Thinning epoxy

Anyone have any advice about a good way to slightly thin epoxy so it will become "self leveling"?



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RE: Thinning epoxy


Don't waste your time or money. The max you're supposed to thin out epoxy for non-structural use is 10% by volume. (Cheaper epoxies are already thinned, BTW, thinner being cheaper than epoxy.) Even when thinned to the max allowed, epoxy is still too thick to self level.



RE: Thinning epoxy

Thanks Laszlo, I was afraid of that...I'll just skim coat the low spots and keep on sandin' till it all blends in nice and smooth.

RE: Thinning epoxy

This is slightly on-topic, which seems to do with how to obtain the finest and fairest surface finish on an epoxy substrate.

I have read that using Mylar film, which is 'rollered' on top of the just applied epoxy to remove air-bubbles, produces an extremely fine finish on the cured surface.   Not the same as peel-ply though, which is more about removing excess epoxy, often used with vacuum-bagging techniques beyond the scope of the amateur builder.

Presumably it's the same principle at work as when cracking cured epoxy out of a smooth plastic mixing container, where the surface of the epoxy that's been against the container is extremely smooth and fine.   We also see the same thing - though usually wrinkled! - when laying a strip of plastic film under a scarf joint to prevent it sticking to the work surface.

I also assume that the Mylar needs to be of reasonable thickness to achieve fairnessa - sandwich-wrap film wouldn't do the job!   Another assumption is that it would work best on flat or mainly flat surfaces, although I could see it working on convex surfaces such as deck structures.

I haven't personally checked this out, although I did go so far as to look into the availabality of Mylar from an art supply store.   It comes in sheet form and in quite long rolls, and was not totally unaffordable, especially if someone was fanatically seeking that ultra-fine surface to put under a clear varnished finish.

For what it's worth.


RE: Thinning epoxy


I've tried them and smooth plastic films never live up to their promise when it comes to avoiding sanding. The first problem is that they leave excess epoxy in the glass. For outer surfaces, this means excess weight or lots of sanding. For inner laminations, it means a weaker layup with the strong glass layers separated by a thick layer of brittle epoxy.

Then, you can never get all the bubbles out, so there'll have to be some filling and sanding anyway.

Next, if the film is thick enough not to wrinkle, then it really does only work well on flat surfaces (which in my experience are never the problem when it comes to finishing). When there's any kind of curve at all, the locally flat areas where the plastic was need to be faired in with the curved areas around them. That means that the lovely smooth surface gets sanded, obviating the use of the plastic.

Finally, the plastic films, when they work at all, leave a suface smooth and glossy, but not fair. So, youy have to sand anyway.

Basically, there's no such thing as a free smooth fair surface. Either you do hand layups and sand, or you go the mold and vacuum bagging route.The best you can do is to minimize the amount of sanding by using thin coats and lots of care. The only way to totally avoid sanding is to decide to have a workboat finish.



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