Sunday, June 24, 2012

64, Double Glazing,......or not?

By May the sashes had been trimmed to fit, sanded and grooved down about 2/3rd's of their sides for the ropes. They were now ready to be painted, just in time for an early onset of a cold and wet Winter!.

For the remainder of this stage, the downstairs windows were to be completed and installed first before I would tackle the rest.
Prior to final assembly, I coated the internal faces of the sashes with a light stain, to darken the timber slightly and reduce the contrast with the Blackwood linings. This was followed by 2 coats of polyurethane. The outsides were primed and then given one coat of gloss enamel, also sealing the glazing rebate. To save my limited space, I knocked up a drying rack, in which I could place 12 sashes at a time. The cold and damp delayed the process and each coat was taking up to a frustrating 3 days to dry.

The Frames were also given a similar treatment and spread around all the available floor space. During my working stints in the workshop, I used a gas patio heater to warm the air to help the drying but, due to the fire hazard, I wasn't game to leave it on when not present. With an 8.5kg gas bottle only lasting up to 3 days anyway, it wasn't proving to be too economical!.
During this time, my research into the different methods of double glazing never waned. After much deliberation I settled on a product called SuperSpacer. The main advantage with this, in my situation, was that was available in a narrow 4.8mm, this would enable the panels to be kept to a minimal thickness of about 13mm. If the air space was made any wider, even though efficiency would dramatically increase, the units would not fit in the frames.
The spacers, reasonably priced at around $2 per metre, are a flexible, desiccant impregnated, pre glued strip. They require some sort of application jig to maintain a uniform margin and straight lines. I travelled across Melbourne to the helpful suppliers, C.R.Laurence, and purchased 4, twenty metre rolls as well as a sufficient quantity of the secondary sealant. A small plastic "Hand notcher", used for the spacers placement was priced at about $230, but was not suitable for the narrow 4.8mm strip. A close inspection of one showed that it would be possible to be modified, but I figured, for the price, I could make my own. The "Hand notcher" was also designed to provide a 4.8mm set back from the edge of the glass, required by the manufactures specs., for the secondary sealant. To reduce the sight line in my sashes, which have a 1/4", (6.35mm), wide rebate I would also need to reduce the setback.

I fashioned my home made applicator from a scrap block of Celery Top Pine. It included a sprung plastic roller, to firmly press the spacer to the glass. I initially made it to provide a 1mm setback, as it could later be shaved to increase this. It worked extremely well and I had intentions of adding a plunge action punch for notching the corners. This would be added after any other fine tuning that was required.
I made a couple of trial units to get a feel of the process and assess the results. It was surprisingly easy to do, but with only one pair of hands it was quite difficult to hold the glass steady, work the applicator and feed in the spacer, which needed the plastic tape removed in advance to expose the adhesive. This led to the spacer drifting at one point when it stuck to the glass ahead of me. 1st negative!. Being a trial, I opted to leave it as is, to see how unsightly it would look.

Once I had fitted a trial unit, my fears were confirmed. Even with the minimal setback, the grey spacer was quite pronounced and detracted from the overall look. 2nd negative!.

On the upper left stile on this sash can be seen where the spacer drifted, not looking too good!. It also demonstrated how much grey would be seen with a more suitable setback, way too much.
I assembled the second trial unit to temporarily replace a broken pane in a bay window in our existing Lounge, the result seems to be somewhat disappointing. On the coldest nights, with the wood stove raging to warm the room as much as possible, there was no discernible differences to the glass temperatures, between this unit and the single panes, inside or out. No doubt, with sophisticated measuring instruments, there would be variances, but would it be worth the effort?, 3rd negative!
Using the 4mm glass that I already had, I found that, although the panels fitted neatly into the sashes, the remaining rebate of 3 to 4mm was too small to be able to accommodate a nailed beading, the rebates on all the sashes would need to be deepened by an additional 3mm for a neat external finish, 4th negative!.

For many years I had been accumulating cast iron window weights from many sources, so long as they were cheap, or free!. My collection received a huge boost, about 10 years back, when I was able to intercept about 84 of them, destined for scrap. I have no idea as to their origin, they were all between 12 and 14 lbs each, (roughly 5.5 to 6.3kg), and I hadn't seen any of this size before. The largest, from the rest of my collection, was 10 lbs, with the average being about 7 to 8. The owner estimated their scrap value to be about $40 and had me part with that for their exchange, not bad for half a ton of iron. I had the notion that these would be more than ample for the increased weight due to double glazing, wrong!.
With the trials made, I was able to start measuring the weights of the glass and sash's to get an idea of the counterbalance requirements. I nearly fell over when the scales told me that I was looking at an average weight of about 40 lb's per sash!, that would require a 20 lb weight each side.
I had designed the hidden pockets, in the pulley stiles, to be larger than normal to allow the insertion of my largest available weight, being 14 lb's and about 650mm in length. With cast iron, there would be no way of fitting 20 lb slugs, even if I could find any. Calculations were made and I concluded that the only way that it would be possible, would be to cast them, in a square profile, out of Lead. This was a path I wasn't too keen in taking, as if I didn't have enough on my plate already!, 5th negative.

The negatives were adding up and at this point, I had yet to find a positive!. I felt that I had given it every opportunity to prove it worthwhile and figured that enough time had already been wasted, so, Double Glazing was out!

The 4mm thick glass also made a large difference to the weight, most early windows that I have seen used only 3mm thick stuff. Even with single glazing, the 14 lb weights were only just going to be suitable for my largest sash's, the average would be about 11 lbs.