Homebrew NE England. Help needed please.

[hughjamton]

DavidS thanks so much, again. Please tell me, shall I just mix a little more mortar and go over the cracks, as they are so small, I wouldn’t be able to get anything ‘into‘ them.

Tony, can I ask, did you use soft sand or sharp sand in your home brew mix?

[TonyPizza]

hughjamton hi, I used soft builders sand.

[hughjamton]

hughjamton hi, I used soft builders sand.

I think that may be part of the problem, sharp sand will bond together better, kind of like a fine concrete, whereas soft sand is really for mortar and will tend to crack if applied too thickly as a render.
Don't help now I know.
If the cast is still a bit soft would it be possible to rake out the cracks, possibly with a Stanley knife, so you have an upside down V shape then force the repair mix in?

[TonyPizza]

hughjamton hi, yes builders sand is possibly the cause, but I got the impression that most used it? I may be wrong though.
I think it was more me rushing it more than I needed to, so fingers crossed it holds up.
Thanks for the advice on the cracks... I already did something similar at the weekend, so we’ll see how she fares.

[david s]

hughjamton hi, yes builders sand is possibly the cause, but I got the impression that most used it? I may be wrong though.
I think it was more me rushing it more than I needed to, so fingers crossed it holds up.
Thanks for the advice on the cracks... I already did something similar at the weekend, so we’ll see how she fares.

I disagree as builders sand is usually graded, ie it has a range of sizes of the grains which is an undesirable characteristic for mortars, but desirable for a castable. Proprietary castable refractories contain aggregates up to 3mm (at least mine does as well as extremely fine material). I think the more likely culprit is that the mix was a bit too wet leading to excessive shrinkage. Because the mix contains a high clay proportion there is a fair amount of shrinkage anyway. Although if the builders sand contains a proportion of clay and often does, this may have increased the proportion of clay in the mix leading to greater shrinkage. Also some clays have higher shrinkage rates than others too.

[hughjamton]

I disagree as builders sand is usually graded, ie it has a range of sizes of the grains which is an undesirable characteristic for mortars, but desirable for a cartable. Proprietary castable refractories contain aggregates up to 3mm (at least mine does as well as extremely fine material. I think the more likely culprit is that the mix was a bit too wet leading to excessive shrinkage. Because the mix contains a high clay proportion there is a fair amount of shrinkage.Some clays have higher shrinkage rates than others too.

Hi David, I think it may be a different country terminology, builders sand, or soft sand in the UK is very fine, the grains are very small and as near as you can get one size, I'll take a picture later to show you the difference between builders and sharp sand over here.
I think your right, the mix was too wet, but it certainly wouldn't have helped using a fine sand.

[hughjamton]

Hi David, I think it may be a different country terminology, builders sand, or soft sand in the UK is very fine, the grains are very small and as near as you can get one size, I'll take a picture later to show you the difference between builders and sharp sand over here.
I think your right, the mix was too wet, but it certainly wouldn't have helped using a fine sand.

[Padraig]

I used "play sand", which is for kids play boxes and it made for great homebrew, a pleasure to work with. I would say it is much sharper than builders sand, though not as sharp as the sharp sand you'd use for under patio slabs.

[david s]

Hi David, I think it may be a different country terminology, builders sand, or soft sand in the UK is very fine, the grains are very small and as near as you can get one size, I'll take a picture later to show you the difference between builders and sharp sand over here.
I think your right, the mix was too wet, but it certainly wouldn't have helped using a fine sand.

Ok, I see. We have a range of sands here in northern Australia and I use them for different purposes. River sand, which was what I thought you were referring to as builders sand has a range of grain size, some of it up to 2mm and is commonly used for concrete slabs and block fill. We also have fine sand and silica sand more suited for mortars.

[hughjamton]

Ok, I see. We have a range of sands here in northern Australia and I use them for different purposes. River sand, which was what I thought you were referring to as builders sand has a range of grain size, some of it up to 2mm and is commonly used for concrete slabs and block fill. We also have fine sand and silica sand more suited for mortars.

Cool, we've both learnt something. Always a good day when that happens.
Mind you, it makes life more difficult for you when your advising people, you'll need to know where they're from. LOL
In Spain the sand that's used for just about everything is like dust with lumps in it! goes off like granite though.
Don't know about the states.

[Nick J C]

Yes, I also got confused on this forum by different countries terminology, but fortunately went with my intuition and used “uk” sharp sand

[TonyPizza]

The cast is currently sat under wet towels and I give the inside a mist with the hose, a few times a day.

Regarding the next steps, I would be grateful, once again, if someone could comment on my plan / fill in a few blanks...

• Make decorative gallery arch, including moulding in four anchors, for the wire to fix to.
• After a week, remove towels and leave cast to dry for a week 'naturally' outside for another week.
• After a week drying, fit thermal blanket and v.crete
• Start curing fire process over the course of a week
• Oven now ready to use.

Can the curing fires be started the same day the V.crete is added? if not, how long after?

I have formed a collar into the gallery mould, for the flue pipe to sit on. The flue pipe is also fairly tight (but not too tight) against the recess it sits in. With this in mind, shall I still try and seal the flue pipe in place, or will the fact it sits on the mould and is fairly snug against the slides be enough? Does the V.crete need to seal up against the flue pipe, or shall there be similar small gap, like there is between the flue and the main cast?

Where can I find the correct ratio / components for the V.crete mix?

david s I believe I read a comment from David S, that suggested using a light V.crete mix to fill the gap between gallery and decorative arch. Did I also see that the arch should be set on a small amount of fire mortar, or will regular mortar be ok?

Shall I mix the V.Crete by hand (again - I have a feeling someone on here said it's the best way) so a mixer doesn't compress the vermiculite?


Thanks to all who contribute, once again.

Tony.

[david s]

Tony,

Regarding the waiting/drying periods, they are dependent on weather conditions. A week of drying in perfect conditions, hot breezy and low humidity is what I'd recommend. If you don't have these then you have to do it by fire which is more difficult and fuel consuming.

"Can the curing fires be started the same day the V.crete is added? if not, how long after?" Answer is no because the cement needs to do its hydration, but as you are not particularly concerned with the strength of the vermicrete layer over the dome, you are more interested in its insulation value, then leaving it a minimum of 24 hrs will result in it being pretty firm. You could start teasing the water out then. If you go at it too hard the vermicrete can swell and crack.

Sounds like your flue pipe fits the gallery collar just about right. I do pack the vermicrete (5:1) tight around the pipe to seal the junction with the flue gallery collar given that a 5:1 vermicrete has fairly low strength and some elasticity. Never had a problem with this method and done lots of ovens this way.

Vermicrete mix (10:1 by volume) 10 parts med grade vermicrete, 1 part portland cement, 3 parts water (a little more if you use fine grade vermiculite). To make the mix more workable you can add a handful of powdered clay for every litre of cement added. Mix dry ingredients then add 1/3 of the water and mix well in a barrow, add 2nd 1/3rd water and mix well knocking down any lumps with the back of your spade. Add last 1/3 water and mix well again. If making a richer mix use the same water quantity.

I leave a gap of around 5-10mm between the flue gallery and outer decorative arch filled with blanket and sealed off with 5:1 vermicrete. Arch set on standard mortar, it doesn't get too hot there.

A mixer tends to abrade the grains and sticks to the mixing blades and sides of the mixer, it's better to mix by hand in a barrow where you can inspect the texture. Being so light it's not difficult. If you end up with water pooling at the bottom of your barrow you've added a bit too much water, add more dry material. Too much water washes the cement off the grains resulting in a poor mix.

Dave

[TonyPizza]

david s Thanks once again for taking the time to dish out so much help.
I'm currently happy to have a coupe of days where I don't need to do much at the moment, but I need to crack on with the gallery arch, when I have decided what it looks like.

[TonyPizza]

I'm currently struggling to finalise how my arch will look. I am thinking maybe some small tiles, set within the concrete mould. Has anyone got any inspiration for such a design?