Weathering your Glawning: why new canvas may let in water

In short

New polycotton may let a little water through the first time it gets properly wet. As it soaks and dries, the fibres swell and close the weave and stitch holes. One or two wet and dry cycles usually do it.

What's happening

The canvas has a water-repellent treatment, but in heavy, persistent rain or strong wind some water can get through on first use, especially along the seams. As the fibres get wet they swell, and as they dry they tighten the weave and close up the needle holes.

Speed it up at home

Pitch your Glawning in the garden and peg it out, not too tightly.
Let it get completely soaked by rain or a hose.
Let it dry out fully.
Repeat if needed. Polycotton usually needs only one or two cycles.

Damp inside?

Some moisture is normal until the canvas has fully weathered, plus general condensation. Lighting the stove reduces it significantly. Water pooling under your matting usually comes from above; the groundsheet itself is waterproof.