Thin spray-on liners (TSLs) have been attracting increasing attention as an alternative to steel mesh in underground roadway support. In order to investigate the shear strength of glass fibre reinforced TSLs, an improved punch test was developed: the steel ring is replaced by TSL plates and four screws are used to tighten the TSL sample between the clamping plates to ensure stable and symmetrical loading. Four different glass fibre contents were tested to evaluate the effect of glass fibre reinforcement on the shear strength of TSLs. The effect of loading rate was studied. The results suggest that the steel punch can shear through the polymer sheet well and the failure mode can be easily identified. The results are consistent and easily calculated. The shear strength increases with glass fibre content. The TSL material samples showed good linear behaviour prior to reaching ultimate load and ductile behaviour that reflects the fibre reinforcement of failed resin during the yielding stage of the sample, which is beneficial to support in underground mines. Although there may be some impact of the shearing rate on the shear strength, the effect is negligible for the loading rates used.