Smoothing out a DIY ding repair

[benjl]

Hey guys

One of my mates stupidly tried to turtle roll his 6'6 the other day while he was paddling next to me and lost control of it as some white wash hit us.
The point of his board sprung to the water surface only to go straight in to my board and produce this crack along the rail!

I dried it out and repaired with epoxy resin as per my other little dings here and there to be safe. Seems to have done the job all good (constructionally) although now I have an area along the rail which is raised slightly due to the epoxy resin on top of the board.
The photos here are before I repaired the crack.

My question is, how do I make this flush with the rail again? What grit of sandpaper do I use and / or what's a safe technique? I'm assuming that smoothing this out will also smooth out the water flow down the rails a bit and possibly give slighly better performance. How do surf shops get ding repairs so flush??
I've got another similar crack (with epoxy resin repairs) on both nose rails of my other board when a SUP'er let go of his board on a 4ft hollow barrel. His fin also sliced through my wetsuit but that's another repair query! I would also like to 'flush out' those DIY repairs with this same method too.
Two boards damaged in two consecutive days from other surfers.. gotta love this sport times!

Thanks guys

[oldmansurfer]

I have heard that an electric sander is the bomb with epoxy resin sanding but haven't tried it. I used a sanding block and varrying grits from 120 to 600 (wet sanding) still it left a bump but it was a smooth bump so I am not worried about it. next ding I will purchase an electric sander

[drowningbitbybit]

The way I've done it before (not these days... I'm a complete slack@rse about my battered boards these days...)

Sand away the major lumps using a sanding circle on a drill and some quite coarse wet n' dry.

Smooth with an electric sander and some quite fine wet n' dry.

You might find at this point that you need to go back and fill in any depressions or cracks. Repeat the sanding if you do.

Spray the effected area with matching spray paint (surprisingly tricky when its white) and/or fill in with a Posca pen.

Use spray lacquer to smooth it all out and make it shiny (unless you have a matt finish board).

Wait. Wait some more. Don't be fooled into thinking that the lacquer is dry. Wait one last little bit. Give it another coat. Wait (etc etc) before going in the water.

On a little diddy crack like that (call that a ding? ) I wouldn't bother with the spraying, and you might not need to do the first rough sanding.

[benjl]

Thanks guys- given that I don't have a sanding drill, would some good ol elbow grease and some 120, 300 and 600 grit sand paper do the trick? I'm assuming just trickle a little bit of water and carefully watch it as you sand away by hand?

[oldmansurfer]

The 120m is to take down the bump the others are to remove the scratches left by the coarse paper. It would help if you had a small block of wood to wrap the paper around so it creates a flat surface.