Porcelain 450x450 tiles on floor... Is this OK?

[Gooner]

I searched the forum and found a very similar thread, but different enough to make me post the question. Basically I want to get some opinions on if I am doing the right thing here.

I am will be tiling my small ensuite floor soon (1.5 x 2m). I have 450x450 porcelain tiles around 9mm thick. The floor is T&G hardwood (110mm wide) laid about 30 years ago over 600mm center joists. The boards are 19mm (3/4") thick. I have placed 6mm compressed fibre cement tile underlay nailed every 150mm. On top of all this I will be placing around 2-5mm of latex based (Ardex Arditex) self leveling compound to correct the small unevenness in the floor and ensure I have a totally flat floor.

Then comes the 450x450 porcelain tiles that I will lay using a 10mm notched trowel using Ardex X77 tile adhesive.

The floor feels quite rigid. Certainly no noticable flex when I bounce my 85kg weight around. (I have very good under-floor access and so I am considering adding extra joists just to be double sure.. but I have a feeling this may be overkill?)

Does this sound OK? I've spent ALOT of time and money in this renovation and it would be soul destroying to see the tiles crack after some time.

Thanks guys. Great Forum.

[grumpygrouter]

Hi Gooner, the real issue you must address is, as you say, the solidness of the floor. As your joists are 600mm centres this is quite a bit of a space between them. As you weigh in around 85kg, your tiles will be very unforgiving if your weight is squarely between the joists. I would be inclined to either noggin between the joists for extra support or remove your cement board and lay some 18mm wpb ply to give additional strength to the floor. Your real saviour is the fact that the floor area is quite small and this will reduce deflaction somewhat. Noggins/joists may be the way to go but overlaying with ply might be the easier option, screwed INTO not through your floorboards at no more than 300 mm centres. Closer if you wish would be even better. If you go with the ply option, I recommend ardexflex 7001 as the adhesive with the tiling face primed with P51 primer. You must seal the back face and edges of the board with polyurethane varnish and let it dry prior to laying.

Also, it is better to level your floorboards BEFORE you over board with your chosen board. Check out Mapei Fiberplan for this.

[Gooner]

Thanks for the reply Grumpy..

I would be inclined to either noggin between the joists for extra support ..

Yep.. I think this is the way to go.

...or remove your cement board and lay some 18mm wpb ply to give additional strength to the floor. ..

Not gonna happen. It would be a nightmare to remove. Shower base already placed over it and floor already waterproofed.

Your real saviour is the fact that the floor area is quite small and this will reduce deflaction somewhat.

Yep.. It's not too bad.

Also, it is better to level your floorboards BEFORE you over board with your chosen board. Check out Mapei Fiberplan for this.

Yes. The leveling decision came after waterproofing. I spoke with Ardex technical support and they tell me it will be OK to use Arditex leveling compound over the existing waterproofing membrane and then waterproof again over the leveling compound. I am hoping they are right, because I'm still not 100% about tiling over the latex based leveling compound. I have zero experience with it.

[grumpygrouter]

Tiling over Arditex isn't a problem at all Gooner. Getting the stuff flat is more of an issue though. All slc takes some work to get them flat and smooth, and as Arditex is a 2 part with latex, it tends to stink a bit so you will need plenty of ventilation.

What was your cement board that you laid and how far "out" is it to require leveling?

[Dave]

i used to use arditex leveller..not no more..mapei fibre plan...pefect for timber floors.....

[craig t]

I would use a 15mm notch trowel as your tiles are large format!

[Gooner]

Tiling over Arditex isn't a problem at all Gooner. Getting the stuff flat is more of an issue though. All slc takes some work to get them flat and smooth, and as Arditex is a 2 part with latex, it tends to stink a bit so you will need plenty of ventilation.

What was your cement board that you laid and how far "out" is it to require leveling?

Thanks Grumpy. Happy to hear I can tile straight over the Arditex. At this stage Ardex tell me it is the only product they would recommend using over their waterproofing membrane, so I am sticking with it for now.

What is so difficult in getting in flat? Do you have to trowel it flat? I thought it was "self leveling". Will I have a problem with such a small floor? (1.5 x 2m).

Cement board was James Hardie "Ceramic Tile Underlay". It is not very far out "of flat". It slopes around 4-5mm at one end of the room.. but that is only over 2 meters.

i used to use arditex leveller..not no more..mapei fibre plan...pefect for timber floors.....

Once again.. going with it as I have already used the Ardex waterproofing on the floor.

Thanks for the response fellas.

[MICK the Tiler]

You can tile over the ardex waterproofing use ardex x7 with ardion 90 as an additive to the addhesive and you'll be fine. Up your notched trowell to 12mm for the larger format tiles.

The 6mm hardies over the floorboards is the way we do it down here perfect. I personally would not have worried about levelling, that's what addy's for isn't it