Does anyone know of a product that can be sprayed / applied to a polycotton cover that can clean it and get rid of the green slimy stuff that starts growing this time of year without damaging its waterproofing properites - preferably avoiding a lot of elbow grease!!! I'm sure there must be product out there. I'd appreciate any ideas. Thanks Paul

Last year cleaned mine with a broom and hot water containing handwash liquid, dried it then painted it with Tent reproofing.  Worked well, but now has gone green again!

Last time I did this job I stretched cover out on a hard surface, poured hot water + detergent over it, left it to stand, and then brushed with a stiff brush, hosing afterwards to get the suds off. It worked well, but - as last correspondent says - it doesn't last.

Pressure washers don't work; some examples down at the Harp bear stripey testatment to this!

Similar to above, stretch out the cover on some concrete.  I used a pressure washer with a t-racer attachment, as the normal lance is rubbish at cleaning the algae off, as you get stripes.

You can also use algaeside suitable for swimming pools/ponds after looking where the run off may end up, to get the stubborn green slime off in a huge trough.  

Re proof with Graingers Fabsil, brush on from tin.  The spray is expensive and you will needs loads. Or use Holmenkol reproofing stuff.  I've used Travis Perkins..waterseal... a bargain compared to the cost of the fabsil £14 for 1    against £14 for 5litres 

 The waterseal uses a white spirit base, as opposed to the Fabsil's Naptha, it absolutely honks, do it outside not in the sitting room.  The water seal will dissolve the glue in the velcro straps if your stitching is a little dodgy, you can come unstuck.

Otherwise I can recommend Dave Haye's North covers..which are on sale

I once ruined an old cover by using a pressure lance in tarmac (not smooth concrete)- the abraision of the high points of the tarmac wore thin patches on the underside of the cover, not to mention the deterioration of the cover in areas than had been exposed to bird excrement for too long.  I've since resorted to letting the 'slime' get really well soaked and giving it a good scrub on the boat - worked perfectly well this time and it looks prety good.

I used bleach. Worked a treat, but then the cover stitching dissolved over the next few months.Doh!

Use polycell 3 in 1 mould remover - available most DIYs such as B&Q. Apply, won't damage cover,leave to dry, will both kill mould and prevent regrowth. Can be brushed on. If waterproofing shot, use Fabsil, avaiable camping shops. I use this combo on the sprayhoods/dodgers of big boat and works well over many years. Courtesy of the MRX fleet.

Thanks everyone, another nice winter job to do!!!!! Paul

Put Fabsil from the tin into a garden pressure sprayer to use - been doing tents that way for years, but wash out the sprayer well afterwards.