature is 68-78 Celsius for Belgian Rice Starch and somewhat lower, about 58-64 degrees Celsius, for wheat starch. Wheat starch is technically different from flour because the gluten (the brown protein material) has been removed.

From a scientific point of view, there are two problems with commercial powder wheat adhesives: additives and side chains. I can’t talk about side chains, since my scientific training ended shortly after the "Mr. Wizard" show went off the air in the late '50's, and anyway, this depth of knowledge is not relevant to mainstream paperhanging. However, the caution about additives is a more familiar problem.

Anyone who's hung a lot of English pulp wallpapers has seen this advice:

Coles: “Gold prints and gold backgrounds are affected by preservatives in some tub pastes and only Coles Tub Paste should be used for this type of paper”

Sandersons: “Certain adhesives may contain substances which cause discolourations of bronze or other metallic prints, especially under damp conditions. We recommend the use of Elite adhesive for such papers. If other adhesives are used, check paste manufacturers instructions to ensure that adhesive is suitable for paper with bronze prints”.

Cowtan & Tout: "Adhesives: (for) Paper: Best quality cellulose or wheat paste. Do NOT use any paste containing a fungicide agent.”

Why is this advice given? My hunch is that at some point there was a huge problem with a stained wallpaper and that someone traced the problem (rightly or wrongly) to the use of an additive in the paste that apparently bled through and stained the paper, or that was thought to produce a chemical reaction with a metallic ink.

I find this to be a very gray area, no pun intended. There are certainly legitimate concerns about additives. But, it's also possible that many of these supposed “staining” problems were actually just garden variety strike-through.

In the old days, many traditional pulp papers were meant to be pasted, booked, and hung, without a lot of sitting around. If they sat around and became saturated, bad things could happen. This was especially true if lining paper wasn't used, because then paste could sit between the paper and the wall for an extended period of time.

Paper, coatings and inks have all improved to the point where we seldom see strike-through anymore, or even much staining, for that matter. Nevertheless, you always want to be on the safe side of potential staining. We can summarize that the simplest way to solve concerns about additives is to do without the additives. This is the whole idea behind using "archival" pastes like P-H Wheat.

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When I began to experiment with cooking I was amazed at the difference. Cooked wheat paste, in the pure form, is almost an entirely different product. At the top of the heap is a paste called Zin Shofu, or sometimes, “Jin Shofu”. It's a highly refined product from Japan used for the most important paper conservation work such as repairing historical books and documents. I don’t offer that paste to paperhangers for two reasons: the cost, and the trouble of cooking it.

But because I kept getting asked about it, a few years ago I published an article about cooking wheat paste for paperhanging work. I was more or less politely told by a few of my paperhanger friends that I was out of my mind. Who, after all, is going to find the space in the truck for a double boiler, sieve, stirring sticks, and all the other apparatus to cook wheat paste on a residential job? And who wants to spend the time?

These objections were neatly solved when I located a source for archival, premium quality wheat paste that's been pre-cooked. Now, with the “Paper-Hangings” line of wheat paste, all you need to do is mix it up. And although straining may be necessary, we think it's a small price to pay for the consistency and strength of the product.

Pure wheat paste usually needs to be strained through a simple cooking sieve or filter because it tends to develop lumps during mixing. My routine is to sit down, and sift the wheat paste little by little into about 2 gallons of lukewarm water, stirring constantly with a large kitchen stainless steel whisk. Restaurant supply houses are treasure-houses for a wide variety of whisks, strainers, and sieves. I have not found any problem using a double wire sieve.

There is definitely something that happens to paste when it's strained and then double-pasted onto the paper. To be sure, we are talking about the molecular level, but it's an observable change. The paste loses water and stiffness during these processes, becomes more “solid”, changes to a glassy sheen, and flows better. It flows best of all if you're willing to do the additional work of intermixing pastes. Wheat usually improves when mixed with cellulose, clear, or clay.

Jeff Evans likes to mix up larger batches in a 5-gallon pail, using a squirrel-cage mixer and large drill, then strain using nylon bag strainers. He also prefers to add up to 20% or so clay (111) right off the bat, since this improves handling properties when rolling paste onto paper.

Intermixing wheat with other pastes is especially important when it comes to pasting machines, because the enhanced viscosity allows it to travel on the machine rollers much better. So, the next time you have paper, give our P-H Wheat a try – it might make you smile!

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