Why Floors Fail: When and how to screed

Laminate & vinyl flooring can fail if the surface onto which it is laid is not level. Screeds are used to form a flat and level surface, with adequate strength and resistance to indentation, on which other flooring is laid.Traditionally, screed is laid around 65mm thick onto a concrete subfloor. It’s a skilled job, usually undertaken by plasterers when the walls and ceiling are plastered. A screed mix is relatively strong but not intended as a wearing surface, the screeds primary purpose, using one part cement to three parts sharp sand, and when done well it gives a smooth and level floor on which to lay your chosen floor finish. A screed is also the preferred medium when laying underfloor heating pipes.

When laying tiles or laminated or vinyl flooring it is necessary to use a screed if the structural floor in not level. As a general rule the floor surface should not vary by more than 3mm per metre.

There’s nothing structural about screeds and some designs do away with one altogether. However, the floor beneath the screed is usually not laid to nearly such a high standard. Also, suspended precast concrete flooring systems, which are now increasingly being used instead of solid concrete slabs, have a noticeable camber which causes problems when it comes to laying most floor finishes. So although a screed can be expensive most builders will lay one when a top floor is planned.

The traditional way to lay screed is to mix the sand and cement on site with a mixer. Screeders are always looking for the perfect mix. This is pretty dry, almost powdery, when compared to brick and render mortars. The trouble is that mixing this by shovelling sand and cement into a mixer, and delivering to the screeders, keeps a labourer fully occupied — in itself expensive. So there has been a marked shift towards using ready-mixed screeds, delivered by lorry at the beginning of the day. Ready-mixed screeds come with added retardants to delay the set, so that you can be working all day with one load.

To standardise the process, there is a new trend towards pumped screeds, supplied and fixed by specialist crews. These pumped screeds use gypsum as a binder; they are also known as calcium sulphate or anhydrite screeds. They cost about 50% more per cubic metre than a cement mix, but they are much faster to lay and can be successfully laid at 50mm, or even 35mm depths where there are no underfloor heating pipes to cover, whereas a conventional screed needs to be at least 65mm deep.

The process of laying is very different to what we have grown used to with cement screeds. The biggest variable is the volume of screed used due to increased depths, especially on irregular sub-bases. It is not uncommon to for the depth of the screed to vary from 40mm to 80mm across a floor. Typical costs for, say, 100m² with an average depth of 50mm depth would be between $2800 and $4800.

The actual pumping process is very quick. The screed has to be carefully separated (via a polythene sheet) from any insulation sheeting placed below, because chemical reactions can take place although this is very rare.

Whichever system you use, ensure ample time for drying out. The rule of thumb is to allow a day for every millimetre depth, so that 70 days is the standard time recommended. If you have underfloor heating pipes buried in the screed, you can speed the process up but only very carefully: experts recommend doing nothing for a month, then putting the heating on at its lowest setting, turning it up by 3°C per day until the working temperature is reached.

Finally, there is the issue of underfloor heating. Best practice recommends that, to avoid movement issues, screeds should not cover an area of more than 40m2 or a distance in any one direction longer than 8m. Expansion joints should subdivide larger screed areas. Alternatively, you can place an anti-crack mesh in the screed or add fibres to the mix itself.

Levelling screeds can provide sufficient depth to incorporate ducts to contain services such as electrical power and telephone cables. Increasingly levelling screeds are being installed on Underfloor Heating Systems as they provide a thermal mass for the heating to dissipate into giving a consistent temperature across an area with a gradual rise and fall over time.

The thickness of the screed allows it to take up normal variations in flatness and levelness of the base on which it is laid. The common types of flooring laid over levelling screeds include carpet and carpet tiles, linoleum, laminate and vinyl flooring and tiles, wooden blocks, and ceramic tiles. Levelling screeds are not intended to act as a wearing surface and should always be covered with a final floor finish.

Download our laminate and vinyl brochures or browse our website. Scroll down to "Lamadeira" here.

For any other inquiries about laminate & vinyl flooring please send us an email.

Why Floors Fail: The Missing Step - Acclimation of Flooring

Part 2

Acclimation (or acclimatisation) of laminate or vinyl flooring is the vital conditioning of the flooring material to the humidity and temperature that it will experience during occupancy. Most manufacturers require the cartons of flooring to be acclimated for 48 to 72 hours prior to installation. OK but why?

Here's an extreme case but it makes the point. A 40 story tower was being constructed in Dubai. It was August, average daily temperature was 40 degrees C and humidity was over 56%. The building was nearing completion when they installed laminated flooring throughout. A week later as the finishing touches were being done they turned on the air conditioning. Within a matter of days every floor failed! As the temperature dropped to a comfortable 20 degrees and the humidity plunged to 27% the planks shrank, creating gaps, becoming loose and warping. The flooring in the entire tower had to be replaced.

The why?
Flooring material needs to be acclimated in the area of installation at the humidity and temperature it will normally experience. This takes time. If the laminate or vinyl is to be installed in a lounge, acclimation of the flooring should take place in the lounge. Storing the laminate flooring in the garage is not acclimation even if the garage is attached. 

When a floor acclimates the product is adjusting to the humidity of the area of installation.

All wet work in the area of installation such as plastering and painting should be completed prior to the start of acclimation.  All windows and doors must be installed prior to the start of acclimation. The heating and air conditioning system must be operational at or near occupancy levels. If installing over concrete the concrete should be tested for acceptable humidity levels for the installation of the laminate.

When a floor is not acclimated prior to installation it can be hard to click together chipping or damaging the edges of the planks. A floor that is not acclimated to its environment is more likely to experience problems such as expansion, tenting, squeaking and buckling after installation. 

All wood, including HDF, is porous on a microscopic level, even though it may look quite solid. These tiny openings allow air inside the core, carrying with it whatever humidity there may be. The more humid the air, the more likelihood that planks will swell; the less humid the air, the more likelihood the planks will shrink. While this swelling or shrinking may be very slight, it could be just enough to cause otherwise snug locking systems to buckle or gap across the floor.

Acclimating allows the planks to become unified in the temperature and humidity that is identical to the conditions found in the room in which they will be installed. Once acclimated, the planks will be uniformly conditioned and the locking system will not be compromised. So you can see why acclimation is so important. In fact, skipping the proper acclimation process will void your guarantee.

The how.
Place the cartons in the middle of the floor, laying each box flat, side-by-side or across each other like a logs on a campfire in the room in which they will be installed. Keep them away from the exterior walls. Allow them to sit a minimum of 48 hours before installation. When the humidity in the room exceeds 60 percent, laminate boards expand and push against each other. This may cause noticeable ridges along the seams, called cupping, or bulges in the middles of the boards, called crowning. When the humidity falls below 30 percent, on the other hand, the boards shrink and the joints may separate, leaving gaps between them. 

In Part 3 Why Floors Fail: When to screed

Download our laminate and vinyl brochures or browse our website. Scroll down to "Lamadeira" here.

For any other inquiries about laminate & vinyl flooring please send us an email.

Why Floors Fail: Everything You Need to Know About Expansion Joints for Flooring

Part 1 

The most common reason for glueless click-system laminate & vinyl floating flooring failure is inadequate expansion joints.
Vinyl body is less hygroscopic but PVC is definitely more heat conscious. Variation in temperature and humidity will lead to expansion or contraction which can lead to gaps appearing between planks or tenting. So for safety sake we recommend in our installation instructions that panel size should not exceed 8m in direction of the panel width and 10m in direction of the panel length without an additional expansion gap. This is obviously in addition to the 10mm gap around walls. Different manufacturers use slightly different measures but all approximate the rule above.

Kaindl, one of the worlds leading laminate manufactures recommends:
Bigger areas must be separated with an expansion gap of at least 15mm.
Laminate flooring consists of wood. Wood is a hygroscopic material and adapts to the ambient humidity levels and as a result, its dimensions are subject to slight changes. The expansion can be 2mm/m length. Keep this physical property of wood in mind when laying down your laminate flooring. 
A minimum expansion gap from 1.5mm/lm room length on both sides should be considered e.g.: Length of the room 10m x 1.5mm/lm = 15mm distance The must be expansion gaps of min. 1.5mm/m between rooms. Those gaps can be masked by using a special profile. When fitting near solid elements e.g. heating pipes make sure there is a distance of 1.5mm/m.

From timberfloors.co.za: Leave an expansion gap all around the perimeter of the room, usually between 8 and 10mm. This will allow the wood floor product to expand when the humidity in the air rises. This expansion gap will later be covered by the skirting. Laminate flooring is known to expand 3mm per meter, if allowance for this expansion is not made the floor will ultimately fail when it needs to expand.
Laminate flooring is also normally not laid more than 8m in length without breaking the length with an expansion joint profile. Most manufacturers have profiles available that look similar to the flooring decor or it can be made from aluminium. It is also strongly recommended that one breaks the laminate floor with an expansion profile at every room entrance. In other words do not take your flooring into different rooms all in one piece, an expansion profile should be fitted under the door entering each room. Remember to also allow for an expansion gap around door frames. This gap around door frames is usually filled with a colour sealant to compliment the floor decor.

For Luxury Vinyl Flooring (LVT) the expansion joints can be slightly smaller but remain just as important. IVC US, a prominent American company recommends the following: "Maintain a 1/4” (1/2 cm) expansion space around all walls, cabinets, pipes, toilet flanges and any obstacle in the floor."

And lastly a compact guide published by The Southern Africa Wood and Laminate Flooring Association: A Simple Guide to Laminate Flooring Installation, which also recommends a 10mm gap and room sizes no larger than 8x10m without expansion gaps. Pdf download here

In Part 2 Why Floors Fail: The missing step - Acclimatisation

Download our laminate and vinyl brochures or browse our website. Scroll down to "Lamadeira" here.

For any other inquiries about laminate & vinyl flooring please send us an email.

What is Ceramic Sintering? Sintering is the process of forming a solid mass of material by heat and/or pressure without actually melting it. Sintering is part of the firing process used in the manufacture of ceramic and porcelain tiles as well as other manufactured objects. Sintering also happens naturally in mineral deposits. The atoms in the materials diffuse across the boundaries of the particles, fusing the particles together and creating one solid piece. A common example of sintering is when ice cubes in a glass of water adhere to each other. The word "sinter" comes an old form of the word "cinder". Sintering is effective in the firing of ceramic tiles because the process reduces the porosity and enhances properties such as density, strength and translucency. As the diagram below shows, the process eliminates the small pores between each particle and fuses them together. Control of temperature and the consistency of the size of particles is very important to the sintering process. Some ceramic raw materials have a lower affinity for water and have a lower plasticity than clay, requiring organic additives in the stages before sintering. The general procedure of creating ceramic objects via sintering of powders includes: Mixing water, binder, deflocculant, binder and unfired ceramic powder to form a slurry; Spray drying the slurry; Putting the spray dried powder into a mold and pressing it to form a green body (an unsintered ceramic item); Heating the green body at low temperature to burn off the binder; Sintering at a high temperature to fuse the ceramic particles together.   Download our ceramic tile brochures or browse our website here. For any other inquiries about Porcelain or Ceramic tiles please drop us an email.   Ciao, The Link International team.