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Did Algae Strip Damage My Customers Boat


Christa de Zee from HC Products asked:

Did Algae Strip damage my customer’s boat? You can see from the attached photograph that it is covered with blisters. He cleaned the bottom of his boat with Algae Strip, carefully following the instructions. He applied it with a paint roller, waited 20 minutes and rinsed it off with a high-pressure washer. When he was through the bottom was covered with blisters. It seems to me like a big problem, the customer wants to know how we are going to solve this.


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Hi Christa,

The problem is called Osmosis Blisters or Boat Pox. This is not caused by Algae Strip, but by water penetrating through the gelcoat on the hull of the boat and reacting with residual chemicals in the fiberglass. He obviously did not notice the problem before he cleaned the bottom because it was covered by marine growth. The cause is either a manufacturing defect or lack of protection by the boat owner. If he had used VS721 Bottom Coat to protect his hull, it would have sealed the pores in the gelcoat and he would not have this problem.

If you were to open up the blisters you would find water trapped behind the blister. Usually an acetic, aqueous solution.

Algae Strip is safe to use on all fiberglass boats. Our lab tests prove that it is impossible for Algae Strip to cause this type of problem. In over 24 years that this product has been on the market there has never been a single complaint of damage to a fiberglass boat. It has been independently tested by Consumer Reporting Magazines like Practical Sailor and Powerboat Reports and rated BEST!

Algae Strip is a very strong acid based cleaner made especially for aggressively removing Algae, Barnacles and Zebra Mussels from fiberglass boats. The formula employs several different acids, plus optical brightiners and inhibitors. These carefully formulated ingredients work synergistically for optimum cleaning power without any damage to fiberglass. Aurora Marine Industries are the inventors of chemical bottom cleaners for boats and the leading experts in the field.

Algae Strip is considered environment friendly because it biodegrades very quickly when it comes into contact with water. When the Algae Strip is applied to the marine growth on the hull, the active ingredients are consumed as it reacts with the growth. The “rinsing with water” process quickly neutralizes any unspent ingredients.

Repair of Osmosis Blisters is done in two ways. In severe cases, especially if there is delamination, the gelcoat must be pealed or sanded from the structural fiberglass and replaced, usually with epoxy and paint. In less severe cases, the blisters can be opened up, the hull left to dry out and then patched with matching colored gelcoat, or epoxy and paint. A skilled craftsman can do the patching with similar materials so that the repair is invisible and the hull maintains its integrity.

Judging from the photographs that you sent me, I suggest that the individual blisters be patched as this is not a sever case of osmosis. A moisture meter should first be used to verify that there are no large amounts of water beneath the gelcoat which would indicate evidence of delamination. Before proceeding with repair, your customer should contact the boat manufacture to see if there is warranty coverage for Osmosis Blistering. Most reputable boat manufacturers will warranty their hulls for periods of 5 years to lifetime against Osmosis Blisters.

All boat owners should protect the bottom of their boats against water penetration and growth attachment, even if they are trailered. The modest cost of protecting your boat with VS721 Bottom Coat can eliminate the very high cost and inconvenience of repair, and the cost is more than recovered when you trade or sell your boat. A well maintained used boat is more valuable and easier to sell, than one that has been neglected or repaired. It will also perform better, use less fuel and give the owner greater pride of ownership.

I’m sorry to hear of your customer’s dilemma, but I hope I have answered your questions.


Thanks for your question,

Captain Aurora

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