The latest construction figures show a slight bump in the economy in the September quarter that could see a slightly lower than expected GDP growth when the latest figures are released next month. But while there is some slowing of construction, what the figures highlight is how important the public sector has been over the past two years in keeping the economy growing.

One of my favourite paradoxes in regard to conservative politicians is their strongly held belief that the private sector, not the public sector, creates jobs; and yet, whenever there is the announcement of some new public infrastructure project, they will clamour over themselves in high-vis vests to proclaim how many jobs it will create.

The reality is that while the private sector certainly does employ more people than does the public sector, the dollars that are delivered to the private sector from governments certainly account for a significant share of that work.

Nowhere is this more apparent than in the construction industry. Less than 1% of those employed in the construction industry are public-sector employees but around a third of all engineering construction work done by the private sector is for public-sector works.

Engineering construction work done is perhaps one of the best ways to highlight the impact of the mining boom – the start, beginning and its end:

Prior to the mining boom, engineering construction used to account for around a third of all construction work – but during the boom it reached 60%. In the past two years, however, the amount of engineering construction has fallen off a cliff – from a peak of $36.7bn in the September quarter of 2012 to $20.5bn in the final quarter of 2016.

That’s an 80% fall, which even the strong pick-up in building construction was not able to counter.

And yet, while there had been a nice improvement in engineering contraction through 2017 and the first half of this year, the latest figures show once again it is going backwards, and the overall level of construction work in the September quarter was flat:

While the annual growth figures remain positive – up 5.6% over the past year in trend terms, even here we see a slight slowing:

And while housing prices are slowing – even falling – the backlog of approvals means that there remains a strong amount of building work to be done in that sector.

In the residential building sector we very much see how greatly the housing boom has been a New South Wales and Victoria-centric boom.

Prior to the start of the rate cuts at the end 2010, the value of NSW and Victorian new residential construction was roughly the same as for the rest of the states but now it is worth more than double:

And, in NSW and Victoria, the growth in new residential building is more than making up for the declines elsewhere:

But while the housing market has done very well out of the low interest rates, the private sector non-residential side of things is less impressive.

After some improvement the value of private-sector engineering construction is going backwards but the public sector infrastructure work continues to grow:

Indeed you could say that the public sector has filled the gap created by the drop in the private sector quite nicely. In an almost in a perfect Keynesian style, the public sector has stepped up to the plate as the private sector shrank.

It’s one of those wonderful thing about conservative governments – they profess to hate government stimulus spending and yet we see here how well it works, and how greatly the government welcomes its results.

The construction sector accounts for around 9% of all employment and yet, since the end of 2015, 20% of the growth in employment has come from that industry. Yes, the housing boom has played a role, but take away the strong increase in government funded infrastructure and you would see a lot fewer jobs.

The period since 2015 has seen public construction contribute much more to growth than the private sector:

But the worry is that this public infrastructure spending is now starting to taper off. And while the housing sector does have more work coming down the pipeline, it too will likely taper off as the drop in housing finance flows through into construction work.

For now things have been good – employment has grown well and the high iron ore prices have helped the exports flow well and the government’s budget figures look quite rosy. The public infrastructure spending and the housing boom has helped the economy cope with the end of the mining boom but the weakness is still there.

One benefit from a coming election is that there is likely to be a continuation of infrastructure project spending. But if the private-sector construction sector continues to falter (and iron ore prices continue to fall as they have recently) it will become harder and harder to disguise the weakness.

• Greg Jericho is a Guardian Australia columnist