Any timbered substrate for tiling is always problematic. What makes it difficult to tile effectively is that timber is particularly susceptible to movement caused by moisture. Most failures, where Schluter-Systems are called in as troubleshooters to solve the problem, are where tiles have been bonded directly to the timber substrate.
Technical Manager Ian Knifton says while certain tile adhesives will allow you to tile directly to timber, they don't always provide a total protection against the effects of movement.
Question.
I've been asked to put new tiles on to a timber base, where the existing tiles have cracked and become debonded.
How can I guarantee that the tiles in my installation don't suffer the same fate?
Answer.
Many failures occur at the joints, where the timber boards are abutted together, because you have differential movement between the two.
We've been on site on many occasions where we can tell from the tiled surface exactly where the board joints are, because the tiles have cracked above every joint.
To guarantee the integrity of your installation, first of all you'll need to verify that the timber substrate is capable of taking the weight.
If it needs to be strengthened, add extra noggins or support, or overply the substrate.
Then, the best way to prevent the transfer of stresses to the tiled surface, is to lay an uncoupling membrane.
Question.
I've been using a polyethylene membrane to uncouple tiles from cracked concrete
screeds and green screeds -- can it be used on timber substrates as well?
Answer.
A membrane such as Schluter-DITRA, with its grid structure of square cavities, each cut back in a dovetail configuration, means it's effective in neutralising joints and differential movement in the timber substrate, ensuring stresses are not transferred to the tiled surface.
A recent example of how it solved a major problem on a timber substrate involved a large old house that was being renovated into flats.
The existing timber floor was simply planked floorboards, about an inch thick and eight inches wide, just butted together.
But in various places there were gaps between the boards of up to eight millimetres wide -- and the floor was about an inch out of level.
To plug the wider gaps between the boards, we used a proprietary filler, poured a fibre-reinforced self-levelling compound over the complete timber floor area; once that had hardened the next day the uncoupling membrane was applied, and then the tiles were laid on top.
The builders also wanted to install walk-in showers on the first floor -- and the membrane provided waterproofing protection, too.
Question.
The property has standard tongue and groove wooden flooring.
Is any similar preparation needed, or can I lay the membrane directly on top?
Answer.
As long as the substrate is capable of taking the weight of the tiled surface, the membrane can be applied directly to any existing timber -- including plywood and chipboard.
And even in older properties with butted planks, small gaps of around two millimetres between the joints can be successfully bridged with Schluter-DITRA without the need for fillers.
To fix the membrane, use a bonding adhesive that's appropriate for the individual timber substrate, and apply using a 3mm x 3mm, or 4mm x 4mm notched trowel.
The anchoring fleece on the underside must be fully engaged in the adhesive to provide a mechanical bond to the substrate.
Then set the tiles directly on top so the
tile adhesive is mechanically anchored in the cut-back cavities of the matting.
Question.
As these membranes are so important in preventing tiling installations from failing should
architects specify their use, or should we offer them to our clients?
Answer.
They are usually specifier-led in large commercial applications, but they're just as important in protecting tiles in the home, even though some installers don't include them in domestic jobs because they're worried it'll push the price up too much.
However, because their use will extend the life of the installation, and guarantee it against bulging, cracking and debonding, many installers are now including them in their price, and fully explain to their customers why they should be used.
----
Any timbered substrate for tiling is always problematic -- floors more so than walls. What makes it difficult to tile effectively is that timber is particularly susceptible to movement caused by moisture.
Most failures, where world market leader in tiling solutions, Schlüter-Systems, are called in as troubleshooters to solve the problem, are where tiles have been bonded directly to the timber substrate. While certain tile adhesives will allow you to tile directly to timber, they don’t always provide a total protection against the effects of movement.
A flooring contractor contacted Schlüter’s technical department recently to ask advice about a refurbishment project he was working on, which involved putting new tiles onto a timber base. The existing tiles had cracked and become debonded. He wanted to ensure that his installation didn’t suffer the same fate.
Many failures occur at the joints, where the timber boards are abutted together, because there is differential movement between the two. Schlüter’s technical team has been on site on many occasions where they can tell from the tiled surface exactly where the board joints are, because the tiles have cracked above every joint.
To guarantee the integrity of such installations, the first thing is to verify that the timber substrate is capable of taking the weight. If it needs to be strengthened, add extra noggins or support, or overply the substrate. Then, the best way to prevent the transfer of stresses to the tiled surface, is to lay an uncoupling membrane.
It neutralises joints and differential movement in the timber substrate, ensuring stresses are not transferred to the tiled surface.
Typical problem of a bowed floor which must be made level prior to fixing the uncoupling membrane such as Schluter DITRA
A recent example of how it solved a major problem on a timber substrate involved a large old house that was being renovated into flats. The existing timber floor was simply planked floorboards, about an inch thick and eight inches wide, just butted together.
But in various places there were gaps between the boards of up to eight millimetres wide -- and the floor was about an inch out of level. To plug the wider gaps between the boards, the contractors used a proprietary filler, then poured a fibre-reinforced self-levelling compound over the complete timber floor area. Once that had hardened the next day, the uncoupling membrane was applied, and finally the tiles were laid on top.
As long as the substrate is capable of taking the weight of the tiled surface, the membrane can be applied directly to any existing timber -- including plywood and chipboard.
Laying Schlüter DITRA
And even in older properties with butted planks, small gaps of around two millimetres between the joints can be successfully bridged with membranes such as Schlüter®-DITRA without the need for fillers.
The contractors also needed to install walk-in showers on the first floor -- and the membrane provided waterproofing protection, too.
To fix the membrane, use a bonding adhesive that’s appropriate for the individual timber substrate. The anchoring fleece on the underside must be fully engaged in the adhesive to provide a mechanical bond to the substrate.
Then set the tiles directly on top so the tile adhesive is mechanically anchored in the cut-back cavities of the membrane.
Membranes are usually specifier-led in large commercial applications, but they’re just as important in protecting tiles in the home, even though some installers don’t include them in domestic jobs because they’re worried it’ll push the price up too much. However, because their use will extend the life of the installation, and guarantee it against bulging, cracking and debonding, many installers are now including them in their price, and fully explain to their customers why they should be used.
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