STOP sanding EPOXY!!!

[rael dobkins]

STOP sanding EPOXY! At Balkan Shipyards we PAINT IT WET, then sand the paint.... Aggressive ADHESION TEST in the VIDEO, proves a very STRONG BOND!!!

 

[dankilb]

Very interesting indeed, thanks for sharing.

I’d often wondered about this, more in terms of comparability between epoxy laminating resins and (other brand’s) epoxy-based paints, fillers, etc… on the basis that not all “epoxy” is the same (some of the paints are very high % solvent, for example).

I can certainly see the practical application of filling the weave and achieving chemical bonding. It could be great on repairs (I’m not a boat builder!).

On the other hand, I already use peel ply to avoid the need to sand most of my epoxy work. It’s not cheap! But I don’t know if I’d have the energy to start mixing and applying paint straight after a big laminating job?!

Presumably you’re aiming to apply the primer during the gel stage? Wet on tacky?

 

[lustyd]

All well and good if the layup is flat, but it usually isn't so if you want a very good finish then you'll have to sand before applying the final surface. That's the reason a lot pf big motor yachts come out of the mould and immediately have their gelcoat sanded back to flat before being painted - the finish out of the mould is wonky at best. When the boatshow is on you can see the difference between something straight from the mould (wobbly reflections) and something that's been professionally finished (like a flat mirror). The adhesion is fine if you prep properly.

 

[Tintin]

A touch shouty OP

 

[dankilb]

All well and good if the layup is flat, but it usually isn't so if you want a very good finish then you'll have to sand before applying the final surface. That's the reason a lot pf big motor yachts come out of the mould and immediately have their gelcoat sanded back to flat before being painted - the finish out of the mould is wonky at best. When the boatshow is on you can see the difference between something straight from the mould (wobbly reflections) and something that's been professionally finished (like a flat mirror). The adhesion is fine if you prep properly.

I guess it's a question of whether you sand a) the layup (not ideal), b) another layer (such as paint/gelcoat) that is not chemically bonded to the layup, or c) whether it is possible to get your high-build primer to bond chemically to the layup itself (and then sand away at the high build)?

Moving away from boat building and thinking about a practical 'repair' example:

I currently have some nice pre-mixed fairing filler (so no powders, mixing, bubbles, etc.). However, I'm reluctant to use it to fill the (very numerous) minor chips, holes and small bilsters in our gelcoat after blasting because I cannot see how the filler, alone, can achieve a chemical bond with the substrate. The filler is Jotun - who don't make a laminating resin - so I have no way of using a 'compatible' resin to prime the repairs. I'd have to apply to filler straight to dry GRP/gelcoat.

This video has made me think of testing the filler on top of laminating resin, to achieve the chemical bond I want. Otherwise you're stuck using powders to thicken a compatible resin, often at equivalent (or even greater) cost and more faff.

So that's just one potential practical example. Not that I'm suggesting this is groundbreaking chemistry or anything. More that it has given me the idea to at least test whether various epoxies adhere to each other, as the OP showed!

 

[Caraway]

A touch shouty OP

Yes. I thought it was a message of extreme urgency.

 

[Spirit (of Glenans)]

A touch shouty OP

Que?

 

[lustyd]

I guess it's a question of whether...

You're right, of course. If you're just going for strength then of course this stuff matters, and for repairs or unseen areas as in the video then it makes sense not to sand the epoxy. I'd rather have a slightly uneven finish than ever have to repaint the inside of a locker! If you want a good finish though it's a different story, and anything on the outside of the boat I would definitely go for finish over raw strength

 

[Refueler]

All well and good if the layup is flat, but it usually isn't so if you want a very good finish then you'll have to sand before applying the final surface. That's the reason a lot pf big motor yachts come out of the mould and immediately have their gelcoat sanded back to flat before being painted - the finish out of the mould is wonky at best. When the boatshow is on you can see the difference between something straight from the mould (wobbly reflections) and something that's been professionally finished (like a flat mirror). The adhesion is fine if you prep properly.

Part of the problem out of mould is the 'Green GRP' .... that is not fully cured and is still quite flexible.

 

[lustyd]

Also that it's very hard and expensive to make a completely rigid and flat structure that's over 20m long

 

[rael dobkins]

Very interesting indeed, thanks for sharing.

I’d often wondered about this, more in terms of comparability between epoxy laminating resins and (other brand’s) epoxy-based paints, fillers, etc… on the basis that not all “epoxy” is the same (some of the paints are very high % solvent, for example).

I can certainly see the practical application of filling the weave and achieving chemical bonding. It could be great on repairs (I’m not a boat builder!).

On the other hand, I already use peel ply to avoid the need to sand most of my epoxy work. It’s not cheap! But I don’t know if I’d have the energy to start mixing and applying paint straight after a big laminating job?!

Presumably you’re aiming to apply the primer during the gel stage? Wet on tacky?

I go wet on wet, they can cure together when they want.......
Happy u like it, all d best