Building large areas of shaped epoxy
filler can be tedious and repetitive.
Mixing it wet enough to stick but thick enough not to sag is a balancing act.
I'd avoid any 5:1 mix ratio epoxies as they tend to blush with an amine coat that inhibits adhesion of the next layer.
There will be more than one layer.
Choose a 2:1 or 1:1 resin preferably a high viscosity resin rather than a laminating resin.
The 2:1 mixes tend to be blush free. and the higher viscosity gives a wetter mix when the thickness is right.
Colloidal Silica is the go to stiffening agent - Aerosil.
The dried mix will be hard to sand but strong.
Ad screws as suggested earlier to give the cured mix a mechanical bond.
Use peel ply.
This is a woven polyester release film that gives a even finish and allows wax and other by-products of the reaction to bleed out resulting in a cleaner surface for the next layer.
Flute can be used as formwork to hold the epoxy mix in place while it hardens.
Spray contact glue the peel ply to the core
flute screw one side to the keel, trowel in excess epoxy mix, wrap the form work
over the mix before it can sag and secure with screws on the other side.
Tight so the epoxy oozes out.
Wipe the excess away.
White vinegar on a rag works well it's also great for other clean up.
The formwork can be removed any time between gel and full cure.
I like to wait until at least partial cure to let the peel ply do its job.
Others like to go early and get the next layer on while the previous layer still holds a fingerprint.
Successive layers can have more easily sanded fillers added.
N.B. micro balloons can absorb water
If you get a result in three applications you are doing well.
Two and you qualify as a pro.
One application is substandard .
There are technical aspects to epoxy engineering but good technique is the most important part of the process.
Have a clear picture in mind of how (micro steps) you will achieve the result you want
Have a box of gloves and change frequently.
Buy a bag of clean cotton rags.
Tongue depressor's make good mixing sticks
Have appropriate sized measuring cups and a bigger mixing cup.
Mix the resin before adding filler.
Maintain a clean work
I use core flute on the mixing bench and keep 4lt resin bottles in a window washing
Everything sticky goes into the bucket then the gloves come off.
New pair of gloves for clean up