Tiling over a wooden floor

[Joana]

Hi guys, I am new to this forum .Me and my partner Ian are renovating a property currently and have some questions about tiling as we are trying to do this between us. The make up of the floor is as follows : dpm / cement / 40-50 cm gap (not much crawling space at the solumn of the house!) / floor joist at about 50 cm centers / treated wooden floors all over the house , 2 cm thick, t&g. We have used hardie backing board of 6 mm directly on the wooden floors. Ian used torque screws. I was hoping that the backing board and screws will stiffen the structure of the floor but no such luck. I can see the floors moving/bending slightly when Ian walks over the hardie board. Should I use ultra or extra flexible tile adhesive in this case ? What would you recommend for such a floor ? I would not like to take a chance, go ahead and tile, and find later that I've used the wrong product. Thanks . Joana

 

[Andy Allen]

Did you stick the Hardie down with tile adhesive as well as screwing it down..?

 

[Bill]

You needed to secure the floor joists to the concrete base so that they do not bounce when walked on.

One support every metre along the joists would have helped.

 

[Joana]

No , just torque screws, every 3 inches or so I believe Ian places them. Quite a few screws on one board. Is that enough ? I must admit this is something totally new to us. I've tiled before but on concrete direct.

 

[Andy Allen]

Sticking the Hardie down as well as using screws will help to fill any voids and make it more secure..

 

[Joana]

The floor joists are running through the house but they are partly independent from the concrete they run through the brick walls 50 cm above the concrete. Here and there the joists are supported by a small brick wall , non load bearing , rising from concrete to just under the wooden floors. Of course I punctured some of these small walls only between the joists to create passages for crawling in below, for insulation, Plummer work and future inspections.

 

[Joana]

How much adhesive would a hardie backing board use before glued on the wooden floor ? 2 mm or so ? And should I glue directly on the wooden floors the hardie board ? Wait to dry and tile directly on that.

 

[Bill]

The floor joists are running through the house but they are partly independent from the concrete they run through the brick walls 50 cm above the concrete. Here and there the joists are supported by a small brick wall , non load bearing , rising from concrete to just under the wooden floors. Of course I punctured some of these small walls only between the joists to create passages for crawling in below, for insulation, Plummer work and future inspections.

Yes, but if the joists are bouncing when walked on then you should have supported them better. Another way is to add thicker layers ontop of the T&G flooring but that could still be a problem.

 

[Bill]

How much adhesive would a hardie backing board use before glued on the wooden floor ? 2 mm or so ? And should I glue directly on the wooden floors the hardie board ? Wait to dry and tile directly on that.

The tile adhesive does not resolve the problem of deflection, it only fills voids under the Hardie and between the T&G flooring.

 

[Bill]

Can you still get under your floor?

If so, go and add some more supports between the bottom of the joist and the concrete base, this will stop the deflection.

 

[Joana]

I understand that. The floors themselves are reasonably solid, not a problem. It's the joists that seem to make the floor a bit bouncy. If we tile on these floors with hardie board , will it crack eventually ? Underfloor reinforcement for the joists would be almost impossible as there is very little space and what we have is already required for a 4" waste pipe through the floors , pipe work, insulation , inspection hatches and so on.

 

[Joana]

We will have another look tomorrow, it's a bit of a nightmare down there ...might be able to get something really small in. Like half bricks and mortar to go just in below the joist

 

[Julian 'Farmer' Bonsall]

Joana sounds a similar construction to part of my property and all the friendly spiders. I strengthened the joists from above with extra cross braces, some steel straps (some areas were cut for the brick access ways and some pipe work) and a 25mm ply on top glued and screwed. The floor movements were very bouncy, and noisy in the past.
[DIy'er]

 

[Dumbo]

Just to reiterate and to make it clear if your floor bounces it will fail no matter what adhesive you use .