Soil Heave – Protecting the Slab After Construction

Once the house is completed it doesn’t mean that you shouldn’t be concerned about the foundations.

This is particularly the case if your house is Built on Clay as there is a risk of ‘Slab Heave’.

This is the result of moisture getting into the clay under the slab causing the clay to swell pushing the slab upwards.

Protection Against  Soil Heave

In South Australia there is a requirement for a 1m path around the building if there is a risk of ‘Soil Heave’,

That is good practice whichever state you live in.

The diagram below shows a suitable detail to protect the ground under your slab.

The key issues are:

  • Paving falls away from external walls for at least 1m with a minimum fall of 1:20 (50mm of fall in 1m)
  • Where the water will not continue to flow away from the edge of the path an Aggi Drain in a trench backfilled with granular material should be provided.
  • Although the requirement for an aggi drain is not as critical where the ground slopes away from the slab, it is nevertheless good practice to have one.

Got Problems?

Generally there aren’t easy fixes for foundation problems, and the cures aren’t DIY jobs

You really need to get an expert involved like Geotech Built 


Also see Agricultural Drains

Liquid Limestone

You might have heard of Liquid Limestone as an alternative paving material…….But what is it?

Really its just a different type of concrete.

It is much more common in West Australia than other states.

The differences between conventional concrete and Liquid Limestone are:

  • Instead of standard Portland ‘Grey’ Cement it uses White Cement.
  • It uses crushed limestone rather than other types of rock gravel and sand.
  • Quite often a plasticiser is added. This means the mixture can be poured without having to add too much water.

Various patterns can be applied to the surface as the concrete sets. (see above photo)

As well as the standard limestone appearance the supplier can add various pigments. If you want a strong colour I think you would be better off  just going for coloured concrete.

Because it can be laid in large slabs like concrete there are less joints than in conventional brick or concrete slab paving. (There will still need to be some joints. For joint spacing see: Concrete Joints 1)

With the lighter colour it can be cooler underfoot than other pavements.

To maintain its appearance liquid limestone will need to be sealed around a week after laying.

Thanks to Concept Concrete WA. for these two great examples of  Liquid Limestone Paving

For  posts on on getting your paths and driveways correct see Concreting


Why Asphalt is a Good Choice for your New Home’s Driveway

A guest post from John Ray

If you are fortunate enough to be building your dream home, there is much to consider.

Having the luxury of being involved at the design stage allows you to really make the home a perfect place for you and your family.

Aside from the many other components, your choice of driveway material is one that requires some thought, as there are several options open to you.

Concrete is one option, but in fact, a popular material for surfacing driveways is asphalt.

If you are yet to be convinced, here are just a few reasons why asphalt may be the best material for a residential drive.

Durability – Asphalt is extremely durable, which is ideal for the harsh Australian climate, and if it is applied correctly, the surface will remain in good condition for many years. If your new home is located in NSW, North Shore are asphalt contractors with many years of hands-on experience in surfacing driveways.

Non-Slip Surface – Asphalt provides a durable, non-slip surface, even when wet, and this is essential in a residential environment, and with professional application, your new driveway will not require any maintenance.

Enhance the Look of your Home – A professionally applied asphalt driveway will really transform the look of your home, and with matching pathways and attractive stone bordering, the look will be complete. There are asphalt suppliers who offer a comprehensive service, and they can even landscape the surrounding area if required.

Maintenance Free – Concrete often gathers mould and moss and needs regular scrubbing, while asphalt gives a very durable finish and it really doesn’t require any upkeep. If you do want to give the surface a clean, a water pressure cleaner would be ideal, as it can easily remove any grease and grime that has built up over time. If you enlist a reputable asphalt contractor, they will ensure that the driveway has an adequate thickness, and this will ensure long term durability.

Choose the Contractor Wisely

There are some small outfits that drift from area to area, preying on unsuspecting homeowners by offering very low quotes on driveway resurfacing.

Once a person has agreed to have the work carried out, there would be little, if any, preparation, and the thinnest of skims would be applied.

In order to avoid this happening to you, it is best to contact a reputable company, one that also carries out commercial projects, as this means they work to a recognised standard.

Any reputable asphalt contractor would be happy to give the customer a full warranty on their work, and with asphalt driveways, time will be the determining factor, as a quality job will remain in good condition for many years.


If you want a durable surface on your driveway that is easy to keep clean its worth considering asphalt, and with a professional installation, you can say goodbye to many driveway issues.

Drain Fail?

How about this picture of the water missing the drain?

Is this a design failure?

Well that’s what, where I found this photo, thought!

Actually its a construction quality failure that is more common than it should be.

Whats happened is the drain is deeper than the base of the paving so the construction crew have had to dig down to solid ground.

The paving has dropped around the drain because

  • either the ground under the paving wasn’t too solid,
  • or the base between the pavers and the ground wasn’t compacted enough.
  • or both of the above.

Too often a poor quality paving job looks good when its new. . . . but after a few months these sort of problems emerge!

For more Unusual House Photos, Wins, and Fails, have a look at: What the………………….?

Front Path – Fail 2

What an imposing facade!

But why is it spoiled by that letter box in the middle of the path? . . . . . Perhaps it’s because the letter box is hiding the water meter!

It’s funny how those water meters always seem to be in the wrong place. We had the same issue at my last new house, but solved it by widening the driveway to avoid the meter entirely.

Thanks to Herman Fong for submitting this photo. (If you see something funny on a house send it in and give us all a laugh)


For more Unusual House Photos, and Fails, check out: What the………………….?


Height Above Ground

For the typical modern house with slab on ground base there are two minimum heights above ground level that need to be considered:

  • Next to the building.
  • Distance of 1m away.

The reason for these minimums is to keep water out of the building, including the structure and foundations.

Next To The House

Floor level above external finished surfaces must be a minimum of:

  • 50 mm above impermeable (covered paved or concreted areas) that slope away from the building
  • 100 mm above the finished ground level in low rainfall intensity areas ( 5 minute intensity of less than 125mm/hour for a recurrence interval of 20 years -see: Rainfall Intensity to check your site), or sandy well-drained areas
  • 150 mm in any other case.

Distance of 1m

The external finished surface surrounding the slab must be sloped away from the building, for the first 1m by a minimum  of the following:

  • 25 mm in low rainfall intensity areas for surfaces that are reasonably impermeable (such as concrete or clay paving)
  • 50 mm  in any other case.

Normally in clay soils I would allow another 15-20mm to allow for any ‘Soil Heave’. (See:Building on Clay Soils)


To meet the Building Code the range of total heights above ground will vary between 75mm and 200mm depending on circumstances. If you want a smaller step between inside and outside (for reasons such as Better Accessible Design) you will need to talk with your House Designer about a detail which meets the intent of the Building Code (Keeps water out of the house).


Front Path Fail

Looks a bit like a Rustic Type Path . . . . So why do I think this is a Fail?

Well even though I was careful, and wearing safety work boots, I nearly rolled my ankle!

Just imagine a woman trying to walk up the path wearing high heeled shoes!

These are the problems with this idea:

  • Most wood has started rot as it’s completely surrounded with soil.
  • The tops of the timbers are uneven
  • The spacing is uneven
  • The average foot is bigger than the timbers.

Front paths need to be smooth and even to encourage visitors to walk to your door, not an obstacle course.


For more Fails and unusual houses go to What the………….?