Porcelain tiling over a liquid screed floor

[Steveb21]

Liquid screed was poured nearly 12 months back.

Floor has wet UFH installed.

Floor is level.

Questions;

Will I need to apply a primer as floor is porous in current state.
i have read that liquid screed floors need to be sanded, however i have been working in the room for past 12 months so there has been heavy foot traffic. I was planning to give it a a good sweep and clean to get rid of the dust.

UFH has been off for 10 months. Would it be advisable to turn on again before installation of tiles? Turn on, get up to heat, turn off and then leave for a few days before tiling.

Any recommendations on specific adhesives and spacers to use?

Many thanks.

 

[robinbanks]

Think you're probably good to go as-is. I have a conservatory with an anhydrous screed floor. It was laid for about 9 months before I was ready to tile so I was well satisfied about it being dry enough etc. Booked the tiler and literally the day before they were due to start a biblical proportion thunderstorm and a blocked valley gutter meant I ended up with over a thousand litres of water (yea, I was sad enough to measure the depth so I could work it out before I started sweeping it out the door) sat on the conservatory screed. I pushed the tiler back two weeks and put the UFH on, got it suitably dry with the cling film test and tiled it; it's been fine since - 8 years no delam etc

Just normal mapei rapid set adhesive, no primer, impervious tile. I like a thin grout line so I had 3mm but the size of tiles you choose and the laying pattern may dictate the spacer - if your tiles are say 597x397 (sold as 600x300) and you're laying them like ||=||=||= you have to use a 3mm spacer otherwise the maths doesn't line up (a standing up tile is 597+5 = 602, two lying down tiles is 297+5+297+5 = 604)

 

[Steveb21]

Hi Robin

Interesting. No primer, straight on to the floor as it is? The floor feels a bit sandy/dusty. Would the adhesive stick?

Tiles are 1200x600
Room area is approx 50m2

What size trowel would you suggest?

 

[serapool]

It's great that you're taking careful steps in preparing your liquid screed floor for tiling, especially with underfloor heating (UFH) installed.

1. Primer Application on Liquid Screed: Yes, applying a primer is advisable. Liquid screed is typically porous and a primer helps in creating a better bond between the screed and the tile adhesive. It also helps in sealing the surface, reducing porosity, and ensuring an even suction, which is crucial for a good tile adhesion.
2. Sanding Liquid Screed: Even with heavy foot traffic, liquid screed floors usually require sanding to remove the laitance layer formed on the surface. This layer can prevent proper adhesion of tiles. After sanding, a thorough sweep and clean to remove dust and debris is essential.
3. Underfloor Heating Consideration: Turning on the UFH before tiling is a good practice. It helps in drying out any residual moisture in the screed. Gradually heat the floor to its operational temperature, maintain it for a few days, and then turn it off at least 48 hours before tiling. This process also helps in identifying any potential issues with the heating system before you lay the tiles.
4. Adhesives and Spacers for Tiling: For adhesive, use a flexible tile adhesive, which is suitable for floors with underfloor heating. This type of adhesive can accommodate the expansion and contraction caused by temperature changes, reducing the risk of tiles cracking. When it comes to spacers, the choice depends on the size of your tiles and the desired grout width. A typical choice is between 2mm and 5mm, but this can vary based on your aesthetic preference and tile size.

Remember to always follow the manufacturer's instructions for each product you use and consider consulting a professional for specific advice tailored to your situation.

Good luck with your tiling project!