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Weber - Saint-Gobain

Tiling with under-floor heating or under-tile warming

 

 

Problem

1. Movement due to thermal expansion and contraction

The screed and the adhesive, being of a similar material, expand at a similar rate to each other. However, the tiles usually have a slightly lower coefficient of thermal expansion - so for a given temperature rise they will grow proportionately less. The result on the tile-fixing products is twofold:

Stresses build at the interface between the tile and the adhesive. At some point this will be too great and the weakest part of the system will yield - usually the bond between the tile and the adhesive.

As the base expands in relation to the tiles they try to move slightly further apart stretching the grout joints. Cementitious products are inherently weak in tension and the bond onto the tile edge can fail.

2. Damage to wires from the trowel

One of the most common reasons for problems with the installation of an undertile warming system is damage made during fitting.

When covering the wires with adhesive it is quite easy to accidentally cut a wire with the trowel.

3. Turning on heating elements too early weakens the adhesive and grout

Cement-based adhesives (and grouts) set hydraulically i.e. water is involved in the hardening reaction.

If the adhesive is allowed to dry out before it has properly hardened it will tend to be weak and crumbly.

It is important that the heating system is off when tiles are fixed and remains off until the adhesive and grout have fully cured.

Solution

Solution 1. Tiling onto electrical under-tile warming mats (solid substrates)

Weber's highly polymer-modified adhesives and grouts have enough flexibility when set to accommodate thermally induced movement. weberfloor flex can be used to cover/protect the wires that otherwise could get damaged during application of the adhesive.

Stage 1: Preparation

Ensure that the floor is rigid, sound, clean, dry and free from any contaminating barrier. Prime the substrate with weber PR360 and allow to dry.

Stage 2: Under-tile warming

Install the under-tile warming system in accordance with the manufacturer's instructions and test that it works. Turn off and allow to cool.

Apply weberfloor flex self-levelling compound up to 50mm deep or until the warming elements are covered by at least 3mm. Allow 3 hours before foot traffic.

Stage 3: Fix the tiles

Fix the tiles into a bed of weberset rapid SPF or weberset SPF at least 3mm thick. Leave joints at least 3mm wide for grouting and make provisions for movement.

Grout the joints with weberjoint wide flex or weberjoint pro and use weberjoint silicone sealant to fill perimeter movement joints.

Stage 4: Allow to cure

Keep the heating/warming system turned off for at least 5 days to allow the cement to cure. Bring the system up to its operating temperature gradually in stages over a few days, do not exceed 27°C and no more than 5°C per day.

Solution 2. Tiling onto electrical under-tile warming mats (wooden substrates)

Weber's highly polymer-modified adhesives and grouts have enough flexibility when set to accommodate the thermally-induced movement associated with under-tile warming on timber substrates. weberfloor flex can be used to protect the warming elements prior to tiling and also helps stabilise movement in the floor.

Stage 1: Preparation

Ensure that the floor is rigid, sound, clean, dry and free from any contaminating barrier. The wooden floor must be capable of supporting the expected dead load and probable dynamic load, without excessive deflection. Additional strength can be provided, where necessary, by taking up the existing boards and stiffening with noggings. Alternatively, the required rigidity can be achieved through overlaying the existing timber boards with either WBP plywood or tile backer board.

Plywood should be at least 18mm thick, primed on the reverse face and edges with weber PR360 and screwed every 300mm. Tounged and groove, chipboard or floorboards must be screwed to joists using two screws per board at every joist. All boards should be primed with weber PR360.

All joints between boards should be filled with weberjoint silicone sealant to prevent leakage during application.

Stage 2: Under-tile warming

Install the under-tile warming system in accordance with the manufacturer's instructions and test that it works. Turn off and allow to cool.

Apply weberfloor flex levelling compound at least 10mm deep to help stabilise the floor and protect the cables. Warming elements must be covered by a minimum of 3mm. Allow 3 hours before foot traffic.

Stage 3: Fix the tiles

Fix the tiles into a solid bed of weberset rapid SPF or weberset SPF at least 5mm thick. Leave joints at least 3mm wide for grouting and make provision for movement.

Grout the joints with weberjoint wide flex or weberjoint pro and use weberjoint silicone sealant to fill perimeters joints.

Solution 3. Tiling onto under-floor heating pipes (solid substrates)

Piped heating systems are buried in reinforced cement/sand floating screeds of not less than 65mm thick. If a polymer-modified levelling screed is used it must cover the pipes by a minimum of 10mm. Weber's highly polymermodified adhesives and grouts have enough flexibility to accommodate thermally-induced movement.

Stage 1: Preparation

The heating pipes should be installed according to manufacturer's instructions, fixed down and tested prior to being encapsulated in a screed or levelling compound.

If the pipes have been laid in a reinforced cement/sand screed this must be allowed to dry fully prior to tiling. A sand/cement screed should be left for 3 weeks with the under-floor heating off to dry. After this period the heating system should be turned on and raised by a maximum of 5°C/day until the maximum recommended operating temperature is achieved. This temperature should be maintained for 3 days and then the system turned off and the screed allowed to cool to 15°C before tiling commences.

If weberfloor flex levelling compound is used to cover the pipes instead of a cement/sand screed, the drying time will be considerably shorter.

Ensure that the cured surface of the floor is rigid, sound, clean, dry and free from any contaminating barrier. Prime with weber PR360 and allow to dry.

Stage 2: Fix the tiles

Fix the tiles into a solid bed of weberset rapid SPF or weberset SPF at least 3mm thick. Leave joints at least 3mm wide for grouting and make provisions for movement.

Grout the joints with weberjoint wide flex or weberjoint pro and use weberjoint silicone sealant to fill perimeter joints.

Stage 3: Allow to cure

Keep the warming system turned off for at least 5 days to allow the cement to cure. Bring the system up to its operating temperature gradually in stages over a few days.

Solution with the following Weber products

Solution 1

weber PR360

Styrene acrylate dispersion for use with tile adhesives, levelling compounds and webersys protect

weberfloor flex

High-performance, fibre-modified, self-smoothing, self-levelling renovation screed (up to 50 mm)

weberset rapid SPF

A rapid-setting, flexible, low-dust, cement-based floor and wall tile adhesive, available in light grey or white for interior and exterior use.

weberset SPF

A flexible, cement-based polymer-modified tile adhesive for internal and external use

weberjoint wide flex

A wide-joint, mould-resistant, flexible tile grout for interior and exterior use

weberjoint pro

A water-repellent, mould-resistant, flexible tile grout for interior and exterior use

weberjoint silicone

Acetoxy curing silicone sealant that cures to form a tough, flexible, water tight seal – available in clear, white and a range of colours

Solution 2

weber PR360

Styrene acrylate dispersion for use with tile adhesives, levelling compounds and webersys protect

weberfloor flex

High-performance, fibre-modified, self-smoothing, self-levelling renovation screed (up to 50 mm)

weberset rapid SPF

A rapid-setting, flexible, low-dust, cement-based floor and wall tile adhesive, available in light grey or white for interior and exterior use.

weberset SPF

A flexible, cement-based polymer-modified tile adhesive for internal and external use

weberjoint wide flex

A wide-joint, mould-resistant, flexible tile grout for interior and exterior use

weberjoint pro

A water-repellent, mould-resistant, flexible tile grout for interior and exterior use

weberjoint silicone

Acetoxy curing silicone sealant that cures to form a tough, flexible, water tight seal – available in clear, white and a range of colours

Solution 3

weber PR360

Styrene acrylate dispersion for use with tile adhesives, levelling compounds and webersys protect

weberset rapid SPF

A rapid-setting, flexible, low-dust, cement-based floor and wall tile adhesive, available in light grey or white for interior and exterior use.

weberset SPF

A flexible, cement-based polymer-modified tile adhesive for internal and external use

weberjoint wide flex

A wide-joint, mould-resistant, flexible tile grout for interior and exterior use

weberjoint pro

A water-repellent, mould-resistant, flexible tile grout for interior and exterior use

weberjoint silicone

Acetoxy curing silicone sealant that cures to form a tough, flexible, water tight seal – available in clear, white and a range of colours