To take stains out of a stiff Canvas, you may want to try oxi clean versatile stain remover.
But make sure to get the free, It is free of perfume, dyes and Chlorine. Mix a little water and dry powder in a bucket. Scrub the canvas with a stiff brush, and sponge. Repeat in 10 min if all the stains were not removed. For stubborn stains, I dipped the corner my sponge in to the water mixture just enough to get the sponge a little wet and then dipped it straight into the Oxi clean powder and scrubbed.
I just cleaned the canvas on my pop up camper and the water stains came out very nicely. Just wish it worked as good on mildew. Good luck
But make sure to get the free, It is free of perfume, dyes and Chlorine. Mix a little water and dry powder in a bucket. Scrub the canvas with a stiff brush, and sponge. Repeat in 10 min if all the stains were not removed. For stubborn stains, I dipped the corner my sponge in to the water mixture just enough to get the sponge a little wet and then dipped it straight into the Oxi clean powder and scrubbed.
I just cleaned the canvas on my pop up camper and the water stains came out very nicely. Just wish it worked as good on mildew. Good luck
