If ply sheets are precoated it saves lots of time.
It is easier to coat areas on the flat
- Gravity works with you to keep the coated surface level so there can be no runs.
- It is easier to get an even distribution of epoxy on the surface
- There is much less chance of missing a bit
- Generally you can work standing upright rather than having to bend into inaccessible places.
- Because the epoxy it got out on the surface faster there is much less chance that the epoxy will cure too fast and go off before it is out on the surface properly
- It is easy to apply the epoxy in three coats wet on wet or in applications where added weight and epoxy cost is less important than labour and apply one thick coat.
I find this the best method, where possible.
It saves the effort of sanding between coats of epoxy and prevents any waxing problems between the wet-on-wet coats.
Mask off all areas that you don’t want coated. (Especially any areas you are going to glue to later – not strictly necessary with some lower stressed designs like paddling canoes)
Lay surface flat where possible.
Mix resin and hardener. You don’t need to add any powder when you are coating – they are only used when gluing one piece to another.
Apply first coat.
NOTE If doing large areas the epoxy will go off too quickly if left in the mixing tin. You will have much more working time if you pour most of it out over the surface first and roughly spread with a squeegee, before going back with a roller to spread properly.
Don’t bother to buy a commercial squeegee – just use an offcut of ply about 200 x 75+mm (8 x 3”). Make sure the working edge is straight and that you have sanded the sharpness off the edges and corners.
Even up the coat using the roller – only add more epoxy to the surface if it seems dry or hard to spread. When it is spread hold roller so it cannot rotate and pull gently along surface of epoxy. It slicks the surface smooth and pop any air bubbles.
When first coat has become quite tacky, roll on second coat. Slick the surface.
When second coat is tacky roll on third (recommended) and slick it down.
IMPORTANT Remove masking tape when third coat is still tacky. You don’t want to glue it down forever.
When epoxy is fully cured turn the panels over, sand off any drips that have come from the other side and repeat process if required.
When the epoxy has cured dewax (if you don’t know the epoxy characteristics well I’d STRONGLY recommend it) sand the panels smooth using a random orbit sander (these tools are a very worthwhile investment but hand is fine too). 180 grit paper is about right. Sand enough to remove gloss.
If you have problems getting a good finish speak to your epoxy dealer.