My UK build is out of the ground!

[vincentvega_uk]

Re: My UK build is out of the ground!

Thanks guys.
I think I may need to cure first anyway. The cold weather is starting to set in here in the uk, and im not going to risk doing the render/stucco if I don't need to.

Anyway, got my brickwork complete, and tiled the hearth in some nice inch thick reclaimed quarry tiles.
Got 75mm on blanket on also, so Im going to omit the vermicrete.

Any advice/comments as always is welcomed.

Thanks

Allan

[david s]

Re: My UK build is out of the ground!

I like to cure before doing the outer render. It gives the water a chance to escape more easily.
Ditto on the arch comment, very Roman.

[brickie in oz]

Re: My UK build is out of the ground!

Whoah, nice arch....

[vincentvega_uk]

Re: My UK build is out of the ground!

Hi Allan,

I didn't use basecoat, just two passes of topcoat to give about 20-30mm overall thickness. For your oven, i think i'd be tempted to use the basecoat and topcoat system, so that it finishes up with a thicker shell to your oven. However, in my research into K-rend, you can appply the topcoat over normal sand and cement render if you want to. You'll probably just negate the breathability of the system though.

Only add water to the render mix, everything needed is added. 4-5ltrs per 25kg bag, and mix well. I used a large bucket and drill mounted plaster whisk. One initial mix, leave it for a couple of minutes and then a second mix before use. It only has around 30-45minutes workable time, so have everything all ready before mixing and getting mucky!

I used a single walled flue for my oven, but changed it after there were definite heat/expansion related cracks eminating from it. The single walled flue gets barsteward hot!

Flue length...there will be optimum dimensions, but go with what looks best and you can get hold of easily. Cob ovens that have no real chimney work fine, along with commercial ovens with extremely long flue systems.
For a 42" oven, 8" flue is just fine. However if you want to use twin wall, then O.D is going to be 10" minimum. Just remember to allow for a heatbreak between any render and the flue, whatever you use.

Winters closing in fast! Quite a frost this morning in East Anglia!
Good Luck.

Thanks again for the advice.
I have opted not to go with twin wall due to the price. I will make sure I get some insulation between my flue and the render!
I too have read that a lot of people are using a sand/cement base coat for the k rend. I think for what I need I will stick with the K rend base itself.

Got my landing area and outer decorative arch in this week, need to now just set some bullnose bricks to tidy up the front of the landing down to my hearth, fire blanket everything up, fix the flue, ( im thinking of getting some sort of anchor plate made up to accept the bottom of the flue), then render/stucco.
Im going to tile whats left of my hearth around the oven in red quarry tiles I think.

When I get to the stage of curing my oven, can this be done once all the final render/stucco is complete or do I need to cure before this go's on?

Cheers

Allan

[Bookemdanno]

Re: My UK build is out of the ground!

Cheers Bookemdanno,

So with the two coat, is that using the k rend base coat they make before the final k rend finish?
With the silicone in the k rend, I take it you don't add an integral waterproofer?
Also what scratch coat mix did you use? 4:1 plastering sand-cement?
I intend on the scarified finish myself.
I also take your advice on the heartbreaks. Would that also be needed in my 'vault' area between the brickwork and render? Bearing in mind I have built a heartbreak out of insulation brick in the hearth between the oven and vault, and also between the oven arch and the vault arch.
It would be interesting to know how hot the vault area and chimney gets with the get breaks installed.

Many thanks

Allan

Hi Allan,

I didn't use basecoat, just two passes of topcoat to give about 20-30mm overall thickness. For your oven, i think i'd be tempted to use the basecoat and topcoat system, so that it finishes up with a thicker shell to your oven. However, in my research into K-rend, you can appply the topcoat over normal sand and cement render if you want to. You'll probably just negate the breathability of the system though.

Only add water to the render mix, everything needed is added. 4-5ltrs per 25kg bag, and mix well. I used a large bucket and drill mounted plaster whisk. One initial mix, leave it for a couple of minutes and then a second mix before use. It only has around 30-45minutes workable time, so have everything all ready before mixing and getting mucky!

I used a single walled flue for my oven, but changed it after there were definite heat/expansion related cracks eminating from it. The single walled flue gets barsteward hot!

Flue length...there will be optimum dimensions, but go with what looks best and you can get hold of easily. Cob ovens that have no real chimney work fine, along with commercial ovens with extremely long flue systems.
For a 42" oven, 8" flue is just fine. However if you want to use twin wall, then O.D is going to be 10" minimum. Just remember to allow for a heatbreak between any render and the flue, whatever you use.

Winters closing in fast! Quite a frost this morning in East Anglia!
Good Luck.

[vincentvega_uk]

Re: My UK build is out of the ground!

8 inch diameter, at least 3 feet tall.

Great, thanks.

Allan

[deejayoh]

Re: My UK build is out of the ground!

8 inch diameter, at least 3 feet tall.

[vincentvega_uk]

Re: My UK build is out of the ground!

Any advice on flue length and diameter for a 40 inch oven anyone?

Thanks again

Allan

[vincentvega_uk]

Re: My UK build is out of the ground!

Cheers Bookemdanno,

So with the two coat, is that using the k rend base coat they make before the final k rend finish?
With the silicone in the k rend, I take it you don't add an integral waterproofer?
Also what scratch coat mix did you use? 4:1 plastering sand-cement?
I intend on the scarified finish myself.
I also take your advice on the heartbreaks. Would that also be needed in my 'vault' area between the brickwork and render? Bearing in mind I have built a heartbreak out of insulation brick in the hearth between the oven and vault, and also between the oven arch and the vault arch.
It would be interesting to know how hot the vault area and chimney gets with the get breaks installed.

Many thanks

Allan

[vincentvega_uk]

Re: My UK build is out of the ground!

Thanks Cobblerdave, hopefully I will have enough cover of ceramic blanket,( I already have it), I think I will.
Then I can just do a course base coat of render before I apply my final base coat and top coat.

Cheers

[Bookemdanno]

Re: My UK build is out of the ground!

K-rend...

I actually liked it, as it was a similar finish to my original Lime render. Its very granular and coarse, but following the mixing instructions and going for a two stage mix made a very workable mix. I didn't go for the usual scarified finish, as i used my curved trowel and the wooden float still gave an open texture. Using a gauging trowel to apply the render first. It goes off pretty quickly so i'd advocate mixing up at a half bag a time. It comes in many colours, and is a reasonable price. The silicone within the render makes any rainfall just bead up and roll off with very little sight of soaking in.
I have to admit that i haven't fired my oven since rendering it, and with winter now closing its grip, i expect i'll leave it until spring rather than risk cracks, no time to fix and another winters rainfall, snow, etc soaking into my lovely dry dome. For safety, i'd always say to set in a heat break between any render and chimneys, etc. There are plenty of heat proof mastics to fill in the heat breaks to weatherproof everything up again.

[cobblerdave]

Re: My UK build is out of the ground!

Brilliant, thanks. Will save me a few ???!

Also what kind of depth coverage with my ceramic fibre blanket do people think I need to do without the vermiculite concrete?
If I have enough fire blanket I intend to chicken wire it then put a base coat of render on before my finished coat.

Cheers

Allan

Gudday Allan
V-Crete V ceramic. Ceramic is roughly twice as efficient as V Crete ie 1 in of ceramic equals the same as 2 in of V-Crete. So if go 3 ins of ceramic you have roughly the insulation value of 6 ins of V-Crete. And no water to dry out!
I used dry insulation and rendered over the top of a chick wire layer. I have used Pearl-Crete before and its a real pain to put on,much harder the rendering away a few lumps and bumps. And you don't have get ride of a huge amount of water furtherest from the heat.
If money was tight and I had the time, and patience V-Crete is the obvious choice.
If I had 3 ins of ceramic I would not waste any time or effort into V-Crete

[vincentvega_uk]

Re: My UK build is out of the ground!

Probably my awful terminology Stonecutter.

Anyway, its a lot clearer now, no matter what its called!

Cheers

Allan

[stonecutter]

Re: My UK build is out of the ground!

Yeah, im beginning to rethink the buttressing. I think I will just create a platform for a chimney anchor plate directly on the arch.
I am going to have a section of twin wall flue, so no great weight as you say.

I want to clarify my earlier posts about buttressing. My posts were directed towards you stating that you were building a vault in post #24 and then vault arch in post #43....I misunderstood what you were doing, and thought you were building a vault surround over your dome......my bad. Correct, you do not need to buttress a semi arch that is only carrying a couple flues.

As a point of reference, a vault is longer than it's diameter... so what you are doing over the vent is technically not a vault. If it is, you will have a long reach into the oven!

[vincentvega_uk]

Re: My UK build is out of the ground!

Cheers Bookemdanno,

Don't mind doing an extra coat, just could do without buying another 4 bags of vermiculite if its not needed.

Yeah, im beginning to rethink the buttressing. I think I will just create a platform for a chimney anchor plate directly on the arch.
I am going to have a section of twin wall flue, so no great weight as you say.

Didn't you do a k-rend finish? how did you find the application? never tried it myself?

Cheers

Allan