However, the main Irish hub in Dublin is expected to remain open, as are airports in Cork in the southwest and Waterford in the southeast.
Obstacle to flights
Eurocontrol, the continent's air traffic control co-ordinator, said the ash accumulation has posed an obstacle because the cloud is gradually climbing to 10,500 metres and into the typical cruising altitude of trans-Atlantic aircraft.
It said it plans to reroute flights between Europe and North America to avoid flying over Ireland's west coast.
The closure on Friday marked the third time this week that authorities ordered flights grounded in Ireland.
Ireland had reopened its airspace on Thursday after much of the same ash was blown southwest over Scotland, Ireland and Northern Ireland on Tuesday and Wednesday, closing airports along the way.
The closures triggered the cancellation of hundreds of flights in and out of Ireland and Northern Ireland, bringing fresh chaos to thousands of people.
Those were the first European air closures since the initial crisis last month, when ash from Eyjafjallajokul forced flight cancellations for about 10 million passengers and closed European airspace for up to a week.
The airspace was reopened after emergency talks between European governments, airlines and regulators.
The international airline industry body, IATA, said last month's shutdown had cost airlines about $1.7bn and it has called on governments to pick up at least part of the cost.
Eurocontrol estimates that more than 100,000 flights to, from and within Europe had been cancelled between April 15 and 21 due to the ash.
Iceland's volcano, which is about 1,500km northwest of Ireland, has shown no signs of stopping since it began erupting on April 13.