Paper-Hangings - Quality Products for the Professional Paperhanger

blankstock 401: The Final Chapter

After the NGPP workshop, while all this blankstock stuff was still swimming in my head, I thought I would take a stab at answering another basic question that frequently comes up: why size blankstock in the first place? So let's see if that question can be answered to make this the final chapter in the saga.

First of all, when I say "size" I mean a diluted wheat paste, brushed onto raw blankstock. I think this is the best size, since the wheat makes for a nice crisp adhesive layer; but, I often throw a little cellulose in for better handling (it makes the size flow better). You could roll this on the wall, but that sometimes leaves skips and roller marks. I like the way that a large brush both distributes the size evenly, and also works it into the blankstock. A 6" stain brush, natural bristle, seems to work well, and is widely available.

Size is part of a system; it's the first half of a size/paste sandwich which locks the seam down in short order. In contrast to this, some paperhangers say that they use clear on Britpulps while hanging on raw blankstock, and get great adhesion and great seams. Their question is - why bother with size? You can't argue with success, but if we look at this question a little closer, some observations come to mind.

Number one, clear is a different animal. It could be described as a paste on steroids. It has relatively high water content, starch, and cellulose, but it's also a very thick product with some mystery ingredients which more or less overpowers the blankstock rather than working with it.

My main objection to clear is that it tends to keep the seam wet. As long as the seam is wet, there is danger that it might contract. For hanging traditional paper, I'm always looking for ways to lock seams down with a minimum of time, effort and clean-up. A lighter paste and a sized wall helps me do that, because they allow better control and shorter seam cycles.

Let's look a little closer. Blankstock is very dry and fibrous, and the first job of the size is to lay the fibers down. This produces a somewhat slick surface. This can be demonstrated by rubbing your hand over a wall of raw blankstock and comparing the sound it makes to the sound from rubbing a wall of sized blankstock. The sized blankstock will have a higher pitch, because the fibers are consolidated and more or less glazed over with the starch from the size.

Size also gives more uniformity to the surface by equalizing the absorption rate; this is important for hanging water-sensitive products, when we want maximum predictability at the seams. The third purpose is to have a thin layer of adhesive in place as the wallpaper is installed. Size has some unique properties. It's slick, and allows for re-positioning, but it's also dry and porous, so it drinks up paste from the wallpaper.

The "adhesive sandwich" created from the size and the paste can be very finely tuned by adjusting each element; even though there's not much adhesive in the sandwich, there's just enough to hold the seam nicely.

I said above that the use of clear on raw blankstock sort of "overpowered" the blankstock rather than working with it. In effect, the heavier solids in the clear lock the seams down. However, if a paste (or maybe even a thinned down clear), were used on raw blankstock, I imagine that it might die into the blankstock and that the formation of the sandwich I described above might be compromised. In that case, I wonder what type of a bond it would have later.

Also, if a strip is repositioned on raw blankstock, the paste often disappears, which requires a trip to the paste bucket, whereas a sized wall holds the paste out, encouraging adhesion. These are some of the other reasons why I like to size all the time when using a high-moisture paste.

End of the saga (for now!).

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