Epoxy - solvent free vs solvent based.

guydickinson

guydickinson

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Can someone please give a quick summary about these two? Its to coat a newly blasted glass boat. One is better for cold weather (ie March) etc I believe - but which is which? Do Blakes/International do both? Thanks.
 
guydickinson said:
Can someone please give a quick summary about these two? Its to coat a newly blasted glass boat. One is better for cold weather (ie March) etc I believe - but which is which? Do Blakes/International do both? Thanks.
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I used Gelshield 200 when doing the job at the same time of year. That's the solvent based one. You need about five coats in all, best to buy half in grey, half in green so you know that each coat has covered fully. For the final coat you need to apply hard antifouling while the previous epoxy coat remains tacky. This gives a good base for future antifouling.
 
guydickinson said:
Can someone please give a quick summary about these two? Its to coat a newly blasted glass boat. One is better for cold weather (ie March) etc I believe - but which is which? Do Blakes/International do both? Thanks.
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A question:
1. When do you want to get back in the water?

if before mid April then go International Gelshield (as per Vyv) if after you have a choice.

I did this last year - 6 coates.
70% of the work is in the preparation. Having slurry blasted, you then need to sand further - using a cheap but effective orbital from Screwfix (£20).

You will probably epoxy to the top of your current boot line, so you will to think about this and how you mark off your new boot line higher up. Use decent masking tape, and always remove as soon as painting is finished.

The international Gel shield is dead easy to apply - use the small rollers - but get the right ones as they disitegrate after 15 minutes (even the right ones)

The Blakes is much thicker (2 coates) and you can get sagging in the coat (runs to you and me) if not applied right. I have not used it, but just quoting the painters on site.

Another advantage of the Gelshield is that you can be weeks apart in over coating - very usefull in rainy weather. Note that the antifouling MUST go on JUSTafter the last coat has gone dry, and not the next day, to get a proper bond.

If you are Solent based there is a good place in Fareham to buy (trade supplier) who will give you a good deal - can't remember the name at the moment.
 
We did the W33 we had years back with Blakes SFE200 solvent free having first had the bottom blasted to remove all antifoul and leave a golf ball type pitted surface as a key (gelcoat still remaining). The solvent free can go on at up to 200 microns thick without sagging or running and it 'flowed' over the dimpled surface to give a smooth finish without any need to rub down or fill unless there were any chunks missing. We applied it by rollers but used special ones designed for applying epoxy which meant we didn't need to brush out after which I think would have been difficult. We actually applied 4 coats using two different colours alternatively (brown and yellow) and each time we put a coat on the hull we put one on a test sheet of old Formica. We could measure the thickness achieved by putting a micrometer on the Formica and confirmed 200 microns per coat. The key is to calculate how much is required per coat for that thickness and apply that amount, overcoating if needs be until all the paint is used rather than stopping with paint left over. You need to stagger the waterline or it will end up as a ridge line, we moved the tape up a few mms each coat that way the last coat was the freshest. You MUST apply a primer within a set time of the last coat of epoxy so that it is only just gone off and this is important for maximum key. In our case we took the Formica home and monitored it, and an unexpectedly warm night had us off to the boat to put the primer on at dawn instead of the planned 10am! minimum temp for curing IIRC was 11 degs C. and we did it in April.

My personal opinion is that you need thickness for it to be a good protection. Gelshield solvent epoxy goes on at 50 microns per coat I think, so that would require 4 coats for each one of solvent free. I believe the maximum advised number of coats with Gelshield is 5 or you risk solvent entrapment so maximum dry thickness is only 250 microns. Make what you will of that, it is many years since we did the job so maybe thinking has changed.
 
Chris_Robb said:
Thats right!!! Full marks, go to the top of the class. They gave me a VERY good discount.
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Chris did you have a chat to him about your boat ??? He used to be the production manager or similar at westerly ! so quite possibly knows your boat inside out. quite an interesting chap to talk too
 
AIDY said:
Chris did you have a chat to him about your boat ??? He used to be the production manager or similar at westerly ! so quite possibly knows your boat inside out. quite an interesting chap to talk too
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No I didn't. I also used to work for Westerly many years ago - in the late 70's early 80's - left when the first liquidation happened - when they committed suicide by stupidly buying all their factories at the start of Maggies recession - used all their working capital up in one go... But thats another story - had they not done that they would still be around today. Sadest day of my life that was!
 
Solvent free v Solvent based epoxy

In answer to OP question.

The difference is primarily in ease of application. Usually a solvent based epoxy will be simpler to apply than solvent free. Major reason is minimum temperature for curing but that has major implications in other areas and is not as simple as many people make out. Usually a solvent free epoxy gives a higher film build than a solvent free one so you need fewer coats.

Usually a solvent based epoxy will cure at a lower temperature than a solvent free one. For instance Internationals Gelshield 200 (contains solvent) will cure at about 5C while Gelshield Original (solvent free) needs 10C to cure. Be aware, however, that these are minimum figures.

For most epoxies the curing process will "switch" on and off as temperature fluctuates around the minimum and that needs to taken into account when calculating overcoating times.

Epoxies, especially solvent free, can suffer from amine bloom, especially if cured at a temperature close to the minimum or if the temperature fluctuates during curing. Amine bloom is very difficult to detect and action should be taken to remove it if you even suspect it could have occurred. This will completely destroy any overcoating plan you have and mean far more work is required than if you can control temperatures and be sure it is not there. Removal is best done by scrubbing the cured surface with a scotchbrite pad and lots of soapy water followed by fresh water rinsing. Of course, to do this the surface will need to be cured hard so when it is dry you will need to abrade to give a mechanical key for the next coat!

Solvent based epoxies are generally easier to roll or brush on than solvent free materials but they will give a thinner dry coat than solvent free so you will need more coats. If you get the overcoating times right and don't need to abrade the solvent will help to give a good chemical bond between coats. On the other hand, if you can use solvent free and get the overcoating times right, you will have a good chemical bond without any risk of trapping solvents that will subsequently blister and you will need fewer coats to build a sufficient dry film.

There is no magical date when it is OK to use one form over another. What you need is a settled period with minimum fluctuations around the curing temperature of your chosen product and that is more likely to be achieved in spring than winter. If you can wait, summer will be better still. Best would be to have the boat in a temperature controlled shed and keep an even temperature throughout the job - not achievable for most people!

International make Gelshield in both solvent and solvent free form. Blakes (Hempel now) have SFE and I'm sure will have a solvent based version. Other companies also will have one or both types. Important thing is to look at temperatures for the product you choose, not generalised comments from people who may have used something completely different. Amount you need varies according to who you talk to. Consensus seems to be between 300 and 600 microns for a good impermeable barrier. I tend towards the bottom of that range but it's just an opinion. If you can get hold of a wet film thickness gauge and use it regularly during application it will help you to be sure what you are applying - disposable plastic ones cost a few pence and basic metal ones on e-bay for less than £10. Good metal ones cost about £40.

Whatever product you choose store it overnight before use between 15 and 20C. It's surprising how long even a 1L tin takes to warm up if it has been stored overnight at 5C and this will significantly affect the curing time.
 
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