How to clean fibrestone

I have some garden furniture which is made out of a material referred to as ‘fibrestone’, which I’m guessing is some kind of resin - it looks like stone from a distance, and is pretty heavy, but is some kind of plastic material - this is a link to the product (table and chairs).

After several years sat outside in all weathers, it has developed some grey streaking which is untouched by simple scrubbing. I tried blasting it with a high pressure water hose that I use to clean stone paving, but it had zero effect.

Is there some magical product out there I can use to clean it?

Interesting - this appears to be a different animal from Fiberstone - which is a ceramic-steel industrial composite (and is presumably not lightweight).

It sounds like this furniture might be made from a composite of resin and wood or other organic fibres - in which case, I would suspect the staining to be some sort of biological activity happening within the porous fibres inside the resin matrix.

The page you linked states that the product is not fully weather-resistant.

Yeah, seems there is a conflict in the tradename. It looks as if this is the material.

Mangetout has it right. Cellulose fibre, acrylic resin, filler, plus melamine to waterproof it. But it remains somewhat porous. I would look towards some somewhat more serious household cleaners. Bleach, bathroom/toilet cleaner. The streaking may be mould - so treat it like you would bathroom tiles. After that, an abrasive would take it down to a new surface, but will expose new fibres.

I wondered about bleach. I might try it on an underside area as a test. I don’t ‘think’ it’s mould, more likely good old fashioned London pollution - the streaking runs down the sides and looks like streaks of dirty water.