Sanding Epoxy

[Avocet]

For the first time since buying Avocet, I've scraped all the old antifouling off back to bare epoxy this winter. In a few places, I've gone through at least one coat of epoxy with the edge of the scraper. Further investigation has revealed that the boat barely has two coats of epoxy anyway! Although I haven't found any sign of osmosis, I am thinking about applying another few coats when the weather gets a bit warmer. To do this I'll have to sand the hull. Also, there are brush marks and various other minor (Ahem!) "imperfections" all over the hull which have retained traces of anitfouling and I'm guessing it wouldn't be the best idea to apply epoxy over these. That means I need to sand quite a lot of epoxy! I was going to attack it with a random orbit sander and a copious supply of 60-grit discs (the coarsest Screwfix sell) but was wondering whether anyone else on the forum had any better ideas for this as epoxy is pretty damned hard stuff! ...or for that matter, if anyone knows where I can get 40 grit discs???

Ta!

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[clyst]

Be careful when sanding - both anti-fouling and epoxy are dangerous if inhaled . Much better to "wet n dry" might take longer but you will live longer !!
Should have no problem in getting 40 grit try local B&Q etc or builders merchants
Hope this is of help.

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[Talbot]

By far the most effective and quickest and cheapest is th Du-it-All disc available from QVC. This is a diamond impregnated disc that can be used as a cutting or sanding disc, and will fit to a drill or an angle grinder. If using it for sanding it will flex (and then will not be any use as a cutting disc). Best of all when it is worn out you can return it and get a replacement for the cost of the P&p.

I would use a proper fairing sander to establish what needs to be ground down, then apply this - but do invest in a good respirator and cover up completely

I have used these discs for several years now and am very happy to recommend them (I have no interest with QVC or Aston Trading who supply them)

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[bob26]

Are you sanding to create a key for the new epoxy or to remove the existing epoxy? If you just want to overcoat surely you need something finer like 80-120?

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[oldsaltoz]

G'day Ian,

An 80 grit on a good orbital with a least a 3 mm orbit will remove it, most domestic orbital sanders only have a one mm orbit so clog up make hard work of it.

The larger the pad better to reduce dips, just take enough off to remove the all the gloss, then remove any small dings with a dremel or grinder and fill with closed cell micro-balloons and epoxy resin. I use the back of an old straight back saw to fair the filler, very little sanding required as it conforms to the curve.

You should need at least two coats of resin, you can save time and sanding by applying the second coat when the first is very tacky but not dry, a roller is best to apply it with but if you tip it off with a brush as you go (or get a helper to do this) it will come up really well.

I hope this helps...



<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[Avocet]

Thanks everyone!

-Yes and No, Bob, I'm sanding to get a good key BUT I'll have to go quite deep in places (probably back through to the gel) to get the last of the old antifouling out of the bottom of various hollows, scratches and chips so I guess I'm going to end up removing quite a lot of material in a number of places.

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[stretch33]

Hi, Doing very similar to you, mines got what l understand is a Blakes epoxy coating applied when the boat was new. You can get 40 grit discs at B&Q no problem. Was going to do mine with West but reckon l'll end up keying hull and using Gelshield, going to poke around paint people at LBS for info tho. Cheers

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[Avocet]

Thanks for that, I was in B&Q this afternoon. I'm reluctant to use their sanding discs because they don't seem to last long so it will work out very expensive! I did, however find some 24 grit discs and a backing pad to go on my 115mm angle grinder which I hope to try tomorrow - I've a feeling it might be a bit vicious though! I also got one of those "Scotchbrite type" scouring pads that goes in an electric drill. I'll see what that does too and will report back...

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[Avocet]

OK, I've been down to the boat this afternoon to try out my new "weapons" and as promised, I'm reporting back.

The B & Q carborundum coated "pan scrub" in the electric drill worked quite well but was initially a bit agressive. Once it had worn a bit, it was quite useful. It was brilliant at cleaning old antifouling and debris out of small hollows and dips.

The 40 grit sanding disc on the angle grinder was AMAZING! Initially it was extremely agressive - even on the epoxy but it didn't clog and has done several square feet so far. It's VERY quick (took me about an hour) but if you stay still for even a fraction of a second or if you hold it at the wrong angle it can dig into the gelcoat. I ended up using it to get all the high spots off and then going back over with the "rotary pan scrub". Ultimately, I'll use a random orbit sander to get the final finish before filling the hollows and slapping on some more epoxy.

Finally, as has already been said, a decent respirator (and nobody varnishing downwind of you!) is a MUST!

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