This was among the great tips i was given by Kaos69 when he was over visiting recently. I haven't tried it yet myself to understand what subtleties there are to make this work well here's the ideas.
Despite all my efforts to date I am still getting small pin holes on the surface of the board both sides. It not as pronounce on the underside of the board but it is still an issue. I'm using a good roller and really working it in but still haven't cracked it. One of the causes is that despite best efforts to saturate the cloth there are still fibres not completely encased in resin prior to going under the pump and so resin gets drawn into the FG and away from the surface. So the great idea Kaos69 passed along was to make use of heat. By warming the fibreglass up first, when the resin does go on it will thin out as it warms up and make it easier to completely saturate the FG. You could use a heat gun or even an electric blanket to warm it up. Then get the resin on it asap.
This will speed up the curing of the resin so I suspect it will take a bit of practice to be able to do this and not have the resin going off before the whole lay up is done.
After taking the board off the table the surface (especially on top) can be uneven because the core surface is uneven and the impressions from the breather etc and can also still be pitted. Kaos69 showed me how to scrape back the surface with a razor blade ( I used a blade from a stanley knife but apparently you can get longer flexible blades. I've seen some that are use in tools for removing stickers of glass that would do the trick). This also removes a layer of lighter molecular weight stuff that comes out of the epoxy while curing and it is this that is responsible for gumming up sand paper so quickly when you try to sand epoxy. On the resin I use it says to take great care when using more than 0.5 bar vacuum because of the risk this separation of components.
When its scraped back, use a air gun to blow all the dust out of all the pits. Apply a coat of resin (the same laminating resin you used) and then use a head gun on this top coat. The heat gun thins the resin and let air trapped in the pits to be released. Apparently it can be quite an exciting show! This also helps the resin self level into a smoother more uniform surface plus makes it cure very quickly so it doesn't have time to pool.
A very light sand at the end of the process and then spray with clear coat ( ideally 2 pack but single coat apparently is better than no at all)
The result is a very uniform, bubble free clear finish.
If anyone tries these it would be great to hear how it goes and if there are any additional tips you can pass on.
It also helps to heat the mould slightly too as this thins the resin at the surface, so putting the heat blanket on the table for a few minutes prior to applying the 1st layer would help. You don't need too much heat to thin the resin out (resin dependant of course)
I use Huntsman Aradur HY 5052 hardener with LY 5052 resin, it has a long pot life (2-2.5hrs @ 25degC, 40mins @40degC). It's viscosity varies: 1200 mPa s @ 18deg, 500-700@25deg and 200-250@40deg so as you can see you can heat the moulds and fibres to around 40deg and still have decent working times. It's viscosity drops akin to infusion resins at 40deg