Liquid screed V sand and cement

badgerhowlin

Hi,

I am putting in underfloor heating.

Can someone tell me which would be better and why they think so
Liquid screed OR sand and cement

Also ground floor 70-75mm of screed.
1st floor 50mm

anyone know the drying times for this?

Thanks

mark2003

If your heat source is an oil boiler,you should go with liquid screed.If its a heat pump, go with concrete floor. The liquid screed releases the heat quicker than concrete,so when you come in after work and turn on the heat you will get a response within 30mins,with the concrete,it could be two hours. 50mm of the liquid screed is more than plenty. I would go 100mm if using concrete.

badgerhowlin

Thanks mark2003.

Its geothermal heat pump im going with.

So it look like concrete i'll be going with then.

The only concern i have with the concrete is that it has a habit of cracking when its heated up. I know of 2 floors that this has happened to. maybe its because of strength of Concrete, im not sure

sydthebeat

mark2003 wrote: »

If your heat source is an oil boiler,you should go with liquid screed.If its a heat pump, go with concrete floor. The liquid screed releases the heat quicker than concrete,so when you come in after work and turn on the heat you will get a response within 30mins,with the concrete,it could be two hours. 50mm of the liquid screed is more than plenty. I would go 100mm if using concrete.

this is not entirely correct.

the whole principle of underfloor heating is that you do not have 'heating up, cooling down' periods in your normal day. The UFH works best when keeping the dweling at a constant temperature.

if you have an UFH system that has the house comfy at 9.00 am but when you come home at 5.00 pm the house is cold, then you have inadequate insulation and / or bad airtightness and / or indequate heating controls.

UFH simply does not suit oil heating. Oil heats the liquid in your system to approx 70 degrees.... under floor heating runs at usually 50 degrees, so some sysetms are designed to mix the return water with the outflow to cool it down before it enters the UFH... doesnt make sense does it.

mark2003

badgerhowlin wrote: »

Thanks mark2003.

Its geothermal heat pump im going with.

So it look like concrete i'll be going with then.

The only concern i have with the concrete is that it has a habit of cracking when its heated up. I know of 2 floors that this has happened to. maybe its because of strength of Concrete, im not sure

You will get a few cracks in the concrete at first,that is why you need to turn on the heat for two weeks before you start putting down your different types of floors. We just sealed any cracks and no problems since.Badgerhowlin, How much floor insulation are you putting down

mark2003

sydthebeat wrote: »

this is not entirely correct.

the whole principle of underfloor heating is that you do not have 'heating up, cooling down' periods in your normal day. The UFH works best when keeping the dweling at a constant temperature.

if you have an UFH system that has the house comfy at 9.00 am but when you come home at 5.00 pm the house is cold, then you have inadequate insulation and / or bad airtightness and / or indequate heating controls.

UFH simply does not suit oil heating. Oil heats the liquid in your system to approx 70 degrees.... under floor heating runs at usually 50 degrees, so some sysetms are designed to mix the return water with the outflow to cool it down before it enters the UFH... doesnt make sense does it.

What floor would you put down with geothermal heating.

badgerhowlin

mark2003 wrote: »

You will get a few cracks in the concrete at first,that is why you need to turn on the heat for two weeks before you start putting down your different types of floors. We just sealed any cracks and no problems since.Badgerhowlin, How much floor insulation are you putting down

Putting down 100mm on ground floor. nothing on the 1st floor. bit of acoustics insulation in the joists

mark2003

badgerhowlin wrote: »

Putting down 100mm on ground floor. nothing on the 1st floor. bit of acoustics insulation in the joists

You should put down 120mm at the least for under heating(2 60mm boards over lapping each other).Did you get a BER assessor to calculate your u-values on materials your using

sydthebeat

mark2003 wrote: »

What floor would you put down with geothermal heating.

its not a significant factor in my opinion.... either 75mm concrete or easi screed will dissipate the heat into the room as frequently as its required. its like choosing a slimline convector storage heater, or an old wide one.

the specific requirement for a slim screed comes from external influences IMHO. For example an easi screed type product can be used without too much difficulty on a timber first floor. Also, if there are height restrictions a narrower screed is preferred.


IMHO if i was spending that amount of money on a geothermal system i would absolutely ensure:-

1. i am installing a MHRV system !!! a must!!

2. i achieve an air tightness result of 5 or less preferred (this equates to a 0.25 air changes per hour, compared to on average 4 air changes per hour for a 'hole in the wall' vent.

3. my construction is as free from thermal bridges as is budget-ily possible.