barrier coat

[sailingdog]

I'd second T37Chef's idea. Sodablasting would do an excellent job of opening up most of the small blisters while removing existing bottom paint and prepping the surface of the bottom of the boat. It's also reasonably priced in many areas. Several people on this site, including myself, have had their boats sodablasted in the last couple years.

Acetone will also clean off the bottom of the boat, and may be a good alternative to grain alcohol. Be careful with either though, since both are quite flammable.

[bob chaisson]

Acetone leaves a residue as well, more so that denatured alcohol. At a previous job, I had to clean special optics that read measurements of 1/2 of 1/1000 of an inch. The equipment manufacturer documents identified grain alcohol as the only fluid that didn't leave a residue. I'm sure for this purpose, denatured works fine.

[townpiper]

Thanks Guys

Soda blasting sounds like the way to go

I never pass up an opportunity to betray my own stupidity. Now to find somebody down here who does this . This area is pretty close to "those" areas of appalachia, and unlike the winos in NYC who use italian bread to strain the wood alcohol, I think some folks drink it straight up here.

Thanks again and Fair Winds to you.

[wolfmt]

Hello all. I apologize for reviving a couple of week old thread on barrier coats but as I'm a couple of weeks away from applying one, I wanted to make sure I understood one point. How low of moisture reading do you need to have in order for a barrier coat to make sense? In this regard, I've read posts on other forums that suggest that most of the epoxy barrier coat manufucaturers recommend that the hull to be coated have such a low moisture reading that any hull that is 20 years or more old and spends six months in the water each year couldn't possibly meet their recommendations. In addition, these posts have stated that applying a barrier coat to a relatively dry hull (but one that has more moisture than recommended) is inviting a blister problem.

Many thanks,

Mike

[sailingdog]

Wolfmt-

I think it depends on whether the boat had a previous osmotic blistering problem and you're doing the barrier coat as part of a repair or whether the barrier coat is being done prophylactically. In the first case, I do believe you need to dry out the laminate, since it is saturated and that is what was causing the initial osmotic blistering problem to begin with. With a preventative coating...the hull and gelcoat are usually relatively dry to begin with, so don't generally require a long drying out period.

[SailorMitch]

The answer in theory is that yes, the laminate should be "dry." The problem is measuring that accurately. I don't think most moisture readers commonly in use are all that accurate. At best they give you a range of comparison for your boat. One area is "dryer" than another area. Even then, you'd need to calibrate the meter with however the barrier coat manufacturer expresses "dryness".

When I barrier coated my boat I hauled it in Oct., punctured the blisters to let them drain over the winter, and then I took moisture readings the following March just before I applied the barrier coat. I used a meter borrowed from a friend, and it is a common one you see advertised all the time. The bottom was "dry" according to the meter so I went ahead with my project. The bottom still looks great. My boat was 17 years old when I applied the barrier coat.

[wolfmt]

Thanks sailingdog. In this case, the boat is approximately 30 years old. The bottom paint has been stripped down to gel coat and there were a handful of blisters (less than 20) that have been repaired. Otherwise the bottom is in great shape. The boat has been out of the water since September. The boat was surveyed in January and was described as dry but I don't have the specific moisture readings for the hull (the deck had a couple of moist spots for which I have specific moisture readings). What do you think?

[sailingdog]

Wolf-

Not having the moisture readings and such... I would suggest you barrier coat it, if the previous blisters have been treated. Do you know if the previous blisters were osmotic or not???

[AA3NK]

This has been a pretty impressive and informative thread in re applying a barrier coat. I'll be rolling the bottom of my Cheoy Lee Luder's 36, probably this weekend and need to estimate the materials required.

The lwl is 25', beam is 10'3", draft is 5'3." What is the size of the area in suare feet? Or, said differently about how many gallons will I need to put on six coats? I am planning to use MAS resin and was thinking of using slow hardener.

The weather in the Mattapoisset, MA area tends to the cool side, under 80 and likely in the low 70s for this time of the year.

[sailingdog]

You're probably about 275 sq. ft of surface area or so... as a really rough guess. As for how many gallons it takes to barrier coat that, why don't you call up MAS Epoxies and ask them. I'm sure they're worked with people doing this previously.