Black spots on GRP, how do I remove?

[seanfoster]

Firstly, I think I may well be posting quite a few new threads as my latest 'project' had just begun!

I have recently bought a Dufour 1800 which has been sitting in a garden for over 7 years.

It is covered in slime and grime, and the deck, hatch etc is covered in black spots. Also there has been a bit of what looks like lichen growing in a few places. I'm wondering if these spots are some sort of mould.

I have just started the cleaning process and concentrated on a small area to see what is the best way to go. I firstly had a hard scrub with a deck brush and general cleaner (flash) and then when most of the grime was off I covered the area with oxalic acid (almost saturated in hot water) and left for a few hours.

The grp has come up pretty well, but the black spots remain untouched.

Has anyone got any ideas what to do? I really don't want to paint because the grp is in very good condition (apart from it's appearance) and also don't want to scrub too hard with abrasives (including scouring pads!)

I've attached some pics, anyone got any ideas?
I'd prefer to use non marine based products because:
1 - I live miles away from any chandlers
2 - I'm pretty sure most specialist yacht cleaning materials are the same or similar to domestic or automotive products, but (at least) twice the cost
3 - I'm a tight ar*e

Any help would be appreciated!

 

[sarabande]

I've come across similar spots, while living under the flight path to Heathrow. I think it's tiny drops of fuel which settle into the gel coat, then degrade under the influence of airborne bacteria, and become 'nests/ for basic vegetation.

The treatment you have given them will stop them growing for sure, and my experience is that regular cleaning and exposure to salt water and fresh air will cause the spots to fade.

One line of enquiry might be to use a biological washingpowder on them, by leaving a warm cloth soaked in Persil or similar. The bio bugs might eat their way into the black spots.

 

[Lady Campanula]

....use a biological washingpowder on them, by leaving a warm cloth soaked in Persil or similar. The bio bugs might eat their way into the black spots.

Would that be 'polyestermites', then?

 

[ralf2]

Chance a fiver on these sponges they really are magic,
http://www.amazon.co.uk/JML-Doktor-Power-Magic-Eraser/dp/B001PNAP10/ref=pd_sim_diy_1

 

[seanfoster]

Chance a fiver on these sponges they really are magic,
http://www.amazon.co.uk/JML-Doktor-Power-Magic-Eraser/dp/B001PNAP10/ref=pd_sim_diy_1

I've got one I'll try it, doubt it would work though.

I've been doing a bit of googling and it may be blackspot algae, commonly found in swimming pools. Bit confused though as water needs to be present, although I suppose that may be provided by rain?
An algae-side is suggested, does anyone have any comments on this?

 

[coliholic]

I'd be tempted to try a pressure washer. Test on an unobtrusive area first maybe?

 

[Stork_III]

I've got one I'll try it, doubt it would work though.

I've been doing a bit of googling and it may be blackspot algae, commonly found in swimming pools. Bit confused though as water needs to be present, although I suppose that may be provided by rain?
An algae-side is suggested, does anyone have any comments on this?

Try http://www.brintonproducts.co.uk/framedset.htm?domestic.php~mainFrame

 

[Ubergeekian]

They are a real bugger to remove - I've got a few growing on the white plastic hatch of the Jouster. Pressure washing and then using a GRP cleaning spray - which from the smell of it is dilute hydrochloric acid - sort of works.

 

[CET1]

If you want cleaning sponges try poundland they have busy bear magic sponges pound a bog.

 

[William_H]

Spots

Did you try bleach. If not it is worth a try. It is great on mold. Also try acetone as it may be an oily stuff from trees. good luck with the project olewill

 

[seanfoster]

Thanks for your replies,

I've bought some Patio Magic as suggested by Stork III, put some on a test area, I'll wait a few days before blasting with my pressure washer and see what happens!

 

[VicS]

Also try a domestic cleaner containing some bleach.
I find "Flash Spray with Bleach" effective on an old white plastic garden table. Needs a good scrub at the same time though.

 

[seanfoster]

Update!

Well, I've tried everything that has been suggested - oxalic acid, jif, high pressure water jet, flash, patio magic.

Nothing has worked! The spots have subsided a bit but have left a very visible mark, so I think it has to be a painted deck!

I was thinking of using a two pack marine paint sprayed. The deck has a very good non slip pattern, will gloss paint over this be too slippy, or should I add anti-slip granules to it?

Advice would be appreciated!

 

[capetown]

I've got exactly the same pox as you It's on my grp caravan roof, seems to grow in the wet winter.

Tried most things, but can't seem to kill the roots, there's aways a stain left.

I've just bought some moss killer from mistral_ie via their Ebay site, not have a chance to try it yet as a dry spell's needed.

It's suggested that it's to be diluted. I'm also thinking of laying some clingfilm or sheeting to keep it moist.

Will report back on progress.

 

[Hoolie]

You could try Dettol (used to be called Dettox) mould and stain remover. I've not used it on GRP but it's pretty good on most other surfaces, including PVC and silicone frame sealant

 

[Monique]

I'd give Spray 9 a try... with magic sponges....

GL

 

[nrbx]

Try Starbrite black streak remover, it tends to do a good job at lots of other random stains for me in the past

Although this seams like it could be a bit more hardcore than what i've had to deal with.

Could you not wet and dry them off?

 

[seanfoster]

.

Could you not wet and dry them off?

I've been trying to avoid any abrasive measures because the grp is actually in very good condition, but after trying everything else, I'm going to have to roughen up the surface anyway to prepare for spray painting.

 

[Mistroma]

A very large proportion of marine GRP/teak cleaners use Oxalic acid as the main effective agent. Other things in the mix are mainly there to get the Oxalic acid in better contact with the surface to be cleaned and keep it there.

So if you want cheap then an Oxalic acid solution should work as well as most cleaners. You can mix in a tiny amount of fairy liqud and wallpaper paste if you want it to spread out and stick to vertical surface. Various places selling Oxalic acid online (eBay etc.).

One key point is to only use above 10 degrees C. The reaction taking place virtually stops below this temperature. At 20 degrees C you can usually see stains vanish before your eyes. After 5-10 minutes you just wash off with copious amounts of water.

It might be worth trying this out. However, to be fair the pictures look more like something stuck to the surface and I think you've come to the same conclusion.

Still worth buying some Oxalic acid though. I use it every year for a variety of cleaning jobs. But remember, to treat it as toxic and wear gloves etc.

 

[seanfoster]

Mistroma,

I have a large 5kg tub of oxalic acid and have been amazed at how well it works, but not in this case unfortunately!

I wasn't aware that it only worked in temperatures above 10 degrees. I have used it in the summer and yes you could definitely see it working as soon as you brushed it on.