Re: [Amel Yacht Owners] Sandblasting Good or Bad?(to remove Antifouling to Gellcoat)


Misters Alby and Lawson give very good and correct advice on stripping the bottom of old paint buildup. While sand blasting is a fast and relatively cheap way to remove old paint, it more often than not has disastrous side effects.


Here is why. Sand is not only very hard, but the grains are not uniform in size. This is a bad combination. High pressure air accelerates the pieces of sand from the nozzle that the operator holds in his hands. The trouble is, the different sized grains also have different mass/weight and get accelerated to vastly different speeds because of this. The higher speed sand projectiles easily penetrate deeper into the laminate than you might ever imagine, especially in areas where the gel coat gets thin or removed by the process. Even the best anti-osmosis coatings that you might apply are not totally waterproof/vapor proof. This fact, in conjunction with the hundreds of thousands of tiny holes created by the larger sand particles, provides an easy pathway for moisture to migrate into the very resin rich layer of mat fiberglass that Amel and other better quality boat builders use as a “veil” to limit the amount of ‘print through’ that the structural woven layers of fiberglass would transfer to the gel coated exterior surfaces if this “veil” were not present. And remember, all Amel boats built from the advent of the Super Maramu onward have the proprietary Amel anti osmotic coatings applied AFTER the gel coat is shot into the mold. It is on the inside of the gel coat.


Water vapor combining with left over elements caused by cartelization of liquid resin into solid resin is the primary cause of osmotic blisters. There are other things that can cause blisters, but for this discussion about sand blasting, enough is enough. Some boat manufacturers that offer blister warranties on new product specifically prohibit employing sand blasting and sand sweeping (adds some water to the mix!! ) and doing so voids the warranty. Trust me. I could go on for pages about all of this but since I don’t want to put anyone to sleep I’ll stop now.


I have fully participated in the surveys of hundreds  of Super Maramus, some four and five times now, that I have been fortunate to have sold. In almost every case of boats having thousands and thousands of little blisters, it was caused by sandblasting the old bottom paint off. It used to shock owners when the boat came out of the water and billions of blisters were there where none were before and I would ask them, “ When did you sandblast the bottom?”


So please, Amel friends, don’t sand blast your boat’s bottom. Whatever method you employ, if you see fiberglass laminate of any description, properly reapply ( That means read the instructions. Twice ) a well-known and proven anti –osmotic coating. Keep moisture out of your laminate. If anyone wants more information or wants to discuss the blisters you may have on your boat, don’t hesitate to contact me by phone or email.


And always, above all, have fun with your Amel!




Joel F. Potter/Cruising Yacht Specialist LLC


954 462 5869 office

954 812 2485 cell




From: amelyachtowners@... [mailto:amelyachtowners@...]
 ESent: Monday, January 16, 2017 12:01 PM
To: amelyachtowners@...
Subject: Re: [Amel Yacht Owners] Sandblasting Good or Bad?(to remove Antifouling to Gellcoat)



 we did clean the hull of our 1982 Maramu april 2016 using cryogenic blasting; quite common now in the industry in Europe.

- boat had been in water since april 2014, unused since april 2015, growing weeds by the bushel & great farm for oysters & mussels -


Cryogenic blasting uses CO2 gas to produce carbonic dry ice pellets blasted on the hull at low air pressure; no dirt or pollution and less agressive on gel coat resins.

cleaned all layers of antifouling paint which had been splattered on during ? ages (no record of maintenance when we boughht the boat 2016) ?

went down to gel coat layers & left them clean to survey the hull and dry out before laying on new protection (époxy coating) underwater.

reasonable price (Euros 2K Euros for a speedy process - took 4 hours (setting up, work & dismantling apparatus) to team of 2 to clean the bottom hull of the Maramu.


If available in your corner of the Oceans, I would recommend that you check industrial cleaning companies for the service - search companies or small operators working for metal, housing (front coatings), wood, stone cleaning using low pressure compressors.


Worth the cost when you gain another 10 to 15 years of trouble free hull & the extra speed from a clean & smooth hull.


fair winds & clean hulls


christian alby, Maramu Désirade VIII, Canet/roussillon




De : "Steve Lawson lawson911@... [amelyachtowners]" <amelyachtowners@...>
À : amelyachtowners@...
Envoyé le : Lundi 16 janvier 2017 16h34
Objet : Re: [Amel Yacht Owners] Sandblasting Good or Bad?(to remove Antifouling to Gellcoat)



I did my bottom a few years ago, and my current boat is a Dufour 39 ( working my way up to an Amel ). It's a dirty, rotten, time consuming job, that you may do once, but will never repeat. Sandblasting is old school, the latest and greatest is soda blasting, which does a great job, is environmentally friendly, and is easier on the hull than sandblasting.

On Jan 16, 2017, at 9:31 AM, Patrick Mcaneny sailw32@... [amelyachtowners] <amelyachtowners@...> wrote:


I have been thinking I would like to get rid of all the layers of bottom paint. I was wondering about chemical stripers , if they work and how well. Seems like you may run the risk of scratching the gel coat scraping , is that a concern and how wide of a scraper would you use. I got a quote of almost $3000. to sandblast, more than I expected , being a one day job , but if it saves ten days of scraping ... Just wondering what others have done. Also wondering how one deals with the bottom of the keel only a couple of inches off the ground and resting on blocking.

Pat SM#123

-----Original Message-----
From: James Alton lokiyawl2@... [amelyachtowners] <amelyachtowners@...>
To: amelyachtowners <amelyachtowners@...>
Sent: Sun, Jan 15, 2017 8:16 pm
Subject: Re: [Amel Yacht Owners] Sandblasting Good or Bad?(to remove Antifouling to Gellcoat)


I have always avoided the chemical strippers myself due to concerns of short and long term damage to the gel coat.  The stuff goes into any cracks in the gel coat and can get into the laminate and or into any voids under the gel coat which is not a good thing.   The suggestion that was made to use a good sharp scrapper is IMO a good way to go,  just take your time.  As was also suggested, go with the carbide blades.  The Bahco 660 or 665 scrapper works well for me,  you can find these on Amazon.  You can also sand it off with a dustless system or use this as a follow up to the scrapping.  Definitely avoid using a heat gun as it is just too easy to craze the gel coat. 


Best of luck,


James Alton

SV Sueno,  Maramu #220

Sardinia,  Italy


On Jan 15, 2017, at 1:11 PM, santorinlo18@... [amelyachtowners] <amelyachtowners@...> wrote:



Hi Forum, Just about to scrap bottom - is sand blasting good method? seen the end result - looks neat but rough compare to manual. Not sure if good or bad, however, about 50% cost compare to manual + chemical. Any experiences or view




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