Treatment based on lactic acid has been developed and optimized for wood modification by Noël et al. (2009, 2015) and Grosse et al. (2016). This treatment aims to improve wood dimensional stability and biological resistance for its usage outdoor. The process consists in oven-dried beech wood (Fagus sylvatica L.) impregnation with lactic acid oligomers (OLA), followed by curing in dry conditions. Treatment efficiency depends on curing conditions and increases with temperature (Grosse et al, 2016). At 160°C, treatment conferred very promising properties to wood, in particular regarding anti-swelling efficiency (ASE), moisture exclusion efficiency (MEE) and biological resistance and it was persistent in wood (respectively ASE*, MEE, WLCV and WLCP, and LR in Table 1). Mechanical performance evaluation through 3 points bending test, showed the modified wood was more brittle but could resist higher loads. OLA polycondensation was assessed by Fourier transform infrared (FTIR) spectroscopy (Fig. 1). In order to evaluate possible up-scaling of this treatment, larger samples were impregnated. Density profile was studied on 100x100x550 mm3 samples and showed a homogeneous repartition of product in wood. Homogeneity of resistance against fungal decay was assessed with EN113 on samples of 15x25x500 mm3 (Fig. 2).