Kono III

Yes, yes, yes - I know I said I'd wait a week before removing the kono grill from its former, but it just felt so solid that I was certain it would withstand being decanted.

I replaced the inside former box, just to add some torsional strength, before tipping it upside down and it slid out perfectly. The clingfilm had done its job, although there was a lot of condensation covering the clingfilm.

As you can see, the top edge is slightly high on one side, but that can be corrected with an angle grinder used judiciously to trim it even. 

I smoothed some of the rough edges off the lip with a mini-grinder and a sanding machine, but I'll leave it a few days more in the engine room before working on it any further. Some clingfilm was trapped in small crevices on the outside, but this was removed easily with the sanding machine.

A week is recommended for curing as the absolute minimum and, the longer you leave it the more it cures and the greater the strength. Maximum strength is achieved, apparently, after 3 to 4 weeks.

What I'll probably do is line the inside with a skim of white fire cement (as mentioned previously - but I'm finding it difficult to obtain white fire cement as it only seems to come in black or buff) and skim the outside with ordinary white cement, as it's quite rough due to the dryness of the perlcrete mix. If I ever have another go at making one, then I'll use a wetter mix to ensure a smoother finish and better gravity levelling of the top edge.

On the basis of the strength it already has, plus the weight, I dare say I could have made the walls a bit thinner, but it's not not bad for a 1st attempt, and the extra thickness may well be needed to retain the heat and prevent cracking. 

I have to say though that it's a lot heaver than I anticipated, unless the perlite is retaining a lot of water, which will evaporate in the next few days now that all the surfaces are exposed to the air. Grinding the top edges to level it out will remove a bit of weight anyway. If I can get away with it, I may even bring it in the house to aid the drying process, although it will have to be sneaked in.

I'm still not sure about using aluminium angle on the edges to give it added strength - any suggestions as to what I can clad it in - purely for aesthetic purposes - are most welcome.

Stop Press: I skimmed the outside yesterday anyway, impatient bastard that I am. Would have been better doing each surface  uppermost, on the flat, and on separate days per surface. It was rather like plastering vertically, which is one of the skills I've never managed to master.

I had to use a sloppy mix, more like double cream, to ensure it got into the crevices, which made a holy mess - as you can see. The problem was that I was using a small pot for the cement and a tiny trowel, rather than a proper, big, skimming trowel. Should have gone to ScrewFix and bought the proper equipment, but I don't want to end up spending a fortune on the damned thing - Hay would kill me. It will sand smooth, so not to worry. What I didn't want was to leave air bubbles in the matrix, which could expand when heated and crack the whole thing - hence the sloppy mix.

If it dries today, I'll have a go at it later with the angle grinder and sander to fair it off.