Flaky bottom paint

[RedRascal]

New to me CHB 34 with what looks to be many coats of bottom paint on it. There are probably 25-50 spots where the paint has flaked off in mostly 3"x3" patches and have been painted over. There are a couple flakes where the gelcoat shows. The boat only has a couple small blisters so blisters are not part of the work detail on the next hullout. I will neither win the lotto and get a bigger boat in 2-3 years or truck this one to the mid-west and run around the Great Lakes and canals for a couple season. Then win the lotto and get a bigger boat. It's probably 50/50 odds if this one takes a truck ride east or not. The bottom stays really clean because I go between fresh and saltwater so 3 years could be realistic on a bottom job. Depending on my lotto fortunes this could be a 1 time paint job before the boat is sold.

Without investing a fortune in the bottom it seems like I could DIY the following:
Plan A - Smooth out the flaky areas with 60 or 80 grit on a disc sander, scuff the hull with scotch-brite pads and paint on another coat of bottom paint
Plan B - Hit the whole hull with 60 grit to thin out the layers of paint while trying to avoid getting into the gelcoat. This would probably leave a botchy thin layer of bottom paint on the hull but it would be smooth. Then recoat with bottom paint.
Plan C - Is there some new inexpensive option out there for getting bottom paint off? Let's remember this isn't a Hinckley we're working with.

 

[psneeld]

I have used chemical strippers buy pretty messy and sanding usually sill need for major sanding in some areas. There are "green" strippers that are less toxic than the ones that seem to work the best.

You do have to use fiberglass friendly stripper.

Hopefully they have gotten better in recent years.

Soda blasting is expensive but worth it if going the whole bottom barrier coat route. Otherwise plan A and live with the bottom.

 

[Comodave]

I have sanded, chemical stripper and soda blasting. By far soda blasting is the way to go. My boatyard will soda blasting it for $1,850. Bargain IMO.

 

[Bacchus]

I did a complete DIY refurb of a prior smaller boat with many small blisters... sanded, sanded, sanded, barrier coat then bottom paint... NEVER AGAIN DIY,!

Our last boat had way too many layers of bottom paint and was like yours - blotchy. I used a sharpened stiff scraper and scraped any / all fairly loose areas off before simp,y touching up the bare areas. Bottom was rough but I used it primarily as a slow cruise boat so so big deal and blotchy was only visible during off season storage on the hard. The key is To thin the bottom paint and apply a couple thin coats vs laying it on thick... especially along water line where the tendency is to recoat every year to maintain a crisp looking bottom where visible in the water.

 

[ranger58sb]

Soda blasting is expensive but worth it if going the whole bottom barrier coat route. Otherwise plan A and live with the bottom.

I have sanded, chemical stripper and soda blasting. By far soda blasting is the way to go. My boatyard will soda blasting it for $1,850. Bargain IMO.

I'm in the process of considering a complete soda blast and restart with barrier coat and bottom paint. Don't have any estimates yet, but...

My thinking is that hand sanding would be less efficient, it'd hurt me too much to do myself, and hiring guys to hand sand wouldn't be as effective as blasting anyway. Complicated somewhat in our case by bits where sanding would be difficult anyway (hydraulic lift hardware, thruster prop tunnel, etc,)

I'd guess better to get local estimates first, before writing it off as a possibility...

-Chris

 

[rslifkin]

I've cleaned up a similar situation on my boat. It's still not perfect, but it's good enough to put off a full bottom strip and re-do for a few more years.

For the first couple of years, I painted only the worn and chipped spots and let the rest of the paint wear down a bit more. Then one year I lightly scraped the whole bottom (over a tarp) to knock off anything poorly adhered and gave it all 1 thin coat of paint. The next year was touch ups again.

Last year I did another round of light scraping and gave the whole bottom a quick sand with 80 grit on a fairly aggressive orbital sander. I didn't go crazy and try to sand all of the paint off, but with a good sander even a quick pass removed a noticeable amount and smoothed things out a lot. 2 fresh coats of paint after that and this year I only have a couple of small chips to touch up, nothing major. At some point I'll still have to strip the bottom, but it's not an urgent concern at this point.

 

[RedRascal]

I am tracking down pricing for media blasting but I am not too optimistic about it in my market. Since I only have a couple blisters I want to avoid getting on a path that will end up requiring a barrier coat. I am cautious about media blaster or sanding getting me on that path. For better or worse it looks like sanding is probably a practical approach for addressing the flaky spots and getting the bottom a bit smoother. Doesn't seem like there are any low effort low cost magical unicorn solutions to address bottom paint buildup.

 

[SteveK]

I am preparing for bottom paint and so far, after wash, 80 grit light sanding is recommended with paints I have looked at. I think the idea is scratch up old so new can grab/fill the scuff marks.

 

[DDW]

If there are many poorly adhered coats of paint, a sharp drag scraper can often knock a lot of it off very quickly. Anything the scraper doesn't pull off is probably adhered well enough to paint over after a quick scuff.

 

[BruceK]

I suggest plan A, and review at next haul out.
We once did a hard full dry sand of an Island Gypsy 36 after osmosis repairs. It was a filthy unhealthy, dirty, hard job. We wore surgical masks. And still felt unwell for days.
Some sanding was done lying on your back on a plank, sander held above. Not recommended!
If plan A fails and you need a full stripback, Soda Strip would be my choice.

 

[Comodave]

I am tracking down pricing for media blasting but I am not too optimistic about it in my market. Since I only have a couple blisters I want to avoid getting on a path that will end up requiring a barrier coat. I am cautious about media blaster or sanding getting me on that path. For better or worse it looks like sanding is probably a practical approach for addressing the flaky spots and getting the bottom a bit smoother. Doesn't seem like there are any low effort low cost magical unicorn solutions to address bottom paint buildup.

Blasting won’t make the blister problem any worse, if there are blisters they are already there and if it were me I would actually want to know how bad the problem is. I would absolutely want to add a barrier coat. It is cheap insurance against further damage. I am going to have the bottom of my boat blasted this spring and am going to add a barrier coat even though Formula laid up the hull with AME4000 resin to precent blisters and so far I don’t have any. But the extra cost of a barrier coat is still worth it IMO. If you have an experienced person doing the blasting they should not hurt the gel coat. The blasting is the low effort method of removing many coats of bottom paint. As to low cost once you do one by hand the blasting will seem much more reasonable.

 

[Frosty]

If you end up doing any scraping, Bahco carbide scrapers are effective. (Not saying I'm recommending scraping, but if you do.)