Soda blast top sides of grp boat

[Restoration man]

Getting an old boat 1970s with hand painted top sides , hull is still in gelcoat , I suspect it was painted by a previous lazy owner who couldn’t be bothered to keep up with the polishing, the paint isn’t pretty , so I’m thinking of getting the paint soda blasted off and seeing what the gelcote looks like and seeing if it can be re polished I’m aware of what’s needed to get bad gelcote back ,done-it many times , this is assuming these no deep sanding scratches,any missing big chunks etc will be properly repaired in colour matched gelcote as needed ,if it’s not good enough for polishing it could always be re painted on the now cleaned up surface so either ways it’s win win , I don’t know what paint had been used previously, I’ve heard soda blasting doesn’t damage gelcote but all I’ve seen is people getting anti foul removed not seen anyone having topsides done , anyone know if this process would be ok me , prob will get a mobile person to do it , just don’t want It to damage the gelcote it’s an older boat so gel cote is usually thicker than on modern boats hence why I’m thinking I might be able to rescue the original gel cote ,any advise welcome

 

[Hurricane]

We had some bad antifoul removed using soda blasting.
Yes, it is very gentle - so gentle that it doesn't damage plastic fittings.
But we were applying Coppercoat afterwards and the finish after the soda blasting is quite rough - great surface to take a next coat but not good enough as a final finish.

This photo might show you the kind of surface you should end up with




The process is so gentle, it even left the barnacles behind!!



My experience is good but don't even think about using sand blasting - far too agressive.

 

[PCUK]

Paint stripper would be safer.

 

[Elessar]

We had some bad antifoul removed using soda blasting.
Yes, it is very gentle - so gentle that it doesn't damage plastic fittings.
But we were applying Coppercoat afterwards and the finish after the soda blasting is quite rough - great surface to take a next coat but not good enough as a final finish.

This photo might show you the kind of surface you should end up with

View attachment 97475


The process is so gentle, it even left the barnacles behind!!

View attachment 97476

My experience is good but don't even think about using sand blasting - far too agressive.

Hmm I don’t agree with your blanket statement about sand blasting.
Soda is just one of the many media you can use for an abrasive blast.
Sand is not one of them!

Anyway with any abrasive blast, the problem comes when the coating is harder than the substrate. As soon as you break through the coating the substrate (the gel coat) in the blast patch is eroded faster that the paint/epoxy whatever that is around it. This doesn’t not happen with soda.

Even if the paint is softer than the gel coat you are left with a rough surface perfect for re coating. But if you want to polish it to a finish you will be left with thinner gel coat and will probably go right through in places. Unless the paint was not properly keyed you will be very luck to get back to a polished gel coat again. And the paint would have been put on for a reason.

I think once topsides have been painted you have two options;

Abrasive blast, flow coat, longboard and polish. This will give you a good as new gel coat finish. But is time consuming or expensive depending on who is doing it.

Or sand thoroughly and repaint. Retains original gel coat thickness.

Sanding removes high spots, unlike an abrasive blast. But it doesn’t removes paint from crevices so you can’t flow coat over a sanded surface that’s previously been painted.

 

[Hurricane]

Hmm I don’t agree with your blanket statement about sand blasting.
Soda is just one of the many media you can use for an abrasive blast.
Sand is not one of them!

Anyway with any abrasive blast, the problem comes when the coating is harder than the substrate. As soon as you break through the coating the substrate (the gel coat) in the blast patch is eroded faster that the paint/epoxy whatever that is around it. This doesn’t not happen with soda.

Even if the paint is softer than the gel coat you are left with a rough surface perfect for re coating. But if you want to polish it to a finish you will be left with thinner gel coat and will probably go right through in places. Unless the paint was not properly keyed you will be very luck to get back to a polished gel coat again. And the paint would have been put on for a reason.

I think once topsides have been painted you have two options;

Abrasive blast, flow coat, longboard and polish. This will give you a good as new gel coat finish. But is time consuming or expensive depending on who is doing it.

Or sand thoroughly and repaint. Retains original gel coat thickness.

Sanding removes high spots, unlike an abrasive blast. But it doesn’t removes paint from crevices so you can’t flow coat over a sanded surface that’s previously been painted.

I bow to your better knowledge.
If you remember, we looked into you doing our job at the time but the logistics of doing it in Spain were a bit onerous.
My comment about sand blasting.
It probably isn't actually sand, but every "dry blasting" job that I've seen in our yard has led to damage.
I think you once said that it is all in the skill of the operator.

 

[Elessar]

Dry blasting is the fastest for sure. But it is about the media (like different grades of “sand” paper) and very very much the skill of the operator.
Soda blasting is a dry abrasive blast with a very fine media.

 

[BruceK]

When I wanted to soda blast my AF off the local gelcoat man (highly respected firm ) was quite clear on this being a bad idea unless I re gelcoated or but on an epoxy coating such as copper coat etc. Something about it eroding any oxidised gelcoat and leaving it porous and exacerbating future oxidation erosion. He droned on a bit about it but the gist was dont.

 

[Hurricane]

Dry blasting is the fastest for sure. But it is about the media (like different grades of “sand” paper) and very very much the skill of the operator.
Soda blasting is a dry abrasive blast with a very fine media.

I'm sure that the one I used was wet.
IIRC it was a hot water mix.

This is a pic of it being done



Is this the gun?

 

[Elessar]

I'm sure that the one I used was wet.
IIRC it was a hot water mix.

This is a pic of it being done

View attachment 97484

Is this the gun?

View attachment 97485

You’re probably right. Even more gentle. But you still have to to the abrasion no matter how gentle. It just takes longer. But mistakes take longer which is good.

The gun is interesting. Looks like soda and water is mixed in the nozzle. With other wet abrasives you mix in the pot.

I note it is well tented.
The soda can go a long way and is coated in anti foul. It dissolves and leaves a coloured film on decks and cars for quite a radius. You obviously had a good job done.

 

[Elessar]

When I wanted to soda blast my AF off the local gelcoat man (highly respected firm ) was quite clear on this being a bad idea unless I re gelcoated or but on an epoxy coating such as copper coat etc. Something about it eroding any oxidised gelcoat and leaving it porous and exacerbating future oxidation erosion. He droned on a bit about it but the gist was dont.

Not at odds with what I said above. It makes the gel coat a bit thinner if you are over coating and a lot thinner if you are going to subsequently polish it to a finish. So I agree with the advice given.

 

[Hurricane]

The gun is interesting. Looks like soda and water is mixed in the nozzle. With other wet abrasives you mix in the pot.

I note it is well tented.
The soda can go a long way and is coated in anti foul. It dissolves and leaves a coloured film on decks and cars for quite a radius. You obviously had a good job done.

After working out that it would be difficult to get you out there (the marina really wanted a Spanish company rather than a UK one) I got Dennis up from Torrevieja to do the work.
He was recommended by Coppercoat - Costa Blanca Yacht Services - he did a great job.

 

[Portofino]

Thought about a wrap instead ?

 

[PowerYachtBlog]

Soda blasting is actually not suggested from gelcoat grp makers. First choice is always a paint remover and scrap it off, second is wet blasting.

Now I am not saying some people do not know how to do Soda blasting well, but is not the appropriate way to do it.

 

[Restoration man]

Thanks for the advise guys , it was wet soda dust free blasting that I was thinking about , as I thought it might be more gentle???
I have also thought about paint stripper but I’ve heard that stuff is pretty useless???? Anyone tried paint stripper that’s Any good on grp on boats ?? Maybe I should try small patch and see what the gel coat looks like under the paint ???

 

[Silvercloud]

Have you thourght about blasting with dry ice?
I have not seen it done on a boat but may be worth doing some investigation.

 

[Restoration man]

Have you thourght about blasting with dry ice?
I have not seen it done on a boat but may be worth doing some investigation.

I might look into that not sure if shifts paint but worth but research ?

 

[Silvercloud]

I know it shifts paint as there is (or was) a company that uses it for removal of antfoul etc.
if you have a look on Youtube you will find several videos.

 

[Flynnbarr]

Friend of mine did the same to an old Broom 30 using Strippit
Works on single pack paint but be careful of ally window frames.
Lazy previous owner had just slapped on the white paint,no keying up the gelcoat so he was very lucky in that regard. Ended up with a pristine boat but it was very hard work,took the whole of a winter to do but some of that was the strippit doesn’t like the cold.
Maybe try on an inconspicuous area and see what happens
My friends started off as simple as picking at a bit with a fingernail,seeing what was underneath and thinking hmmmn!

 

[Restoration man]

Friend of mine did the same to an old Broom 30 using Strippit
Works on single pack paint but be careful of ally window frames.
Lazy previous owner had just slapped on the white paint,no keying up the gelcoat so he was very lucky in that regard. Ended up with a pristine boat but it was very hard work,took the whole of a winter to do but some of that was the strippit doesn’t like the cold.
Maybe try on an inconspicuous area and see what happens
My friends started off as simple as picking at a bit with a fingernail,seeing what was underneath and thinking hmmmn!

thats what I’m Hoping for?I don’t really like painted Fiberglass , but worst case I will have to re paint but worth a try first ,

 

[Elessar]

I might look into that not sure if shifts paint but worth but research ?

It’s very expensive as it’s logistically difficult.
And is is just another type of media in an abrasive blast. But clear up is easy.
The problem is if you buy 25kg of dry ice today you’ll have 17kg when it arrives tomorrow. And how much do you need? You don’t know. So you have to over order and it doesn’t keep.