Plywood

Plywood is a simple, but effective material. This is used a lot in the world of construction due to its strong structure, but light weight. It’s quite a flexible material, not physically but in the sense that you can add many layers and make it as thick as you need.

Modern plywood as we know it was invented in the 1800’s. The famous two seater aircraft of World War Two, De Haviland Mosquito was mainly made of different grades of plywood. Furniture makers and Architects started using this material around the 20th century after the second world war when production of plywood became a bit more commercial, and also due to its economic value.

Plywood’s strength comes from the way in which it is made.

It is made up of different layers of veneer, with the inner layer being called the core, and the outer layers being called the faces. The number of layers included is always odd so that the faces look the same. This is good for objects which you’d see both sides of, like a door as it gives the illusion of it being one solid piece of wood rather than lots of layers stuck together.

Each layer is turned at a 90 degree angle from the last, this strengthens the structure of the product because the grains are going in different directions. It is then put together using glue. The type of glue depends on where the plywood will be used:

  • Interior – this type of plywood could be glued using either highly resistant glue which is fairly resistant to moisture in the air, or intermediate glue which is resistant to mould, bacteria and moisture. Neither should be used for exterior plywood though.
  • Exterior – This plywood is made using waterproof glue.

The plywood is then placed between two large hydraulic shelves and squeezed together whilst being heated to dry the glue, it can then be trimmed and sanded to give a better finish. The outer layers can be made of more expensive layers of wood to make it look better as they are usually thinner.

The more layers of veneer you have in the plywood, the stronger the structure will be and the more resistant to impact it will be, so that it won’t split, chip, crack all the way through or crumble. These layers also make it more resistant to shrinking, warping, twisting or swelling so much as ordinary wood.

You can get exact sizes and thickness’s when you buy plywood, which is handy if you’re on a budget, you’d only be paying for exactly how much you’d be using rather than having any waste.If you do buy plywood, be sure to look out for the initials APA (American Plywood Association), or DFPA (Douglas Fir Plywood Association) as these two companies represent most of the plywood manufacturers and test all plywood to ensure that the quality is to a high standard.

Written by Jade Turney – Building Tectonics Ltd.

Plasterboard

Plasterboard is one of those clever materials that seems to get overlooked a lot of the time. It has revolutionised the way in which buildings are built. We thought we would send out a reminder in the form of a blog as to why it is such a useful material.

Plasterboard is made up of an inner layer of Gypsum (which is made up of crystals containing a small amount of water) between two outer layers of lining paper. Different additives can be added to the inner gypsum layer and you can vary the weight and strength of the lining paper, which in turn will give the finished board different properties. For example, standard plasterboard should not be used for damp areas, like bathrooms or kitchens, but you can have silicon additives added to the core to make it suitable for those areas.

One of the properties of plasterboard which makes it so useful is the fact that it is fire resistant. If a fire were to occur, fire resistant plasterboard would give you extra time to get out of the building (up to around 30 minutes) by slowing down the rate at which the fire spreads at.That would definitely help give you those few extra moments needed to get out of there! As well as being fire resistant, plasterboard is also sound resistant. So it can cut down on airborne noises such as speaking or music. Add to these points that it is lightweight, so if you had a plasterboard ceiling for instance, and there was an earthquake, if the ceiling came down, the plasterboard would not cause so much damage.

Most plasterboard has one ivory side and one brown side, and the liner on the ivory side is specially designed for plastering. Plaster should not be applied to the brown side. This is due to the differing absorption rates. The paper liners on plasterboard is made from recycled paper, which is a big positive for the environment.

Perhaps now, we are enlightening you all as to just how useful and versatile this material really is! We hope that you’ll not overlook this material quite as much in the future.

Written by Jade Turney – Building Tectonics Ltd.

Flitched Beams

A client has just asked me about Flitched Beams and I thought it might be an interesting topic for others. As alway, I am not going to be too technical and so this is going to be a quick introduction to the wonderful world of the Flitched Beam. As you will know, steel is stronger than wood because it can withstand compression, ( being squeezed ) much more than wood and it can withstand tension ( being stretched ) more than wood. However a long slender piece of steel will still buckle and so if you can stop it buckling under load, its ability to withstand the compressive forces will be greatly enhanced. So, if you bolt a fat piece of wood either side of a piece of steel so that they act together, the steel will take the compressive forces and the wood will stop the buckling of the steel. Most typically a flitched beam consists of a plate of steel about 10mm thick and 150mm deep with a timber plate also 150mm deep and about 50mm wide each side to form a sandwich. The assembly is bolted together with bolts along its length at about 300mm spacings.

In any beam spanning across an opening, the top of a beam is in compression and the bottom is in tension. The wood clamped either side of the steel will help stop the top half of the steel buckling, thus enhancing the strength of the assembly much more than the wood could do on its own. Clearly a piece of steel of the overall size of the assembly would be much stronger but much heavier too. Furthermore, the wood element is easier to fix too as you can screw or nail into it and the assembly can be assembled on site with can be a blessing if access is restricted. Another very useful characteristic is that in a fire steel loses a lot of strength and collapses quite quickly, whereas timber initially burns until the surface becomes carbonized and chars which creates a protective layer. Also the wood does not conduct heat as well as steel, for these two reasons the Flitched beam performs better in fire than a steel beam. To ensure this we often make the timber constituent a little bigger, creating what is known as a sacrificial layer, so that the beam can be exposed to fire for say half an hour without collapsing.

I am not sure when they were first used but I am aware of Victorian flitched beams. I am also not sure where the name comes from and that would be interesting to know as the word flitch is used to describe many ancient items.

Any feed back would be appreciated.

Written by Tony Keller – Building Tectonics Ltd.