Remove Black Stains from Deck/Old Rope Stains

[MAGTRAD]

I've got quite a few old back stains on my GRP deck along with stains left by old ropes. Does anyone know of any "magic" solutions to remove these or is it good old fashioned elbow grease?

So far used normal deck cleaner, traffic film remover and normal detergent to no avail.

My boat is a Moody 346 if it helps......looking forward to your replies!

 

[RJJ]

I've got quite a few old back stains on my GRP deck along with stains left by old ropes. Does anyone know of any "magic" solutions to remove these or is it good old fashioned elbow grease?

So far used normal deck cleaner, traffic film remover and normal detergent to no avail.

My boat is a Moody 346 if it helps......looking forward to your replies!

Oxalic acid is pretty good.

Mix a near saturated solution, then add wallpaper paste and stir. When it just starts forming a gel, add a squirt of washing up liquid to "fix" the mixture.

 

[AntarcticPilot]

Few, if any, stains on GRP will resist a pressure washer.

 

[Stemar]

Few, if any, stains on GRP will resist a pressure washer.

Unfortunately, nor will the GRP if there are any voids in the gelcoat, and you won't know if there are until the pressure washer finds them.

 

[AntarcticPilot]

Unfortunately, nor will the GRP if there are any voids in the gelcoat, and you won't know if there are until the pressure washer finds them.

Never had any problems on my Moody 31, and I've used a pressure washer many times. Nothing else will clean the diamond pattern non-slip effectively.

I haven't encountered the problem of voids, but surely if they exist it's better to know about them and fix them?

 

[Dukester52]

You could try Starbrite MSR Black Stain Remover on the black stains... which could actually be mould. Worked a treat for me after years of trying to find something!
MSR Black Stain Remover

 

[robmcg]

Never had any problems on my Moody 31, and I've used a pressure washer many times. Nothing else will clean the diamond pattern non-slip effectively.

Really? You can usually spot a power washed Moody deck from a distance. The moulded non skid tends to get the very tops of the moulded bits blown off. It manifests itself as black bits on the deck. You can assume it's ingrained dirt in the valleys of the non skid but often (not always) it's dirt accumulated in the blown off peaks of the non skid. Suds and a soft brush will remove most build up, except leaf stains which tend to be particularly stubborn if they have been there for a while.

 

[AntarcticPilot]

Really? You can usually spot a power washed Moody deck from a distance. The moulded non skid tends to get the very tops of the moulded bits blown off. It manifests itself as black bits on the deck. You can assume it's ingrained dirt in the valleys of the non skid but often (not always) it's dirt accumulated in the blown off peaks of the non skid. Suds and a soft brush will remove most build up, except leaf stains which tend to be particularly stubborn if they have been there for a while.

As I say, it's dirt in the valleys between the peaks that is hard to remove. A brush won't usually touch it, and the difference in colour between a deck that has been brushed and the same deck that has been power-washed is obvious and striking.

 

[Dukester52]

Starbrite Non-Skid Deck Cleaner is your friend for that kind of thing

 

[jwilson]

The fact that one deck moulding survives repeated pressure washing doesn't mean every deck will. Also a lot depends on the power and how close you use the jet. Personally I will not let a pressure washer on my deck - seen too much damage done on other people's boats. Two apparently identical Moodys (or any other make) could have very different deck moulding quality depending on how thick the gelcoat is and how well the first layer of glass is incorporated when being made.

 

[johnalison]

Starbrite Non-Skid Deck Cleaner is your friend for that kind of thing

I am amused that a non-skid deck cleaner should contain PTFE. I should like to think that it washes off.

There are several kinds of black stain. I rather imagine that the OP's problem is similar to the grey streaking down some boats' topsides, for which there are proprietary cleaners with names like grey streak cleaner or removal. It would be worth trying one of these, or a non-specific detergent cleaner such as gelcoat cleaner from various companies. Oxalic acid as mentioned might work. It could also be mould, in which Patio Magic would be the answer. If the stain is very old it could be very hard to remove. For a gloss area it might be necessary to use an abrasive cleaner. I think the gentlest of these would be Starbrite's Color (sic) Restorer Polish, which I find very effective for tired areas.

 

[robmcg]

One pass with the soft brush and some suds does do wonders. A second pass and it's sparkling .