Epoxy Two Pack Blacking

[Guest]

1 hour ago, Dr Bob said:

 

 

 High humidity on cold steel causes condensation which is a killer for adhesion of epoxies unless they contains 'stuff' to make them more hydrophylic (water loving) .....but they dont always work.....

 

Pretty much what the guy said who epoxied our hull. He had the boat for a while so he could pick the "right day." Certainly has stayed on well and looking good after 5 years.

[Sea Dog]

6 hours ago, ditchcrawler said:

We use to use a Sigma product offshore and that was covered by the tide within 6 hours but of course uncovered on the next one, as for temperature then colder than the canals

 

See, I think there must be  a lot of such applications around, where either the tide comes in quicker than the (insert number of days here) specified for Narrowboat epoxy blacking or where there's simply no way to grit blast and achieve an exacting standard before application.  The harsher the environment,  like perhaps seaside jetties or North Sea Rigs, the more difficult these standards of prep and cure must be to achieve.  Is there not a product out there that the average competent boater could use which doesn't involve such exacting standards? 

 

There must be  stuff out there you could accidentally spill on something and the damned stuff would still be there in 20 years!

 

Is there a doctor in the house?

[rusty69]

5 minutes ago, Sea Dog said:

There must be  stuff out there you could accidentally spill on something and the damned stuff would still be there in 20 years!

 

Is there a doctor in the house?

Curry sauce?

 

Think he's playing wiv the sheep.

 

I used some west epoxy last week between tides ,seemed to cure nicely (dunno if its the same kinda stuff being discussed here, i'm nowt but a humble beagle)

Edited July 27, 2018 by rusty69

[Dr Bob]

49 minutes ago, Sea Dog said:

See, I think there must be  a lot of such applications around, where either the tide comes in quicker than the (insert number of days here) specified for Narrowboat epoxy blacking or where there's simply no way to grit blast and achieve an exacting standard before application.  The harsher the environment,  like perhaps seaside jetties or North Sea Rigs, the more difficult these standards of prep and cure must be to achieve.  Is there not a product out there that the average competent boater could use which doesn't involve such exacting standards? 

 

There must be  stuff out there you could accidentally spill on something and the damned stuff would still be there in 20 years!

 

Is there a doctor in the house?

Coal tar epoxies were traditionally used in offshore rig splashzone areas. They cure when the tide is out and carry on curing every time the tide goes down. I have sat on a North sea rig watching paint dry. I've also spent weeks on Shetland trying to paint leaking heat exchangers. They are not easy applications. Applying 2 pack to a narrowboat is easier but still problematical and needs to be done to control the variables. Temperature and humidity being the most difficult. This week it would have been too hot unless in a covered paint shop.....you certainly couldnt do it outside in the sun. Jotun recommend 'proffessional only' for that coating so they can get the variables right viz, temp, humidity, dew point, surface prep, mixing ratio, application equipment, wet film thickness, applicator skill, wind, dust, etc etc.

There is no 2 pack coating that can be applied successfully without controlling the variables. It, however, is not rocket science and as long the 'average competent boater' knows what he needs to do, then with a bit of practice, it can be done very successfully. It's obvious from this and other threads that the average boater does not know the variables. It is also true that a number on here do know what to do and have had very successful coating experience. Problem is it is a once in 10 year job so practice is difficult.

I spent 10 years in the coatings area and despite knowing the variables and what to do, I would not dream of trying to apply 2 pack to a large part of my boat....patching yes or the engine hole, the hull no. One reason is that airless spray is the best way of applying and that needs professional kit. The other reason is that there are a lot of professionals out there and they will do it better than me. Mine's booked in for topsides repaint in November....in a heated paint shop.

[Dr Bob]

1 hour ago, rusty69 said:

Curry sauce?

 

Think he's playing wiv the sheep.

 

I used some west epoxy last week between tides ,seemed to cure nicely (dunno if its the same kinda stuff being discussed here, i'm nowt but a humble beagle)

Found me wellies. Finished playing with them now.

Yep, West Epoxy is a typical epichlorhydrin/Bis-phenol-A epoxy. That's the base of most epoxy coatings, adhesives or resin for composites.

[rusty69]

5 minutes ago, Dr Bob said:

Found me wellies. Finished playing with them now.

Yep, West Epoxy is a typical epichlorhydrin/Bis-phenol-A epoxy. That's the base of most epoxy coatings, adhesives or resin for composites.

What is added to the base please dogtor? 

 

(I'm guessing not tomatoes, cheese and anchovies) 

Edited July 27, 2018 by rusty69

[Dr Bob]

34 minutes ago, rusty69 said:

What is added to the base please dogtor? 

Not sure what you are asking.

If you are buying West epoxy for laminating, then nothing. It will be essentially epichlorhydrin in one part and Bisphenol-A in the other, so no solvent. Adhesives will be similar. Coatings will have solvents added - usually a cocktail of 3 or 4 - plus wetting agents, flow agents and bubble release. The chemistry will be altered to allow cure down to 5°C for adhesives or for Araldite Rapid.... but that will result likely in a lower cross link density. Prices for lamb will be higher in the next few months as the farmers are having to feed their lambs rather than them eating grass. Dont ask me how I know.

 

eta..... Another variable is the molecular weight of the two main components which can be varied, formulation to formulation. 

Edited July 27, 2018 by Dr Bob

[rusty69]

2 minutes ago, Dr Bob said:

Not sure what you are asking.

If you are buying West epoxy for laminating, then nothing. It will be essentially epichlorhydrin in one part and Bisphenol-A in the other, so no solvent. Adhesives will be similar. Coatings will have solvents added - usually a cocktail of 3 or 4 - plus wetting agents, flow agents and bubble release. The chemistry will be altered to allow cure down to 5°C for adhesives or for Araldite Rapid.... but that will result likely in a lower cross link density. Prices for lamb will be higher in the next few months as the farmers are having to feed their lambs rather than them eating grass. Dont ask me how I know.

Thanks. Sorry, i wasn't clear. I meant what is added to the base to make it suitable for a coating in a submerged  marine environment. 

 

Think you answered it. 

[rusty69]

2 minutes ago, rusty69 said:

If you are buying West epoxy for laminating, then nothing

Oh, oh. One more question if you don't mind, I've never had my own expert before (sorry op) 

 

When mixing epoxy, i often thicken it, typically with something called colloidal silica or micro balloons. Does this have a detrimental effect on the cross-linking, and hence final bond strength? 

 

Thankyou

[Dr Bob]

18 minutes ago, rusty69 said:

Oh, oh. One more question if you don't mind, I've never had my own expert before (sorry op) 

 

When mixing epoxy, i often thicken it, typically with something called colloidal silica or micro balloons. Does this have a detrimental effect on the cross-linking, and hence final bond strength? 

 

Thankyou

Fumed silica is added to laminating resin (polyester or epoxy) to give it thixotropy, so it doesn't run. As it's usually applied with glass fiber, then no it won't have any effect. On its own? I guess it will help prevent micro cracking. It may affect cure slightly,maybe faster or slower, but I wouldn't worry. Ditto for micro glass spheres. Polyester gel coats have a lot of fumed silica in to make it very thixotropic and they  work well. Mrs Bob likes lamb chops.

Edited July 27, 2018 by Dr Bob

[plainsman]

On 26/07/2018 at 18:52, plainsman said:

How long should I leave the epoxy to cure before returning to the water?   I suppose longer the better would be an answer but one has to be realistic.  Advice appreciated as I am getting mixed messages from supplier and boatyard.

For anyone interested I've had a reply from Hempel as follows:

 

"The Data sheet information states a full cure of 20 days in a temperature of 5C, even that is on the generous side, the 10 days that yard state is  more than adequate, the 45143 will have completely cured by then and be ready for immersion. 

Your yard have coated many, many boats with our product and we feel they are one of the most competent and professional applicators in the Inland Waterways Market, we are confident that you won’t experience any problems".  

I have to say Hempel have been very helpful and prompt with their replies.

 

Thanks everyone for your contributions 

 

[rusty69]

3 minutes ago, plainsman said:

 

"The Data sheet information states a full cure of 20 days in a temperature of 5C, 

I did query this yesterday iirc post#14

Edited July 28, 2018 by rusty69

[rusty69]

Next question for Dr Bob, if he's still reading.

 

Given "normal epoxies will not cure under 15°C" 

 

What would manufacturers add to their product to allow a cure at 5 degree c? 

 

Or is it just a different type of Bisphenol? 

 

Also, "would you like some toast?" 

Edited July 28, 2018 by rusty69

[Dr Bob]

1 hour ago, rusty69 said:

Next question for Dr Bob, if he's still reading.

 

Given "normal epoxies will not cure under 15°C" 

 

What would manufacturers add to their product to allow a cure at 5 degree c? 

 

Or is it just a different type of Bisphenol? 

 

Also, "would you like some toast?" 

A couple of Beagles Bagels would be nice.

 

When I was working on epoxy coatings, we were using ethanolamine as a component of the hardener side (ie the epichlorhydrin). I think many primary or secondary amines attached to the hardener molecule will work. IIRC you also needed OH groups on the molecule. The crosslinking reaction is therefore different and will work to lower temps -  we used it in an underwater sealant application that was designed for north sea temps ie 4°C (ie sealant applied underwater). A lot of the work we did showed that the final physical properties of adhesives and sealants based on amine cured epoxies (cured at low temps) were never as good as the properties of normal epoxies cured at 23°C, hence my references to it as a compromise. There may be other chemical routes to lower temp cure as well but amine cured epoxies are likely to be the most common.

[rusty69]

Yeah, obviously, i knew all that basic stuff! I was wondering if their were any recent developments 

[Dr Bob]

44 minutes ago, rusty69 said:

Yeah, obviously, i knew all that basic stuff! I was wondering if their were any recent developments 

I'm now 10 years out of date on these curing systems but in reality, there have been very few new 'chemistries' appearing. Most of the developments have been in changing the solvent systems to water based ones. It is interesting that most of the coating and adhesive systems are still using 25-30 year old chemistry.

[nicknorman]

1 minute ago, Dr Bob said:

I'm now 10 years out of date on these curing systems but in reality, there have been very few new 'chemistries' appearing. Most of the developments have been in changing the solvent systems to water based ones. It is interesting that most of the coating and adhesive systems are still using 25-30 year old chemistry.

Has chemistry changed in the last 25-30 years?

[David Mack]

33 minutes ago, nicknorman said:

Has chemistry changed in the last 25-30 years?

Dunno about chemistry, but ye cannae change the laws o' physics!

[nicknorman]

2 minutes ago, David Mack said:

Dunno about chemistry, but ye cannae change the laws o' physics!

...nor the laws of chemistry!

[rusty69]

Ye cannae change em, but can add to em! 

[Paul C]

The chemistry doesn't change but the economics (of manufacturing chemicals) does. So something which was brilliant but just too costly 30 years ago, might come into the market because various advances in manufacturing make it cheaper to produce at the quantity/quality required etc etc...