A large share of new apartments, offices, hotels and ground floors are built on concrete. For a wood floor, concrete changes the conversation. A slab cannot hold a floor nail, it can carry moisture long after it looks dry, and its surface is rarely as flat as a plywood deck. None of that rules out an oak floor, but it does mean the board, the installation method and the site preparation have to be agreed together. This article sets out what a buyer should specify for engineered oak over a concrete slab, and which decisions belong to the installer and the adhesive maker rather than to the factory.
Why concrete needs its own conversation
Three properties of a slab shape the specification.
- It cannot be nailed. Mechanical fastening needs a wood subfloor. Over bare concrete, the floor is normally glued down, or laid over an underlayment where the board and method allow it.
- It holds moisture. Concrete is made with water and releases it slowly. A slab can also take up moisture from the ground below. Wood responds to moisture, so the slab condition matters as much as the board.
- It has its own flatness. A glued floor follows the surface it is bonded to. Hollows and ridges in the slab show through as rocking boards, hollow spots or uneven joints.
Our general guide to installation method and the specification covers nail-down, glue-down and floating across all subfloors. This article stays with concrete.
Who decides what over a slab
| Decision | Who makes it | What the factory needs to know |
|---|---|---|
| Whether the slab is ready for wood | Installer, testing on site | The result, if it affects construction or timing |
| Moisture test method and acceptable result | Installer, following the adhesive maker and local guidance | Nothing to set; it is a site decision |
| Adhesive, trowel and any moisture control layer | Adhesive maker, applied by the installer | The adhesive chosen, if known |
| Flatness and preparation of the slab | Installer | Any floor height limit after leveling |
| Installation method | Installer | Glue-down, or floating to be agreed |
| Construction, thickness, width, profile, finish | Buyer, with the factory | All of it, written in the RFQ |
The factory does not test the slab and does not set moisture limits. Those belong to the installer and to the adhesive maker, whose product has to perform on that slab. The factory’s part is to build a board that suits the method and to hold the specification consistently across the order. The NWFA publishes installation guidance that many installers reference for concrete subfloors.
Construction: why engineered is the usual choice
We make three constructions: solid, 2-layer engineered and 3-layer engineered.
- 2-layer engineered is a sawn oak wear layer bonded to a stable core. It is our main engineered construction and a practical choice where floor height is limited, which is common in apartments and renovation work on slabs.
- 3-layer engineered puts the oak wear layer over a cross-layered core with a backing layer. It is well suited to wider boards and larger open areas where dimensional stability matters, such as open-plan ground floors.
- Solid oak is more demanding about subfloor conditions. It can be glued in some situations, but over concrete the installer and adhesive maker should confirm it for the specific project before it is specified.
The 2-layer vs 3-layer comparison goes into the two engineered builds in more detail.
Thickness and floor height
On a slab, floor height is often fixed by things that already exist: door frames, thresholds to tiled areas, kitchen units, lift landings. Any leveling compound or moisture control layer the installer adds also takes up height. Work back from the finished floor level the drawings allow, subtract what the installer needs for preparation, and the remaining height is what the board can use.
Our standard builds are 5/8” (15mm) overall with a 3mm sawn wear layer and 3/4” (20mm) overall with a 6mm sawn wear layer. Other thicknesses from 3/8” (10mm) to 13/16” (21mm) are made to order. A thinner build helps where height is tight; a thicker wear layer leaves more material for future sanding. The choice is a balance between the two, and it is easier to make before the slab is prepared than after.
Glue-down or floating
Glue-down is the usual method over concrete. The adhesive maker specifies which adhesive suits the slab, how it is spread and what preparation is needed. Full-spread adhesive holds the whole underside of the board, which is one reason wide engineered boards are often glued down. If a specific adhesive has already been chosen, tell us, because the underside of the board is part of what the adhesive bonds to.
Floating means the floor rests on an underlayment and is held together by its own joints. Our Tongue & Groove profile is machined on all four sides and is intended for glue-down or nail-down installation. If a floating floor over the slab is being considered, raise it before the specification is fixed, so the installer, the buyer and the factory can agree whether the board and method suit each other.
Width and length over a slab
Wider boards show more grain and give a calmer floor, and they also make any unevenness in the slab easier to see along the edges. Over concrete, width should be chosen with the installer’s view of the slab in mind. Our widths run from 3-1/4” (83mm) to 9-1/4” (235mm) in current production, with 3” (76mm) to 12” (305mm) to order. Longer boards bridge more of the slab surface, so flatness matters along their length as well. Our wide plank guide covers what changes above 7-1/2” (190mm).
Moisture: two sides of the same problem
Moisture has to be controlled at both ends.
At the factory. Lumber is kiln-dried and checked against the moisture target for the order, and moisture is checked again before packing. Boards leave in cartons that are wrapped on pallets. Our article on moisture control in flooring production explains these steps.
On site. The slab must be ready before the wood arrives. The installer tests it using the method the adhesive maker and local guidance call for, and decides whether a moisture control layer is needed. Boards should stay in their cartons until the site conditions are right, and acclimation follows the installer’s instructions. If the slab is heated, the heating system maker adds its own procedure; see engineered oak flooring over radiant heating.
Pattern floors over concrete
Herringbone, chevron and parquet are often glued directly to a slab. Blocks meet at angles, so the slab’s flatness affects every joint, and the end profile matters as much as the side profile. With T&G on all four sides, each block engages its neighbors; with square edge, available on request, the floor depends entirely on the adhesive and the slab. Agree profile and method together with the installer.
What to put in the RFQ
- The subfloor in each area: concrete slab, and whether it is new or existing
- Whether there is radiant heating in the slab
- The installation method: glue-down, or floating to be agreed
- The adhesive system, if already chosen
- Any floor height limit after slab preparation
- Construction, overall thickness and wear layer
- Width, length, grade, color, texture and sheen
- Profile: T&G on four sides, or square edge
- Quantity in sq ft per area, and delivery address or port
Working with Vu Uy Wood
We manufacture made-to-order solid and engineered French White Oak flooring in Song Than 3 Industrial Park, Ho Chi Minh City, and have done so since 2006. The route from kiln drying to profiling and packing is shown on our Production page. Tell us the subfloor, installation method and any height limit along with your selections on the Specify page, and the specification is reviewed with them in mind. We normally reply within one working day.