Cleaning the hull for Barrier Coating

[madhatter66]

Winter project thinking here. If I don't soda blast the bottom, what's the roughest sand paper can I go to remove years of bottom paint? She's a old Hatteras so no gel coating on hull. Want to do an epoxy barrier coating and fresh coat of bottom paint. Thanks​

 

[DCMY #92]

She has gelcoat on the bottom. It's the gelcoat you don't want to remove, except where there are blisters. I think 80 grit is the courses sandpaper you should use to avoid deep scratches in the gelcoat and greater risk of removing the gelcoat in places. Sanding is a dirty, long, slow process and may not be less expensive than blasting when you include the cost of the considerable quantity of sandpaper you will use - even if your labor is free.

After paint removal I used a Drimmel tool (carbide burr) to open blisters and remove the un-bonded gelcoat. There were hundreds of them ranging in size for 1/4" to 1.5". After letting them drain and dry for several days, filled with them with MarineTex, then sanded them smooth. Then applied the barrier coat and new bottom paint. After 30+ years no blisters have reappeared.

 

[Boatsb]

We recently dry blasted a boat to ro the bottom.

It's a bit more aggressive than soda blasting but much faster. It was not that expensive and when done right leaves a good surface for the next steps.

We usually smooth with 9"pads or 80 or 100 then 120. After that 5 or 6 coats of barrier coat in a day or day and a half then the first coat of bottom paint immediately after the barrier is dry to the touch.

 

[dsharp]

60-80 grit on a foam backing pad. I would have it blasted. Sanding the bottom is a horrible job. I started out on the bottom job crew like everyone else and got away from it as soon as I could. You’ll want a fresh air mask if you do it yourself.

 

[madhatter66]

Which is better or more effective, Soda or Dry Ice blasting the bottom? I figure sand is too harsh or is that similar to soda? I noticed Harbor Freight sell a soda blaster.

 

[Boatsb]

Breathing the dust from the sander the soda is bad enough but when you're blasting bottom paint it is absolutely deadly.

Hire it out to somebody set up to do it sand wet or dry soda doesn't matter as long as they know how to work with the abrasive

 

[Cricket]

Our yard uses the Farrow system to remove bottom paint, really works well.
Do yourself a favor and have somebody remove it, make sure they know what they're doing or you could have a big mess.

 

[jim rosenthal]

Amen to that. Not a job you want to do yourself unless you just happen to have a hood and pressure-fed respirator around. And even then get someone else to do it.

 

[oscarvan]

I do everything myself..... except this. Get a guy with a rig, and stay upwind while he does it.

 

[dsharp]

Standard sand is #3 which is pretty aggressive. They make a #4 which is finer and a lot less likely to cut through the gel coat. I don’t have any experience with soda or dry ice. See if someone in the area has a wet blaster or a farrow system which is the same thing. I have a lot of experience with a 8” air sander and you don’t want to go there. I don’t know if anyone even sands bottoms anymore.

 

[madhatter66]

[SUB]​Thanks for the input everyone. I'll look into having a company doing the job. [/SUB]