Friday, July 6, 2012

Epoxy Variations: I (Allegro con moto)

I hope you all had a fun Fourth!

As you will recall from the post before last, my next task is to rehabilitate the window casing boards. I've been doing some work on them since then.

The first thing I did was to wire-brush the fronts of the boards in order to dislodge the loose oxidized paint and dirt, and to sand off the paint ridges and mineral deposits (from water seepage) from the backs. With this superfluous stuff removed, let's take a closer look at what I'm dealing with. Here's a close-up on the tops of the boards, arranged in their proper position on the dormer from left to right:

Note the lack of sun damage on the right one; it's interesting that the right side of the dormer should be so much less exposed to the sun than the left, when the sun's travel is on the right (south) side of the house. Believe it or not, it's the shade provided by the eave that has protected the top of the right board, while the top of the left one is subject to an hour or so of sun at the end of the day; over 126 years, that adds up to 46,018 extra hours of sun, give or take a rainy day or two (and that doesn't include the partial year on top of that), and that may account for the difference. An hour here, an hour there, and pretty soon you're talking about some real time.

Here's a close-up of the bottom end of the backs:

You can clearly see the mill marks on this unsurfaced side (remember, these boards were only surfaced on the front side). You can also see the water damage and oxidation.

For all my wailing, they are actually in remarkably good shape for their age; with the exception of the bottoms, there is no internal lignin damage, the oxidation and water damage are only superficial, and there is no cracking or splintering. They are certainly in far better shape than the casing boards were on the south side windows; all that's wrong with them for the most part is that they are very dry and thus somewhat brittle.

Then again, these boards are off the house, and they are all somewhat warped. As I re-attach them, I need to coax them back into a semblance of flatness without cracking or splintering them.

You may recall that I restored resilience and flexibility to the casing cap I rehabilitated on one of the south side windows by soaking it in epoxy. That was a feasible operation because the piece was fairly small, and was porous enough to provide ample spaces for the epoxy to enter. To give the window casing boards the same treatment would be a huge undertaking requiring great amounts of LiquidWood, and even then the soundness of the wood would not admit the epoxy much further than an eighth of an inch in. No, for this job I needed to take a different tack.

And so, I decided to try an experiment I'd been thinking of for some time: thinning the epoxy. Abatron provides a thinner specifically formulated for their epoxies; it's a foul-smelling brew, like smog concentrate in a can, so I avoid its use; denatured alcohol works very well to clean epoxy off tools and containers, so I use that rather than the thinner for clean-up.

But alcohol only dilutes the epoxy enough to effect its removal; it doesn't actually dissolve it. In this, it is like water with latex paint. A proper thinner must dissolve what it is thinning; it must mix with it so that the thinned material is evenly dispersed throughout the mixture.

My theory was that the thinned epoxy would travel much more readily through the sound wood, and would be transported much further into it by the thinner. Once the epoxy cured and the thinner evaporated, the epoxy density, and thus its effect, would be lessened compared to un-thinned epoxy, but a lesser degree of the same effect is precisely what I wanted, because that was what the wood needed.

And so, after mixing the LiquidWood and letting it sit so that the reaction got well underway, I mixed it thoroughly with an equal amount of epoxy thinner and brushed it on.

As I had hoped, the wood drank the mixture up thirstily, so much so that I had to mix another, larger batch to finish the job. When I was all done and the epoxy had cured, enough remained on the painted surfaces to leave a glossy sheen, but on the unpainted surfaces very little epoxy remained on the surface. In the heavily damaged areas at the bottom, I could have brushed a great deal more into it before the wood was saturated. In fact, the absorption pattern clearly indicates where the lignin-damaged areas are by their relative lack of sheen.

But no matter, for my experiment was a resounding success! I was able to flex the boards easily, just as new boards would flex, and the surface of the unpainted wood was firm and resilient, with all the oxidized wood now incorporated. This is a good thing, for I can't afford to lose any of the boards' thickness, lest they not lie level with the top casing board when they are put back in place.

The only downside is that the boards positively reek of thinner. I might have expected this, had I considered that a great deal of the thinner remains trapped within the cured epoxy. The morning after I applied the epoxy mixture, I was half-flattened by the fumes when I opened the garage door; I had to take the boards outside to make the garage safe to occupy. 24 hours later, the odor of thinner still hit me over the head when I got within five feet of the boards, even out in the open air, although by the end of the day the odor had at last begun to dissipate. This procedure is not one I would recommend for interior wood, needless to say.

* * *

"What's that foul odor?"

1 comment:

  1. Who will rid me of this stench? Actually a good trade-off to look that good after 126 years.


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