Designing for Polished Concrete

Polished concrete floors look great. They’re a hard-wearing, durable and attractive floor finish that can add value to your home. But not every concrete floor is suitable for polishing because cracks in polished concrete floors are hard to hide.

If you’re building or extending your home and you’d like to use polished concrete, then this is something your engineer needs to know during the design process so that the appropriate precautions can be built into the structural engineering drawings.

What is Polished Concrete?

Polished concrete is any of several decorative concrete surface finishes that leave the concrete surface exposed. Polished concrete used to be grey concrete that was coated with a wax product and then polished. These days, polished concrete includes burnished (glossy steel trowelled)finishes, honed (finely ground and polished ) finishes exposing coloured aggregates, chemical stains or dry-shake pigments.

How long does polished concrete last?

Polished concrete surfaces are easy to maintain and with regular cleaning should last a lifetime.

Regular cleaning of polished concrete floors ensures that the floor does not become slippery caused by surface contamination.

A surface warranty of between 10 and 20 years is not uncommon for residential polished concrete floors.

Five tips for Engineering Polished Concrete Floors

A good polished concrete slab finish starts with good engineering design. Here are our five tips for a great polished concrete slab.

1. Use a higher grade concrete

A higher grade of concrete strength is a great way to improve the finish of a polished concrete slab. A higher strength concrete has better curing characteristics, cracks less but is harder to work and place.

If you normally use N20 for your slabs, consider using N32 or even N40 concrete for your polished concrete slabs. The difference in price is minor compared to the improved concrete characteristics.

2. Use a higher grade of mesh

Concrete cracks. You know that. A heavier slab reinforcing mesh in will help keep those cracks evenly distributed and will keep the cracks so fine that you can barely see them.

If you normally use SL72 mesh in your concrete slabs, use two layers of SL82 or better still SL81 mesh.

3. Concentrate on Curing

Concrete curing is THE most important aspect of a good polished concrete surface. As the poured concrete dries out it shrinks. If the concrete shrinks before the concrete has gained strength it cracks. Curing allows the concrete to dry out slowly enough that the cracks distribute evenly through the concrete as micro cracks.

I recommend curing your polished concrete slabs by covering it with plastic for seven days. Only lift the plastic in this time to moisten the surface more before replacing the plastic again.

4. Keep the Cover Consistent

The depth of the slab reinforcement in the slab is commonly known as reinforcement cover. For a great polished concrete result, the reinforcement has to be not too deep and not too shallow. The reinforcement has to be well supported on bar chairs and positioned according to the design engineer’s specification which will take into account the environment and the particular finish you are looking for.

For instance, bar chairs at 800 x 800 centres that support the mesh reinforcement about 35mm from the top of the concrete slab would be appropriate for most polished concrete slabs.

5. Vibrate Vertically

Compaction of concrete during placement is a must and polished concrete needs very careful vibration. Insert the poker vibrator vertically and at a regular spacing to ensure the concrete is evenly consolidated and free from entrapped air.

Laying a vibrator down in a slab during concrete placement could cause uneven distribution of in the stones in a honed concrete surface so careful and consistent vertical vibration is a must.

Find Out More About Polished Concrete

Find out more about polished concrete floors with CCAA.

Check out this handy guide by BGC Concrete.

Structural Engineers – What they do, where they work and how much money they make

Structural engineers are civil engineers that design structures. They design, check and certify structures such as buildings, bridges and tunnels.

What do Structural Engineers Do?

Structural engineers study how forces are applied to parts of buildings, how those forces are transmitted and resisted, and the effects that those forces have on the parts of structures and on the structure as a whole.

For example, a structural engineer that designs houses thinks about things like:

  • How strong the roof has to be so that the roof does not sag too much under its own weight or under the weight of a worker on the roof.
  • How strong a roof has to be so that it is not blown away by a cyclone or a tornado.
  • How strong the walls have to be to support the wall cladding and the roof structure.
  • How strong the floor has to be to support furniture, people, special items like grand pianos and floor coverings like special floor tiles.
  • How strong the foundation has to be to support the whole house, how deep the footings have to be to stop the house being moved by a tornado or a cyclone, and how strong the footings have to be so the building is not affected too much by the ground moving.

The process that a structural engineer follows when designing structures is always fairly simple: Determine the forces. Determine the load path. Design the structural elements. However, the amount of work this might entails varies wildly depending on the structure. the type of the structural parts and how they are joined.

A structural engineer that designs a high rise building has a lot more forces and a lot more load path to consider than a structural engineer that designs a small footbridge.

How Do You Become a Structural Engineer

Structural engineers study civil engineering at university. Civil engineers study basic concepts such as statics (how forces transmit through things). dynamics (how forces move things), thermodynamics (how energy changes things), chemistry (the chemical make up of things), materials (how construction materials get their characteristics), geomechanics (how soils affect things), transport (roads, traffic and things) and hydraulics (how water moves and affects things).

After university, structural engineers learn more about structures such as buildings, bridges and/or tunnels by either undertaking further study or getting their first job as a structural engineer.

Whether at university or on the job, structural engineers learn complex and simple ways of designing the structures they intend working with. Special computer programs called finite element analysis programs and 3d analysis programs (like SpaceGass) improve the speed and accuracy of complicated structures. However first principles hand calculations on note pads are still used in many offices because they are easy to check and can be used to prove overall theories.

Many localities require structural engineers to have around 4 years of experience working under the close mentorship of a senior structural engineer before they are allowed to apply for registration. In Queensland, that process is managed by BPEQ. After registration, many structural engineers tend to keep working in larger firms for the technical support and camaraderie that working with other technical specialists offers.

Where Do Structural Engineers Work?

Structural engineering is a great mix of indoor and outdoor work.

How’s this for a mix of work:

  • Start the day checking emails and responding to enquiries.
  • Head out for a site inspection with the head contractor to check compliance of a concrete slab prior to pouring.
  • Meet with an architect at a new project to discuss technical constraints and opportunities.
  • A couple of hours in the office writing notes form the site inspection, sending some emails, completing calculations to determine the size for a steel beam for the architect.
  • Receive a phone call from a commercial building owner concerned about a sagging ceiling. Make an appointment and head out to inspect the problem. Determine a course of action for repairing the damage and upgrading the deficient structural elements.
  • Answer the phone call from a builder with a question about a design you completed last year. He asks you to consider an approach that allows the builder to keep working while waiting for a missing beam. You come up with a solution that the builder likes and send him a confirmation email that he can show to his certifier.
  • You receive two photos by text message from a real estate agent that is enquiring about some damage in a rental property. You contact the agent, talk about the damage, the access requirements for the property and make a time for an inspection next week.

The life of a structural engineer is constantly challenging. It takes a lot of training, a lot of study, a great personality and a heap of humility to make a good engineer.

It’s fine to be a little bit nerdy sometimes, but good engineers need to be able to mix and communicate with a wide variety of people. The old days of back-office structural engineers are long gone.

So where do structural engineers work? Everywhere there is a building, bridge or tunnel. Everywhere there is a phone signal, email connection or notepad. Everywhere there is a problem, a new building being planned, and every now and then, in an office.

How Much Money do Structural Engineers Earn?

I would love to tell you that by being a structural engineer you are going to be rich.

But that isn’t the case.

As a structural engineer with a good work ethic, the ability to lead a team, knowledge of the local industry, contacts in the local industry and incredible smarts that allow you to juggle about a hundred jobs a day, you are going to be comfortable. You are going to be middle class. You are going to be awarded a very average pay.

If you want to be rich, I suggest you don’t become a structural engineer. There are many ways to become rich but being a structural engineer is not one of them.

The benefit of being a good structural engineer is:

  • an average pay. Your partner will love you for who you are, not how much you make.
  • a new challenge each day. Each day is exciting and different.
  • that you get to help people who really need your help. Engineers are needed for so many challenges people face with buildings.
  • you get to see your ideas come to fruition. An idea is just an idea until you explain it to someone and they build it.
  • you get to see your plans being built. You get to walk past your finished buildings for many,, many years and know that you contributed to that building and you did a good job. You get to work with some funny, smart, clever, experienced engineers, architects, builders, labourers, homeowners and clients. You get to earn a decent living and you get to hold your head high because you are contributing to society, You are providing a useful, worthwhile service and making our society better.

4 Secret Tips for Graduate Engineers Seeking Employment

I have employed and worked with some amazing young graduate engineers. When we look for graduate structural engineers to employ at Cornell Engineers we use the standard job search pages that you already know about, ie Seek and Indeed.

Every time we advertise a vacant position for a structural engineer we are flooded with applications. Our priority is shortlisting applications by removing the applications that do not show a determined approach to gaining our attention.

If you want to make it past round one of the job application process, here are my four secret tips for graduate civil and structural engineers seeking a graduate or junior structural engineer employment role in their first years out of university:

  1. Think like a business
  2. Clean up your resume
  3. Work really hard all the way through university
  4. Choose experience over pay Continue reading 4 Secret Tips for Graduate Engineers Seeking Employment

Hey building industry lets get metric

So if you’re in the building industry in Australia you’ve probably noticed by now that the sizing and spacing of structural members aren’t exactly metric. I mean, we’re working in millimetres and all but have you noticed we still bow to imperial measurements in nearly all structural framing?

Here is how pervasive the imperial system is in our construction industry:

  • 75mm x 50mm studs are really 3 inch x 2 inch studs in imperial
  • (70mm x 45mm studs are just the seasoned timber equivalent of 75 x 50)
  • Roof frames are at 900mm (3 feet) or 600mm (2 feet) centres
  • Studs are at 450mm (1.5 feet) or 600mm (2 feet) centres
  • Residential wall heights are commonly 2.4m (8 feet), 2.7m (9 feet) or 3.0m (10 feet)
  • Windows are 900mm (3 feet), 1200mm (4 feet), 1500mm (5 feet) etc wide

The list goes on.

Why are we hanging on to these old imperial dimensions when we turned metric many, many years ago? Wouldn’t it be easier for set out, planning and ordering to be working in metric?

Our materials are made better and are stronger and more consistently than ‘the old days’ when these systems were first put in place.

  • Why can’t studs be placed at 500mm centres instead of 450mm centres?
  • Why don’t we have trusses at 1000mm (1 metre) centres?
  • Why don’t we have wall heights at 2.5 metres and 3.0m standard?
  • Why don’t windows come in 500mm width increments to suit metric stud centres?

So I’m calling out to industry, to suppliers, to product technical advisors and other structural engineers. Let’s make the move to metric in the construction industry. It doesn’t have to be overnight, but when we learn to work in metric numbers, in easy multiples of 10, 50 and 100 I think we’ll make it easier for ourselves, use our modern materials more efficiently and finally close the door on outdated imperial standards.

How does a structural engineer check engineering drawings

Join Matt Cornell as he checks the drawings for a single storey concrete masonry (bessa block) home to be built in a cyclone region. He goes through the process of checking a set of structural engineering drawings with some tips for checking and good construction.

Today we’re going to go through the process that I normally
follow when I’m checking a set of engineering plans.

So a job comes into – a set of plans come into the office and they’ve asked us to do the engineering.

One of my engineers has done up some engineering drawings.

Here you can see the engineering, the AutoCAD file. They’ve set up a form 15 ready for me to fill in. I’m doing the checking.

So a lot of the works already been done. There’s a checking folder already as you can see, so the first thing I’m going to do is to check to see what the client has asked for.

Continue reading How does a structural engineer check engineering drawings