Does Soda Blasting Degrade Gelcoat

[keensailor]

hi
Plan to have hull soda blasted, several small osmosis blisters fixed and then antifoul.
My question is: is it necessary to put an epoxy barrier coat over the clean gelcoat and before the antifoul due to the possibility of the soda blasting degrading the gelcoat outer layer.
thanks in advance

 

[EugeneR]

If you're having all that work done, why not go all the way and put on coppercoat which includes a few layers of epoxy? If you apply it yourself, the incremental cost should not be that much.

 

[Gwylan]

If you're having all that work done, why not go all the way and put on coppercoat which includes a few layers of epoxy? If you apply it yourself, the incremental cost should not be that much.

+1 for that!

Get a real professional to do the soda blasting - get recommendations and be sure they really know what they are doing.
Let the hull dry out for a while after the soda blasting. Measured in weeks not days, I was told

You put a couple of epoxy coats on, after the soda blasting and before the CopperCoat. Make sure you have some reliable mates [2] to help you especially a mixer. Have a mixing station and time it so that the mixture is ready for the next coat when the painters are.
It sort of goes in a routine - well it did for a 10m boat.
Get to one end and it's time to get back to the other with the next coat.
Have a supply of rollers, a set for each coat and each painter, lined up. The resin goes off and make the rollers useless.
Wack on the CC and Bob is your mother's brother.

We did that in 2006 and have only had to pressure wash and abrade the hull since then. 3M green kitchen pads the best material we have found.
Avoids the expense of the lift, environmental issues with collecting waste anti-foul and the cost of new anti-foul.

Other copper coating treatments are available.

Buy copper powder on the internet and use it with epoxy to make tiny batches that become necessary. It will look different but less bad than any scrapes or whatever and ensure surface integrity.

 

[youen]

Can you get rid off Coppercoat without degrading the gelcoat by soda blasting?

 

[Deleted member 36384]

My understanding is that it does not degrade the gelcoat. So you do not need to apply an epoxy barrier because you have soda blasted. You do of course have to repair any breaches in the gelcoat which the soda blasting may reveal.

I found the quote below here: http://www.practical-sailor.com/issues/37_10/features/sodablasting_101_10610-1.html

In fact, sandblasting has become less popular as a prep method in major blister repairs because of how much surface destruction occurs during the cure. Sodablasting is a very different story, and the unique softness of the calcium carbonate powder yields an abrasive capacity that’s just enough to strip bottom paint but will leave the gelcoat intact.

 

[superheat6k]

I would contact Ellessar on the Mobo forum as they prep for copper coat for a living.

 

[Marsupial]

definitely get a professional with references to do the soda blasting, the process shouldn't damage the gel coat. watched in awe a "professional" operator blow holes in the gel-coat and layup of a fairly new boat in Messolonghi - the owner only wanted the anti fouling removed! to parody Michael Caine I only wanted you to blow the bloody anti fouling off!

being Greece the operator did n't understand what the problem was . . . .

anyway, grind the blisters off then wash the boat with lots of fresh water and leave it to dry for a week or two - if it wont dry wash it some more - sounds crazy but that's what you have to do. It could take a month or two to dry out so you can begin treating the blister craters and final coating.

 

[Elessar]

hi
Plan to have hull soda blasted, several small osmosis blisters fixed and then antifoul.
My question is: is it necessary to put an epoxy barrier coat over the clean gelcoat and before the antifoul due to the possibility of the soda blasting degrading the gelcoat outer layer.
thanks in advance

there is a huge amount of contradictory replies here, some of it wrong.

some facts:

you don't need to apply epoxy after abrasive antifoul removal if it was done well. This applies to soda or wet "sand" blasting, despite that practical sailor nonsense. I have magazine articles that state that our system didn't cause a single pinhole when they tested it. But anyway epoxy - it is an opportunity to do so that would be a shame to miss.
Coppercoat is an ideal antifoul and epoxy all together. Ignore the b0ll0x about making imitations that keeps being bandied about, if it were so easy somebody other than coppercoat would be selling one that works.
You can't blast coppercoat, or any epoxy, off gelcoat. It has to be sanded off. But why bother, sand to key then overcoat.
GRP boats do not dry when left on the hard. Any talk that leaving them for weeks to dry is nonsense. They would maybe dry a tiny bit after 20 years.


But, your problem.

You have some osmotic blisters. The hull is going to be no drier between the blisters, it just hasn't blistered there (yet).
So if you fix the blisters and epoxy the hull, you will likely induce further blistering.

So......

Forget a blast, you are wasting your money. Hack out the blisters, dry them by washing (that was good advice) and fill them with epoxy filler.
Antifoul the boat, sail it and enjoy it.

When the blistering gets worse, have it fixed properly by peeling off the gelcoat, then blasting it, then steaming it or jetwashing it every day until it is dry. Replace the gelcoat with epoxy, then, if you have any sense, coppercoat over the top.

 

[keensailor]

there is a huge amount of contradictory replies here, some of it wrong.

some facts:

you don't need to apply epoxy after abrasive antifoul removal if it was done well. This applies to soda or wet "sand" blasting, despite that practical sailor nonsense. I have magazine articles that state that our system didn't cause a single pinhole when they tested it. But anyway epoxy - it is an opportunity to do so that would be a shame to miss.
Coppercoat is an ideal antifoul and epoxy all together. Ignore the b0ll0x about making imitations that keeps being bandied about, if it were so easy somebody other than coppercoat would be selling one that works.
You can't blast coppercoat, or any epoxy, off gelcoat. It has to be sanded off. But why bother, sand to key then overcoat.
GRP boats do not dry when left on the hard. Any talk that leaving them for weeks to dry is nonsense. They would maybe dry a tiny bit after 20 years.


But, your problem.

You have some osmotic blisters. The hull is going to be no drier between the blisters, it just hasn't blistered there (yet).
So if you fix the blisters and epoxy the hull, you will likely induce further blistering.

So......

Forget a blast, you are wasting your money. Hack out the blisters, dry them by washing (that was good advice) and fill them with epoxy filler.
Antifoul the boat, sail it and enjoy it.

When the blistering gets worse, have it fixed properly by peeling off the gelcoat, then blasting it, then steaming it or jetwashing it every day until it is dry. Replace the gelcoat with epoxy, then, if you have any sense, coppercoat over the top.

Thanks Elessar!
This is exactly the answer I was after. I have decided not to get the hull blasted and epoxied now, will just get blisters fixed until such time as the blisters get far worse.
Guess we will have to live with a rough bottom for a while.
Can you tell me why you say "So if you fix the blisters and epoxy the hull, you will likely induce further blistering", is it that the blasting may degrade the gelcoat and if the epoxy does'nt form a proper barrier water will penetrate causing more blistering ?

 

[Deleted member 36384]

This moisture, which is already in the hull before any blasting process, is reacting with products in the resin that have not cured fully and make new compounds e.g. osmosis. In the hull that is not epoxied but where osmosis is happening the pressure build up due to the new compounds can be less as the remainder of the water moisture that has not reacted can still move. In the epoxied hull, it cant, or is restricted much more as the epoxy is a better barrier to water moisture, this trapped water now contributes to the pressure build up which can be shown as bigger blisters, or more of them, forming faster. The only cure for osmosis is something like a hot vacuum process after scraping away and washing solvents out. Thats how I understand it as an amateur who owns an old boat and looked into this aspect. There is probably a more accurate description by experts.