All About

By Robert M. Kelly
Paper-Hangings

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OK, the topic for the day is GSM. GSM (sometimes rendered "GMS") stands for "grams per square meter", and measures the weight of paper.

The main reason (and really, the only reason) for bringing this up is that at Paper-Hangings we've made a few changes in our pricing and product line, and since these relate to the weight of the paper, an explanation seemed in order. This article is intended to answer any questions you might have, but by all means, if you have more questions, let us know at either the blog, or at our email.

Let's start with the definition of blankstock…..

Blankstock is a traditional product, made of groundwood. It’s used under fine wallcoverings to absorb moisture from the finish wallpaper. It allows seams to dry sooner and safer, and promotes stability of the installation. The purposes of blankstock are similar to those of an underlayment for carpet or a lining for a curtain or drape.

One of the big misconceptions is that blankstock "smooths out the wall". This is true to a limited degree, but if someone wants a smoother wall there are better ways to do it. The best way is better prep, i.e., skimcoat or similar.
Another way is to use a bridging liner. These are made of a roughly 50/50 blend of cotton and polyester (or other synthetic material such as rayon). We don't sell bridging liner, but it’s readily available. In any case, blankstock is not a bridging liner.

As I have written elsewhere:
"… blankstock is a skin. If you have a small bump or sheetrock nail divot on your wall, and put blankstock on it, you will then have a wall with a blankstocked bump or divot…"

Blankstock is a skin, and designed to absorb moisture. This explains why you might want to use it even if the walls are so-called "perfect", for example, over new construction sheetrock or plaster. The important thing is not so much what blankstock is going over, but what is going over it, namely, really good (and usually really expensive) showroom-type wallpaper. Blankstock is a tool. It gives you much more control over the installation, specifically, how quickly and how well the seam areas dry out.

We now carry only a 28.5" width in the standard weight (90 gsm). Let's talk about this gsm thing more. Anyone familiar with paper knows that there are many ways to weigh it. Here's a good web site that covers the basics:

www.paper-paper.com/weight.html

Clearly, numbers of sheets in a ream and basis weights and so on (which are really based on the size of the mould) are not the best way to keep track of paper weights. For example, we learn in wallpaper history that different countries have different ideas on how many sheets make up a "ream". This confusion is not too different from the argument about the size of a "roll", and ….. let's not even get started on that one!

This is why the grams per square meter scale makes a lot of sense as a yardstick. To find grams per square meter, you just cut paper to the size of a square meter, fold, and weigh. To take this a step further: we all know the meter is about 39 inches (from dealing with Italian and Japanese papers), so, we multiply 39 x 39 and come up with 1521 square inches.
If we have blankstock which is 28.5 inches wide, we divide the 1521 by 28.5 to get 53.375 inches. So, a piece of paper 28.5 x 53.375 will amount to around 1521 square inches, which is - one square meter.

Next step is to cut and weigh the product. I weighed some of our new shipment at random and learned that one square meter weighed 3.2 oz. Converting the 3.2 oz. to grams (via the handy-dandy Google calculator) I confirmed that one square meter = 90.7 gsm.

So, this shows you how this gsm designation is arrived at.

It’s possible to get groundwood paper which is lower than 90 gsm, however, this is not used for blankstock, but for a related use which we all know about, namely, paper-backing. Fabric is the primary material that is paper-backed, though lighter grades of groundwood are also used as laminates for foils, vinyls, and even nonwovens. It is true that occasionally you will find heavier weights used for vinyls and foils, but these laminates tend to be less than 90.

On the other hand, blankstock as a separate liner for wallpaper starts at 90. Blankstock weights traditionally vary between 90 and 120 gsm.

This puts into perspective that our new acidfree paper at 120 gsm, in addition to being acid free, is at least moderately heavy, though not as heavy as the previous acidfree paper we stocked, which was 150.

Not surprisingly, the "150" stands for 150 gsm, "120" stands for 120 gsm and so on. This same description extends into those English paperhanging guidelines that we see which call for "1000 grade" or "1200 grade" high quality liner, and so on. Same thing, 100 gsm or 120 gsm, respectively.