How to Make an Easy Sanding Filler Using Laminating Resin

[albergsailor]

Seems like it would be better to make my own fairing putty out of laminating resin and ??? As opposed to purchasing a polyestor filler that surely contains wax. I want a laminating filler to assure the best bond between the gelcoat/and or additional layers of filler. We have laminating gelcoat in the stores why no specification for laminating filler? So anyone have a good recipe for a bondo like filler?

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[Zach]

You don't see laminating filler, because filler is something you sand, laminating resin isn't something you sand... so much as grind. The gummy surface on laminating resin isn't sandable unless you mix up a real hot batch of it as a flow coat over the top surface and get a near surface cure.

Most folks would be filling the lows with mat and grinding it back until things are straight. Once it is fair, a thick rolled coat of waxed gelcoat would cover the rest of the issues and get sanded down with 40 grit until fair and until you just can see the old high spots with 80 on the pad sander.

That skips the lions share of spot fairing. The rest, spool up gelcoat with a taste of cabosil in it so it acts like fairing putty...

For raw glass spot filling I like straight milled glass fiber. It sands and grinds the same as mat so you don't get soft spots that disappear under the grinder. 40-80 grit range just about right to get through the sticky stuff.

If you want to do it the hard way:

Talc is cheap, easy sanding and heavy.

3M glass bubbles cut 3/4 to 1/4 cabosil works and doesn't sag. Spreads like whipped cream. Acts a lot like 3M's Vinylester putty. Medium cost...

I don't like phenolic microballoons in laminating resin as it seems like it they have a tendency to stay gummy the whole way through the filler and not just at the surface. Most expensive.

Don't use cotton flock or wood fiber if you can help it. Cotton flock is hard as nails, wood fiber takes on water in polyester.

Edit:

You've also got a minimum thickness that you can go with MEKP cure polyester. Most gelcoat is promoted hard enough that it will cure in thin film, polyester laminating resin doesn't always cure out in the thinnest of films, particularly in high humidity! Waxed will... Unwaxed, not so much. Remember that your "thin" skim is an 1/8th inch thick. BPO cream cured fillers go down to a feather edge and cure out in thin films... Part of the reason they exist.

Cheers,

Zach

[model 10]

Right on, Zack.

[albergsailor]

Thanks alot. Also have another question. I used laminating resin on the repair. Would i want to pva the fiberglass before gelcoating or would the waxed gelcoat do the same job?

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[Stumble]

Btw. Don't use talc below the water line. Above it is fine.

[Zach]

Waxed gelcoat over laminating resin.

Laminating resin offers up a chemical bond to the new work, after it has surface cured it is a mechanical bond. (For the most part... yeah the styrene softens up the old work...)

Waxed gelcoat works to do the same job as PVA... Surface cure the resin so it can be sanded.

I use PVA on parts that I want to build a good even thickness coat of gelcoat, that have dark spots or low spots I'm aiming to fill. The goal being, don't wax the gelcoat so you can shoot another round if you want to. Think bath tubs, shower stalls and shapes that are hard to roll and hard to spray evenly. If you wax, you are going to have to sand. If you still have dark spots and you wax... there isn't an option for spraying another round in an hour. 3 hours maybe, but not one hour...

Cheers,

Zach