Primer and/or Barrier Coat?

Ok, I have a lot of fiberglass starting to show up in the shop. This makes you start to think about how you will paint and finish it.

The glass is usually a single layer of some 1150gsm (34oz) triaxial with the warp against the core and the smoother biaxial outside.

I have pre-faired the foam cores to make the proper shape for most of my parts before putting the triax on. I am also infusing just about everything now, so the surface is pretty nice and smooth.

Using fairing compound to fair curves that are out will come next, but...

The question is... now what??

Some people paint on some neat epoxy to make it more waterproof. That sounds heavy for a catamaran.

Is there a single step something or other I should be using as a filler of weaves, self leveler and paint primer?

I've heard of flow coat, but have no clue what it is or does.

What do most people do at this stage?

 

Hey Cat, I can tell you what NOT to do

Don't try and put painters plastic on it when the wind is blowing and you are working by yourself.

The first pic is the morning after the plastic disaster.

the second pic is the other side of the hull with a flow coat atop a saturation coat. You can still see some print through, but it came out pretty good, I thought.

I have the same questions as you though now, about the next step

that is ten ounce cloth

 

Flow coating is great for flat panels.

I would think that the level of prefairing you do to your panels and the technigue depends on how much structural secondary bonding will be needed for construction.

Rolling on a slurry of thickened epoxy works well is you will need strong secondary bonds..

Roling on a thin coat of epoxy, waiting for it to go green, then filling the weave with lightweight fairing compound and a large blade, like a two foot piece of plexglass ,works for situations not needing strength in secondary bonds..

Product systems like alwgrip 545 and High Build primer work if the weave is not so course and you do not need structural strength secondary bonds.

 

What I do is first fair the boat with a light weight bog, outside 1:1 phenolic microspheres/microlight and inside 1:1 Q-Cell/microlight. Initially just by troweling on a thin overall coat and after the first sand top up the hollows and screed of excess.
Next I roll on a coat of high build epoxy primer, rolling does a better job at covering pinholes. Later on the same day or early following morning I spray on a coat of HB with addition of 25% vol microlight, a home version of super HB, spray with a 3mm nozzle.
Sand this down with a long board and repeat with SHB if required otherwise if nice and fair spray on two coats of HB with a 1.8mm nozzle, spray on a mist of black guide coat and sand with 240 grit random orbital.

Below waterline when you come to applying antifoul, roll on a coat of resin first and when it has tacked off roll on the first coat of antifoul.

This is just one way of doing it that works for me so newer tried alternatives, but I do not like the idea of applying first lot of bog with a notched trowel.

 

The technique of applying bog with a notched trowel works well when you have an unfair surface to fill. If you are just removing surface imperfections and weave its overkill. One problem with the notched trowel technique is that its near impossible to mix your bog, resin microballoons ratio the same for each batch. As a result your first bogging session many use a slightly denser, harder, mix than your second bogging. The result is a mixture of soft and hard surfaces to sand. Inevitably this causes a " pattern " to print thru the finished surface. If you use a notched trowel use pre mix bog that will have the same density for both sessions.