All of our 34 plants around the world are operating and we are satisfying all of our customer needs.
Overall, our sales were down 27% from the second quarter last year on a pro forma basis and down 24% from the first quarter.
I think it is helpful to understand where the 24% decline in sales from the first quarter came from and I'll first do this on a geographic basis.
The Americas declined 35%, EMEA declined 23% and Asia-Pacific declined 4%.
Asia-Pacific declined 4%, with most of declines in India and Southeast Asia.
April was the lowest month of the quarter and May was only a little better as we saw a 1% sequential monthly increase in net sales.
In June, we did see a much more significant improvement as net sales increased 20% from May's levels.
Metalworking declined the most and decreased 30% sequentially from the first quarter, due primarily to automotive OEM and related suppliers having prolonged shutdowns or significantly reduced production in the quarter.
Our other customer industry groups of metals and global specialty businesses were less impacted and showed declines of 21% and 16%, respectively.
I hope these different cuts of our 24% sequential sales decline help provide insight into what was happening in the quarter.
As our analysis continues to show, we had total organic sales growth due to net share gains of 2% in the second quarter of '20 versus the second quarter of '19.
What may not be apparent is that our product margins actually increased approximately 2% from last year with our raw material synergies being the vast majority of the increase.
This pandemic and its impacts has been similar in many ways to what we went through in late 2008.
We stopped new hires, executive pay cuts were implemented, some positions were furloughed, and our planned capital expenditures have been cut by over 30%.
For 2020, our current estimate is $53 million of cost synergies achieved versus our earlier estimate of $35 million.
In this quarter, we achieved $12 million of synergies and we expect sequential improvement during our future quarters.
Also, while our EBITDA was nearly cut in half from the first quarter, we still generated good cash flow and have less net debt now by $13 million.
Last quarter, we said that we expect our full-year adjusted EBITDA to be more than $200 million.
So please see slides 6 through 8 now while I review some highlights.
So, while our actual sales are up significantly to $286 million in Q2 compared to $206 million in the prior year, this is due to the inclusion of Houghton and Norman Hay.
On a pro forma basis, including Houghton in Q2 of last year, net sales declined about 27%.
But we also saw a negative foreign exchange impact on the top line of about 4%, due primarily to the significant weakening of the Brazilian real, the Mexican peso and the RMB versus the dollar.
Our gross margin of 34% for Q2 was down from 36.5% in the prior year quarter, which we attribute primarily to the steep decline in volumes and the related impact on fixed manufacturing costs.
As Mike mentioned, we realized meaningful procurement synergies in the quarter and our product margins were up approximately 2%, which was masked by the impact of fixed manufacturing costs on our significantly lower volumes.
The drag from COVID is also evident in our non-GAAP operating income of $11.2 million compared to $25.5 million in Q2 of '19 and $36 million in Q1 of 2020.
Similarly, our non-GAAP earnings per share of $0.21 was down from $1.56 in Q2 of last year and $1.35 sequentially.
Our effective tax rate in the current quarter was 57.9% compared to 24.2% in Q2 of last year.
Excluding all unusual items, we expect our effective tax rate for the full year 2020 will be in the range of 22% to 25%.
As Mike mentioned earlier, our Q2 adjusted EBITDA $32.1 million is in line with our guidance at roughly half of our Q1 adjusted EBITDA of $60.5 million.
And we continue to expect our full-year adjusted EBITDA will be more than $200 million.
With the decline in adjusted EBITDA, our net leverage has picked up about 0.2 times to 3.7 times on a reported basis and 3.1 times on a bank calculated basis, which is still comfortably below our bank covenant of 4.25 times.
In addition, we're benefiting from the current low interest rate environment as the average interest rate on our debt is now about 1.9% as compared to 2.4% at March 31.
We're pleased to report that our operating cash flow doubled year-to-date to $44.7 million versus first half of last year of $22.4 million.
In addition, our Q2 operating cash flow of $24.5 million exceeded the prior quarter of $20.2 million.
We saw this in the 2008-2009 crisis, and we are seeing it now.
In addition, our low capital intensity allows us flexibility in our capex spending and we're on pace to reduce capex by about 30% from our initial combined company estimates as we mentioned last quarter.
But we're encouraged by some positive trends in business performance and the increase in cash flow I just mentioned, as well as the $12 million of cost synergies realized this quarter.
In addition, the increase in total synergies we expect to realize this year, which is up from $35 million to $53 million and the disciplined cost reduction actions we've taken will help mitigate the impact this difficult economic and business environment.

Summary:
Last quarter, we said that we expect our full-year adjusted EBITDA to be more than $200 million.
So, while our actual sales are up significantly to $286 million in Q2 compared to $206 million in the prior year, this is due to the inclusion of Houghton and Norman Hay.
Similarly, our non-GAAP earnings per share of $0.21 was down from $1.56 in Q2 of last year and $1.35 sequentially.
And we continue to expect our full-year adjusted EBITDA will be more than $200 million.