epoxy finish on a steel hull

[mikewade]

I have been searching PBO Forums & also boatdesign.net and have read with interest the recent discussion about the steel boat in France and the comments about finishes etc.
My steel van de stadt is on the hard and I am about to have her blasted clean then epoxy coated.
My questions really relates to film thickness to be applied. The epoxy I am looking at is 3M 152 LV and the manufacturer suggests that this gives a film thickness of 500microns per coat. At this thickness, is 1 coat enough or are 2 or three really the best. Also the touch dry time for 152LV is around 12 hours which is going to be a problem in our inclement North east weather. Does anyone have a suggestion as to a more appropriate epoxy taking into account cost & speed of application etc. I struggle to find a definitive answer and the manufacturers are of course unable or unwilling to give a straightforward answer. Any guidance the panel can give me will be gratefully received and thanks for taking the time to consider this.

 

[idpnd]

You got to get the product data sheet for your epoxy. It says exactly how many microns and coats etc. Usually its 5+ layers for primer and another couple two component stuff to seal it. As a dutchie steel boat architect said to me just the other day, the first coat is what matters most - get it on there immediatley after blasting.

Theres some discussion about using zink primers for the first coats. I understand little about that but I think theyve gotten out of fashion.

 

[nedmin]

Why not contact Awlgrip by e-mail, Their products are first class

 

[Bobobolinsky]

Sigma do a stunning primer, 280, you can roller it, brush it, conventional spray it or airless spray. Touch dry in a couple of hours. 500 microns in a coat is going to be airless applied, roller or conventional spray, you are looking at 125 microns per coat. Don't forget that epoxies are not UV stable and colour coats should be two pack poly or may be single pack, but something that is stable in sunlight

 

[Pasarell]

Steel Coating

Why not just go down the road? International are at Felling, next to Gateshead. I don't suppose they will supply you directly but one of the yards along the Tyne will get materials for you. Speak to the Marine (not yacht) Tech Service Dept and they will tell you what to use. All data sheets can be downloaded from their web site

500 microns of epoxy will be enough but not in 1 coat. Just because it CAN be applied at 500 microns does not mean it WILL be applied at that level. There will always be variations in film thickness, especially at edges, corners and welds, the most vulnerable parts. You should always use at least 2 coats to give you a fair chance of avoiding holidays and pin holes. Also apply a stripe coat to edges, corners etc to build film.

The earlier comment about 5 coats is only relevant if you are applying a thinner film product. Total film thickness is what matters. If you are managing the job yourself (even if someone else is doing application for you) suggest you look at getting a dft gauge. Basic ones on e-bay for around £100 new.

I think 12 hours to touch dry for the product you mention means it is not suitable for your application. The chances of avoiding rain or significant changes in temperature and humidity in that time are pretty slim and they will cause you problems later. There are many faster curing products that will be much easier to use. Go for a good marine product with a track record.

 

[rogerthebodger]

This is what I used when I did my steel Lavranos 50 after grit blast inside and out a couple of years ago. Very similar to awlgrip. http://www.alexseal.com/en/technical.php

 

[oldsaltoz]

Why not just go down the road? International are at Felling, next to Gateshead. I don't suppose they will supply you directly but one of the yards along the Tyne will get materials for you. Speak to the Marine (not yacht) Tech Service Dept and they will tell you what to use. All data sheets can be downloaded from their web site

500 microns of epoxy will be enough but not in 1 coat. Just because it CAN be applied at 500 microns does not mean it WILL be applied at that level. There will always be variations in film thickness, especially at edges, corners and welds, the most vulnerable parts. You should always use at least 2 coats to give you a fair chance of avoiding holidays and pin holes. Also apply a stripe coat to edges, corners etc to build film.

The earlier comment about 5 coats is only relevant if you are applying a thinner film product. Total film thickness is what matters. If you are managing the job yourself (even if someone else is doing application for you) suggest you look at getting a dft gauge. Basic ones on e-bay for around £100 new.

I think 12 hours to touch dry for the product you mention means it is not suitable for your application. The chances of avoiding rain or significant changes in temperature and humidity in that time are pretty slim and they will cause you problems later. There are many faster curing products that will be much easier to use. Go for a good marine product with a track record.

Good post Pasarell,

DFT's (Dry Film Thickness) and holidays (Imperfections in the cured paint) in paint finish, many old memories flooded back.

Though I was a little surprised you did not emphasise the importance of preparation like blasting to class two and a half and coating as soon as possible.

One thing about painting we should be remember is the finish is only as good as the start.

The last steel hull we painted was grit blasted then given a coat of zinc, note the thickness of zinc is critical too thick it mud cracks, too thin it won't work. Then faired and primed, sanded an washed then 4 top coats, the first being just a mist coat and working through to the final full thickness coat.

As others has indicated you need to select that is less vulnerable to changes in temperature and humidity, the latter being the hardest to control.

The good news is that today these products are available, though you end up looking at Industrial quality products rather then commercial.

And thank you Pasarell for stirring some old memories.

 

[DavidMcMullan]

My van de Stadt was painted with International products, who prepared a full painting spec for the builder, which included:
Topsides: Blast to Sa2.5, Interprime 820 65DFT, Interfill 830 5000DFT, Interfill 835 500DFT, Interprime 820 125DFT, Polyurethane basecoat 50DFT x 2, Interspray 900 35DFT x2.
Underwater hull: Blast Sa2.5, Interprime 820 65DFT, Interfill 830 5000DFT, Interprime 820 125DFT x2, Interprotect 135DFT, Micron Extra 60DFT x2.

I suggest you contact your preferred paint supplier and get them to prepare a spec for you to follow.
Good luck.

 

[mikewade]

epoxy finish on a steel boat

Thanks guys for all the comments - you've given me the wealth of your experience and helped set my mind at rest.
the best forum!
Mike

 

[oldsaltoz]

My van de Stadt was painted with International products, who prepared a full painting spec for the builder, which included:
Topsides: Blast to Sa2.5, Interprime 820 65DFT, Interfill 830 5000DFT, Interfill 835 500DFT, Interprime 820 125DFT, Polyurethane basecoat 50DFT x 2, Interspray 900 35DFT x2.
Underwater hull: Blast Sa2.5, Interprime 820 65DFT, Interfill 830 5000DFT, Interprime 820 125DFT x2, Interprotect 135DFT, Micron Extra 60DFT x2.

I suggest you contact your preferred paint supplier and get them to prepare a spec for you to follow.
Good luck.

Good choice Dave,
Interpray 900, my all time best pick.

 

[vyv_cox]

My van de Stadt was painted with International products, who prepared a full painting spec for the builder, which included:
Topsides: Blast to Sa2.5, Interprime 820 65DFT, Interfill 830 5000DFT, Interfill 835 500DFT, Interprime 820 125DFT, Polyurethane basecoat 50DFT x 2, Interspray 900 35DFT x2.
Underwater hull: Blast Sa2.5, Interprime 820 65DFT, Interfill 830 5000DFT, Interprime 820 125DFT x2, Interprotect 135DFT, Micron Extra 60DFT x2.

I suggest you contact your preferred paint supplier and get them to prepare a spec for you to follow.
Good luck.

This is an excellent specification. It is very similar to the one used for the offshore oil platforms of my ex-employer. The spec was not specifically for International products, being more generic, but the coating descriptions were very similar.