Grit blasting

matt1

matt1

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I'm sure there are variations of methods / materials, but am looking to get 12x seasons of AF removed in the autumn and I only want to go back to the original epoxy (not GRP) then maybe add an additional coat of epoxy before starting again with new AF (and a tie coat). Any thoughts from those who have had it done? Any recommendations? Symblast appear to be the "go to" co locally

When I applied the original epoxy it was somewhat "agricultural" as I wanted to ensure I achieved the correct film thickness - any suggestions for smoothing it upon application (eg to avoid sanding smooth afterwards)
 
I had Capricious grit blasted prior to applying Coppercoat. The operator used Olivine as the blasting medium, and obtained a very good result - took the old antifouling off while leaving the gel-coat pretty much untouched. I think, though, that it's down to the skill of the operator and the flexibility of the equipment. Unfortunately the person I used did not endear himself to the Marina, as he made a bit of a mess - partly not his fault, but due to miscommunications between him and the marina about moving Capricious to an isolated area.
 
matt1 said:
I'm sure there are variations of methods / materials, but am looking to get 12x seasons of AF removed in the autumn and I only want to go back to the original epoxy (not GRP) then maybe add an additional coat of epoxy before starting again with new AF (and a tie coat). Any thoughts from those who have had it done? Any recommendations? Symblast appear to be the "go to" co locally

When I applied the original epoxy it was somewhat "agricultural" as I wanted to ensure I achieved the correct film thickness - any suggestions for smoothing it upon application (eg to avoid sanding smooth afterwards)
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I have used Symblast. explain to Paul what you want done and the finish you want and he will do it. He is very experienced.
 
Last winter I have my Rival blasted to remove 44 years of built up antifouling. It was mm thick on places. The previous winter I'd removed some of this (about 75kg of it) with a scraper.
Marineblast (Dunoon) did the job using salt, and a good job, but whatever media is used operator skill is a high requirement, and almost any media CAN go too far removing gelcoat and or some of the GRP.
Mine came completely clean ready for epoxy coating.
 
Tranona said:
I have used Symblast. explain to Paul what you want done and the finish you want and he will do it. He is very experienced.
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I used Symblast a couple of years ago and I wasn't over-impressed. It was done by Paul and an employee. Everything was a mad rush as he wanted to get on to the next job before the light went. Despite that, Paul spent a lot of time moaning about how much he hated the job but didn't know what else to do, and slagged off his employee as useless. The process was far more aggressive and uneven than I expected and some patches were missed altogether which I had to scrape off later myself by hand. Fortunately it's an old boat with a thick gel coat so it didn't go all the way through, but I definitely wouldn't recommend the firm especially considering how much it cost for 2 or 3 hours work.
 
matt1 said:
I'm sure there are variations of methods / materials, but am looking to get 12x seasons of AF removed in the autumn and I only want to go back to the original epoxy (not GRP) then maybe add an additional coat of epoxy before starting again with new AF (and a tie coat). Any thoughts from those who have had it done? Any recommendations? Symblast appear to be the "go to" co locally

When I applied the original epoxy it was somewhat "agricultural" as I wanted to ensure I achieved the correct film thickness - any suggestions for smoothing it upon application (eg to avoid sanding smooth afterwards)
Click to expand...

Gritblasting is a horrible job, I used to have a company that did it. An experience operator is required, but its so unpleasant a job that staff retention is difficult.

If Paul from symblast does it himself he will do a good job he is very experienced - the most experienced of all i'd say. He uses a very fast machine that needs the experience more than any other . And where do operators learn?. Paul blasted my last boat before i had my business and it was very good.

The person who bought my machine now operates out of the top of the itchen. He never subs it out and is a GRP tech who is an expert at GRP repairs of all types. He uses a farrow machine (hot, wet) with recycled glass (which in itself is much like olivine) he's another Paul - Paul Shotton. He will take as long as it takes to blast the boat, but as it's a fixed price who cares. He doesn't advertise as he doesn't need to, he's always fully booked. pm if you want his number.
 
I took advice and, as my boat is too far from the sea for commercial operators to travel - Bath - I hired/borrowed equipment, bought the abrasive medium, and did it myself.

I used crystalline sodium carbonate, which is a far 'gentler' abrasive material than most others, which removed the many layers of old a/f down as far as an original 'tie-coat' of VC Tar, and I was advised to leave that well-adhered layer intact, by Jotun Paint's rep - who judged the 'job's a good un'.

Beware! The spray nozzles I had were controlled by short handles operating a little ball valve similar to that within most through-hulls. With the valve half-closed to control the rate, the abrasive material cut through the side wall of the handle in minutes, and jetted at high pressure onto my hand. You can imagine that I was well pleased I was wearing leather gauntlets and eye protection....

The used soda material was mostly collected on a tarpaulin, and the rest dissolved harmlessly later in rainfall.
 
I blasted a few boats myself for a while. People will often find fault where the problems lie with the boat and how it's been painted, it's possible to end up with holes due to voids in the lay, poor repair work and osmosis. The other issue is with epoxy and undercoat layers that aren't properly bonded to the GRP. They tend to flake off or not blast well because they have been inconsistently applied.
 
Be VERY careful when getting your boat blasted.

A while ago a guy approaced our club, 5-6 of the larger boats clubbed together to have their antifoul build-up removed.

The clown removed their gelcoats as well !

I don't know the legal outcome but all boats had to have new gelcoats and missed an entire season.

So check credentials and speak to previous customers...
 
i'm sure that's correct, the prat who removed my friends' gelcoats as well was just a cowboy; but considering the risk I'd be very careful and choosy about getting someone to do it, I'd definitely want to talk to previous customers or like Zoidberg get the kit and do it myself.

I knew someone who did just that, built up a small - medium successful business blasting boats, I think turned it into a franchise - built his own steel blue water boat and cleared off over the horizon - seemed a very decent guy.
 
savageseadog said:
Not so. If the right grit is used and the boat blasted correctly then there's no issue with gelcoat damage.
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Seajet said:
i'm sure that's correct, the prat who removed my friends' gelcoats as well was just a cowboy; but considering the risk I'd be very careful and choosy about getting someone to do it, I'd definitely want to talk to previous customers or like Zoidberg get the kit and do it myself.

I knew someone who did just that, built up a small - medium successful business blasting boats, I think turned it into a franchise - built his own steel blue water boat and cleared off over the horizon - seemed a very decent guy.
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+1. Grit blasting DONE RIGHT is very effective, and produces a perfect finish for applying things like epoxy or Coppercoat without damaging the gel-coat at all. It also has the advantage that it can operate over a wide range of pressures, so the same setup can do both the glassfibre and a cast iron keel - the latter requires a much more aggresive blast than the former! But to do it properly requires both skill and the right equipment, so that the pressure of the jet can be varied rapidly as required. The guy who did mine had a compressor, a hopper and some kind of pressure vessel in the line, talked over the grit he would use (olivine) with me and wore professional positive pressure safety gear (which he needed - I got out of range pretty quickly once he'd started!). He also didn't skimp on the grit - every minute or two he seems to be tipping more into the hopper; he must have used several hundred kilos.

However, grit-blasting will certainly find any weakness in your gel coat or elsewhere. I was fortunate - the gelcoat on Capricious was in excellent condition, and the blasting didn't uncover any problems, leaving it as smooth as the proverbial baby's bottom. But the cast iron keel was another story - one side was full of inclusions and bubbles and after blasting it looked like the surface of the moon! Fortunately I was able to get epoxy and filler from a local source, and was able to fair it roughly immediately. But that shows the strength of the system - it could be gentle enough to leave the gel coast, but also aggressive enough to remove imperfections from the keel. I think that less aggressive blasting media wouldn't offer that range of capabilities.

As others have said, go for recommendations. It's something that is easy to get wrong, and there are cowboys out there who are learning on the job! But done by someone who knows what they are doing, it provides a perfect finish for subsequent coatings.
 
I blasted a few boats successfully a while ago. The most difficult issue was dealing with badly bonded epoxy on gelcoat. The antifoul was no problem but the epoxy might hold on in patches, there really wasn't a solution as a concentrated blast could damage the gelcoat.
 
savageseadog said:
Not so. If the right grit is used and the boat blasted correctly then there's no issue with gelcoat damage.
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So what type of grit would you use.

I can get all kinds of grit from the refining of various base metals we produce and most are to hard for gel coat even gold refining grit which is relative soft is too hard
 
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