Theresa May told the Commons it was a 100% failure rate, as all of the samples submitted so far since the Grenfell Tower fire had failed.
She urged local authorities and housing associations to "get on with the fire safety checks".
At least 79 people are feared to have been killed in the blaze on 14 June.
Meanwhile, regulator NHS Improvement said it has written to all NHS trusts and foundation trusts  to ask them to carry out urgent fire safety checks.
There are 36 organisations that need additional support to find out if they have cladding similar to Grenfell, it said, and fire safety tests on building material is expected to be completed "by early next week".
Mrs May told MPs that she expects to name a judge to head the public inquiry into the disaster soon.
She said 282 temporary properties had been identified for residents of the tower, 132 families have had their needs assessed and there have been 65 offers of temporary accommodation.
The government has made almost Â£1.25m of discretionary payments and will be giving an extra Â£1m to a local group of charities, trusts and foundations, Mrs May said.
Labour leader Jeremy Corbyn said the tragedy had "exposed the disastrous effect of austerity" and said: "Fewer inspectors, fewer building control inspectors, fewer planning inspectors - we all pay a price."
The blaze, which started in a fridge-freezer, destroyed 151 homes in the north Kensington block and in the surrounding area of the London Borough of Kensington and Chelsea.
Questions were raised about the cladding used on Grenfell in the immediate aftermath of the disaster and a nation-wide operation has taken place to identify and test buildings with similar cladding.
It has emerged that London Fire Brigade issued a warning to all 33 London councils about panels attached to the exterior of buildings in May this year, in a letter seen by the BBC.
On Tuesday, Mrs May said there should be a "major national investigation" into the use of cladding on high-rise towers.
Cladding from 120 high-rise buildings in 37 local authority areas in England has now failed fire safety tests, the prime minister has said.