Category: Construction

Polished Concrete

So you like the idea of Polished Concrete. . . . but with costs ranging from $55/m2 to $120/m2 there are quite a few things to think about.

Slab Design and Construction

Quality of finish starts with the design and specification of the slab. That includes:

Colour

Although a standard concrete can look good when polished there is also the opportunity to make the following changes:

Aggregate Talk with your specialist subcontractor who should be able to provide a range of different aggregates. (NB some porous aggregates such as sandstone and limestone are unlikely to polish up well)

Cement Paste In addition to the standard light grey a range of concrete colours can be provided with the addition of various oxide based pigments.

Typically if you want either, or both, of these options the slab will be laid with a layer of concrete with your selected finish as a final delivery of the pour, over a standard concrete.

Grind and Seal Finish

Suitable for indoor and outdoor concrete.

In this process the floor is generally ground twice . The floor can then be grouted (see below) followed by 2 coats of sealer to give the concrete a shiny appearance (The sealer will eventually wear and need to be sanded back and re-applied.).

There are typically between around 5 steps in the process.

An advantage of this process is that you are able to make it anti-slip by puting  grit into the sealer. Great for around pools.

Mechanically Polished Concrete (MPC)

This high end process is really only suitable for inside concrete

This concrete polishing process the floor is generally ground twice depending, as above.

It’s then grouted (see below).

A densifier is then applied to harden the floors surface.

Next is up to 7 passes with diamond impregnated resin pads to get the desired shine (the concrete itself shines rather than a sealer which could scratch off).

Finally a penetrating sealer is applied to leave a stain resistant floor that that looks and feeling like glass.

The process has between 10 – 14 steps.

Aggregate Exposure

There are 3 levels of grinding exposing various levels of the aggregate commonly known as:

  • Nil Exposure –(less than 1mm) – Very little/no stone shows on the surface of the concrete (Difficult to achieve unless the concrete has been poured perfectly)
  • Minor/Random Exposure or Salt and Pepper Look (1-2mm) – Small amounts of aggregate visible on the surface – some areas may have minimal exposure while other areas some may have heavy exposure.   – approx 1-2mm from surface.
  • Full exposure (5mm) – this is where you can see all the stones on the surface.

Grouting

Any insitu concrete will have some defects such as small ‘air’ voids or small cracks.

To get the best finish they need to be filled with grout.

With a  natural cement concrete grouting may be carried out with a cement paste in the case of a grind and seal.

If you have a coloured concrete a better grout result is achieved by mixing a latex based product with the concrete dust from the grinding procedure to get a better colour match. This procedure should always be done for mechanically polished concrete.

Summary

There are a lots of options when thinking about ‘Polished Concrete’ so make sure that you understand the options and specify exactly what you want.

 

For more information see Concrete

 

 

 

Soil Heave – Protecting the Slab During Construction

There has been a lot of talk in the Melbourne papers recently about ‘Slab Heave’ when Building on Clay so I thought I would explain how to minimise the risk during construction.

A key issue when building on clay is to avoid any extra moisture getting into the clay under the slab. causing the clay to swell, by keeping the area around the slab well drained.

This is particularly important where part of the slab is below the natural ground level such as when ‘Cut and Fill’ is required to get a level site.

Detail For Protection Against  Soil Heave

The diagram below shows what you should be looking for, during construction, to protect the ground under your slab from gaining moisture.

The key issues are:

  • The excavated surface falls away from the edge of the slab for at least 1m with a minimum drop of 75mm.
  • Where the water will not continue to flow away from the slab an Aggi Drain in a granular back filled trench should be provided. This drain should be a minimum of 100mm below the surface level of the clay and fall to a suitable discharge point.
  • Any trench in the area between the slab and the aggi drain should be topped with well compacted clay to ensure there is no easy passage for water to penetrate under the slab.
  • Roof drainage should be connected to a suitable point of discharge as soon as possible after the roofing material is fixed. (See Temporary Downspout)

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.

 

Also see Agricultural Drains

 

Window Abbreviations

When you are looking at builders plans it can be hard to understand what all the abbreviations mean!

Here are some common window Abbreviations /Acronyms:

AL – Aluminium (also Alum)
AW – Awning Window
CG – Clear Glass
CLR.OPG – Clear Opening
CR – Curtain Rod
DG – Double Glazing
DH – Double Hung
FG – Fixed Glazing
FO – Finished Opening
FR – Frame
FRG – Fire Resistant Glazing
FS – Fire Shutter
GB – Glass Block (also GL BLK or GLB)
GP – Glazed Partition
HSW– Horizontal Sliding Window
IS – Insect Screen
LVR– Louvre
MUL – Mullion
OB – Obscured (e.g Frosted also OG -Obscured Glass)
OPG– Opening (also OW – Opening Window)
PG – Plate Glass
PW – Pivot Window
RS – Roller Shutter
SD – Sliding Door
SGS– Silicone Glazing Sealant
SH – Side Hung
SW – Sliding Window
tr – Transom
UPVC– Unplasticised PVC
VP – Vertical Pivot
VS – Vertical Sliding
WERS– Window Energy Rating System
WF – Wood Frame
WG – Wired Glass
WS – Window Sill (or Cill)
WW – Window Wall

If you have seen an acronym you don’t understand, then let me know, and I will try to give you an answer.

See Jargon for more posts

 

Builders ‘Security’ Fence

These days all the builders provide, at our cost, a 1.8m high ‘Security Fence’ around the site.

When you ask them “Why is it there? “. . .  They say “Its for Occupational Health and Safety and/or to prevent theft. ”

If those are the reasons why do less than 1% have a padlock?

For most of them the highest security level is a piece of wire twisted around a couple of times!

The only positive thing I can say about all this is the lack of security makes it easier for me to access the site in the evening to check whats happened during the day!

 

For more posts about your new home build see Construction

 

Placing Fill

Of so you want to place some fill. . . .perhaps behind a retaining wall to level a garden . . . So what do you need to understand?

Here are some things to consider.

Final Volume – Loose Volume

Most people underestimate the volume of material they need because they measure the volume they have to fill, and then quote that volume in the order.

The problem is that the material for delivery is measured by the loader bucket, or the truck load, which is when the material is loose.

Typically the loose volume will compact down by around 10% so if you are filling a large volume to advise the supplier you may need more than the measured volume and you will advise them you may need to add to your order as the job proceeds.

 Consolidation and/or Compaction

There are two ways of getting to the final volume:

  • Consolidation This is letting the material compact under its own weight. This can work quite well for sand, especially if it is ‘washed in’. For other materials it takes much too long (0ften many years) which means you will be forever topping up and re-levelling the top surface.
  • Compaction This is making extra effort to pack the fill down. Considerations in compaction are:
    • Compact in layers the thinner the layer the better the compaction. (Layers should be no more than 150mm)
    • Even compaction will give better result (Covering the whole area several times with a vibrating plate or roller will give a much better result  than running a bob cat up and down a few times on each layer)

For DIY jobs you can hire a vibrating compactor for around $60/day.

If you are engaging a contractor to do the fill ask people giving you a price how they intend to compact the fill. (The cheapest price will be to place the whole lot, level, and run the machine over it. . . .a recipe for an area that will remain soft and continually sink)
 

If you are planning to build on the filled area you really need to have ‘Controlled Fill‘ professionally placed and tested.

 

 

Fixing Stage Inspections

This is the time when all plasterboard lining (or internal cladding) architraves, skirtings, doors, built in shelves, baths, basins, troughs, sinks, cabinets and cupboards of a home are fitted and fixed in position.

The waterproofing of all wet areas will also have been completed.

The house will still require painting and things like cabinet doors may be missing.

Why Inspect At This Stage

Bringing defects to the attention of the builder at this stage usually means they can be more easily dealt with than at the PCI Stage.

This could mean less delays overall.

Things To Look For

Here are some things you, or your inspector, should be looking at:

  • Doors correctly fitted without sticking and catches and lock operating correctly.
  • Architraves neatly fitted.
  • Window Frames correctly fitted and sealed.
  • Correct glass specification, with safety markings for glass doors
  • Skirting neatly fitted .
  • Correct cabinets fitted with good workmanship.
  • Correct tiles  / splashbacks installed neatly
  • Correct shelves and rails in Wardrobes
  • Ceiling/wall linings and cornices neatly fitted.
  • Electrical switches, light fittings, smoke alarms. and power sockets correctly located.
  • External structures such as pergolas, verandas, decks, and carports constructed with adequate workmanship and the correct materials.
  • Al Fresco / Patio surface finished correctly and draining away from the house
  • Termite protection / Vermin proofing in place.
  • Step heights.
  • Balustrades for balconies and landings securely fixed
  • Anything else that looks wrong!

 

Only Completion Stage to Go!

 

 

Avoiding Splitting Responsibility

I often come across people who want to exclude certain items of the work from a house building contract to save money.

They may want to do the work themselves, use their own tradie (relative or friend) or use a different supplier to install things before or during the build.

Liability for Problems

The main issue of splitting the House contract is that you can finish up with split responsibility,  giving the Builder a  ‘Get Out of Jail Free Card’.

If there is a problem during construction, or defect that is any way related to the service you excluded from the contract then:

  • Who do you chase for remedy; Builder, Supplier, or even accept responsibility yourself?
  • The Builder, and the Supplier, will usually deny all liability blaming the other.
  • Whoever you believe is at fault you will to take it to an appeal, or arbitration,which will take time and money
  • To support your claim you will probably need an independent professional opinion which will add to the cost.
  • There is no guarantee that the finding will be totally in your favour.

Examples of Issues

Here are a few common issues:

  • Delay If your build contract goes over time one of the Builder’s strategies to avoid paying Liquidated Damages is to claims your supplier delayed the works as they were slower than his normal supplier.
  • Theft Stealing is rife on building sites. Even though the Builder lets your supplier on the site there is normally an exclusion of liability for theft.
  • Damage Scratches, dents, marks, breakages, at best the builder may provide compensation at a level related to the cost related to the value of the cheapest standard replacement. (for example a standard GRP bath not your $2000 free standing ceramic bath)
  • Failure To Work Properly This mainly occurs on issues like plumbing or electrical items. Because of a lack of communication the wrong pipe or wiring has been installed, or the locations are incorrect. Again each blames the other and you can be up for an extra cost.
  • Damage Scratches, dents, marks, breakages, at best the builder may provide compensation at a level related to the cost related to the value of the cheapest standard replacement. (for example a standard GRP bath not your $2000 free standing ceramic bath)
  • Future Building Movement I have heard of people doing their own site preparation including cut or fill. In WA I know some people want to install their own drainage work (Soak wells). If you then get any building movement you may find you have given the builder a get out to avoid bills of tens of thousand of dollars.

I hope this helps you understand the issues, and also the risks, of splitting supply and/or work from the main building contract.

Personally I have always let the Builder provide a finished house and installed any extras later.

 

 

 

 

Protect Your Block From Dumping

A regular problem with vacant new house blocks is they are used as a convenient dumping ground for other builders.


It’s much cheaper to dump on a nearby site than haul the material to a tip and pay tip fees.

If you are are really unlucky the material may be contaminated (for example asbestos waste). . . . which may mean you have to pay for testing and additional tip fees to dispose of it.

Fence the Site

The best advice I can give is to make your site seem loved by erecting a fence,  mowing any grass and/or keeping weeds under control.

It doesn’t have to be an expensive fence, something like a 1.2 m high dog mesh supported by steel star pickets at 4-5m intervals will be fine, and should only cost around $5-6/m.

If you have got quite a few posts to put in it can be worth hiring, borrowing , or buying a post driver.

Light fencing like this is not foolproof, but it makes things a little more difficult for the dumper. This means they are more likely to look for a block where nobody seems to be taking an interest.

 

See Guide to Buying a Block for more advice.

 

Retaining Walls – Besser Blocks

If  you want a rendered surface on your retaining wall one of the best ways of achieving this is by using ‘Besser Blocks’.

These are hollow concrete blocks which are designed to incorporate steel reinforcement within the block.

A few  issues when building these walls are:

  • Don’t skimp on the foundation. Even a 600mm high wall will need a concrete foundation 600mm wide by 250mm deep.
  • Make sure that the cement grout is well packed around the steel reinforcement.
  • Buy some of the yellow safety caps you see here to put over  the reinforcement bars and ‘Keep Yourself Safe.
  • Don’t backfill behind the wall for at least a week


As well as free standing retaining walls Besser Blocks are also used as basement walls and to provide structural strength for external walls when building against a slope.

This photograph shows a typical example where the Besser Block wall will provide the external wall of a garage. ( You can also see the builders plastic which will form part of the ‘tanking’ to keep damp from passing through the wall)

 

See Retaining Walls for other  solutions to slopes

How Many Construction Inspections?

Well I do my own inspections, so for my houses they have been at least once week. . . . . but if you are paying $4-500 an inspection for a professional you might want to consider the options below!

Just remember the fewer professional inspections the more you should take an active interest yourself.

Option 1

Five Inspections based on the Standard Progress Payments

  1. Base – Best to inspect before the slab is concreted to check:- The slab is in the right location, plumbing is in the right place, and site is properly drained to avoid the ground becoming waterlogged.
  2. Frame – This is the main structural component of your house. It should be assembled properly and according to the engineering details. The slab can also be checked for problems.
  3. Lock Up – Time to ensure that the outer shell of the house is weatherproof and the brickwork is satisfactory. At this stage check  if pipe work and electrical cabling are in the right places. You may also be able to check if  the insulation is correctly installed.
  4. Fixing – Waterproof membranes in wet areas correctly installed.  Architraves, skirting, doors, baths, basins,  sinks, troughs, wall cabinets, cupboards, bench tops, shelves, properly fixed in correct locations.
  5. Practical Completion (PCI) – The last chance to get mistakes and omissions sorted before Handover.

Option 2

Three Inspections

To save money you could reduce the number of inspections to the following three.

  1. Base – As 1 above.
  2. Pre-Plaster – As the frame is still visible before the plasterboard is installed this becomes a combined Frame, and Lock Up  Inspection.
  3. Practical Completion (PCI) as 5 above. 

Option 3

Some people might only be prepared to pay for one inspection and go for the PCI.

My thoughts would be the Pre-Plaster Inspection would be the one to choose.

This is a chance to pick up any serious structural issues before they are covered up.

The PCI Inspection really is more about picking up finishing quality issues than structural issues.

 

See the PCI Guide for advice and extensive checklists….only $4

 

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