Jump to content

Epoxy Two Pack Blacking


Featured Posts

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.

Link to comment
Share on other sites

As you say,  as long as possible. 

Dacrylate dries very quickly and you can get (.is recommended as well) to get two coats on in a day in these temperatures. 

It's still best to leave it 48 hours before going back in though.

Link to comment
Share on other sites

Depends on the product and the grade of the hardener. The point is that as soon as it goes back into the water curing will effectively stop.

 

I used Jotamastic 87 with standard hardener in the summer of 2015 which wasn't a particularly hot summer. I thought a couple of days would be ok but when I called Jotun they told me I needed to leave it out the water for at least a week. I spent another £200 on the dry dock which fortunately wasn't booked! Moral of the story is to use a winter grade hardener unless it's really hot weather like this year. With the WG hardener 2 or 3 days would have been fine.

 

Anyway, listen to the paint supplier (or even better the manufacturer), not the boatyard. People in boatyards don't know anything - that's why they work in boatyards! :lol:

Edited by blackrose
Link to comment
Share on other sites

Yes use the datsheet for the particular product. I would be inclined not to agree with blackrose’s comment about going back into the water - it is a chemical reaction, not evaporation that cures it, so the issue will be predominantly one of temperature not whether wet or dry. The stuff we used on our boat could be put in the water pretty quickly, but it didn’t reach full hardness for quite a while.

Link to comment
Share on other sites

Its a chemical reaction - some products can be applied and will harden underwater. However for cosmetic reasons its best to leave it dry, then it will dry/harden in an even black application - if its wet during hardening it will be blotchy grey.

Link to comment
Share on other sites

Just now, Paul C said:

Its a chemical reaction - some products can be applied and will harden underwater. However for cosmetic reasons its best to leave it dry, then it will dry/harden in an even black application - if its wet during hardening it will be blotchy grey.

Yes, however usually the wet blotchy problem is only an issue for the first few hours or a day, long before the product fully hardens.

Link to comment
Share on other sites

5 minutes ago, nicknorman said:

Yes use the datsheet for the particular product. I would be inclined not to agree with blackrose’s comment about going back into the water - it is a chemical reaction, not evaporation that cures it, so the issue will be predominantly one of temperature not whether wet or dry. The stuff we used on our boat could be put in the water pretty quickly, but it didn’t reach full hardness for quite a while.

Nick is not quite right.

Agreed, use the info on the data sheet.

The word 'Cure' refers to the crosslink reaction that bonds the polymer chains together. Most epoxies will continue to cure underwater and therefore harden after going back in. BUT......evaporation of solvent is also important to allow full hardness and if you put it in the water before the solvent is out then that will never come out and the coating will not achieve full hardness. Most paint chemists will use the word 'cure' to mean both the crosslink reaction and solvent evaporation. If the temp is 25°C most of the day then likely a couple of days will be sufficient but at normal summer temps where the night temps fall to 10-12 °C and daytime up to 25°C then maybe a week would be better. In the lab, we always used to cure at 23°C continuous - which is a damn site hotter than a normal summer.

Follow what the data sheet says, not the boatyard. Most normal epoxies dont like to cure under 15°C but the 'winter' grades use agents that allow cure to happen quicker but it is a bit of a compromise and solvents dont tend to come out well below that temp.

  • Greenie 1
Link to comment
Share on other sites

40 minutes ago, Dr Bob said:

Nick is not quite right.

Agreed, use the info on the data sheet.

The word 'Cure' refers to the crosslink reaction that bonds the polymer chains together. Most epoxies will continue to cure underwater and therefore harden after going back in. BUT......evaporation of solvent is also important to allow full hardness and if you put it in the water before the solvent is out then that will never come out and the coating will not achieve full hardness. Most paint chemists will use the word 'cure' to mean both the crosslink reaction and solvent evaporation. If the temp is 25°C most of the day then likely a couple of days will be sufficient but at normal summer temps where the night temps fall to 10-12 °C and daytime up to 25°C then maybe a week would be better. In the lab, we always used to cure at 23°C continuous - which is a damn site hotter than a normal summer.

Follow what the data sheet says, not the boatyard. Most normal epoxies dont like to cure under 15°C but the 'winter' grades use agents that allow cure to happen quicker but it is a bit of a compromise and solvents dont tend to come out well below that temp.

I’m sure it varies according to product but for the stuff we used (Sigmacover 300) at 20C the initial cure is 24hrs after which the product can be immersed in water. Full cure to full hardness is 7 days at that temperature. I guess it depends on the relationship between solvent evaporation rate and crosslinking speed.

Link to comment
Share on other sites

7 minutes ago, nicknorman said:

I’m sure it varies according to product but for the stuff we used (Sigmacover 300) at 20C the initial cure is 24hrs after which the product can be immersed in water. Full cure to full hardness is 7 days at that temperature. I guess it depends on the relationship between solvent evaporation rate and crosslinking speed.

That would assume all solvent gets out in 24 hrs at that temp.

 

I was more getting at you statement of 'not evaporation that cures it'. A paint chemist would include solvent evaporation as part of the cure. As you say it will vary product to product. They all use different cocktails of solvents so unless you look at the msds sheet you will not know what's in them. 

It is important to make sure the Average temp is high enough to get all the solvent to evaporate. Lows of 10 deg C at 6.00am can cool the steel down bringing the average too low. Not a problem this summer!

It was a lot better when we used real solvents rather than the namby pamby water miscible stuff of today.

Link to comment
Share on other sites

I've used interzone 954 and their data sheet just specifies a hard dry time of 18 hrs @15C and 8 hrs @23C

 

it doesn't mention any additional time to cure apart from this

 

For the record there were 24hrs between coats and immersion in water.

 

Edited by Bloomsberry
Link to comment
Share on other sites

15 hours ago, Bloomsberry said:

I've used interzone 954 and their data sheet just specifies a hard dry time of 18 hrs @15C and 8 hrs @23C

 

it doesn't mention any additional time to cure apart from this

 

For the record there were 24hrs between coats and immersion in water.

 

It is  Hempadur 45143.  Data sheet says 20 days for full cure and yard says 10 days back in the water.  Don't know if it will cure when in the water, I have a call in to Hempadur makers for clarification.  I'll post result when Hempadur 45143 get back to me.  Thanks for comments

Link to comment
Share on other sites

15 hours ago, nicknorman said:

I’m sure it varies according to product but for the stuff we used (Sigmacover 300) at 20C the initial cure is 24hrs after which the product can be immersed in water. Full cure to full hardness is 7 days at that temperature. I guess it depends on the relationship between solvent evaporation rate and crosslinking speed.

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

 

Link to comment
Share on other sites

9 minutes ago, plainsman said:

It is  Hempadur 45143.  Data sheet says 20 days for full cure and yard says 10 days back in the water.  Don't know if it will cure when in the water, I have a call in to Hempadur makers for clarification.  I'll post result when Hempadur 45143 get back to me.  Thanks for comments

Is that 20 days at 5 degrees c? 

Link to comment
Share on other sites

16 hours ago, nicknorman said:

I’m sure it varies according to product but for the stuff we used (Sigmacover 300) at 20C the initial cure is 24hrs after which the product can be immersed in water. Full cure to full hardness is 7 days at that temperature. I guess it depends on the relationship between solvent evaporation rate and crosslinking speed.

Yes, it must vary by product because according to head of Technical at Jotun UK, the temperature drop means that curing will effectively stop as soon as the boat goes back into the water, not continue as Dr Bob says. That's for Jotamastic 87, not sure about other Jotun products, but it highlights the importance of allowing adequate time to ensure 87 is fully cured before going back into the water. 

Edited by blackrose
Link to comment
Share on other sites

25 minutes ago, blackrose said:

Yes, it must vary by product because according to head of Technical at Jotun UK, the temperature drop means that curing will effectively stop as soon as the boat goes back into the water, not continue as Dr Bob says. That's for Jotamastic 87, not sure about other Jotun products, but it highlights the importance of allowing adequate time to ensure 87 is fully cured before going back into the water. 

Depends on the temperature of the water, surely? I would imagine canals are currently 20C or more.

Link to comment
Share on other sites

2 hours ago, blackrose said:

Yes, it must vary by product because according to head of Technical at Jotun UK, the temperature drop means that curing will effectively stop as soon as the boat goes back into the water, not continue as Dr Bob says. That's for Jotamastic 87, not sure about other Jotun products, but it highlights the importance of allowing adequate time to ensure 87 is fully cured before going back into the water. 

Then he is talking through his ***se. Epoxies WILL continue to crosslink underwater unless they are something special which I very much doubt for a Sigma coating. I think he is confusing you with the word 'cure'. Remember I said paint chemists treat cure as both crosslinking and solvent evaporation. Therefore to him, underwater there will be no evaporation of solvent so it wont cure. Nick is also right that normal epoxies will not cure under 15°C so if it is in water under that temp then all crosslinking will stop. People need to be more accurate in what the say!

Link to comment
Share on other sites

Just had a quick look at the Jotamastic 87 data sheet. It quotes a curing time (to full cure .....ie can be put into final duty) of 7days at 23°C. That seems quite long. Remember, overnight the temp drops so you need to have an average temp of 23 C to use that time. There is a winter grade that cures to full cure in 2 days at 23 C ....but as I said earlier, that faster cure will have a degree of compromise. The 'normal' coating uses xylene and naphtha as solvents so likely solvent evaporation is tricky in colder weather.......good solvents though. I guess they use more volatile solvents in the winter grade.

Link to comment
Share on other sites

22 minutes ago, Dr Bob said:

Then he is talking through his ***se. Epoxies WILL continue to crosslink underwater unless they are something special which I very much doubt for a Sigma coating. I think he is confusing you with the word 'cure'. Remember I said paint chemists treat cure as both crosslinking and solvent evaporation. Therefore to him, underwater there will be no evaporation of solvent so it wont cure. Nick is also right that normal epoxies will not cure under 15°C so if it is in water under that temp then all crosslinking will stop. People need to be more accurate in what the say!

"Therefore to him" ? I wasn't aware that you knew him and his background personally? I think you're making a lot of assumptions about people you don't know. He wasn't talking about solvent evaporation and he certainly wasn't talking out of his arse (assuming that's what you meant?)

 

It wasn't a Sigma coating - I think it's you who is confused! I'm sorry but I will go with the advice head of Jotun's technical dept rather than some bloke I don't know from the internet. 

Edited by blackrose
Link to comment
Share on other sites

Just now, blackrose said:

"Therefore to him" ? I wasn't aware that you knew him and his background personally? I think you're making a lot of assumptions about people you don't know. He wasn't talking about solvent evaporation and he certainly wasn't talking out of his arse.

 

It wasn't a Sigma coating - I think it's you who is confused! I'm sorry but I will go with the advice head of Jotun's technical dept rather than some bloke I don't know from the internet. 

Apolpogies, i dont know where Sigma came from. Should have been Jotun.

Rest of my post stands. Epoxy crosslinking takes place under water when using standard epichlorhydrin curing systems and amine systems (the one used in the jotamastic product). That is a fact. Perhaps he is not a polymer chemist. I also would follow the instructions on their tech data sheet and allow 7 days after application if the average temp is 23°C.

 

Link to comment
Share on other sites

Well when he said "curing effectively stops" I don't think he meant that cross-linking stops completely at low temperatures, but perhaps he meant was that the rate of cross-linking would be retarded to the extent that a full cure wouldn't be reached? I don't know if he's a polymer chemist so I'm guessing about what he meant exactly too.

 

However, from a very quick google search it seems that cross-linking is not the only aspect of an epoxy coating that may be adversely affected: https://www.emeraldinsight.com/doi/abs/10.1108/PRT-06-2015-0059

 

The key sentence from that 2015 paper is:

 

The performance of epoxy coating on metal substrate at low temperature and high humidity application has adverse effect on cure rate, film properties and adhesion. 

 

 

  • Happy 1
Link to comment
Share on other sites

29 minutes ago, blackrose said:

Well when he said "curing effectively stops" I don't think he meant that cross-linking stops completely at low temperatures, but perhaps he meant was that the rate of cross-linking would be retarded to the extent that a full cure wouldn't be reached? I don't know if he's a polymer chemist so I'm guessing about what he meant exactly too.

 

However, from a very quick google search it seems that cross-linking is not the only aspect of an epoxy coating that may be adversely affected: https://www.emeraldinsight.com/doi/abs/10.1108/PRT-06-2015-0059

 

The key sentence from that 2015 paper is:

 

The performance of epoxy coating on metal substrate at low temperature and high humidity application has adverse effect on cure rate, film properties and adhesion. 

 

 

I think this is why I said early that we need to be more accurate in what we say. 'Regular' epoxies ie epichlorhydrin and amine cured, cure well above 15C but the crosslinking slows down significantly below that. It will crosslink to some extent but not good enough for a good coating. Below 15C, you can bodge it with other compounds that allow cure to much lower temps. Can full cure be reached? The actual answer to that in a paint is No...unless it is cured in an oven. Typically epoxies used in composites are post cured in an oven at 80-100C to get 'full' cure. Without that post cure temp, the crosslinking never reaches the ultimate. Epoxies in paints is usually the same chemistry so no paint (cured at room temp) is ever 'fully' cured. In the lab, we alway tested at 23C and this is the industry standard.

I am sure he meant that the rate of cross-linking would be retarded to the extent that a full cure wouldn't be reached....as you said, as that will be true under 15C.

 

To comment on your link, ......Absolutely. There is a lot more to coatings than epoxy crosslinking. 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..... Adhesion as you know is vital for good performance. Flow of the coating to give the right wet film thickness is vital to allow solvent evaporation and give a consistent thickness without dripping or brush marks. Low temps can affect the flow additives that are in there getting to the surface so you can get surface imperfections, not enough bubble release etc etc. A paint chemist is playing with around 8 or 9 variables, some of which are not easy to control. This is why Jotun recommend this coating is applied by a professional ....so most of the variables should be controlled.

 

Edited by Dr Bob
  • Greenie 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.