We started our adventure into the deeper mysteries of blankstock with "Blankstock 201", which explained why blankstock is so important to the high end paperhanger. I wanted to get beyond FAQ and simple recommendations, and show more clearly why blankstock is so effective in the hunt for the perfect seam.
A section of that article was called "The Seam Cycle" where I introduced the idea that for every paper, there was only a certain amount of time during which the seam could be rolled. Too early, and you have the danger of the paste gushing out. A related worry is that the seam may contract later. This is because wet paper may continue to contract. On the other hand, if you roll the seam too late, it's no longer possible to adjust the seam.
I tried to define the seam cycle by saying that "The seam cycle is the time between installation and the best time to roll the seam".
This definition takes into account that you should be rolling the seam as soon as possible (so long as it doesn't gush paste) and continue while you can adjust it as needed.
While this definition is true as far as it goes, on second thought, it's not as accurate as it could be, and here's why. The seam cycle clock starts ticking when the paper is put on the wall. It continues to tick as the strip is swept out and as the seam is tented (puckered slightly). But, the seam clock continues to tick well past the theoretical "best time" all the way to a certain terminal point beyond which the seam is essentially dry, and there is no possibility of moving the seam any more.
So, actually, the seam cycle is quite a bit wider than previously described in Blankstock 201.
For the occasion of the March 8th Berkshire Chapter Workshop for the NGPP (National Guild of Professional Paperhangers) in West Springfield, Massachusetts, I spoke to director Roger Coupal about a potential demo on this subject. We decided that a test board would likely illustrate better what the seam cycle was all about. I prepared the tests about 10 days in advance, with several samples of paper, in an effort to nail down this elusive concept of a "seam cycle" a bit further.
The workshop was well-attended by perhaps 60 paperhangers, and a lot of feedback was given to me by colleagues as I made the presentation and explained the results of the test board.
I will now describe the testing process, followed by results, and then conclude with some general observations.
First, I prepcoated an oilbase painted 4' x 4' piece of plywood with Prep-Coat (Swing, Ltd.) and after dry time, I installed blankstock from Paper-Hangings on both sides.
After suitable dry time, the blankstock was sized with a light wheat size. Size was made by mixing up one part wheat paste to a pancake batter consistency, then diluting with one part water. Size was brushed onto the blankstock surface with a natural bristle brush.
After dry time, the following were installed on the blankstock: screenprint, 21" blankstock, blockprint, machineprint, and a pulp 1930's paper. Each piece was about 10 inches high.
The paste for all papers except the screenprint was as follows: mix wheat paste, mix methyl cellulose (both from Paper-Hangings), and then mix one part wheat to one part methyl cellulose (50/50). This mix was then thinned by adding about 25% water. This rather thin paste was made because I knew that the 1930's paper was very delicate and difficult to handle from acid deterioration and needed a minimum of paste and that a heavier paste might damage it. I also knew that the others would probably hang ok with the thin paste, so the decision was made to use the thin paste for all in the interests of having good controls for comparison.
However, when it came time to paste the screenprint I soon found out that the thin paste was not going to fly, since there was too much of an ink laydown on the screenprint, and the thin paste resulted in poor adhesion and also caused the wide open ground to expand more than the inked portions of the screenprint, causing severe differential. I therefore switched to clear and this was a much better way to hang the screenprint - not only was the differential less, but the additional solids in the clear allowed the screenprint to hug the wall better and resulted in better uniformity in sweeping the paper to the wall.
You can see the results of the testing in the graphic printout entitled "The Seam Cycle". It shows the following results:
1. The 1930's paper sat, without booking, for 3 minutes after the first pasting. At that point, I could see paste beginning to dry out on the back of the paper. I started the second pasting. The second pasting sat on the paper for 3 minutes, after which I judged it was ready to take to the wall because the paste was uniform and tacky, and the paper was relaxed. I then spliced the paper so that I could butt left edge to right edge. The paper hit the wall at 6 minutes and I began sweeping it and tenting up the seams (pushing them to slightly more than a butt seam).
At 8:00 the seam cycle clock started ticking. By this I mean that at 8:00 (which was 2 minutes after it hit the wall) it was ready to start rolling. By "ready" I mean that I felt that it was safe to roll lightly, with a wooden seam roller, so that no paste would come out of the seam.
I kept rolling it lightly for about 15 seconds before observing that it was dry. Now, 15 seconds is not a long time! But, this was the time that I got. If you bear in mind that this paper had probably been sitting around in Grandma's attic since the Hoover Administration, you'll understand why it was in such crappy and desperate shape, plus, with a blankstocked wall and thin paste, it does not take long to lose the paste.
While taking one last attempt at pushing this seam together with my thumb, I succeeded in ripping the paper. This proved how fragile it was (or, how anal-retentive I am, depending on your interpretation).
2. The machineprint was a William Morris print from Sanderson. This pretrimmed paper was rather thick and had a factory finish to make it wipeable.
First paste: 4:00, after which the paste began to dry in spots. Second paste: 5:00. At 9 minutes this was put to the wall, but was not ready to roll for another 3 minutes. The seam could be very easily pulled and pushed into shape for about a minute. By about 13:00 the thin paste had dried out, and it was set and no longer possible to move.
3. This blockprint was from the Cooperstown Farmer's Museum blockprint shop and was colored with distemper paint, making it extremely water sensitive, on a French art paper.
First paste: 4:00. Second paste: 5:00. Even though it went on the wall at 9 minutes, like the screenprint, this paper was by no means ready to roll right away. The reason is probably that the more absorbent paper retained the paste longer. I felt it was only safe to start rolling at 15:30, as opposed to 12:00 for the machineprint. From 15:30 onward, there were about 2 minutes during which the seam could be pushed around. By 17:30, the seam was dry.
4. The 21" blankstock was ready to roll at 10 minutes and could be rolled up to 12:30, so a "seam cycle" of 2:30 applied.
5. The screenprint was pasted with clear. This product needed a lot of time to get tacky after the second pasting, so I waited a good 14 minutes in all before putting it on the wall. Once on the wall, there was a considerable amount of time available to play with it (4:00) before it froze up.
The results above in numbers 1 through 5 were reported to workshop attendees during the March Madness workshop. In addition, I ran through another complete set of samples. In other words, I pasted and installed the same papers on the other side of the test board before a live studio audience. (This testing was staggered throughout the day so as to not take up too much time).
Incidentally, during the second go-around, and while trying to get the seam closed up on the 1930's paper one last time, I successfully duplicated my previous feat of putting my thumb through it, proving once again that it was structurally weak, or, that I continue to be anal-retentive, depending on your point of view.
The critical difference for the overall results was that this time I used a thicker paste. I mixed up the 50/50 paste, but I didn't thin it by adding 25% water as I had the previously. This produced what the British might call a "rounder" paste (thicker). "After using the glass paper to remove the pips from the cross lining and whilst pasting, use a rather round tub paste, well brushed out, pip pip".
I wanted to see if the thicker paste would have any effect on the pasting, double-pasting, and, most especially, on the seam cycle.
To save you the suspense, the thicker paste did, indeed, have an effect on the seam cycle. In all cases, the seam cycle increased, usually dramatically so, giving the installer more time to work the seam.
Specifically, here is the table for the workshop test batch:
# type 1st paste 2nd paste install seam cycle
1. 1930's paper 1:00 3:00 4:00 7:00 - 9:00 (2:00)
2. machineprint 4:00 5:00 9:00 11:00 - 13:00 (2:00)
3. blockprint 4:00 5:00 9:00 14:00 - 17:00 (3:00)
4. 21" blankstock 5:00 5:00 10:00 12:00 - 17:00 (5:00)
5. screenprint 3:00 5:00 8:00 10:00 - 16:00 (6:00)
There are probably many lessons that could be drawn from this data, and I'd be glad to hear what you think. You can reach me here at <firstname.lastname@example.org>. Let me address three observations for starters.
Lesson One: adjustment of pastes affect cycle.
The most telling difference in the two batches was: when a thicker paste is used, the seam cycle increases. This could be a good thing, because it would be no fun at all to try and roll a seam of the 1930's paper in 15 seconds or so. Another example might be blankstock. It would be more beneficial to have a longer seam cycle, because then the installer could be a little more footloose about filling in over doors, starting a new wall, etc., without worrying about seams drying out before they are rolled. But is it always a good thing to increase the span of time? I would say that it is not.
Consider, if you're working with a Zuber or an Adelphi or any water-sensitive product, and if using clear, the area behind the seam could easily be wet for 15 minutes or longer. Do you really want that? I say no. You would not want to be hanging around each seam wondering if and when the seam might be ready to roll. A better strategy would be to shorten the seam cycle so that you could accurately predict when the seam would be ready to roll.
The reason is simple. For the water-sensitive types, if one bad seam in one area results from rolling early, that's one seam too many. It's very difficult to recover from such a mishap, and may be impossible. This compromises the installation, and may result in a financial hit, or a hit to your reputation, or at least a hit to your nerves.
Of course the standards are different for "normal" types of paper. But I would say that even when hanging the other types, it would be a better thing to control your seam cycle, rather than otherwise.
This type of thinking is probably the opposite of the intuitive approach, where each seam is more or less done by the seat of the pants. I'm not saying that a more scientific method could, or should, replace intuition. But, you could very quickly learn what the seam cycle for any particular paper is, just by taking a few notes. This information, coupled with street smarts, will bring you much closer to the "perfect seam".
Lesson Two: adjustment of size is likely to affect cycle.
These tests show that thickness of paste affects seam performance. Do they also show that the choice of size affects performance? Not directly, because the size was never changed in this series. But, if we accept that the reason the thickness of paste changed the timing was because of the addition of solids, then it would be a reasonable inference that the same affect could be accomplished by changing the size.
This is because the size is also a water-borne starch material. If we increased the solid content of the size by avoiding dilution of it prior to application, or by adding clay or clear to the mix, the additional starch deposits left behind when the size dried would likely change the way that the seam performed.
On a micro-level this is similar to putting a stripe of clay on the wall to achieve better adhesion, producing the "velcro-type" effect that is familiar to most installers.
In practical terms, the value of this observation is that, supposing that a paste was working well, but not quite providing enough tack, it opens the door to changing the size on a wall than to start playing with the paste.
By changing the content of the size, you could add more time, or more adhesion, or both, to the seam. You could also shorten the time, because usually, adding clay to a size would have the effect of making it grab sooner. This is a way of getting the advantage of clay without the danger of actually pasting the paper with clay or a clay mixture.
Lesson Three: changing pastes affects performance.
For the second set of tests I decided to go with the 50/50 paste for all papers, including the screenprint, even though I knew the screenprint was not likely to perform well on the wall. Sure enough, when pasted during the workshop, the ground of the screenprint ballooned out from the high-moisture paste, while the inked areas at the seam kept those areas tighter. Result: severe differential - also, an inability of the paste to hold the paper to the wall that resulted, after drying, in a noticeably loose area that would not adhere to the wall.
This is a graphic demonstration that the paste must be matched to the product. For this particular screenprint, which was grounded a dark red with solvent-based inks and printed on a thin paper substrate, what was needed was a paste with enough "guts" or solids, to hold the paper to the wall while it was contracting and drying out. Lacking enough solids, the paste composed of 50/50 was just not up to the job.
It should be noted that wheat is about 90% water and methyl cellulose even higher, about 95% water. So it's not surprising that these pastes have little holding power on their own. They work through a mechanical process - the paper conforms to the wall as the moisture leaves through evaporation, leaving behind only a thin layer of starch or a cellulosic film to create a permanent bond between the paper and wall.
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