Ablative problem

[Quoddy]

The situation: Ablative bottom paint was applied 5 years in a row while partially flaking off each year. Now after pressure washing 1850psi to remove all flake, some areas are gelcoat, some barrier coat and some 5 layers of well-adhered ablative. I want it smooth but don’t want to remove what there is of the none ablative barrier coat. The boat is a centerboarder on a trailer so most work is upside down.

Question 1.would a rotating pressure washer brush with detergent wash off the ablative?

Question 2.could a mild chemical stripper be used that would leave the barrier coat?

Question 3.dry sanding, what is the best sander, keeping in mind the upside down position of the work and the toxic dust?

Question 4.is there a form of wet sanding?

 

[jdhohmann]

Hey Quoddy
After doing this job several times on several different model of sailboats, I would say you WiLL have to use some old fashioned ELBOW GREASE... I never found any tip[ on a pressure that would completely remove bottom paint, especially when a NON-Ablative paint was used. It sounds like your bottom was not pre-finished with a fairing compoun. This really helps maintain your hull, and helps in removal of Bottom paint..My tried and true and tested format was to make a scraper with a long (16") T-handle and start scraping, then pressure wash , then apply your fairing compound then your Ablative Paint!!!!! Good Luck!!!

 

[sailingdog]

If you're going to bother taking the hull down to the gelcoat, and the hull's moisture content is relatively low, it also might be an ideal time to barrier coat the boat's hull.

 

[BobM]

Your best bet may to be try Peel Away. Others have used it. They have a marine version too, but it is expensive and some have reported contacting the manufacturer who said there is no difference. One of their marine versions (Marine Strip 2) says it won't harm barrier coats. I checked and the MSDS's report the EXACT same actives and percentages for Peel Away 1 and Marine Strip 2, so I'd buy the former at your local home depot for about $27/bucket.

For overhead work, personal protection is an absolute must as this stuff is VOC free, but 46% pure caustic. Full bunny suit, gloves and eye protection are a must and keep a hose handy just in case. Strong bases are very soapy feeling and very hard to wash off your skin...pretty much because they are too busy dissolving it! I am a chemist and I used to work with 50% sodium hydroxide...lets just say working with it overhead would make me don a bunny suit with a hood and googles, not just safety glasses.

Try a search on sailboatowners for more information and the site below.

http://www.dumondchemicals.com/html/peelaway2.htm

 

[jdhohmann]

If you're going to bother taking the hull down to the gelcoat, and the hull's moisture content is relatively low, it also might be an ideal time to barrier coat the boat's hull.

Barrier Compound, that's the word I was looking for, NOT Fairing Compound, Sorry!!!!!

 

[Randy Burns]

I don't think ablative should be flaking off, I use it and it mostly rubs off. I wonder if some other old paint layer may be failing. I did my boat using scrapers, Peel Away, and a 6" Porter Cable oscillating sander (Makita makes one that is variable speed, much better.)

 

[Dan Johnson]

Usually...

when paint begins flaking off it's an issue with the solvents in the paint that may have changed due to a paint manufacturing change, brand change, or application mixing issue. Best thing to do is to scrape it down to gel, barrier coat it and apply compatible paint (same mfgr).

 

[Allan12210]

Wet Sanding

When I haul my boat I wet sand with a big sponge and 60 grit sanding screen. They have it at the marine store or some hardware stores for sanding drywall. That gets through the flaking layers. I usually end up with a few spots of the barrier coat showing, but still have some coverage of the probably original layer of bottom coat.

Wet is best to avoid the toxic dust. The screen is good because it doesn't clog. We can usually do the entire bottom of our 34 footer with one sheet. Cut it into four pieces and hold it and the sponge together. Dunk in a bucket of water to keep it really wet and clear. Wear rubber gloves taped to the sleeves of the bunny suit.

Allan

 

[Larry Wilson]

Re: Wet Sanding

Multiple layers of Ablative paint will flake off. It is probably an issue of different VOC's.
The rotating pressure washer heads scare me. If there is enough pressure to spin the head, there is almost certainly enough to remove gel coat.
I have had success applying cheap paint remover, letting it dry and then wet sanding with 80 to 120 grit wet paper.The remover softens the paint and makes it much easier to sand. If you don't get too aggressive with the sandpaper it won't harm the barrier coat or the gelcoat.
I wonder if someone at some point just gave up trying to remove an old barrier coat and went ahead and painted over top of what was left.
If you don't have blister issues now, I wouldn't spend the money or the time barrier coating, unless you've moved the boat from cold fresh water to warmer salt water.
Take off as much of the old ablative as you can, rough it up, and apply new ablative.