Here is how to pour a flange without a mold
and get a nice shape...
For one, put down the electric
sander as it is the wrong tool for sanding
fillets. The best sanding
method for fillets, is not to sand fillets for shape... but for adhesion of primer.
The best release agent on epoxy
, is mylar packing tape.
Use tropical hardener for the initial pour. It won't go exothermic... West systems is forward and backward compatible. Call their help line and ask.
Do the initial pour in two phases. Green on green where once the first stage of structural filling material like cotton flock or milled glass fiber begins to cure you go over it with a second lighter fairing compound like west 407. Use the hatch
edge as the guide, and keep it clean with no epoxy
You put the structural stuff on thicker than peanut butter and go inside and pack the stuff straight, then put a layer of mylar packing tape over the goop, backed up by blue painters tape so that when you pull the excess off the outside, with squared off corners it doesn't mush back through to the inside.
To pull it off, go 3-4 inches and clean the putty knife... Keep it in contact flat to the deck
and put the excess on a board.
Once it starts to tack up, do a real light acetone wipe of the deck
around it so there are no boogers for your filet knife to catch.
In an hour or so once it starts to harden up enough that it won't drag against your knife, use the flange of the part as a guide for the next pass you pull your radius fillet by adding a significant amount 3/4 the way around your part. The last of it you can fill in up to the point you started to pull. You want to reach what is already filled with next to no filler on the tool. Start and Finish, in the most comfortable spot sand.
If its going to take a baseballs worth amount of epoxy mix a softball size blob so you can apply it with no air voids space and remove what shouldn't be there... without having to go back and fill anything. I use a paint
stirrer to apply the putty. Flatten out the epoxy on a board and pick up a strip off the board and apply it like cake batter to work the air out. Put on more than what you need.
To pull the fillet you can use a PVC pipe, a west systems tongue depressor, or a putty knife ground to shape... Just keep it clean, and keep it handy for the next round.
To get a clean pull, the first time you take off all the excess. Then you apply putty to your fillet tool, and fix the holidays and low spots by putting a dab back on in places.
When you have a clean pull, (probably pass 2-3) leave the excess on the board and don't re-use it or go back and putty up your problems once you get a clean run. I call a clean run when all the problem areas are smaller than a 3/4 inch and they are low spots, not high spots. No air voids, bubbles... No problems with outside corners. Once the epoxy starts to tack up and drag you are done, no matter what it looks like. Any further work is wasted effort.
When it tacks up, solvent wash the deck and keep it clean. The deck is already fair... any excess has to be sanded off, so don't let that happen.
When that cures, water
wash and red scotch brite. Solvent wash... Make sure your putty knife is clean, and go around and lightly sand anywhere that it doesn't make contact at the two guide points. The fillet will have shrunk down just enough that it won't make contact in the middle, not missing by much... Keep the deck surface perfect and the top edge perfect against the part.
If it looks good the whole way around you can fill any small holes with your finger tip.
If you have any long drag marks, you can lightly sand any holes and pull it one more time. This time make it just thick enough it won't run on a vertical so it pulls without balling up... There is a spot when mixed smooth that 407 cures out and self levels on the surface almost glassy smooth, that is the goal.
This second pull means that if you used a PVC pipe... You can use that as a sanding tool as it won't shrink back, as you applied less material.
If you don't get glassy smooth pull, you can come back on top with neat resin an hour or so later and brush a few light coats over the top. This is harder to sand, but smoother in finish. If you have no high spots, it makes it easier to jump to primer.
It helps to throw a little cabosil into the resin if it is a very hot day, so it lays out on the vertical without running down hill. I like fast hardener for resin coats just because it cures out before it really starts to run, particularly if you give it a few minutes to start to exotherm (deliberately...) before you brush it on...
Use an old t-shirt or lint free rag and wipe off the excess on the deck. Do a real light solvent wash around the deck so you don't have to sand any excess epoxy off.
When that cures, if it turns out glassy smooth you can red scotch brite... and scuff it up. Finger sand any of the high spots, but don't go nuts.
Look it over with your fillet tool, and see if you've got any big low spots. If you do, you can fill them with a putty knife pulling top to bottom. Any dime size holidays, you can spot fill the same way.
If you've got any lumps and bumps that the fillet tool catches on you can sand them out lightly with 220 grit on a soft pad to keep your finger pressure off it... If you used a piece of PVC pipe you can stick sandpaper to it and lightly twist it until they are almost gone.
Prime it, roll on or brush on 4-5 coats of your primer of choice following the recoat window. I like Awlgrip Awlfair, as it builds up dry thickness quick and sands easy. It won't take much product to do the job, but you will have to come back around for a few hours to add another few coats.
T-shirt or rag to keep the excess primer off the deck, as any puddles have to be sanded off... The deck is already fair.
Once you are in primer, you can use Evercoat 407 Ultrasmooth to fix any slight pin holes or holidays in the primer. Finish prime it and top coat it.
It's an all day event... 20 minutes every other hour, but you don't have to grind anything or be a sculptor and sand for days. Just do clean work and don't over-sand it looking for work. Sand for paint
adhesion... when you prime, prime heavy enough not to burn through. Fix the paint grade errors in the primer and move on to the next project