Floor Levelling & Screeding QLD 2026 Costs: $30 - $120 / m² - Get Free Quotes

What Floor Levelling and Screeding Covers in Queensland

Floor levelling and screeding is the preparation work that makes a floor flat, sound and ready for whatever covering goes on top. It corrects the dips, humps, slopes and uneven patches in a slab or subfloor so that tiles, vinyl, timber or carpet sit true rather than following every imperfection beneath them. The work is rarely seen once the finished floor is down, but it is what that floor relies on, and a poor base shows through no matter how good the covering. A good specialist reads the existing floor, works out what correction it needs, and prepares a base the next trade can lay on with confidence. The result is a floor that lies flat and stays that way.

The scope covers several related jobs that all aim at a sound, level base. There is filling and smoothing a slab with a self-levelling compound, laying a thicker sand-cement screed for bigger corrections or wet-area falls, grinding off high spots, patching damage, and overlaying a timber subfloor to give a flat panel surface. Each suits a different problem, from a slab a few millimetres out to a floor that slopes noticeably across a room. Choosing the right method for the floor in front of them is part of what a specialist brings. The method follows the floor, not the other way around.

Who does the work is a screeding or flooring-preparation specialist, often working just ahead of the floor layer. A tiler may level minor dips themselves, but a floor that is genuinely out of true, a wet area needing falls, or a large area calls for someone who prepares floors for a living and gets them flat to a tolerance. The skill is real, since self-levelling compound and screed both have short working times and unforgiving habits if the substrate is wrong. A specialist who prepares the base properly saves the floor layer, and the home owner, a great deal of trouble. The preparation specialist and the floor layer are often two different trades working in sequence. Getting the base right is what lets the visible floor go down cleanly.

The sections that follow set out what floor levelling and screeding costs in Queensland in 2026 and the things that decide whether the base lasts. They cover the difference between level, flat and falls, the methods, why flatness matters under each kind of floor, the substrate and the all-important moisture, wet-area falls, timber subfloors, grinding and the tolerances a good floor meets. The aim is to leave you able to judge a quote on the preparation that matters, rather than treating levelling as an afterthought to the floor you can see. They also cover concrete slabs and grinding, the flatness tolerances a good floor meets, screeding over underfloor heating, the DIY-versus-professional question and the licensing side. The pricing section sets out what the work costs in Queensland in 2026. Taken in order, the guide runs from the methods and why flatness matters, through the substrate and the wet-area falls, to what the job should cost.

Level, Flat and Falls: the Difference

Three words get used loosely in this trade, and pulling them apart makes everything clearer. A level floor is horizontal, sitting true to a spirit level across the room, while a flat floor is even and free of dips and humps, even if the whole thing happens to sit on a slight slope. They are not the same thing, since a floor can be perfectly level yet rippled, or dead flat yet gently sloping. Knowing which one a job actually needs is the start of getting it right. The words sound interchangeable but describe genuinely different outcomes. A specialist keeps them apart because the floor covering cares about one more than the other.

For most floor coverings, flatness matters more than being perfectly level. Tiles, vinyl, hybrid and timber all need a flat base within a tolerance so they sit without lipping, rocking or telegraphing, whereas a tiny overall slope across a room is usually invisible once the floor is down. This is why a specialist talks about getting a floor flat to a tolerance rather than chasing a perfectly horizontal surface that the covering does not require. Understanding this stops money being spent levelling a floor that only needed flattening. Chasing perfect level on a sloping room is effort the covering never asked for.

Falls are the deliberate exception, where a floor is sloped on purpose. In a wet area, a balcony or anywhere water has to drain, the floor is screeded to a fall, a gentle, controlled slope toward the drain or waste so water runs away rather than ponding. Here the goal is not level at all but a precise slope, which is a different skill from creating a flat floor. A floor that should fall to a drain but is laid flat will pond water, which is a defect. Here the slope is the whole point, set to a fall fine enough to look flat yet enough to drain. Reading a fall by eye is harder than it sounds, which is why it is a trade skill.

Being clear about which of the three you need shapes the whole job. A living area wants a flat base, a bathroom floor wants a fall to the drain, and a perfectly level result is rarely the actual requirement, so the specialist matches the work to the need. Confusing them leads to a wet area that ponds or money wasted chasing the wrong target. A specialist who explains whether your floor needs flattening, levelling or falls is thinking about the right thing. The need, not the jargon, is what should drive the method.

Methods: Self-Leveller, Screed and Grinding

Self-levelling compound is the most common method for interior floor preparation. It is a cement-based material mixed to a flowable liquid and poured over a primed substrate, where it spreads and finds its own level to leave a smooth, flat surface, which makes it ideal for correcting dips and creating a flat base under tiles, vinyl, hybrid or timber. It works in thin to moderate builds and sets quickly, so it suits levelling a slab that is close but not quite flat. Its strength is the smooth, true finish it leaves with no trowelling. For tiles in particular, this kind of flat base is what a tiling job needs to sit without lippage. The pour does the levelling that hand-trowelling would struggle to match over a whole room.

Sand-cement screed is the traditional method for bigger corrections and for falls. It is a stiffer mortar laid and trowelled by hand to a level or to a fall, used where the correction is too thick for a self-leveller, where a wet area needs a slope, or where a robust bed is wanted. A screed can build up far more depth than a self-leveller and can be shaped to a precise fall, which is why it remains the choice for wet areas and larger level changes. It takes more skill to lay true and needs curing time before a covering goes on. For falls and depth, a screed is what a self-leveller cannot do.

Grinding is the method that removes rather than adds. Where a slab has high spots or humps, grinding takes them down to bring the floor closer to flat, often used together with a self-leveller that fills the low spots, so the two methods complement each other. Grinding is also how old adhesives, coatings and laitance are removed to give a sound surface to work on. It is the subtractive side of levelling, dealing with what is too high rather than what is too low. Often a floor needs both at once, the humps ground down and the hollows filled, to meet in a flat plane. Used together, the two methods reach a result neither could alone.

The right method, or combination, depends on the floor. A slab a few millimetres out suits a self-leveller, a floor sloping across a room may need a screed, high spots call for grinding, and many jobs use more than one together, which is exactly the judgement a specialist makes on site. Timber subfloors add the option of a plywood overlay to create a flat panel base. Matching the method to the actual problem, rather than forcing one approach onto every floor, is what gives an efficient, lasting result. The floor in front of them decides the mix of methods.

Why a Level Base Matters

The reason levelling matters is simple: every floor covering reveals the base beneath it. Tiles laid on an uneven floor lip at the edges and are prone to cracking or drumming, vinyl and hybrid planks telegraph every bump and dip so the light catches each imperfection, and timber on an uneven base creaks, gaps and flexes underfoot. The covering cannot hide what is under it, so a poor base shows through as a poor floor. This is why the unseen preparation is what a good finished floor depends on. This is the heart of why the trade exists at all, since the covering simply cannot improve on the base. A flat base is the one investment in a floor that never shows but always tells.

Different coverings have different tolerances, but none forgives a genuinely uneven base. Large-format tiles are especially unforgiving, since the bigger the tile the more a small dip shows as lippage, and click-together hybrid and laminate floors rely on a flat base to lock and stay locked without movement. Even carpet, which hides a lot, telegraphs a sharp hump or a soft spot. The flatter the base, the better and longer-lasting the floor on top of it. Bigger formats and harder floors are the least forgiving of all.

Getting the base right also protects the warranty on the floor above. Many flooring products specify a maximum unevenness the substrate must meet, and laying over a base outside that tolerance can void the manufacturer's warranty as well as produce a poor result, so the levelling is part of doing the floor properly. A floor that fails because the base was never flat is rarely the covering's fault. Investing in the preparation is what makes the spend on the finished floor worthwhile. Spending on a quality floor over a poor base is money half wasted. The preparation is what protects the rest of the spend.

Substrate, Priming and Moisture

A levelling compound or screed is only as good as the substrate it bonds to, so preparation comes first. The existing floor has to be sound, clean and free of dust, old adhesive, coatings and anything that stops a bond, which is why grinding and cleaning often precede any levelling. Priming the substrate is then essential, because a self-levelling compound poured onto an unprimed or dusty slab will not bond and can lift later. Skipping the preparation to save time is exactly how a levelling job fails. The bond is everything, and the bond starts with a clean, primed base.

Concrete moisture is the issue that catches the careless, and it matters especially in Queensland. A slab can carry moisture up from the ground, particularly where the vapour barrier is poor or absent, and a levelling compound or a floor covering laid over a damp slab can fail to bond, blister or lift as that moisture tries to escape. This is the same moisture problem that troubles other floor coatings, and in the humid climate it is a real and frequent risk. A specialist tests the slab for moisture before levelling, rather than assuming it is dry. Reading a slab as dry because it looks dry is exactly how a floor ends up lifting months later. A meter, not a glance, is what tells the real moisture story.

Where a slab is damp or marginal, it has to be managed rather than ignored. A moisture-tolerant primer or a dedicated moisture barrier can be used so the levelling and the floor above are protected, but that is a deliberate step taken because the slab was tested, not something a standard pour handles by luck. New slabs also need time to cure and dry before they are levelled and covered. Treating moisture as a first question, not an afterthought, is what separates a lasting floor from one that bubbles. Moisture handled early is a non-event; ignored, it is a callback.

The substrate work is unglamorous but decisive, much like the rest of this trade. Cleaning, grinding, repairing cracks, priming and checking moisture all happen before the satisfying pour, and they are where a careful specialist spends real time, because the levelling can only be as good as the base it is keyed to. A floor that is rushed onto a poor substrate looks fine on the day and fails later. The preparation is the half of the job that decides the other half.

Wet Areas and Screeding to Falls

Wet areas turn levelling on its head, because there the floor must slope rather than sit flat. A bathroom, laundry, shower or balcony needs the floor screeded to a fall so that water runs to the drain or waste rather than ponding, and getting that fall right, gentle but consistent, is a particular skill. A floor laid flat in a wet area, or with the fall in the wrong direction, ponds water, which causes problems above and below the surface. The screed to falls is what makes a wet area drain as it should. A fall that is too flat leaves water sitting, while one that is uneven pools in the low spots, so consistency is everything. The drain only works if the whole floor leads to it.

The fall is part of a wet-area system that includes the waterproofing. The screed creates the slope, the waterproofing membrane goes over it, and the tiles go on top, all built to the wet-area requirements of the National Construction Code, the framework administered by the Australian Building Codes Board. The falls and the waterproofing work together, since a fall with no membrane, or a membrane on a floor that ponds, both fail. This is why a bathroom waterproofing specialist and the screeding work hand in hand. Falls and membrane are two halves of one waterproof floor.

Getting wet-area falls wrong is a costly and common defect. Water that ponds on a bathroom or balcony floor sits against the waterproofing, finds any weakness, and eventually leaks into the structure below, which is exactly what the falls are there to prevent. A balcony that ponds is a frequent source of leaks into the rooms beneath it. A specialist who screeds the falls correctly, under proper waterproofing, is building a wet area that stays dry where it should.

Timber Subfloors and Queenslanders

Timber subfloors bring their own levelling challenges, and Queensland has plenty of them. The classic Queenslander and many older homes sit on timber bearers and joists, and over decades those floors can sag, slope, spring and develop high and low spots as the timber and the stumps move. Levelling a timber floor is a different job from levelling a slab, because you cannot simply pour a heavy screed onto a flexing timber surface. The approach has to suit the structure beneath. A timber floor flexes underfoot in a way a slab never does, so the levelling has to allow for that movement. Ignore it and a rigid material simply cracks.

The methods for timber subfloors work with the structure rather than against it. Minor unevenness can be taken up with a plywood overlay that creates a flat, sound panel base, larger problems may mean packing or sistering joists to lift sagging areas, and specialised flexible levelling products can be used where a rigid screed would crack. The right approach depends on how the floor moves and how far out it is, which a specialist assesses before choosing a method. Forcing a slab method onto a timber floor is a recipe for cracking and failure. Match the method to the movement and the timber floor stays sound.

Old Queenslander floors often need this work before a new floor goes down. A century-old hardwood floor may be beautiful but far from flat, so levelling it to take modern tiles, vinyl or hybrid is part of a renovation, done in a way that respects the timber structure and its movement. Where the existing timber floor is to be kept and refinished instead, a floor sanding and polishing approach is the alternative. Choosing between levelling for a new covering and restoring the original timber is part of planning the floor.

Concrete Slabs and Grinding

Concrete slabs are the most common substrate for levelling, and they bring grinding into the picture. A slab may be close to flat but carry high spots, trowel marks, old adhesive or coatings, and grinding removes these to leave a sound, even surface for a self-leveller or a covering to bond to. Grinding the slab is often the first step, taking down what is too high before filling what is too low. The two together bring a slab to a flat, sound base efficiently. The slab sets the starting point, and how flat and sound it already is decides how much levelling follows. A good slab needs little; a poor one needs both grinding and filling.

Grinding concrete carries a real health hazard that a professional controls. Cutting and grinding concrete releases respirable crystalline silica dust, which is dangerous to breathe and tightly regulated, so a professional uses dust extraction or wet methods and proper respiratory protection rather than filling the room with dust. The duties around silica dust are set out by WorkSafe Queensland. An operator grinding a slab in a dry cloud with no extraction is cutting a corner that matters for health, not just for the finish. Dust controlled at the source is the mark of a careful operator.

The condition of the slab can also reveal work that belongs to the concreter. A slab that is cracked, drummy or badly out of level may need repair, or in extreme cases replacement, before levelling makes sense, since a leveller follows a failing slab rather than fixing it. Where the concrete itself is the problem, a concreting specialist addresses the slab before any levelling. Sorting the slab first is what lets the levelling deliver a flat, lasting base.

Flatness, Tolerances and Standards

Flatness is measured against a tolerance, not judged by eye, which is why specialists talk in millimetres. The common measure is the deviation under a straightedge laid across the floor, with a flat floor varying by no more than a few millimetres over a couple of metres, and different floor coverings specify their own acceptable tolerance. A floor that meets the tolerance the covering requires will lay flat and true, while one outside it shows as lippage, rocking or telegraphing. The tolerance is the objective target the levelling aims at. Without a tolerance, flat is just an opinion, and opinions vary between the person laying and the person paying. A measured target removes the argument.

The standards behind flooring and its preparation set these expectations. Recognised standards published by Standards Australia cover floor coverings and their installation, including the substrate flatness they need, and flooring manufacturers reference these in their own requirements. A specialist working to a tolerance is working to a defined target rather than a vague sense of flat enough. Knowing the tolerance exists helps you understand why a careful preparation job measures rather than guesses. A straightedge tells the truth a confident eye sometimes does not.

For the home owner, the practical takeaway is to ask about the tolerance. A specialist who can tell you the flatness the floor will achieve, and that it meets what your chosen covering requires, is one preparing the base properly, while a vague answer about it being good enough is less reassuring. The tolerance is what links the levelling to the floor that goes on it. Asking what flatness the job will deliver is a fair and useful question.

Screeding Over Underfloor Heating

Underfloor heating and screeding go together, because a screed is how heating is built into a floor. Hydronic pipes or electric heating mats are laid over the substrate and a screed is poured over them to encapsulate the elements and spread the heat evenly, leaving a flat surface for the floor covering on top. The screed both protects the heating and acts as the thermal mass that radiates the warmth, so it is integral to how the system works. This is a specialised pour where the depth and the cover over the elements matter. Too little cover over the pipes risks damage and uneven heat, while too much wastes energy warming the screed. The depth is a balance the specialist gets right.

The detail of screeding over heating has to suit the system. The screed has to fully encapsulate the pipes or mats without voids, be the right depth for the heat to spread, and be allowed to cure properly before the heating is run, since rushing the heat can crack a green screed. Coordinating the screed with the heating installer ensures the elements are protected and the floor performs. A underfloor heating installation specialist and the screeding work closely on these floors. The heating and the screed are really one system.

For most Queensland homes underfloor heating is a comfort feature rather than a necessity, but where it is wanted the screed is central to it. A well-screeded heated floor is even, warm underfoot and ready for tiles or another covering, while a poorly screeded one can have cold spots or crack over the elements. Planning the screed and the heating together from the start gives the best result. It is a job where the preparation and the system are inseparable.

DIY vs Professional

Floor levelling looks simple and is one of the easier jobs to get wrong. Self-levelling compound, in particular, tempts people because it is sold as self-levelling, but it has a short working time, demands correct priming and mixing, and waits for no one once it is poured, so a first attempt often ends with a floor that is far from flat. A patch of unprimed slab, a mix that is too thick or too thin, or a pour that sets before it is spread can all leave a result worse than the starting point. The material is less forgiving than it appears. The very name promises a result the product does not deliver on its own. Skill and preparation, not the bag of compound, are what make a floor flat.

A professional gets a floor flat to a tolerance because they prepare and work to a method. They grind and prime the substrate, check the moisture, mix the compound correctly, and pour and work it within its window, which is exactly the discipline a one-off DIY pour lacks. Screeding to a fall, in particular, is a real trade skill that is hard to learn on your own bathroom floor. The cost of a professional is set against the cost of a floor that has to be ground off and redone. Redoing a failed pour costs far more than doing it once.

For a small, simple, dry-area patch a careful DIY attempt can work, and it is fair to say so. For a whole room, a wet area needing falls, a timber subfloor, or any slab where moisture is unknown, the professional result is the spend that actually lasts and keeps the floor above it sound. Since the floor covering depends entirely on the base, a poor levelling job is rarely a cheap mistake. Knowing which situation you are in is the key to not wasting money.

Licensing and Who Does It

Floor levelling and screeding sits in a lighter licensing space than the structural trades, but it intersects with building work. Levelling and screeding as preparation for a floor covering is often not separately licensed, but where it forms part of building work, particularly wet-area work tied to waterproofing, it falls within the building work the QBCC regulates. Wet-area work in particular is treated seriously because of the waterproofing and leak risk. A specialist should be clear about where a given job sits. Dry-area levelling and wet-area screeding are treated quite differently because of the waterproofing risk. A specialist who knows the line is one worth trusting.

Beyond licensing, the skill and the method are what really matter. Getting a floor flat to a tolerance, screeding a precise fall, and managing priming and moisture are genuine trade skills that a licence alone does not guarantee, so a track record on similar floors counts for a great deal. An established specialist also carries insurance against the damage that work inside a home can cause. Choosing on demonstrated skill, with the right licensing where it applies, is what gives a base you can rely on.

The practical approach is to match the specialist to the job. For a dry-area level, the priority is proven skill at getting floors flat, while for a wet area the waterproofing and falls bring licensing and certification into play, so confirm the right people are involved. A specialist who is upfront about the method, the moisture and any compliance is the one to trust with the base your floor depends on. The right preparation is invisible in the finished floor, which is exactly why it is worth getting right.

What Drives Floor Levelling Pricing in Queensland

Floor levelling pricing follows a few clear drivers, and understanding them helps you read a quote rather than just compare per-metre rates. The first is the method and the depth, because a thin self-levelling pour is far cheaper per metre than a thick screed, a wet-area fall or a timber-subfloor overlay, and the right method follows the floor. The second is the condition of the substrate, since grinding high spots, repairing cracks, priming and managing moisture all add work before any levelling material goes down. A quote that separates the preparation from the levelling lets you see what you are paying for. The specialist who inspects the floor before quoting is giving you a number that holds.

Area, access and the wet-area factor round out the cost. A larger floor costs more overall even as the rate eases, a difficult or cluttered space is slower to work, and a wet area needing precise falls under waterproofing is more involved than a simple dry-area level. A job well outside the metropolitan South East can carry a travel component too. None of this is hidden when the specialist explains it, and a good one walks you through what your particular floor needs. The floor in front of them, not a standard rate card, is what sets the real price. A walk across it tells the specialist most of what the quote depends on.

Moisture and substrate condition can change the price once the floor is examined. A slab that reads damp and needs a moisture barrier, a badly cracked substrate, or a timber subfloor that is worse than it looked all add to the cost, which is why a sight-unseen figure can move. A specialist who checks the floor and the moisture before quoting is giving you a realistic price rather than an optimistic one. A quote built on a proper look at the floor is one you can rely on.

An honest quote sets out the method, the preparation and the moisture rather than burying them, and the specialist who explains how the base will be made flat and sound is usually the one to trust. When one price comes in well below the rest, the question to ask is what it leaves out, because a cheap quote that skips priming, ignores moisture, or uses a thin pour where a screed is needed will cost more when the floor above it fails. Real value in levelling is a base that the finished floor lies flat on for years, not the lowest figure per metre. That is the standard worth measuring any quote against.

What to Look Out For

Start with the substrate preparation, because it is where the result is won or lost. A genuine specialist grinds and primes the substrate, checks it is sound and clean, and chooses the method to suit, while a quote that is vague about preparation, or assumes a quick pour over whatever is there, is a warning sign. The preparation is invisible in the finished floor, which is exactly why it is tempting to skimp on. Asking how the substrate will be prepared and primed is the single most useful question. How a base is prepared decides almost everything about how the floor turns out. A specialist confident on preparation is one who has done it properly before.

Be just as firm about moisture, especially on a slab. In the humid Queensland climate a leveller or floor laid over an untested, damp slab is at real risk of failing to bond or lifting, so a specialist who tests the slab for moisture and explains how a damp one will be handled is doing the job properly. An operator who never raises moisture is overlooking the most common cause of a failed floor. Asking whether the slab will be moisture-tested separates the careful from the casual.

Watch the method against the job, particularly in wet areas. A wet area needs a screed to falls under proper waterproofing, not a flat pour, so an operator who treats a bathroom floor like a living-room level is heading for a ponding, leaking result. Equally, a deep correction forced into a thin self-leveller, or a heavy screed on a flexing timber floor, is the wrong method for the situation. A specialist who matches the method to the floor and the use is the one doing it right.

Beyond the specifics, the ordinary signs still apply. A clear written quote, examples of previous floors, safe handling of grinding dust, public liability insurance, and a straight answer about preparation, moisture and the flatness to be achieved all point to a professional, while a price far below the rest, vagueness about prep, or silence on moisture point the other way. The consumer protections that sit over the work are administered by the ACCC and the Queensland Office of Fair Trading. Judging the job on the preparation and the method, not just the price, is what keeps a floor flat.

How to Get Useful Quotes

A useful levelling quote starts with a clear picture of the floor and what is going on it. The area in square metres, the substrate, whether it is a concrete slab or a timber subfloor, how far out of flat it is, and the floor covering that will go on top all shape the method and the price. Whether it is a wet area needing falls matters a great deal, as does anything you know about cracks, moisture or how the floor moves. A description and some photos, ideally with a straightedge or level showing the dips, let a specialist quote far more accurately. A clear photo with a level across it answers half the questions.

Be clear about the covering and the conditions, because they decide the method. Telling the specialist whether tiles, vinyl, hybrid, timber or carpet are going down sets the flatness the base must reach, and mentioning a wet area, a timber subfloor, or a new slab tells them what they are dealing with. If the slab is new, say when it was poured, since curing affects when it can be levelled. The more the specialist knows up front, the closer the quote lands to the final cost.

It is worth getting more than one quote, and posting once puts the job to several Queensland levelling specialists at the same time. When the quotes come back, compare what each includes, the method, the preparation and priming, the moisture testing, and the flatness to be achieved, rather than only the price per metre. The cheapest figure often turns out to skip the priming, omit the moisture check, or assume a thin pour where a screed is needed, and the gap shows the moment you ask. Listing the job on The Quote Yard reaches several specialists in a single step, and asking them all the same questions gives a like-for-like view.

Warranty, Insurance and Australian Consumer Law

Warranty on levelling and screeding is mostly about the base staying sound and bonded. A properly prepared, primed and laid base should stay flat and bonded for the life of the floor above it, and a reputable specialist stands behind that, so a base that lifts, cracks or fails through how it was prepared or laid is theirs to put right. Because the floor covering depends on the base, the levelling warranty matters to the whole floor. Keeping the quote, the invoice and a note of the method and any moisture treatment protects you if a problem appears.

Insurance matters because the work happens inside a home and involves grinding, dust and wet materials. A reputable specialist carries public liability insurance covering damage during the work, and an established one confirms it readily, which is reasonable to expect for work that can affect the surrounding home. A reluctance to discuss insurance is a fair reason to look elsewhere. That cover is built into a professional's rates, and carrying it is part of what makes a business real rather than casual.

Australian Consumer Law applies on top of all this and cannot be contracted out of. The protection requires goods to be of acceptable quality and services to be carried out with due care and skill, so a base that fails and takes the finished floor with it is not simply your bad luck. Where a dispute cannot be resolved directly, the Queensland Office of Fair Trading and the national consumer regulator provide the avenues for consumers, and the framework is published by the ACCC. The full range of flooring options across Australia sits on the national flooring services hub, and tradespeople looking for work can find paid job leads on the Queensland tradie job leads board and at flooring installer jobs. Knowing what makes a base sound, and choosing a specialist who prepares, tests and levels properly, is what keeps a floor flat for years.