Most engineered-wood floor failures are not product failures, they are moisture failures. Cupping, gapping, adhesive breakdown and lifted boards almost always trace back to a subfloor that was too wet, too uneven, or commissioned too fast. The good news for a specifier is that the controls are well established and entirely writable into a specification. Here is what to set.
Moisture: the number that matters
The single most important check is subfloor moisture. Engineered oak should be laid over a base tested to a maximum of 75% relative humidity (BS 8203) before installation, or with a surface damp-proof membrane applied where that level cannot be achieved. Cementitious screeds dry at roughly a day per millimetre for the first 50 mm and slower beyond, so this is a programme item to test, not assume. On anhydrite (calcium sulfate) screeds, the surface laitance must be removed and the screed verified dry before bonding.
Flatness and substrate condition
For a bonded floor, the substrate should meet Surface Regularity SR1, a maximum 3 mm deviation under a 2 m straightedge, and be sound, clean and free of contaminants. Out-of-tolerance areas are corrected with a suitable smoothing compound before laying. Flatness is not cosmetic: hollows put point loads on the bond line and the board edges.
Acclimatisation and adhesive
Boards are acclimatised on site to the in-service conditions per the manufacturer’s instructions before laying, and bonded with FG MonoSil, a single-component MS-polymer adhesive, over the prepared substrate. A flexible MS-polymer bond accommodates the small seasonal movement engineered oak makes, which rigid adhesives do not.
Underfloor heating
Engineered oak is well suited to underfloor heating, with one rule that protects the floor: keep the maximum floor surface temperature at 27 °C, and commission the system gradually, bring the screed up and back down to protocol before and after laying. Rapid heating of a green screed or a newly laid floor is a common, avoidable cause of gapping.
The specifier’s checklist
Put four things in the specification and most moisture risk disappears: a subfloor RH limit of ≤75% (BS 8203) or a DPM; SR1 flatness; on-site acclimatisation; and a controlled UFH commissioning sequence to 27 °C max. Get those tested and recorded, and the Winderen or Vermont floor performs as specified.
Specifier reading
- Engineered oak acoustic performance and Part E
- Engineered oak fire rating explained
- Engineered wood flooring, the specifier pillar
Order Winderen samplesSee the Winderen range
Scottish projects raise particular moisture and heating questions, see specifying engineered oak for Scottish projects.