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Staining After Using VS721


John Paull asked:

Hi, I used two coats of VS721 on the bottom of my boat last year. It sat in the marina for the season and I didn’t get a chance to clean the bottom in the fall. All the years before using VS721 I was able to clean the bottom with just vinegar. This time though I am unable to get the brown staining off. I have tried CLR, vinegar, and your boat scrub, none of which have done anything to remove the staining under the top layer of algae growth. I am just looking for your opinion on other options that may work. I hate to use them,, but I am leaning towards trying a fiberglass stain remover like Davis FSR or Y-10. Thanks for your help.


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The longer a stain remains on any surface, the deeper it can penetrate and the more difficult it is to remove. The cause of the stain also is an important factor in understanding how to remove it. Tannin or Tea Stain is one of the more common stains affecting boats (it’s caused from rotting vegetation around the shoreline) and it’s one of the more challenging stains to remove. It can stain anything; stainless steel, fiberglass, VS721 and even porcelain. There are other causes of stains as well; chemical run off from agriculture or industry and some marine growth, etc.

It’s fortunate that you at least have some VS721 on the fiberglass as it will make it easier to clean up than if the fiberglass was unprotected. VS721 seals the pores and prevents the stain from penetrating too deep into the pores and also prevents osmosis blisters or boat pox.

The best way to remove the stain is with Waterline Stain Remover. Apply it with a paint roller, wait 15 or 20 minutes and pressure wash or rinse away the stain with a garden hose. Waterline Stain Remover is a powerful cleaner, but it won’t hurt the fiberglass. A heads up: it’s stinky stuff so work upwind when applying it. The water from rinsing will cause it to degrade so it won’t hurt the environment.

A lot of boat owners wipe the slime off the bottom from time to time during the season, either by hauling the boat and giving it a quick wipe with a Marine Power Mitt or while swimming around the boat when it’s in the water. The slime comes off easily with the Marine Power Mitt. This will keep the bottom clean all summer, improve the performance of the boat and reduce fuel consumption.

Thanks for your question.

Captain Aurora
Richard Kittar

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