Advice required for tiling conservatory floor

[MdeB]

I will be tiling the floor of a conservatory and need some advice on how to proceed.

 

• The conservatory is new-build with a cement-based screed.
• No underfloor heating.
• Size 5.8 by 3.8 metres
• 600 x 300 porcelain tiles; 0.9mm thick.
• Flexible adhesive will be used.

 

I would appreciate guidance on the following:

1. Does this size and environment need an expansion joint?
2. Is this environment suitable for tiling direct to the screed, or do I need decoupling mat?
   (I have received conflicting advice from tile shops: one saying mat is required, the other saying it is not required).
3. How long do I need to allow the screed to dry before tiling?
4. Should I use a 10mm half-round notched trowel for this, or would another profile do a better job?
5. I have been advised to leave a 5mm gap between tiles and walls, with silicone across doorways (where there will be no skirting board).
   Does this sound reasonable?
6. Anything else that your experience suggests I should consider/do (and my lack of experience means I haven't thought of)?

 

The screed has not yet been laid, and the builder says depth can be set so that the tiled surface will end up level with the carpeted surface in the next room (so I need to know what I will be putting under the tiles ?).

[joe90]

I tiled my conservatory 10m x 2.6m with 300mm x 300mm x 9mm porcelain tiles. Flexi adhesive, no decoupling mat, back butter the tiles, no expansion gap (but 10mm gap around the outside covered by skirting). And flexi silicone at doorways (just remembered I for got to do that, note to self!!,)

[Temp]

Cement screed is good as there can be issues with anhydrate screed.. https://www.bal-adhesives.com/tiling-onto-calcium-sulfate-anhydrite-screeds/

 

1. I don't believe you need an expansion joint at that size (unless tiling through from one room into another).

2. We have stone direct onto cement screed using flexible adhesive. I have seen decoupling membrane recommended for large format tiles as screed can sometimes shrink and damage them. Only issue i can think of is that perhaps the sun might cause rapid temperature changes in a conservatory?

3. Recommendations vary. Typically one day per mm thickness. Some places say one day per mm upto 40mm then two days per mm for the rest. Eg 60mm would be (1*40) + (2×20) = 80 days. Some places say a lot sooner. Have seen people suggest use a decoupling membrane to allow them to cheat a bit on the drying time.

4. 10mm rounded is ok. Should leave a 3-4mm thick adhesive layer when tiles fully bedded. Make sure there is enough adhesive under the corners of tiles.

5. Normally perimeter insulation is fitted before screening to reduce heat loss and prevent any expansion of the screed damaging walls. This is typically a blue roll 8-12mm thick. The exposed top is trimmed back after the screed has dried and covered with skirting after tiling. So yes leave a 5-8mm gap around tiles  for same reasons.

6. Seal grout after fully dry to make cleaning easier. Consider dark coloured grout? Aside: Alkaline cleaners seem to work best for cleaning dirty grout.

 

I'm not a professional tiler. Opinions vary on all this!

[nod]

As Joe has already pointed out 

A clear expansion joint around the perimeter is so important On a floor that size there’s no need for cross expansion joints 

No need for Matt on a new screed 

You should normally allow a day per millimeter Not always practical I would still allow a month 

The thickness of your tile dictates the notch on your float Ie 10 mil tile 10 mil adhesive 

 

 

[MdeB]

Tanks Joe, Nod, Temp.

 

10 hours ago, Temp said:

Cement screed is good as there can be issues with anhydrate screed.. https://www.bal-adhesives.com/tiling-onto-calcium-sulfate-anhydrite-screeds/

I've had fun with anhydrite in the past, when my son got me to tile part of his extension: sanding and sealing.

 

 

10 hours ago, Temp said:

2.  Only issue i can think of is that perhaps the sun might cause rapid temperature changes in a conservatory?

That was a worry of mine.

• almost white tiles.
• West side of house, so no sun until after noon.
• (supposedly) heat-reflecting glass in roof and walls

so probably not a problem???

 

10 hours ago, Temp said:

3. Recommendations vary. Typically one day per mm thickness. Some places say one day per mm upto 40mm then two days per mm for the rest.

I knew those times for anhydrite.  I had an inkling (hope) that cement screed dried more quickly.

 

 

10 hours ago, Temp said:

4. 10mm rounded is ok. Should leave a 3-4mm thick adhesive layer when tiles fully bedded. Make sure there is enough adhesive under the corners of tiles.

I've used that trowel for previous jobs, but I wondered of a square-notched trowel might make it easier to compress the adhesive to attain a solid bed.

 

 

10 hours ago, Temp said:

5. Normally perimeter insulation is fitted before screening to reduce heat loss and prevent any expansion of the screed damaging walls. This is typically a blue roll 8-12mm thick. The exposed top is trimmed back after the screed has dried and covered with skirting after tiling. So yes leave a 5-8mm gap around tiles  for same reasons.

Interesting.

I shall look out for this to see if my builder is doing it properly.

 

10 hours ago, Temp said:

6. Seal grout after fully dry to make cleaning easier. Consider dark coloured grout?

Thanks for reminding me to seal the grout.

 

Grout not yet chosen, but definitely not white to go with the almost white tiles (that is probably the only input I will get on the colour ?).

 

 

One more thing, is a cement screed likely to need sanding before tiling?

Edited July 2, 2021 by MdeB

[Temp]

7 minutes ago, MdeB said:

I've used that trowel for previous jobs, but I wondered of a square-notched trowel might make it easier to compress the adhesive to attain a solid 

 

Here you go..

 

https://www.rubi.com/en/blog/how-to-choose-the-right-tile-trowel-size-step-by-step/

 

Since a 10mm U-notched trowel and a 6mm square-notched trowel will both leave a 3mm layer of adhesive mortar beneath an installed tile, why choose one over the other?

The difference in trowel notch shapes determines how easily the tile becomes fully embedded in the bed of adhesive. In basic terms it is easier to wiggle a tile into a bed of adhesive put down with a u-notched than with a square-notched. You collapse rounded ridges rather than square ridges. 

The square ridges, put down with a square-notched trowel, tend to collapse over on each side when you embed the tile into the bed. Pushing the tile down into the bed of square ridges causes the ridges to fold over from the top of the ridge, then spread out.

A U-shaped ridge, on the other hand, spreads OUT when embedding a tile into the bed. Pushing a tile into the bed of rounded ridges causes the ridge of adhesive to spread out, from the bottom, with less possibility of trapping air.

 

[Gus Potter]

12 hours ago, MdeB said:

I will be tiling the floor of a conservatory and need some advice on how to proceed.

 

 

Hi MdeB

 

I think you're taking a risk. As new build the substrate, founds, what is under the slab ect will still be settling in, adjusting to the ambient moisture regime and possible curing if you have masonry. There will be quite a lot going on under the screed and the supporting structure that you can't predict.

 

The aspect ratio of the screed looks borderline. For a simple concrete ground bearing slab in an extension we consider amongst other things the aspect ratio. Here you have 5.8 / 2.8 = 2.07.. for unreinforced concrete slabs in say an extension once the aspect ratio goes over 2 then it is a flag. For a thin screed.. potential trouble. for slabs we often locate saw joints to control the location of the cracking.

 

I would screed it, saw cut it into three sections 5.8 /3 = 1.93m x 2.8m as soon as it has hardened enough (24 hours) and leave it for as long as you can. Keep the screed covered and wet for at least 7days (preferrably a month!) so it cures, then slowly dry it out. It's a conservatory.. it could be pretty hot.. misstreat the scread and it will return the favour later! Even at these saw cut panel sizes you may still get some hairline cracking unless you are using a screed with polymer / steel fibres in it.

 

Be safe and use a decoupling mat. You don't have to saw it all the way through. If the screed is 60mm thick then saw it to a depth of 40mm. You promote the cracking here as you have weakend the screed. What your are doing is allowing it to crack where you want it to and trying as best you can to limit the size and orientation of each crack.  It's important to put a sheet of plastic under the screed so it can slip over the substructure easily as it cures.

 

Get the screed right and the laying of the tiles should be the worry free part.

 

All the best.

[joe90]

9 hours ago, MdeB said:

One more thing, is a cement screed likely to need sanding before tiling?

I didn’t with mine but sealed the concrete with two coats of sealer, one left to dry, the second still tacky when tiling. my tiles are black to absorb heat into the floor to keep the conservatory warm during the evening/night. (Works very well), no cracking or settling at all ?

[MdeB]

Thanks guys.

I shall take your comments on board

[MdeB]

All done now.

I used Durabase matting and a 10mm half-round trowel (and a tile-leveling system).