I've used the WEST System epoxies for almost 30 years. I've never done a delam repair with them, but I've done just about everything else:
Repaired broken front pylon "shoe" on a 16 with carbon fiber tows
Glued the tramp frame together on a 14 (rock solid - use the colliodial silica thickening agent)
Built a sailbox that's lasted 21 years - not a nail or screw in it other than the door hinges. Been extensively modified on two occasions - once to fit under a 17 and again to fit on a new trailer.
Go to the Gougeon Bros. WEST System website http://www.westsystem.com/
and they have all the info you need.
Here's what they say about thinning their products:
There are epoxy-based products specifically designed to penetrate and reinforce rotted wood. These products, basically an epoxy thinned with solvents, do a good job of penetrating wood. But the solvents compromise the strength and moisture barrier properties of the epoxy. WEST SYSTEM epoxy can be thinned with solvents for greater penetration, but not without the same compromises in strength and moisture resistance. Acetone, toluene or MEK have been used to thin WEST SYSTEM epoxy and duplicate these penetrating epoxies with about the same effectiveness. If you chose to thin the epoxy, keep in mind that the strength and moisture protection of the epoxy are lost in proportion to the amount of solvent added.
There is a better solution to get good penetration without losing strength or moisture resistance. We recommend moderate heating of the repair area and the epoxy with a heat gun or heat lamp. The epoxy will have a lower viscosity and penetrate more deeply when it is warmed and contacts the warmed wood cavities and pores. Although the working life of the epoxy will be considerable shortened, slower hardeners (206, 207, 209) will have a longer working life and should penetrate more than 205 Hardener before they begin to gel. When the epoxy cures it will retain all of its strength and effectiveness as a moisture barrier, which we feel more than offsets any advantages gained by adding solvents to the epoxy.