The installation of Vinyl Flooring is only half the story; the other half, and the part that will make or break the floor's appearance in a month's time or its peeling and graining after just a year's use, is subfloor preparation. A smooth, dry, clean and level subfloor is essential. Small bumps show through vinyl, moisture trapped under them will ruin any adhesive used, and dust or residue will invalidate any manufacturer's warranty. With UK homes, the following important steps towards achieving this essential subfloor integrity should be taken: appropriate moisture testing, removal of any old adhesive, levelling off hollows using an appropriate levelling compound, and confirming that the overall subfloor flatness meets the requirements established by the flooring manufacturer. The installer must also use the appropriate underlay (acoustic, thermal and adapt to subfloor movement) and allow sufficient time for the vinyl to acclimatise prior to installing. If any of these steps are not accomplished, the quality of the finished floor will suffer regardless of how many current-style tiles or planks have been installed; if accomplished correctly, the quality of the finished floor will have seamless visual integrity, long life expectancy and be comfortable for walking on. Prior to commencing work, request the results of moisture testing and a written description of the subfloor specification; this is the best written assurance or protection you can purchase.
Why Choosing A Subfloor Is More Important Than A Plank:
Why is subfloor preparation so important? Well, vinyl has to be thin to be easily installed and because of that, it's also very sensitive to the surface it's laid on. Think of your finished floor as a picture frame, your planks are now the picture, the wall the subfloor: if the wall is out of shape, the picture will never hang straight. A well-prepared subfloor provides four things:
A properly prepared subfloor does four things:
a. Ensures the vinyl is flat throughout and doesn't crease or wave. Supports the vinyl so it will be completely flat.
b. Keeps dry and prevents the masking tape from softening and allowing moisture in the vinyl to lift the adhesive, causing failure or mould.
c. Is clean and bonded, so primers and spreading compounds stick.
d. Is stable (floating click systems versus full adhesive installation) and compatible with the vinyl system and traffic predictions.
Almost every problem you may see later, popping ridges, open seams, buckling in warm weather, can usually be traced to one of these four failures. Let's start here.
Pro-Tip: Get the fitter to confirm that all subfloors are checked and signed off before they lay any vinyl. If they refuse/don't know how to do this... run!
Recognize The Sort Of Vinyl You Have Because It Alters The Subfloor Rules:
Not all vinyl is installed the same way, and that changes the subfloor requirements:
1. Glue-down vinyl sheet or tiles: require a permanently clean and dry, level, solid surface. Moisture can cause adhesion failure.
2. Loose-lay or high-weight click vinyl (rigid core, SPC/WPC) is more forgiving of a small in levelness but must still be laid onto a rigid, flat subfloor. Most are laid with an underlay and require a flat surface to prevent "rocking".
3. Click-lock plank (LVT with float): must have expansion gaps and uniformity of subfloor to keep joints from opening when moved.
4. Vinyl with underlay already bonded/attached: Still requires a flat, dry surface, but underlay assists with aesthetics (though a step or gap) and acoustics.
Ensure you consult the installer company's installation manual for that particular product first; their tolerances for flatness and moisture are the contract you are required to comply with.
Pro-Tip: Find out which vinyl each installer feels will work best on your uneven subfloor. If one has an installer who says you can get away with a glued installation on an uneven subfloor without levelling, have a second installer give you a second opinion.
The Narrative of Moisture: Hazards, Tests & Management
Moisture is the biggest killer of any vinyl installation. It will attack adhesives, will cause vapour blisters, will promote mould growth and will certainly damage your warranty.
There are several ways that moisture can gain access to your subfloor:
a. moisture escaping from the ground via a rising slab or screed;
b. leaks in the plumbing or unnoticed wet trades;
c. damp external conditions with insufficient time for new screeds to cure;
d. over condensation due to poor ventilation of building voids.
Tests available:
1. In-situ relative humidity (RH) probes: modern and non-destructive. Their popularity has grown since their introduction and they are now considered the best method of taking readings from new screeds.
2. Surface hygrometers measure the surface RH of the slab, but are less reliable indicators of the actual moisture contents.
3. Calcium carbide test: destructive (small core) but provides a quantitative measure of the moisture content of any concrete. It is still used by some older setup contractors.
4. Moisture meters for wood measure the surface moisture available. Useful for timber subfloors, but should not be used as a moisture test for concrete slabs.
Don't guess: Ask for written test results if an installer claims that the floor is "dry enough" without them.
Moisture management:
1. If tests are within product limits: Continue and use a vapour-resistant adhesive or primer as per recommendation.
2. If tests indicate high moisture levels, you may require an appropriate DPM bonded or loose-laid, special moisture-resistant primers and levelling compounds, or a drying period for the screed. In certain circumstances, the only safe solution is a sealed system with an independent DPM beneath an engineered screed.
Pro-Tip: Get a copy of the moisture test and the manufacturer's maximum allowable moisture number for the flooring on the same page; that way, you can see whether the subfloor conforms to the vinyl's specifications.
Levelling & Surface Flatness: What "Flat" Actually Implies
Vinyl can stand up to less discrepancy than many would think; variations, however subtle, will show through. Any inconsistency will 'telegraph through' with the finest ripples, showing up as visible lines.
What to check:
a. Straightedge and visual inspections: Use a long straightedge or spirit level across spans to identify high and low spots.
b. Walk the room: listen for hollow sounds, which represent empty spaces or rubble beneath the subfloor.
c. Measure critical tolerances: product documents will state the acceptable flatness (e.g., "no more than small millimetre variance over a given length" adhere to spec).
Uneven floors renovations:
1. Grinding high spots: for concrete, grinding takes the peaks off.
2. Cementitious levelling compounds: for larger imperfections and a flatter surface, use a suitable self-levelling compound for vinyl. These can be pumped and screeded to the manufacturer's thickness specifications.
3. Plywood overlay: where timber floors are used that have deflection or the joists are too uneven, a plywood overlay may be the best solution (possibly with a levelling screed). This provides a sound, uniform surface suitable for vinyl (especially a floating installation).
Use levelling compounds which are approved for use beneath a vinyl many gypsum-based products can clash with humid areas or specific types of adhesives.
Pro-Tip: Show them the levelling compound's drying & cure instructions and leave enough time for a full cure before continuing. Cutting corners here is a recipe for failure.
Contaminant-Free, Clean Surfaces: What Should Be Eliminated & Why
Must be free of anything that inhibits bonding:
1. Old glues and adhesives, filler and grease.
2. Paint overspray, gloss, sealants, oils or trade residues.
3. Lumps of dust, debris, plaster or drywall compound.
4. Laitance or free silicates from concrete or other abrasive deposits are to be removed mechanically.
The most common mistake is putting down a new adhesive over existing glue or paint. Adhesives need to be adherent to a primer and free of any residue. If your installer says, "Let's go over it," ask, "how are you going to mechanically prepare it (shotblast or grind) and why?"
Pro-Tip: Request a photo from your installer of the primed and dried floor prior to applying the adhesive, it's good records.
Why Primers are Important:
Primers assist the adhesion of the levelling compound and the adhesive. They seal the wall to prevent pinholes in the adhesive and help the final bond of the vinyl.
a. Use the primer as recommended by the levelling compound and adhesive manufacturers. Do not mix and match without approval.
b. Tough primers are moisture-tolerant and aid a degree of vapor control, and this should be incorporated into a vapor control plan if moisture is evident.
c. Primer must be applied to clean, dust-free surfaces; a dusty primed surface bonds poorly.
Pro-Tip: If an installer recommends "we don't need primer", get a manufacturer's signed waiver. Most systems require a primer to meet warranty.
When & How To Utilize Damp-Proof Membranes (DPMs):
A genuine DPM (damp proof membrane) is a barrier to the movement of water vapour from the substrate. In the past, a DPM would have been installed below the ground floor slab, however in today's retrofit market, the DPM will be surface applied systems or systems designed to stop the ingress of vapour.
When to consider a DPM:
a. Ignoring more than acceptable moisture results, then it is not practical to dry using moisture tests.
b. Pattern to be formed over existing floors with no information or a history of rising damp.
c. Where local law or the product manufacturers require it for warranty purposes.
Types:
1. Liquid-applied DPMs painted on or rolled on coverings applied to concrete that adhere to the surface and serve as a vapour barrier.
2. Sheet membranes pressed and taped; more typical under new construction.
3. Surface applied membranes with levelling: some systems combine a bonded DPM with a levelling layer bonded integrally.
Keep in mind: Moving DPM without solving edge drainage or trapped moisture may lead to other problems. Never undertake DPM works in isolation but ensure these are addressed in a broader moisture and drainage management scheme.
Pro-Tip: A DPM impacts how the floor 'breathes', so get the skirting and door junctions worked out so you don't trap the moisture in the fabric of the rest of the building.
Timber Subfloors: Rigidity, Repair & Isolating Movement
Timber subfloors will have different properties from concrete. They move and creak and can be sensitive to localised humidity swings.
Key checks:
1. Structural Integrity joist fixings, stiffness of system and bounce (would prefer limited bounce or none in vinyl application). Vinyl needs a firm base.
2. Flatness of surface: Boarded or plywood-faced panels are frequently the finish for vinyl. Use bridging or overlay if the joist spacing is wide to minimise deflection.
3. Moisture timber expands and contracts with humidity; check it travels and where outside tolerances, don't put it in. If you cannot control the room humidity, then...
Fixes for timber:
a. The plywood overlay (tongue and groove, or screwed and bonded) forms a stable face. Use suitable screws, seal the screwheads, and make sure the overlay is ready for priming or, is surface prepared for bonding.
b. Isolating underlay where click systems are used, a compatible underlay ensures the floating floor gives the desired acoustic/comfort performance.
Pro-Tip: Do not fit vinyl over pre-existing, deflecting old hardwood flooring unless the floor is braced with a stiff overlay. Adhesive to the old floor is not a DIY patch.
FAQs:
1. How can I tell if the concrete subfloor has dried sufficiently for the vinyl?
Don't touch. Request a moisture test, either an in-situ hygrometer (RH probe) or a CM (carbide) test in the case of certain specifications. Use the test reading against the limit set for the moisture content of the vinyl by the manufacturer. If it is higher, don't go ahead and rather dry it out properly or reach a written agreement regarding an approved DPM system.
2. Can I put Vinyl directly on wood/tiles?
Sometimes, but only after detailed checks. Tiles tend to telegraph through vinyl unless a stable, flat levelling layer or plywood overlay is applied. Timber boards need to be in excellent, rigid condition, sealed and stable, usually with a plywood overlay. No exceptions without the manufacturer's recommendation.
3. Installer estimates that levelling will be completed 'by the end of the week', is this feasible?
Drying and curing times for levelling compound vary with depth, room temperature and the product- it can take days to weeks. An honest installer will specify how long it will take for the compound to dry and will not proceed until the manufacturer's cure time and moisture levels are reached- don't accept vague times, ask for the spec.
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