Getting ready to blast

[Maestro]

Getting ready to have the bottom of the hull hydro-blasted.

I know the paint needs to go on ASAP after blasting...but the guy thinks it could take up to 4-5 hours to do the whole job.

For those who have done this, what kind of "working time" do I have with the aluminum before has sat exposed for too long to paint?

Thanks...

[Fastjeff]

My guy took several hours and a pallet of sand to do my 32 footer. I'm still finding sand in the wine cellar and window tracks--and that was 10 years ago!--so be sure to mask thoroughly.

Jeff

[bcassedy]

I had the bottom sand blasted 4 years ago. Seems like it took the guy I hired about 2 hours to complete. After (quickly)tearing down of the plastic I'd erected around the boat (had taped it to the gunwale all around the perimeter which kept the sand inside the "tent"), I applied the 1st coat of 2 part epoxy primer (Interlux's Interprotect 2000E) starting at the point where the blaster has started. Figured this area had been exposed to the air the longest. Day was a low humidity one and it appears that the process I used worked ok - no peeling/failing issues.
Moral - get the 1st coat on as soon as feasible but I wouldn't wait any longer than 2 - 3 hours after exposure if it can be helped.

Bill

[jralbert]

Crew I hired did all the taping (except for the Capac which I wanted to be certain was protected so I covered it with an aluminum pie plate and the raw water intakes). Took two guys about 6 or 7 hours. Immediately afterwards, the yard air blasted the dust off the hull then sprayed on the first primer coat (I think that was Interprotect). So, by the end of the day - perhaps 5pm or 6pm - we had finished phase one and two and could take whatever time was necessary for the remaining coats on subsequent days. About $1,200 for the blasting and a little more for the painting.
The blasters earned every penny working under the tent on a warm day, wearing masks and protective suits.

[jtalberts]

Plug any thru hulls tight with old rags or tshirts. I dropped plastic from the edge of my decks down, but this was on a houseboat so the structure is different. After getting mine blasted I rinsed mine down before painting. There was a lot of residual dirt/sand on the hull of the boat and I was worried about adhesion. I started on the side he blasted first and worked my way around. I had primer on the entire bottom half in about 4 hours. 4 years later the coal tar and paint I applied are doing great. My buddy did a similar thing but waiting days to paint and his is peeling like crazy all over the hull. Make sure he starts it in the morning and you at least get a coat of primer on all the metal by the end of the day and you will be fine.

[MetalHead]

Go find one of these guys. They are all over CL

http://www.dustlessblasting.com/videos.html

I've looked into these and they seem line a good setup. Uses glass beads instead of sand, backed by water.

[Fastjeff]

Hate to say it, but aluminum corrodes within SECONDS after being sand blasted (or sanded) so etching is essential for a proper bond--and even with epoxy.

If you want to observe this happening, try the Gudeon Brothers technique: Using a coarse piece of sandpaper, 'wet sand' some bare aluminum with some clear liquid epoxy. In a few seconds you'll see the clear color become steel grey--that's the oxide coating being removed and replaced by epoxy. A perfect adhesion method, but a bit awkward to do for the entire boat bottom!

Jeff

[Maestro]

I was looking for Sherwin-Williams dual Etch to etch the hull prior to painting and had a hard time finding it. A local auto parts place was able to find me an equivalent product - it's called Chem-Fil DX-533 Aluminum Cleaner. Basically the same ingredients as the Sherwin Williams.

However, when I read the instructions it said "not necessary or recommended for freshly sandblasted metal."

Think I should do it anyway? Would I be hurting anything? It's a phosphoric acid-based cleaner. You spray it on, let it sit for 2-3 minutes, and rinse off.

THANKS!

[Maestro]

link to the stuff: https://www.chemfil.ca/product_categories/cleaners/

[Calivanos]

If you are using interlux epoxy a thorough wash down with their 202 solvent will work. It's wipe on/wipe off on a clean rag until no more black comes off. If you are using sherwin williams Seaguard 5000 you can use MEK or Acetone depending on how fast you are at wiping. Aluminum immediately begins to put a protective layer between it and the atmosphere (that's the black sheen). As long as it's off you will be okay. We paint aluminum crew boats daily down here and the main thing is to make sure it's clean and give it time to cure. If you don't do it yourself be sure that the last coat of epoxy and first coat of antifouling stay within manufacturer recommendations (timing). Usually 2-4 hours.