Use of epoxy for levelling

[Rich]

Have you considered whether the fault lies with poorly mixed resin? The cure is a polymerisation. If the relevant components aren't available in sufficient quantities, the density of the film may change, leading to variation in final thickness?

Epoxy resin tends to be quite sensitive and there's little mention of preparation in this thread.

Using a good set of scales will ensure the right amount of resin and hardener is used. Really important if you want to resin to perform per manufacturers specifications e.g. hardness

Mixing. Spend at least five minutes mixing before use. Hand mixing is fine, an electric mixer is easier, but a slow speed. Avoid mixing in air. Once you have mixed for a minute, use a pop stick to ensure the resin sitting on the side and in the crease of the cup is integrated properly. Mix for the remaining four minutes. Once the batch is mixed, poor into a separate cup - leaving a little behind, so as to avoid any un-mixed resin transferring across.

The surface to be coated needs to be clean and dry.

The video was helpful in some respects. Personally, I wouldn't put a heat gun near epoxy without wearing a mask - air bubbles or no. But he's right epoxy loves heat and it does affect the viscosity of the poured resin. Personally, I'd lift the temperature of the resin prior to mixing using a water bath, especially here in the UK. I'd also be more interested in ensuring the ambient temperature of the room remained constant - especially in a hot climate.

I understand the target thickness for the film is 3-5mm. There's no reason why this need to be done is one pour: http://www.westsystem.com/ss/epoxy-chemistry/ A second layer can be applied once the first layer has started to gel, sufficiently. This might well be the best approach, assuming the underlying cause is human error

I'm not entirely certain what steps are taken after the film has been applied, but if the variation remains say 0.3mm i.e. human error is not a factor, could a high viscosity resin/compound then not be used to seat the rail? I believe that what is taking place here? http://www.moglice.com/ . You'd need to wait around a week before seating the rail. Ambient cure epoxies take a while to reach a state of final cure, which could be a problem, as you don't want an ultra thin layer of epoxy being exposed to pressure, when not chemically bonded to the layer below .... all my epoxies are heat cure, so I'm not in a position to run any tests. So lets hope its human error and applying two layers to create the desired thickness produces a lower error rate.

Oh yes. Vinegar is a good solvent for any split epoxy.

Personally, for this job, I'd been thinking about urethanes - but I'm not any way near needing to do this yet.