Note: When this parodi on paperhanging column first appeared in PWC Magazine I could not mention brand names. But here on the internet I can. The key to the pastes involved in the testing are
The Wheat referred to in the article is Bob Kelly's Wheat
The Potato Paste is Eco Fix P-7
The
Clay was Roman's Professional 774
Brand X Clear Dynamite 234
Brand Y Clear Roman's Professional 838
Brand Z Clear Roman's Professional 880
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The Gel Factor --by Jim Parodi
The brothers Goofus and Gallant were about to cross the desert. Goofus had prepared a bucket of water to make the journey. Gallant, the smarter of the two, had prepared a bucket full of plain Jell-O. Shortly after setting out, Goofus tripped over a dead iguana and spilled the bucket of water which quickly disappeared into the desert sand. Gallant also spilled his bucket as he tried helping Goofus up, however, the Jell-O remained a shimmering blob on top of the desert sand. They were able to scoop it back into the bucket and later after both consumed the moisture contained in the Jell-O they died a slow and horrible death from thirst after five days. The moral of this fable is that gels prevent the transfer of water to porous surfaces and that you shouldn’t attempt desert crossings by foot what with Greyhound offering such low rates.
Before their untimely deaths, Goofus and Gallant were paperhangers. Gallant spent much of his time “repositioning” Goofus’s work by undoing all the sheets he installed upside down. While Goofus tried to explain to the customer that his upside down hanging was just part of “the inherent beauty of the material,” Gallant had noticed that the jellier a paste was the easier it was to remove even an hour later. He searched and searched for the “jelliest of them all”—(hold on, I think I may be fading into another fable)—and when he found it he also discovered that there were good and bad features to consider. Now that Gallant is gone I’ll try to take up where he left off.
Both paperhangers and manufacturers differentiate pastes by many attributes: high moisture vs. low moisture, high solids vs. low solids, high tack and low tack, strippable and non strippable, high slip to no slip. But no one besides Gallant ever talked about gel vs. no gel. This surprises me since any paste manufacturer worth their salt should have by now gotten the marketing folks to gin up excitement for this neglected paste quality. I will attempt in this column to point out both the good and bad about this neglected gel factor.
We all “book” wallcoverings to make them manageable. In the process we hope that the moisture in the paste has been transferred to the material to expand and soften pulp or to pre-expand whatever backing the pattern layer is laminated to… be it cotton fabric, synthetic fabric, backing paper, or non woven material. Failure to let the material book long enough will result in material expansion on the wall after application leading to unwanted “expansion bubbles.” Paperhangers for years have added things to the paste to quicken the process of “wet out” like fabric softener or dish detergent and stranger stuff. (My father Harry told me once that hangers used to pee in wheat paste to make it perform better. Are you listening Gibson-Gardner?) That aside, with the myriad array of paste types available to the modern hanger it is possible to control this wet out time if you keep one eye peeled for the gel factor of the paste.
To demonstrate just how widely varied the wet out times of different pastes are, I have included below a photo of a brown paper shopping bag. On the bag I placed dollops of wheat paste, potato starch paste, clay, and some premixed clears from various makers.
As each paste sample spends time on the light brown paper, it turns the material dark brown underneath. Eventually they all transfer moisture but at markedly different rates. After applying the pastes I noticed right away that wheat paste goes through the brown paper like Mexican food through a goose. 
It completely wet out the spot right through the paper in less than one minute. After 10 minutes elapse Brand X Clear has completely saturated the paper.
After 30 minutes the potato paste and Clear Brand Y are just starting to transfer moisture to the other side of the paper.
And after one hour, 5 minutes, I backlit the samples to show that the clay and Clear Brand Z had made almost no headway in wetting out the paper.
Several years ago I did a similar test using another brand of clay. At that time, the clay wet out the brown paper in about 5 minutes. In the new test the clay proved itself to be surprisingly gelly and radically different in nature from the clay in the previous test.
Just this past week I was helping another hanger on a job and I used the leftover clay from that job for this column. I can’t recall ever using it before and I doubt if I will ever use it again. I hung about 40 linear yards in one room by myself and the next day I came in to discover my room bubbling like a cauldron with about 40 mid- to large size expansion bubbles. Funny, I had checked the whole room with a halogen held close to the wall right before I left the night before and everything looked fine. After the way this clay performed in the brown paper test it explains a lot. I guess I should have let the pieces book for about two hours before hanging them.
In the future I will bite my tongue if I ever say, “You should use a clay or a clear for such and such material.” It appears that advice like that is meaningless after these samples yielded such different results. I encourage you to make no assumptions about “how clays behave” or “how clears behave” and do a simple test like this for the products that are available in your area.
I was glad to see my usual Brand X clear wet out so quickly. It was the fastest pre-mixed saturator by far in this test. On jobs in the past ten years I don’t recall ever having had a problem with expansion bubbling.
Brand Z Supergel Clear behaved exactly as it did in my test of several years ago. It simply is anemic in the wet out department. Occasionally I get a call or email from a frantic paperhanger somewhere in the US with a tale of horrific bubbling where a clear was used. My first question is always, “Did you use Brand Z paste?” with a remarkable number of affirmatives in the replies.
Even though gelly pastes can wreak havoc with expanding substrates that expand long after book time and after smoothing on the wall, there are times when this slow moisture transfer attribute is just what the doctor ordered. I’m thinking of a job I did where I was hanging a pulp over a paper blankstock in an old mansion with god-awful crookedness. I wanted to be able to simultaneously reposition 5 long strips in order to eyeball how straight they would appear from a distance. Ever try to reposition a pulp that is hung with wheat over paper blankstock even after just a few minutes? Good luck with that. The wheat sucks into and fuses with the paper blankstock almost immediately. But hanging with the Brand Z Supergel I found that I could reposition pieces almost indefinitely. And by the way, if you are having trouble with booked paper “freezing” and not being “unbookable” try throwing a supergel into the bucket to control open time.
Understanding how quickly paste water transfers to material can really make jobs easier and result in fewer callbacks. For instance, many of the paper substrates used for thin paperbacked vinyls are similar in wet strength to toilet paper. Even with a new blade you can still get the crappy bits of paper clinging to the blade or tiny wads of paper you have to pick off by hand. However if you switch to a gellier paste or just start adding a gelly paste to the bucket it can control that annoyance. The converse is also true. Adding wheat to a gel paste can increase its moisture transfer rate. I mixed the clay used in this test 50/50 with wheat paste and was able to “push” it to give up moisture to the brown paper in about a half hour.
As I mentioned at the beginning, paste makers are always talking about high solids for adhesion or low moisture for various reasons, but they have completely missed out on a paste attribute that can make or break a job.