Fluid or traditional screeds? Technical Masonry Solutions

ifashionclothing
05/04/2023
383 Views

Batirama.com 01/02/20080

They can be coated, separated, floating or added… but will only be made using two competing techniques: traditional (under the DTU) or fluid under Technical Assessment; the second is more and more practiced at the expense of the screed drawn to the rule.

A screed is an interposing structure, with an average thickness of 5 cm between a paving or slab type support and a sealed or glued covering. The screed can be adherent, in the case of prefabricated floors; separated by a sheet of polyethylene 150 to 200 µm thick when there is a risk of rising damp or floating on thermal and/or sound insulation, intended for example for underfloor heating, etc.

Watch out for the patch layer!

In the presence of pipes, ducts, etc., an additional work underlying the screed called a screed layer is essential. Be careful not to forget this when designing, because the total opening height depends on it. A reservation of 15 or 20 cm for the laying of tiled floors on heated floors is common and having neglected the 3.4 cm of repair for the incorporation of pipes is problematic... and their integration in the screed mortar prohibited!

The rise of fluid screed

Because of its thickness, the screed is a technical work to which great care must be taken during its execution, otherwise the coating may crack or peel off... Moreover, the fluid screed market is currently in booming, but the traditional screed resists and still represents two thirds of the market… What are the reasons which motivate certain masons, screeds, tilers to move towards one of these two techniques?

Source: batirama.com / Hubert Koenig

The three questions to ask yourself... before starting the project!

Question 1

Can all floors support a screed?

Traditional or not, the hydraulic screeds of common aggregates, belong to the family of wet screeds, whose density is close to 2100 kg /m³. Consequently, 5 cm of screed without patching will add an additional 105 kg per m²... This is not negligible! On an old wooden floor, laying tiles intended for a bathroom, without generating any subsequent noise pollution, is a challenge...except in the case of using a damp screed comprising either polystyrene beads, such as XXLight from Poly Stone Technology (300 kg/m³ and 0.082 W/mK of thermal conductivity), or in wood aggregates such as Agreslith-C from Agresta, under Avis Technique 16/05-487 …

Lightened screeds and dry screeds

An alternative to lightweight screed is dry screed, commonly used in renovations. In most cases, these are plasterboard or plasterboard placed on light aggregates such as expanded clay aggregates, cellular concrete... (Bâtirama no. 379 of October 2005). Knauf, Lafarge Plâtres, BPB Placo, Xella Fermacell…offer dry screed systems under CSTB Technical Approval.

Product	Manufacturer	Technical Assessment No. *
Pregyp BD13	Lafarge Plasters	12/04-1409
Placo	BPB Placo	12/03-1359
Aquapanel floor	Knauf	12/04-1404
Fermacell	Xella Fermacell	12/00-1226

* On www.cstb.fr and under the heading Avis Technique, in simplified search and by entering the n° of the Avis Technique, the file technique accompanied by the opinion of the experts of the specialized group is available, printable and downloadable free of charge.

Example of a coating screed intended for a heated floor on an insulating underlay with studs.

Can pipes be incorporated into the screed?

Warning! Do not confuse leveling and ravoirage. In fact, leveling is a surface optimization operation by applying 3 to 30 mm of an industrial smoothing coating such as weber.niv from Weber and Broutin or 123 Planisol from Parex... mission to catch up a level or to integrate pipes in a flat layer, on which the possible insulating sub-layer will be arranged. The thickness of the scouring is at least equal to the outer diameter of the largest diameter of the sheath or of the pipe... The scouring can be carried out either by means of 0/4 sand stabilized with hydraulic binder, in this case the maximum thickness shave will be 4 cm, either by means of concrete or a lean mortar of cement or hydraulic lime.

Caution, for premises subject to high stresses, the repair must be carried out with cement mortar dosed at 325 kg/m³ and possibly supplemented by a welded mesh of maximum mesh 50 x 50. It should be noted that some manufacturers offer fluid products intended for scouring, some products even being made of lightweight concrete. So, can we remove the ravoirage? It has been understood that when there are incorporations, mending proves to be essential and leads to extra floor thicknesses and weight constraints...which can be avoided by incorporating the pipes in the insulation, but at provided that Ultra Th EPS trunking is used. This type of trunking is associated with the Isoleader floor system from KP1 and allows the incorporation of sanitary water pipes or electrical ducts at the level of the insulating layer, thus eliminating the recovery operation.

Fluid or traditional screeds? Technical Masonry Solutions

Question #3

How to limit noise pollution and impact noise?

The thermal insulation of floors is essential; however, the neighbor moving furniture, the children playing, the neighbor moving around with high heels…constitute noise pollution called “shock noise” by acousticians. As floor coverings do not make it possible to respond to this nuisance, manufacturers offer acoustic underlays intended for tiled screeds. It is thin (2 to 3 mm), it cannot be seen and yet it must be acoustically and mechanically efficient... Following numerous disputes, the acoustic underlays are now certified by the CSTB and to date 5 underlays have been certified, but with different performance or areas of use.

This is Arken's Fibrarken; d’Assour screed 19 and Assour screed plus of Siplast Icopal; Velaphone comfort from Soprema and finally Trami screed from Tramico. These 5 products are at least SC1 ("1" for the highest incompressibility index) and A ("A" for acoustics with Delta LW > 15 dbA) certified.

PRODUCTS	MANUFACTURERS	"INCOMPRESSIBILITY	a=500 kg/m² b= 200 kg/m²	DELTA LW MINIMUM OF 15 DB	USE IN FLOOR HEATING
FIBRARKEN	Arken	SC1	a2	A
b2	Ch
ASSOUR CHAPE 19	Siplast Icopal	a2
ASSOUR CHAPE PLUS	b2
VELAPHONE COMFORT	Soprema	a2
b2	Ch
TRAMI SCREED	Tramico	a2	Ch
b1

Solution #1: Traditional screed

By traditional, we mean a screed executed by tamping, adjusting and smoothing according to the desired surface condition; therefore, fluid screeds (solution n°2) are not concerned. However, hot water underfloor heating circulating in synthetic material or copper tubes is defined in DTU 65.14. The coating of the heating elements can be done either in ready-to-use concrete, or in concrete manufactured and plasticized on site, or in mortar for fluid screed based on cement or calcium sulphate, ready to use or ready to mix. .

Dose the cement screed well

A screed for a single-family home garage will not have the same characteristics as a screed subjected to significant static or dynamic loads, such as those of a hypermarket or a collective kitchen. Therefore, its design must take into account the type of stresses. Traditional screeds, which meet the requirements of DTU 26.2, and authorizing pedestrian use and usual human activities such as residential premises, offices, shops or classrooms, i.e. premises P2 or P3 of the UPEC classification, are carried out with a cement of resistance class 32.5 dosed at 300 ± 50 kg /m³ of dry sand 0/4. For rooms with higher stresses P4 or P4S, it is necessary to use ready-to-use performance mortars.

4, 5 or 6 cm?

The minimum thickness depends on the type of screed, separated or on an insulating underlay, and on the type of stress, weak or strong (table below). In addition to the shrinkage and construction joints of the support, fractionation joints must be made every 40 m² and at most every 8 linear m in the case of uncoupled screeds. The flatness tolerances are 5mm under the 2 m rule and 2 mm under the 0.20 rule in the general case and 1 mm under the 0.20 rule for bonded flexible floors. The incorporated screeds (fresh on fresh) have, for their part, tolerances of 7 to 2 mm, under the rule of 2 m and the ruler of 0.20 m.

	THICKNESS	SODA/FIBER MESH
DISSOLIDARIZED CLOVE
Premises with low stress P2 or P3 of the UPEC classification (residential premises, offices, etc.)	5 cm without being locally less than 4 cm	Not necessary
Premises subject to moderate to heavy stress P4 t P4S (shopping malls, communal kitchens, etc.)	6 cm without being locally less than 4.5 cm	– i.e. TS with a 100 x 100 mesh and a nominal mass of 325 g/m² – or fibers under Technical Approvals
SCREED ON ACOUSTIC UNDERLAY
Screed on "incompressible" SC1 underlay	≥5 cm without being locally less than 4 cm	– i.e. TS with a 100 x 100 mesh and a nominal mass of 325 g/m² – or fibers under Technical Advice
≥ 6 cm without being locally less than 4 cm	Not necessary
Screed on "low compressibility" SC2 underlay	6 cm without being locally less than 4.5 cm	– i.e. TS with a mesh of 100 x 100 and a bominal mass of 325 g/m² – or fibers under Technical Approvals

Solution n° 2: Fluid screed based on anhydrite or cement

The Technical Assessment imposes a scrupulous implementation and does not allow approximations, it is for this reason that these screeds can only be used by approved applicators and trained by the manufacturers (see address book ).

The field of use is that of building interiors, in uncoupled or floating installation, on any acoustic underlay. Adherent laying is not currently covered by the Technical Assessments for anhydrite-based fluid screeds; conversely, cement-based fluid screeds allow this type of installation.

* Anhydrite is an anhydrous calcium sulphate, most of the time resulting from the chemical industry or from the desulphurization of gases and fumes from thermal power stations.

Fluid screeds under Technical Approvals in anhydrite or cement:

COPE TYPE	MANUFACTURER	PRODUCT	TECHNICAL NOTICE
ANHYDRITE	Liquid screed	Liquid screed	04/12-1392
Duoflow	Duoflow System	12/05-1455
Sika	Sika Syntichape	12/06-1486
Knauf	FE 80	12/99-1186
Maxit	Maxitplan	12/01-1253
CEMENT	Maxit	IP88	12/99-1170
Sika	Sika viscochape	03-12-1357
Vicat	The Vicat Cope	03-12-1377
VPI	Baticem Flow	12/03-133

Screed based on calcium sulphate: a pathology finally under control…

A screed is a thin mortar structure, with or without welded mesh, drawn with a rule, floated and possibly smoothed. With an average yield of 20 m²/hour and physical implementation, making a screed is demanding. Then appeared on the market, 20 years ago, fluid products, simpler to implement, some even making it possible to get rid of seals... but also sources of pathology and justified reservations on the part of insurers.

Pathologies

Cracking, peeling and blistering of floor coverings have long affected calcium sulphate-based screeds. But since July 2003 and following major efforts to inform and train users, insurers have finally lifted their reservations. But that does not mean that the risk is no longer present, because these screeds remain technical. If the screeds based on anhydrous calcium sulphate can claim about fifty years of existence (they were born after the war in Germany, at a time when cement was rare), very paradoxically the fluid screeds based on cement are more recent, but are also subject to Technical Advice. As with calcium sulphate-based screeds, fluid cement-based screeds require very careful installation and are reserved for applicators approved by the manufacturers, whose contact details are specified in the address book.

So traditional or fluid and under technical advice?

According to Florent Seignez, Customer Relations Manager at Liquid Screed, given current and future thermal regulations, the fluid screed market is buoyant; moreover, the significant reduction in arduousness, associated with high productivity gains, makes the fluid product economically attractive, despite a higher purchase cost.

Comparative table of the performances and limits of the two techniques

Traditional and meeting the requirements of DUT 26.2	Fluid and under Technical Advice
All types of premises: from individual houses to industrial premises	Not suitable for industrial floors Furthermore, the anhydrite screed is not designed for floors with drains
Thickness ≥5 cm depending on the type of premises	Anhydrite: ≥2.5 cm without underlay ≥3.5 cm on undercoat	Cement: ≥4cm
100 m² in 5 hours with two companions	100 m² in ¾ hour with 2 companions (excluding preparation time)
80 to 100 euros/m³	Cement screed: 150 euros/m³
Cement + fiber screed: 180 euros/m³
Anhydrite screed: 180 - 200 euros/m³