Hullo Rebecca,
Okedokee, a few things.
First off, nice job. Fixing a busted board, well, getting the alignment right is the key. Looks like you did it right.
Next, yes, the resin plus filler is whatâs giving you problems. Youâre having unhardened unwaxed resin gooing up your sandpaper, not fun. See, hereâs the thing, the styrene wax (styrene is the thinner/solvent thatâs in polyester resin so thatâs the wax they use. Itâs also why polyester resin eats styrene foam) thatâs added to laminating resin to make sanding resin rises to the surface and forms a molecules-thick boundary between the air and the resin and allows it to harden. When you sand that, you go through the layer and sand hardened resin, all fine.
Now, when youâre laminating, ideally you want a chemical bond between your lamination layer and whatever you put on top of it, another layer of cloth or a hot coat, say.
But the bond between your lamination and the underlying foam (or between the hotcoat and the gloss coat) is a mechanical bond: the resin permeates the surface a little and hardens and thatâs how it sticks. For instance, if you look at the underside of the glass that ripped off when the board broke, youâll see a thin layer of foam and if you scrape it a little youâll get to foam thatâs sort of saturated with resin.
Okay, Iâve told you how it works, but what can you do now? Well, what Iâd do is take a little catalyzed waxed or sanding resin and very carefully brush it on top of your uncooperative filler and wait, when that is well hardened I think youâll be able to sand it and your filler, without gumming up your sandpaper. Youâll sand through that molecules-thick layer of wax no problem.
A few other things-
Cabosil, or glass microballoons, they are whatâs called âthixotropicâ additives. Like the name says, they act to make the resin thicker, like corn starch or flour when I make gravy or thicken a sauce. Thereâs nothing particularly magical about them, when doing dings on an island in Panama I didnât have any so I used sugar ( makes it sparkly) or talcum powder, both of which worked fine. I didnât want to be wandering around Central America with bags of white powder, yâknow? When I sanded the talcum powder filler it smelled nice too.
Some of the epoxy boat guys use sawdust to make filler. Itâs all rock and roll.
Now, again, with the sanded filler, youâre not gonna get the chemical bond you get with resin to an underlying layer of laminating resin. But the mechanical bond will be fine.
But letâs say you only have sanding ( waxed) resin and you have to laminate with it and you want a better bond for whatever ( hotcoat/filler coat, letâs say) youâre putting on top of it. But, youâll never get all the wax, considering the weave texture of your lamination, without sanding away a lot of the cloth. Whatcha gonna do?
Like I said, the wax is on the surface, a few molecules thick. Wash it, with either styrene monomer or acetone and scrub gently with a new white rag or a new chip brush. Colored rags, the stuff can dissolve the dyes and pigments and transfer them to your lamination. The natural bristle brushes wonât dissolve in the resin or the solvent. The fumes from either one ainât good for you, so be sure to use a mask with organic vapor filters, like you should use whenever doing glass work.
Okay, hope thatâs of use
docâŚ..
