is 75mm screed enough for floor tiles with underfloor heating.

[macken]

hi everyone.

i need help to decide whether to do this job or walk away.

customer has 150m2 of floor with underfloor heating.(water)

it has 150mm of insulation and a sand and cement screed of 75mm.

screed already has hairline cracks and the heating has not been turned on yet.

customer is prepared to pay for dittra matting.

60 x 60 porc will be the tiles if tiled.

im not happy with screed, feels like its bouncing on all that insulation.

thanks.

 

[DHTiling]

That thickness meets the requirement for piped heating..

Cracks are common in cement based screeds as they cure and curl... there will probs be a few more hairline ones once the heating is turned on.

 

[Ajax123]

Minimum depth of sand cement screed floating to meet british standard is 65mm in domestics. Insulation plays a bigpart in flexural strength though. The screed must be reinforced with pp fibres or d49steel mesh. If the insualtion is too spongy at 150 mm it will feel like a cushion floor. If it feels spongy jump on it in a corner of the room and get someone to watch it and see if moves. If it does it will need to be sorted as the level of deflection could cause it and any floor coverings to fail. At 150mm insulation i would look to specify a minimum of eps 100 polystyrene. The norm for domestics is eps 70. At 150 mm this will feel spongy.

 

[macken]

thanks ajax,

i would have been happy if there was mesh put in but they didnt do that.

im sorry but i have no idea what eps 100 polystyrene.😳

i know you are screed advisor, but as a diy tiler would you tile the floor or walk away.

thanks again.

 

[Ajax123]

Eps100 is the modern term for high density polystyrene. The important thing is whether the floor physically moves. Try the "jump" test. If it moves walk away. Meh or fibres is a requirement for floating s c screeds

 

[macten]

Screed bloke I was talking to last week told me the new minimum was 120mm - don't know if thats true though

 

[Ajax123]

Screed bloke I was talking to last week told me the new minimum was 120mm - don't know if thats true though

No it isnt true. The minimm depths are set by bs8204 part 1 which was published in 2001 and has not been reviewed since. It will be up for review i think next year or the year after.