On Sandblasting...

[Dave, 397]

Well, here's a question that is burning in my mind.

I have seen the results of bottom strippage by sandblasting and it has been either hideous or rather nice. I think this has a good amount to do with the operator, possibly.

Now, I am still haranguing around with the Medalist deal, but I am thinking ahead to the bottom. At one point in her life she had the mega-crater-face type gelcoat blistering (as opposed to the individual bulging goiter laminate variety) and was blasted to remove the gelcoat. Owner then applied something like 9 coats of plain Epoxy resin and no bottom paint. This alone, while a bit lumpy, would be OK, but the boat has been on the hard for over two years with no UV protection on the bottom.

I'll admit here, that I am always looking for a faster pussycat in anything unpleasant. I have a 7" air grinder, a 6" DA and a terrific old 7" vertical air polisher that polishes the bottom quite clean if you put 40-grit on it!

All the same, I'm looking for faster/easier/less hassle, and I do have a decent sandblaster at my disposal. B-L-A-S-T-E-R, as in Noun, tool type...the operator would be the Blastor, B-L-A-S-T-O-R, as in noun, person type. But, I digress. I'm actually pretty handy at media blasting things, but I have never done a boat.

Does anyone have experience with this, and would it be a quicker way of knocking off all that crap than Grinding/Sanding? Also, what flavor of sand would you suggest for the job? I was thinking #30 silica, but that might be a bit too rough...I dunno. U Know?

Thanks,
Dave

[Tim]

I'm sure that the quality of a sandblasting job(or perhaps we should call it "media blasting") is almost entirely dependent on the operator's skill and experience.

Given that, if you choose to do the job yourself, then you can decide on the spot whether it is working for you, or creating too much ancilliary damage. I see no problem with sandblasting under these circumstances. It's when the job is blindly hired out to the yard apes that trouble can arise.

Give it a go. Done correctly, it is a fine way to remove the material. By doing it yourself, you can determine at any given time whether it is being done correctly or not (i.e. done to your standards).

It if doesn't hurt the bottom, then it doesn't hurt the bottom.

[JetStream]

I've looked at media blasting fairly seriously and have done a little myself. I have used silica, Black diamond and walnut shells.

I have found that for fairly soft bottom paint over gelcoat, walnut shells or a plastic media can do a really nice job without harming the gelcoat (assuming the proper pressure and technique is used).

For more difficult coatings, like the UV damaged epoxy, silica could probably strip it fairly well but would be very sensitive to operator skill. Once the bottom is stripped with silica, the gelcoat will likely be quite porous and need an epoxy barrier coat before bottom paint.

I would save the black diamond for steel stripping jobs. It is also notable that specialty houses use plastic media and walnut shells to strip the paint from vintage Corvettes.

As a parting shot, be careful of too much pressure so you don't fracture the polyester in the laminate.