ᐅ Cement screed heating report with Estrifix additive from PCI

Hello everyone,

Last week, we installed screed over an underfloor heating system with 15cm (6 inches) pipe spacing in our future kitchen. We carried out the work ourselves and want to finish the kitchen as soon as possible. The screed thickness is 6.5cm (2.5 inches), and in addition to a retardant, PCI Estrifix was mixed into the cement screed. The material was delivered by a building materials supplier and used immediately.

Usually, the screed installer provides a protocol for this, and the heating engineer sets the temperature. Since we are doing it ourselves, this step is not done, so I would like to know the best way to start heating the screed.

Typically, heating begins only after 21 days at 25°C (77°F) and is then gradually increased up to the maximum temperature.

How much time can I save by starting the heating early, and is it necessary at all?

I have also considered simply running the heating at 25°C (77°F) while using a construction dehumidifier to dry the room. Is that possible?

Best regards,
nils123

nils123 schrieb:
Normally, the screed installer provides this report, and the heating technician sets the temperature.
In our case, this doesn’t apply due to doing the work ourselves, so I’d like to know the best way to warm up the screed?

You can get a heating-up protocol from PCi.

1. Functional Heating
This tests the functionality of both the screed and the underfloor heating system (function check, stress relief in the screed, avoiding cracks in the screed later on). Basically as you described, but with a maximum temperature. There is some debate on what the maximum temperature should be (many screed installers allow heating up to 50°C (122°F) during new construction, even if the heat pump only requires about 32°C (90°F) in the coldest winter…).
This is an absolutely essential step that should not be skipped.
2. Drying Heating
This allows the screed to dry out slowly and thoroughly.

nils123 schrieb:
How much time do I save by preheating, and do I even have to do it?

You’ve already learned that there is no simple “preheating.” And yes, it’s mandatory!

nils123 schrieb:
I was thinking of just running the heating at 25°C (77°F) while a dehumidifier dries the room.
Is that okay?

No. You can do it, but don’t be surprised if your floor covering cracks next winter.

Use a classic heating protocol and follow it. You can add a dehumidifier later if needed (during the drying heating phase).

Look forward to getting your new kitchen installed in six weeks. What kind of house is it? What heating system and temperatures are used? Why a 15cm (6 inches) pipe spacing – that is unusually wide and generally inefficient, as it requires higher temperatures. Has someone designed and calculated the whole system?

Hello Nordanney,

Thank you for your reply, I will check PCI right away. Also, many thanks for the explanation regarding the functional and drying heating phases.

I gave the wrong spacing for the installation earlier. According to the grid on the insulation roll, it is about 10-12cm (4-5 inches). The kitchen is approximately 20m² (215 sq ft) in size and has two heating circuits, each about 75m (246 ft) long. The underfloor heating covers the entire room, including beneath the future kitchen cabinets. I researched the pipe spacing myself and also double-checked with the plumber. Currently, there is a gas boiler installed, but it will be replaced by a heat pump in about 5-8 years due to aging.

In your opinion, is the pipe spacing way off? I’m not planning to change anything now, but it seemed fine to me.

nils123 schrieb:
Do you think the pipe spacing is very wrong in your opinion?

10-12cm (5 inches) spacing is okay. You just need to consider that the heating water has to be warmer the larger the spacing is. This means your heating costs will be higher. Ideally, you would have had an external engineering office calculate the spacing for around 250€ (room-by-room heating load calculation + underfloor heating design based on a heat pump target). With gas, this is less critical. It will still warm up with the heat pump, but with somewhat higher heating costs. So look forward to the underfloor heating and don’t take my comment too personally. But please make sure to warm it up properly ;-)

Just for comparison (I renovated my house, also upgrading it to roughly KfW 55 standard): my "fireplace room" is also 20sqm (215 sqft). Because of the room geometry with three exterior walls, two of which are mostly glass, and no floor above, I have 360m (1,180 ft) of pipe at 5cm (2 inches) spacing in there. This results in extremely low heating costs, and the heat pump never exceeds a supply temperature of 30 degrees Celsius (86°F).

Hello Nordanney,

enough time has passed now to start the heating process. Unfortunately, neither the screed supplier nor PCI was able to provide me with a protocol.
Can I simply use a standard protocol for cement screeds?

General procedure:
- heat up to 25°C (77°F) and maintain for three days
- then increase by 5°C (9°F) daily until reaching a maximum of 55°C (131°F)
- maintain 55°C (131°F) for 4 days
- reduce temperature by 10°C (18°F) daily until reaching 25°C (77°F)
- keep temperature until the surface is ready for covering

This is based on a form I found on Google from Holthaus Screed and Flooring.

Would you do anything differently?

Best regards
Nils