Thinning Epoxy...

Mark-1

Mark-1

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I've googled, but I consider YBW a more reliable source.

Can I thin Epoxy Resin (Or Araldite) to pour into Gelcoat/GRP Crack or even better can I get a thinner equivalent off the shelf?
 
you can try thinning epoxy with isopropyl alcohol, works on "proper" epoxy like West Systems and others. Not sure what it does in araldite though, never tried!
From experience adding isopropyl on epoxy lengthens cure time (a bit)
 
I don't believe that thinning epoxy provides such a reliable bond.
The solvent has to find a way out so you get something more like a sponge than solid.
If I need epoxy thinner I tend to heat the 2 components (put the cans in hot water). You obviously get a shorter time to mix and apply it but the end result should be as strong as usual.
Araldite is pre-thickened epoxy so while heating it will thin it, it may not be ideal for what you want.
 
I thought I read that meths mixed to the epoxy BEFORE adding the hardener was the way to go.

Just found someone who experimented with it via Google:

“100% Epoxy resin is quite thick like treacle, and although I tried to be consistent with application, it has pooled and formed a layer on top of the cloth. It looks shiney and feels smooth, there is resin on top of the cloth, visible on the left.

10% Meths there is a big improvement, more consistent application but still some pooling/inconsistency of resin.
30% still has a bit of pooling on top, but is much better.
50% very consistent finish, but still smoothish on top.
70% Also very consistent, I can feel the glass cloth is protruding more.
90% The cloth hasn't bonded well to the wood, and is loose in a few places. The weave of the cloth is really noticeable, and strands are sticking up.”
 
Wing joints on models often were resin and bandage jobs ... with Polyester resin - but it melted the foam inside if not sealed well. Epoxy did not melt the foam - but was thick and difficult to use - so METHS was a way to thin it out.
Then Laminating Epoxy Resin became more available ...

It is not weakened as is case with thinned Epoxy ..
 
Do remember that when you thin epoxy, it will be 5-10 times weaker. Yes, it is that bad. It sort of makes it like foam, and when the solvent evaporates, what remains is not a strong structure. Obvious, but MUCH worse than you think. Same with penetrating epoxies, to a slightly lesser effect. There is a reason that West Systems, for example, does NOT make a penetrating epoxy. They are very, very weak. Google the specs.

The OP's question for thin cracks may be valid, but it is just a water tight fill, not anything structural. For harden soft wood, for example, you are much better off with slow cure epoxy, which is full strength and actually soaks in nearly as far.

The other thing that happens is like ink being drawn into blotter paper. The wood fibers filter out the polymers, and only the solvent actually soaks in deeply.

I did a bunch of side-by-side testing.
penitrating epoxy tests
 
Don’t thin it. Just put the container in hot water (which will make it flow better) before you add any catalyst.
 
You could try a casting epoxy mixed with micro fibres. The casting epoxy this is formulated to flow, but from thinwaters' post above, this is about 70% to 80% weaker than full strength epoxy. But adding micro fibres would increase its strength.
Fairly obviously the micro fibre would entange and log jam at some point, limiting the penitration down a crack. But it may well increase the epoxys' strength in compression and shear.
I certainly wouldn't use it as a structural repair, but might make a good filler, which would flow down delamination cracks. It might prevent the gelcoat from peeling for a while, and a lot quicker and cheaper than grinding off the gelcoat, and going through the hassle of applying colour matched gelcoat and refinishing.
Just a thought, it's always difficult to advise withe very limited information.
 
You can also heat up the area being repaired with a hair dryer or heat gun - warm epoxy trickling into a very narrow crack will very rapidly cool to the temperature of the surrounding material.
I might be inclined to mix the epoxy at room temperature, so the setting reaction doesn't kick off too fast, and warm up the repair area pretty thoroughly. That way the epoxy only gets hot, and starts setting more rapidly, once it's where you want it to be.
 
SvenH said:
Lets be clear, there is no catalyst involved in epoxy.
Click to expand...
Quote :

"In epoxy systems, the hardener (or curing agent) is a chemical compound that reacts with the epoxy resin to initiate and complete the curing process, transforming the liquid resin into a solid, durable material. Without the hardener, the epoxy resin remains liquid and does not harden.

Elaboration:
  • Function:
    The hardener acts as a catalyst, speeding up the chemical reaction between the epoxy resin and the hardener itself, leading to the formation of a cross-linked polymer network.
  • Types of Hardeners:
    Various types of hardeners are used, including amines, anhydrides, and polyamides. The choice of hardener affects the curing time, mechanical properties, and chemical resistance of the cured epoxy.
  • Curing Process:
    When mixed, the hardener reacts with the epoxy resin, causing the resin to undergo a chemical change and solidify.
  • Importance:
    The hardener is crucial for achieving the desired properties of the cured epoxy, such as hardness, strength, and resistance to various environmental factors. "

    and ....

    Kemipex - Epoxy Hardeners

    In general terms - Epoxy Hardener falls into the category of a Catalyst -according Epoxy manufacturers.




 
no one has mentioned mixing the epoxy in a container surrounded by ice; I used to do this a lot in British Summertime when using expoxy 20 odd years ago to lengthen working time.

Sealing a crack, the meths thins the epoxy before adding the hardener; whether I read it per West instructions or from a peer I cannot remember.

It works. As per 100% structural integrity I do not know; are you aiming for that?

Use polyester resin?
 
SvenH said:
Lets be clear, there is no catalyst involved in epoxy.
Click to expand...
You are technically correct. Catalysts are bystanders in reactions and are not consumed by them.

Epoxy doesn't use a catalyst as such - the hardener directly reacts with the resin via an epoxide reaction and polymerises with it. That's why the mix has to be bang on otherwise you get an incomplete reaction.

Polyester does use a catalyst in the truest sense as it is not involved in the final polymer. That's why you can add less to prolong working time without ruining the result. Within reason,of course.

With that said, I don't think it's worth worrying about as even the manufactures have used the coloquialism 'catalyst' and we all know what they mean
 
Mark-1 said:
I've googled, but I consider YBW a more reliable source.

Can I thin Epoxy Resin (Or Araldite) to pour into Gelcoat/GRP Crack or even better can I get a thinner equivalent off the shelf?
Click to expand...
What is cracked? If you have a crack in the gelcoat, you may have cracks in the laminate below. If this is the case, you would likely need to grind out the gelcoat to the laminate and grind out and cracks in the laminate. Add a layer of suitable glass then repair the gelcoat. It really depends what you are repairing. Often trying to fix a crack doesn't work because the laminate needs repairing first
 
geem said:
What is cracked? If you have a crack in the gelcoat, you may have cracks in the laminate below. If this is the case, you would likely need to grind out the gelcoat to the laminate and grind out and cracks in the laminate. Add a layer of suitable glass then repair the gelcoat. It really depends what you are repairing. Often trying to fix a crack doesn't work because the laminate needs repairing first
Click to expand...

Basically some gelcoat has lifted and I reckon it will be quicker and tidier to "glue" it down than to rip it off and re gelcoat it.
 
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