Shell Building
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Paper Glue and string
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                        Paper, String and Glue


Paper, String and glue are 3 important basic materials used by fireworkers
and especially for cylinder shell building. They find use in rolling shell casings, making fuse assemblies, quick match leaders, shell pasting, spiking, tube rolling, nosings and many other applications.

The type of paper, string or glue used is important and while alternatives to the traditional
type of materials used can often be used successfully there are reasons why these traditional materials have stood the test of time and are still used by the discerning shell builder today.
The following overview of materials is not exhaustive but is intended to give the reader some idea of the basic considerations involved when choosing suitable materials.


There are many different types, grades and qualities  
of paper on the market today made from different materials. Paper can be made from wood pulp obtained from different tree species and other cellulose fibres from a variety of plants like cotton as well as recycled papers and even from old rags. The 2 most important paper based products used in fire working are Kraft papers and various types of cardboard.

Kraft paper made by the Kraft pulping process uses wood chips as the raw material. The chips are treated with a solution of Sodium Hydroxide and Sodium Sulphate that break down the wood chips
to give a watery pulp consisting of almost pure cellulose fibres. This pulp is sprayed onto a long wide screen called a wire where the water drains from the pulp leaving a mat of fibres. Due to the process used this mat has most of the long fibres aligned in one direction. This alignment is what gives
the paper its grain. After the fibres have been squeezed between felt covered rollers to remove more
of the water the still wet paper is passed through steam heated rollers that heat and dry
the fibrous mat further and press and bind the fibres together to make what we know as paper.
A final process of running the paper through a machine called a calendar consisting of heavy cast
Iron rollers presses the paper to a smooth and uniform thickness.

Kraft paper has a pronounced grain or direction in which the long fibres in the paper are orientated
in the same way as does cloth fabric or wood. This grain direction is important as the paper
is significantly stronger and more resistant to tearing and compression in one direction than the other. This difference in directional strength is exploited when rolling shell cases to ensure the paper
is orientated to give the shell maximum strength.

Grain direction can be detected in a number of ways. Tearing the paper across (against) the grain
will result in a jagged uneven tear, tearing along (with) the grain will give a much straighter even
tear that follows the direction of the grain
. Try to tear the paper in a straight line first along
the length of the paper then in the opposite direction. The tear will be noticeably straighter
and even in one direction; this is the direction in which the papers long fibres are running.

Folding the paper with the grain (parallel to the grain direction) is easier than trying to fold it against
the grain and will give a smoother crisper fold
but this is only noticeable in the heavier grades
of paper.

Perhaps the easiest and most foolproof way
to determine grain direction is to take a square
of the paper say 6 x 6 inches and quickly wet one side of it with a sprayer or sponge. The paper
should immediately curl up. The grain always
runs parallel with the direction of the curl.

Kraft comes in a wide range of colours from light tan to dark brown and even in a bleached white form. Internationally paperweight is expressed in grams per square metre (g/m2) which makes it
easy to compare different types of paper. In North America and Canada weight is expressed in terms of ‘basis weight’ meaning the weight of 500 sheets of a particular size. Since sheets of different types of paper are cut to different sizes this makes comparison of paper types difficult.

To convert any basis weight to grams multiply the basis weight by 1406.13 then divide by the number of square inches in the sheet. E.g. 20 pound bond paper has a basis size of 17 x 22 inches (374 square inches)  20 x1406.13=28122.6 divide by 374 to get 75g/m2.

Kraft paper is available in sheets of 24x36, 30x40, 36x48 and 40x48 inches as well as other sizes
and also in rolls ranging from 12 to 72 inches wide. Thickness ranges from .003 to .009 inches.

Because of its high tensile and crushing strength Virgin Kraft paper is favoured for rolling shell
casings and making spolette tubes as well as for the pasted layers applied to the shell after spiking
is completed.
Paper suitable for pasting should be able to be saturated in wheat paste and crumpled and still hold together after smoothing it out again. Paper that rips easily or falls apart after soaking in paste is not suitable for pasting or shell case rolling though maybe used for other purposes such as when giving
a shell it's 'lift wrap'. 
There are also partly recycled Kraft papers on the market that may or may not be suitable so you
will need to test them first ensure they are strong enough for your intended use.
Different calipers of papers are needed for different applications eg. 30 to 50 lb paper is generally
used to roll casings. For smaller shells in the 1 ½ to 4 inch range while 60, 70 and 90 lb is used
in 4 inch and larger shells and multibreaks. 30 lb paper is mostly used for the final wrap containing
the lift charge, quick match leaders as well as for nosings around fuses and for insert shells.
A table showing the common applications and paper sizes is shown in the shell building tables.

Apart from virgin Kraft paper other papers can be used for certain applications where strength
and grain direction are not critical. Maltese type shells often employ recycled papers such as old cement bags and the like to roll their casings. This is possible because of their unique spiking
method of covering the entire shell surface with a single strand Jute twine and the use of cardboard layers with the paper that give the shell sufficient strength.

Cardboard, Chipboard, Paperboard, Binders Board.

I'm sure someone will pull me up on this but basically we are talking about thick paper!
In the U.K, Australia, New Zealand and most countries outside of North America Chipboard
is not a paper product: it refers to a product made from compressed sheets of resin bound
wood chips. Cardboard is usually multi layered and often has a white layer on the top or both
sides and grey layers in the middle.

Most cardboard is made from part or totally recycled paper and like paper some but not all has
a distinct grain direction to it.

Common uses for the thinner grades (.018” to .025”) of cardboard are postcards, magazine covers, boxes for shoes, toys cereals and foodstuffs etc. This thickness of cardboard is perfect for rolling
shell case liners that provide a little extra rigidity to the casing as well as giving a ‘fill level’ indicator
for the shells contents and a rim for the end disk to sit against firmly. This type of cardboard is also employed in making cases for Maltese type shells.

Binders Board or Rag Board is a thicker type of cardboard made from laminated layers of low grade paper and rags, normally a grey colour it is used by bookmakers for hardback book covers. It comes in a range of thicknesses from 1/16” to 1/8” and makes an ideal material for shell end discs.

Kraft board is a product made form virgin fibres and is a brown colour; it is stronger than Binders Board it makes excellent end discs.

Twine is used for many manipulations in shell building including shell spiking, tying off nosings on spolettes, tying on black match as well as securing lift wraps around the pasted shell.
Traditionally Flax twine is used because of its high strength to diameter ratio and good knot tying qualities but due to the high cost and difficulty in finding good quality flax twines in recent years Cotton, Hemp as well as Jute (for Maltese shells)
are being used more frequently and used correctly can produce acceptable results. The important characteristics required of string for most purposes
is that it makes good secure knots, has good tensile strength in thinner diameters and is able to absorb paste well. Synthetic and synthetic/natural mixes
are not suitable for shell making due to their higher elasticity and their inability to absorb paste well

Cotton.  3 to 4 ply is used to make black match, tie nosings and lift wraps while the stronger
8, 10 and 12 ply can be used for shell spiking. The string should have no wax finish or treatment
that inhibits the absorption of paste into the string. Cotton string can have a fair amount of stretch
which is undesirable when spiking and also produces less friction than Hemp, Flax and Jute
making it more likely to slip when tying knots. It is also only half as strong as Hemp or Flax string
in any given diameter and may need to be used doubled up when spiking shells larger than 4 inch
to make up for it’s lack of strength. Overall Cotton is not the best choice for spiking but is often
used because it is cheap and easy to find.

Flax (Linen) The finest flax twines come from Belgium, Italy and Ireland. They have the advantage of being far stronger than Cotton twines of a similar size and have very little stretch.
A 2 ply Flax twine is often stronger than 6 ply cotton. Flax has a rougher surface than cotton
holds knots better and is considered along with Hemp to be superior to other twines in most
respects for spiking and tying purposes.
As with other twines they should be unwaxed when used for spiking so that they can absorb
paste well.

 Hemp. has a tensile strength almost equal to that of Flax and is far cheaper. It makes an excellent twine for spiking shells. It normally has a rougher finish than Flax and makes good secure knots.
It stretches very little and absorbs paste well. 20lb – 25lb Hemp string is suitable for small shells
up to 4 inch whereas 48lb and over is employed for larger shells and joining together multibreaks.

Jute. Jute has poor tensile strength, loses some of its strength when wet and does not make good secure knots. For this reason it is not a good choice for shell construction. A notable exception
is in the manufacture of Maltese style shells where a special 2 ply Jute twine is used to spike shells. The twine is laid down 4 strands or more at a time in a pattern to cover the entire surface of the shell vertically and horizontally. When the spiking process is complete no part of the shell casing is visible.  paste is applied by hand to the twine after spiking is completed rather than before.

An important consideration when building large shells or multibreaks is that a thick twine can cause
an excessive build up around the top, bottom and sides of the shell when spiking especially with multibreak shells. The higher strength of Flax and Hemp twines allows for a thinner twine to be used that reduces this build-up as the twine lies flatter against the shell casing.

Glues and Paste.

Glues used in shell building include white PVA type glues, wood glues such as Elmers, 2 part Epoxy resins, hot melt, 'super glue' and general paper
glues as well as wheat paste used for shell pasting.

White glues are used to glue the pleated paper in place when closing shell casings, gluing spolettes
and time fuses in to the end discs, rolling tubes, securing twine and a multitude of other operations.

Each glue has advantages and disadvantages depending on the application. For example wood glue
or white glue is quite brittle when dry. This is not a problem for gluing the pleated paper folds when closing the shell case ends or securing end discs but when used to secure and seal spolettes/time fuse into end discs the glue seal can sometimes crack when the spiking twine is pulled and tensioned
around the fuse during the spiking process. A crack in the glue around the fuse could allow lift gasses into the shell when the shell is fired.
Some builders prefer to use the more flexible hot melt glue for sealing around the fuse for this reason. Others use white glue around the fuse on the inner side of the disc and hot melt glue on the outer side after spiking is completed.

Wheat paste mixed with warm water is used for pasting shells, it penetrates the paper well and dries rock hard. If you cannot find a comercial brand Wheat Paste such as Golden Harvest then Wheat Starch or SGRS boiled with water makes an excellent substitute paste.

Adhesive tape used in cylinder shell construction is mainly the gum backed brown Kraft paper type.
It is strong and lends a neat professional appearance to your work as opposed to using masking tape which as well as unsightly also has a tendency to burn for a long period of time. Used to hold black match in place around spolettes, secure end disks, secure lift leaders to the sides of shells and many other uses it is available in various widths.

Try to use as little glue and tape as possible in your shell construction. Many builders glue and tape their shells excessively. If it doesn't need it don't use it. End discs on shells can be held in place very well with the spiking twine alone and just a few dabs of glue to hold things in place till the spiking is secure.
Bands of masking tape around and over end discs to 'seal' the shell from ingress of lift gasses are not needed if you have pasted your shell correctly and just contribute to building cost and burning debris.


Copyright Bangkok Pyro Company Thailand 2011