3M Compound/Polishing

[gjgm]

Gavin, tell me you didn't use those new wool pads with car products..

No ,no no....

 

[Marine Reflections]

This is a question I had been planning to ask here, because my dinghy's hull is yellowed and scuffed, with numerous shallow scratches and immovable tyre-marks, as well as the contrasting bright white patches where enormous name-decals must have been in place for thirty years, while the rest of the hull is variously creamy grey or a bilious yellow...

...just how cheap can I go, in terms of a rotary polisher? Is there a Li-ion battery option? Not that that will be cheaper, but I keep the boat very far from any power points.

For the fairly neglected condition my hull is in, is there an obvious choice for which grade of rubbing compound I need?

And...given that a certain thickness of the gelcoat will be removed by rubbing, is there any greater consequent water-ingress/moisture in the glass, afterwards? Not much of a problem in a dry-sailed dinghy I can see, but I'd gladly paint her with epoxy if it was recommended.

Even though you have described the condition of the dinghy very well, I can't seem to picture in my mind as well as I could with some photo's, but I think you could do with a few stages in preparation that would serve you better than taking a polisher to it.

In answer to the cheapest polisher options, yes, there are some as cheap as £30, these will hurt the back and annoy those nearby, but as you are some distance from any electric points it may be easier for you to use some very fine (3000) sanding foam discs. These will do the work of 'flatting' the surface for you as a compounding pass would offer and you will only need a bucket of water and a few drop of detergent.

It sounds as if it could do with an Oxalic treatment as this would help with the yellowing. Once dried, a wipe over with acetone should rid the hull from any tyre marks.

Some coarser versions of the foam sanding discs, say 1000 or just some ordinary wet n dry (used wet) will help work down the fine scratches, just go over them after with some 1500 then 3000 to bring back.

On the subject of gel coat thickness and if there would be a greater risk of water ingress, the answer is no.

Think of the old rough gel coat as a plank of raw wood, sanding and then finer sanding will close the grain on the wood, making its grain less porous. The same is sort of true with gel coat, as you work the surface up to a better condition you are actually closing any tiny pores making it more resistant to water if anything.

On thickness, you will only be removing a few microns (1000 microns in a mm) even with fairly coarse compound, if you really went at it for quite a while you may be able to remove a few hundred microns, but that is still only 20% of a mm and you would have to really be trying to go through the gel, keeping the polisher in the same spot with all your body weight on the polisher.
It will burn (turn brown) before you are able to remove more than a few microns and it would take all day in the same spot before you could remove a mm.

The scare mongrels in the past I'm sure set these rumors with the hope it would keep owners from attempting any work themselves. Just use common sense.

Tony

 

[Concerto]

Most boat gel coats are thicker than you think. On my Westerly Fulmar (Westerly's are known for double coated gel coats), the surveyor commented a small impact damage on the topside had caused some delamination. When I removed the gel coat ready to grind away the damaged fiberglass, I found the only damage was in the gel coat and that measured about 3 to 4mm thick. It would take a lot of compounding to cut through that thickness of gel coat.

 

[Greenheart]

Even though you have described the condition of the dinghy very well, I can't seem to picture in my mind as well as I could with some photos...

I'll attempt to take some photos which show what I mean, next time I visit the boat...but meanwhile, your experience and evident knowledge has put me in no doubt that I can use the products available without fear of harming the hull. I'm really very grateful for your taking the time to reply in such detail. :encouragement:

Count on some before-and-after pictures here, as the pre-season work goes on...

 

[Heckler]

I gave the boat a once over before winter and , for a change, tried some Autoglym Resin on a small area as an experiment . ARGG.. it was like glue on the wool bonnet and almost impossible to wash out. What the hell is in that stuff !!
Back to the 3M for me !![/QUOTE
My Swmbo uses Autoglym Resin BY HAND! Wondeful stuff and doesnt oxidise. Loads of compliments fly her way
S