Austin Shackles

Total flow should be OK, it's a 6" chimney so the outlet holes in the brickwork are made to be larger than that.  Counting the oven and the bench there are 2 such holes at the base of the flue.

I need to check on space available.  It should be do-able, especially with the proposed divider, to make the bench inlet a bit higher than the outlet.  The ports in the stove are at the same level but obviously the bench feed (from the stove) is nearer the "hot" end of the path, while the bench outlet is at the bottom of the flue.

It's also entirely possible that I'm over-thinking it

This picture shows the lower level of the stove.  


On the left side above this level is the descending passage from the top after the hot gases have gone under the cooktop.  Where Iggy (the grey dragon) is sitting is the exit from the bottom of that hot descending path which can be connected to the bench.  That exit is closed above this level by the outer wall.  There's an inner dividing wall between the core space and that descending path, as seen below.  The inner wall extends down until 2 courses above the base.  On the right of this pic is the exit from the oven space in the lower part of the stove, into the base of the flue.


There's another port which connects from the bench to the base of the flue, over on the back right.  As the base of the stove is above floor level by a couple of courses of brick, the top of those bench ports is not gonna be far off the height I want the bench strat chamber to be but will likely still be a little low.  I can close off or restrict the oven exit at the back right in order to bias the flow of gases more towards the bench outlet, if need be.

Seems to me that if I just build the whole bench as a cul-de-sac, the hot gases will scoot around the corner and head straight for the exit flue.  So I was contemplating dividing the bench at least part way down with a thin vertical wall, so the gases have to run along one side of the bench and back the other to reach the exit.  Here's a crappy sketch of what I have in mind, also showing the way the gases flow.  Matt assures me that it works if you connect it to a bench and I see no reason to disbelieve him.  

Ah well that I can't say.  Since the whole core is made from the same bricks, and only 1 or 2 have issues, I'm gonna optimistically assume that it was a bad brick.  The one that broke is in quite a hot place, but so are quite a few others which seem to be ok.

As I'm soon* going to embark on building the heated bench for our Matt Walker tiny cookstove a thought occurred to me.  

The bench will be a strat chamber rather than a mass, simply because that's easy to build and from what I'm hearing pretty similar in effect.  The question I have is about the bottom of the chamber.  As things stand at present the floor of the house isn't finished - it will eventually be an inch or so higher after putting some concrete screed and then tiles on it.  The stove, though, sits on a concrete slab I made for it which is sort-final floor level, and then the bottom of the stove is a solid layer of bricks as per the design.  

If I just build the bench on the floor as-is, the bottom of the chamber inside will be 5 or 6 inches (12-15cm) below the bottom of the outlet ports in the lower part of the stove body.  So the question is this:  is that extra space below the level of the stove going to adversely affect it?  Secondary question, is it actually going to do any good, or would I be better off filling it up to near-stove-base level with, say, some gravel or something?

* FSVO "soon"

Time for a stove update I reckon.  She's been running well this year, much easier lighting than last year.  I did have an issue recently with some of the firebricks in the core either getting loose (see another post about clay-sand mortar) or in a couple of cases breaking.  

Now, the core gets pretty hot.  However, I would expect fire bricks to cope with that. A bit of the clay mortar that was filling a gap fell out and it's semi-fired the clay so it's almost like stone.

Anyway, lifted the cooktop off and removed enough of the core top to get at the broken/displaced brick which was the top rear one in the firebox which defines the far end of the flue path.  That brick turned out to be in about 3 pieces.  As I didn't have a spare one that size to hand, I glued it back together with "massa refrataria" which is 1500°C-proof stuff in a tube, used to join chimneys onto stoves etc. and glued it back into place with the same.  I also found a couple other cracked bricks to fix while I was in there.  Mostly, though, it's all stayed together.

Next job is to build the bench, when I have time, then we can burn it more than 3 firebox-loads at a time and harvest some more heat.  Without the bench, by the end of the 3rd firebox of wood there's what I consider an unacceptable amount of heat going up the chimney.  3 fireboxes of good wood burnt leads to the whole stove body being nicely hot, so tend to do 2 or 3, then leave it for a few hours so the heat gets used up some, and then burn it again later in the day.

I'd sort of thought it might be the sand.  In the UK we had "sharp sand" used for bricklaying and such, and "soft sand" which you used for rendering or base coat for plaster.   Here in Portugal there's river sand (areia do rio) which is only really good for making concrete floors, normal sand "areia" which one supplier told me when I asked was "made from brita" (brita is screened crushed hard stone, in various sizes, like you'd use as aggregate in concrete) and then there's yellow sand "areia amarelo" which is the same as what I call soft sand.

It so happened I had a couple of bags of yellow sand available when I was doing the stove, so I used that.  I'll probably build the bench using cement mortar but the plan is to used some nice granite slabs which were originally kitchen worktops, with suitable support, for the top of the bench and those I would like to be able to remove in case of need for inspection or cleaning.

The other thing I can easily get is gun-tubes of "massa refrataria" which is I believe mainly for sealing steel chimney sections or for sealing the chimney to the stove.  I've used that to re-stick the fancy corners I made on the stove top, which look cool but are prone to fall apart :D

As I'm about to attach a bench to our Matt Walker stove, this thread contains invaluable information.

On my stove, I built in a bypass at the back of the core direct into the chimney for easy lighting, and also for the possibility that some day I may want to cook on the stove without heating the whole thing and the bench.  Yes, it does require thought and discipline not to leave the bypass open and waste heat up the chimney, but it's well worth that in my view for the ease of lighting.  We live in a fairly warm climate with only 2-3 months of not super-cold weather.

When I built my Matt Walker stove Matt Walker build in Portugal I built the lower part of the body using refractory mortar.  The top part I built using clay-sand mortar as recommended by many folks, on the grounds that it's possible to get it apart if need be.

Now, the problem I'm seeing is that it tends to come apart by itself.  The clay-sand mortar adheres poorly to the bricks, so poorly that some of the one on the top came loose and had to be stuck back with alternative stuff to hand such as high temperature silicone or some fire cement stuff intended for sealing chimney flue joints.

Now, it might be that the sand I used was an issue.  It's sold as "yellow" sand and is what you would normally use for rendering, as distinct from building a wall.  I guess in the UK I'd call it soft sand, rather than sharp sand.  It's also possible I should've had more, or less, clay in the mix.

As I'm soon going to embark on building the bench, and I would like the top of that to be removable in case of need, can I ask what sand and what mix ratio other people are using in their clay-based mortar?   The clay I have is dry powder in a sack.

Can confirm, properly dry eucalyptus is excellent rocket fuel.  

As for splitting it tends to have a twisty spiral grain so it doesn't split straight, also it tends to make little thin bits that try to join the 2 parts you are attempting to split.  It is easier split when green.  I recommend a hydraulic log splitter, biggish logs are a mare to do with an axe or wedges.  Good exercise I suppose...

If you spot anyone replacing old tiled roofs, the beams were often eucalyptus as it grows straight, is fairly strong, and somewhat resistant to rot.  Old roof beams (aside from the nails they contain) are a superb source so worth trying to make a deal for them.

If you have mimosa/acacia where you live that is also invasive and is also good fuel, and dries quite fast as well.

Well yesterday was the first burn of the season.  I did prime the flue just in case, and I lit it with a regular lighter 'cos I'd mislaid the gas blowlamp.  But she did us proud and fired right up and burned very nicely.  As yet still no bench, that's lined up for building this winter with luck.

Today, didn't bother priming just bypass open and off she went.  Feels like I can shut the bypass sooner but that may just be the wood is nice and dry, so it gets going fast. Anyway, the stove is burning nicely.  It's not all that cold here, mind, but recent rain made the house damp downstairs.