Sandblasting hull

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tyce

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I'm fed up of the ever growing and slowly flaking layers of old antifoul on my hull, as are many others on here it would seem.

Wandering around aldi today I noticed they had a 3 hp 50litre air compressor so it got me wondering. Has anyone any experience of how good it would be to blast my hull using a sand blasting attachment, I am not totally convinced it would work but anything has to be better than the manual labour scraping option.

Compressor is 150 quid is it worth a punt.
 
Sand blasting is very aggressive. It's generally used for taking the gelcoat right off prior to epoxy treatment. Depending on how expertly it is used, a lot of work will be required to fair the hull afterwords (which is why planing is usually preferred). Slurry blasting is preferred for simply removing coatings such as antifoul and keying the gelcoat.
 
macd said:
Sand blasting is very aggressive. It's generally used for taking the gelcoat right off prior to epoxy treatment. Depending on how expertly it is used, a lot of work will be required to fair the hull afterwords (which is why planing is usually preferred). Slurry blasting is preferred for simply removing coatings such as antifoul and keying the gelcoat.
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True - but there are softer materials that can be used with confidence with the same kit
 
You will be very frustrated using a sand blasting attachment if its the kind I am thinking of with a 3 hp compressor.
Is it the type that looks like a spray-gun with a hardened steel nozzle?
In which case, forget it.
I used one fairly successfully for cleaning small areas of steel prior to welding in car restoration. That was with an industrial 25cfm 150 litre 3 phase Ingersoll.
If I had bigger bits to clean, such as chassis, I took them up to a professional.
 
I've had my hull blasted professionally, but considered doing a DIY job first. Having seen it done professionally, I think I was crazy to consider DIY!

Basically, you need pretty high power equipment to start with. It needs to be able to run continuously with a high air-flow. The professional used a big compressor on a trailer, with all sorts of air handling kit in the line (don't ask me what it all was!). You then need protective clothing - the professional was using a positive pressure mask, with full-body protective clothing. Having been close by while he was working, I think his protective clothing was entirely necessary; I had to retreat to a safe distance pretty smartly - flying chips of antifoul sting, and of course, the air is full of dust. Next, you need to consider the best blasting medium - the usual grit will, as others have mentioned, remove the gel-coat. Mine used olivine, and varied the pressure to achieve good results on both the cast iron keel and the GRP hull; choosing the right medium is part of the required skill set. Finally, he had a high degree of skill and experience that allowed him to leave a perfectly fair finish.

Also, don't underestimate the amount of blasting medium required - I don't know how much the guy who did mine used, but it was quite a few hundredweight! Every few minutes he was emptying another sack into the hopper.
 
macd said:
Sand blasting is very aggressive. It's generally used for taking the gelcoat right off prior to epoxy treatment. Depending on how expertly it is used, a lot of work will be required to fair the hull afterwords (which is why planing is usually preferred). Slurry blasting is preferred for simply removing coatings such as antifoul and keying the gelcoat.
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sand plasting with a 3hp is not agressive! Scraping it with your nail would be faster.
And it is is not what's used for removing the gelcoat - intentionally anyway. Plane then blast is what you do to remove gecoat. You are right though that slurry blasting is gentler, but sand blasting with a skilled operator can be OK.
 
A friend of mine bought one of those to do a small patch on his boat. It was very disappointing. Don't bother! Put the money towards a pro job but make sure they have done boats before and know you only want the paint removing or you will end up like Michael Caine in the Italian job.
 
Mine came with six blades and I still have five of them unused! They are very hard carbon steel. Only suggestion is to grind the corners off each side as they tend to dig in.

Ref ghostlymoron's post, it does take some muscle so don't expect the A/F to fall off when it sees the scraper! However I am no muscleman but managed it fine. Used it again last year to take off the top 12 inches or so all around the boat, no problem at all.
 
tyce said:
I'm fed up of the ever growing and slowly flaking layers of old antifoul on my hull, as are many others on here it would seem.

Wandering around aldi today I noticed they had a 3 hp 50litre air compressor so it got me wondering. Has anyone any experience of how good it would be to blast my hull using a sand blasting attachment, I am not totally convinced it would work but anything has to be better than the manual labour scraping option.

Compressor is 150 quid is it worth a punt.
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I just had this debate as part of my winter refit. After a fair bit of research I concluded that blasting was too aggressive, and required too much making-good afterwards. In the end I hired someone to scrape 10 years worth of antifoul off by hand, I was down at the boat this morning (they started today) and two of them will have it done by the end of tomorrow.
 
jimmy_the_builder said:
I just had this debate as part of my winter refit. After a fair bit of research I concluded that blasting was too aggressive, and required too much making-good afterwards. In the end I hired someone to scrape 10 years worth of antifoul off by hand, I was down at the boat this morning (they started today) and two of them will have it done by the end of tomorrow.
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If blasting is done correctly, there will be NO making good afterwards. The guy who did mine did not remove any gel-coat, the surface was slightly abraded; ideal for application of (in my case) Coppercoat.
 
AntarcticPilot said:
If blasting is done correctly, there will be NO making good afterwards. The guy who did mine did not remove any gel-coat, the surface was slightly abraded; ideal for application of (in my case) Coppercoat.
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You simply can't generalise like that. From all the people I spoke to about this, the blasting will reveal any defects in the gelcoat, and you just cannot know about these defects until they are revealed.
 
jimmy_the_builder said:
You simply can't generalise like that. From all the people I spoke to about this, the blasting will reveal any defects in the gelcoat, and you just cannot know about these defects until they are revealed.
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But if there are defects in the gel-coat don't you want them exposed, so you can fix them? Naturally I was assuming a sound surface under the antifoul; not an unusual thing - my boat is 26 years old, and the hull was perfectly sound under the antifouling.
 
AntarcticPilot said:
But if there are defects in the gel-coat don't you want them exposed, so you can fix them? Naturally I was assuming a sound surface under the antifoul; not an unusual thing - my boat is 26 years old, and the hull was perfectly sound under the antifouling.
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Yes, for sure - but that's a different point to the one I was making, which is that you cannot just say that blasting done correctly will require no making good afterwards. The blasting people that I spoke to said that finding a completely defect-free hull after blasting is very much the exception, not the rule.
 
vyv_cox said:
Mine came with six blades and I still have five of them unused! They are very hard carbon steel. Only suggestion is to grind the corners off each side as they tend to dig in.

Ref ghostlymoron's post, it does take some muscle so don't expect the A/F to fall off when it sees the scraper! However I am no muscleman but managed it fine. Used it again last year to take off the top 12 inches or so all around the boat, no problem at all.
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Thanks again.

I've just ordered one, to give it a try....will report back.
 
Pretty much what I was thinking, the sand blasting would just be a pipe dream, the reality being either lots of elbow grease or pay a pro spraying outfit.
 
I hired someone with all the gear to sandblast my hull (48') and it took a full day. Great result with gel coat in fine shape. Then applied 5 coats of gel shield 200 plus a coat of antifoul. Lots of work but well worth it.
 
If one wants to remove just antifoul 'buildup', then the optimum medium to use is not sand/silica, but SODA....

This is far less abrasive, does no damage, and fairly 'wheechs' away old a/f paint, leaving the substrate - gelcoat or w.h.y - ready for application of antifoul or manufacturuer's recommended tie-coat.

I did that meself and, although there was a learning curve with the kit and the medium, a proper job was done.... and cheaply! Well pleased.....;)
 
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