The only epoxy that is thinned with water is a water misceble, like some copper underwater treatments.
We dilute copperbot, or whatever it is called now, up to 20% for spraying.
Meths can be used on other epoxies, but I suggest a test piecce first.
Standing the components iin warm water will also make them runnier but will shorten the pot life.
After splashing epoxy around, I wash out my brush with acetone a few times - each time just with a tiny bit of acetone - this seems to thin the epoxy down significantly, and I then brush it out on any odd bit of plywood that needs coating, and it seems to work quite well.
I have also (on a couple of times) intentionally diluted some epoxy with acetone to coat plywood panels before painting them, and this seemed to work OK.
As Oldsalt says - Meths ...... but note that the colour will often change. I would advise though that thinning too far will affect the chains in the cured epoxy reducing the strength. We used to do it for joining model wings .... but found that the laminate produced could be either too flexible due to colourants / additives in the meths or brittle by over dilution.
Try these people: They seem to sell the same Araldite resins from Huntsman that we used a few year ago.
I do not know which grade it was, but it was the best resin I have ever used for absorbing into the wood.
Absolutely unbreakable bonds!
Call them and ask.
(Personally I would not mess with the resins except their temperature as you need all the constituents available in the same place. "Wash" some into the wood and leave the bigger ones behind would not make for a good bond)
I suspect you are spot re laminating with thinned epoxy, though I have also found that the amount of epoxy left in the laminates also makes a huge difference, the thickness is controlled by the amount applied and the pressure applied when clamping or weighting.
I would never used thinned resin for any structural work but for models perhaps but fine for helping it get into ply to preserve it.
You can get proper meths, wihout the additives in some places, try industrial suppliers, we get it un-messed with in spain, holland, germany, itlay. that I know of.
im only using it as an coating for bare wood nothing structural and it will be painted over so no worrys about colour change. i hear sp have a epoxy thats thinner for coating wood but i can't find a supplier. anyone know where to buy it, but as i have loads of west systems epoxy i would prefer to use that instead.
For epoxy coating with SP resins, use 106 or 320 and apply with a brush or roller with a hot air gun - without any filler it will be absorbed into the grain. The heat will make it very runny, and will also heat up the air in the grain of the wood - as it cools and contracts it will draw the resin in. I seem to remember that they recommend three coats, which sounds a lot, but, especially after the first coat, it will spread over a large area. Best to use very cheap throwaway brushes (or rollers), as the heat will quickly ruin them. If you want to build up a good thickness to rub down flat, then Malthouse's suggestion of adding colloidal silica will work very well.
If you have plenty of epoxy you should thin that rather than purchase more that has been thinned. Epoxy has a limited shelf life and should be used, the sooner the better.
As you are only looking for an improvement in penetration the meth's will work fine, just add the meth's after you have mixed the resin and hardener together.
We did new cabin sole boards for a client many years ago and started by applying a water based wood preserver to the uncut ply sheets, after drying this out we then cut the required shapes, epoxy coated them with epoxy and Meth's as a thinning agent, The cut edges took several coats to get a good seal. When cured the underside was given a good wash then a light sanding and a couple of coats of epoxy primer, can't remember what we we put onto that (if anything). The topside was washes and sanded as above and primed the same, then given 3 coats of reaction lacquer with grit added to the second coat to provide an easy to clean but non slip surface.
It several years for the grit to start showing through, the owner just applied another coat of reaction lacquer, never had any problems at all.
PS. Epoxy laminating resin (the most commonly used) is not UV stable, so must be coated to protect it; though it will be OK even outside for a bout a year.
PPS. Warming the resin alone will not improve penetration by much if the item it's being applied to is cold. Heating the resin and the item with a heat gun after applying resin will not only thin the resin but also trap curing residue under the the surface, rapid heating of uncured resin is not recommended.
Only commenting on it as we used to use Polyester for wing joints .... taking great care to make sure the joint was sealed well. The wings were foam with obechi veneer on top. Epoxying the foam ends together was insufficient joint strength so we applied a 2" bandage around the joint. Many I knew advocated thinned epoxy for the job - to prevent any mistakes - Polyester and foam don't like each other !. But I saw too many failures from it ....
Main problem was use of over counter epoxy glues like Devcon etc. instead of a laminating eopxy as Wests etc. So meant thinning to get it to run sufficiently.
West System epoxy thickened with colloidal silica is very hard and difficult to sand - I know from experience. West System make other fillers that are supposed to be easier to sand.
If you think adding colloidal silica makes sanding hard, try sanding after adding some Micro-fibres.
I take great care not to overfill when using them, but if you are looking for a very strong glued joint you would be hard pressed to improve on this stuff.
Avagoodweekend......
PS Good luck with the early retirement, I managed to stay retired for only 3 years, because that's how long it took me to refurbish the family home and our monohull; now we alternate between home, catamaran and work.