The team finished the session with Lance Stroll in 18th and Fernando Alonso in 20th, but neither driver got in representative laps on soft tyres after a scrappy session.
Once again Stroll’s running was compromised by an issue outside his control as he lost time in the garage with a stuck left-front wheel.
It required some extensive hammering from a mechanic before it could be removed and he could continue. Alonso meanwhile made a mistake and had a spectacular spin early in the session.
More: What we learned from Friday F1 practice at the Mexico GP
Like others, when the Aston drivers went out at the end for a soft run, they were caught out by light rain that compromised lap times.
“Basically we had the normal start of the session,” Krack told Sky Sports F1. “Then we didn't manage with soft tyres to put the lap together. Fernando spun in Turn 8.
“We had an issue to remove the front-left tyre from Lance's car. Then we were not ready when the sky opened. We were on track with the new softs, and unfortunately, we could not set a lap.”
Aston is running its new package on both cars in Mexico, having split the drivers for the Austin race. Krack conceded that it’s not an easy track at which to optimise the revised car.
“Coming to Mexico with the altitude is always something that you have to get used to,” he said. “You have a lot less downforce, less than Monza, despite the big wings. So that's something that all the drivers need to get used to. Also it's very, very smooth surface here.
“We have the softest tyres, and it's something you have to get used to. But it's the same for everybody. At the end of the day, we continue to learn about our upgrades.
"We did some experiments this morning, and also this afternoon and it was actually quite encouraging. Obviously, when you are finishing on the board like this, nobody's happy. But it is not a true reflection.”
Despite his position at the bottom of the order, Alonso remained upbeat.
"It was good,” said the Spaniard. “We focused a lot on race pace today and high fuel running and things like that, so difficult to read the times. But the car felt good, and we’re understanding more about the package.”
