Pouring Hearth Question

[telehort]

I have been going through many posts and pictures about pouring the hearth and a question keeps popping up in my head. I don't have the answer although it may be much more obvious than I realize. If you use block construction for the stand and fill ever other core, when it comes time to pour your hearth with framing to the flush outside of the block stand...don't you just end up filling all of the other cores with cement that drops down during the pour? Also what keeps the cement from dropping through the front blocks that are supported by angle iron? Are you using a screen or some other material after the 3rd course so that any fill only goes down 1 course? I am assuming it just fills up the cores, but then if that is the case I don't see the advantage of filling ever other core prior to the hearth pour.
I apologize if this is a silly question, I am pretty good with construction and just finished building a 600+ bottle climate controlled wine room in my house and now am moving on to the oven so they can compliment each other, but have just been puzzled by this question.
Thanks in advance.

[Xabia Jim]

Re: Pouring Hearth Question

I cannot tell you the number of times I've seen paper bags used to stuff holes and cracks in masonry, as well as bits of block and wood, or rocks.... before the wall is capped or the floor poured. Just find something if you don't want to fill the cavities. The mixture will usually "bridge" if you get most of the hole plugged.

[jahysea]

Re: Pouring Hearth Question

The directions used to call for aluminum flashing on top of the block wall to provide some slip when expansion occurred. Someone proved this was not needed and James somewhat recently removed the flashing from the directions.

I had used the flashing and it covered the empty cores. You could still do this. I got a roll of 8" flashing at our local building supply place. A cut up cardboard box would probably serve the same effect.

I've attached a pic, the flashing you see around the edges covers the blocks out onto the plywood.

[redbricknick]

Re: Pouring Hearth Question

I filled and rebar'd all my cores. I had originally planned on filling the cores and pouring the slab on the same day to bond the two to eachother, but it didn't work out time and laziness wise. One thing we did, which I thought was cool, was to leave the core rebar extending out the top about five feet or so, then bending then into a rebar mesh grid for the hearth slab..

Incidentally, When I learned stonemasonry on my family winery in Tasmania, the alcoholic stonemason Ken would drink beer all day and put the bottles the backfill of the wall we were building. It's a four foot high wall, that runs about five hundred yards, and he calls it the wall of beers. (the great wall of China is often referred to as the wall of tears)

[Hendo]

Re: Pouring Hearth Question

Rubbish from building sites can be used to plug all sorts of holes. For block cores, paper cement bags scrunched up would be ideal. Or if empty cement bags aren't to hand, try thick paper shopping bags if you have them in your part of the world.

For my wall, I've gone down a similar route to redbricknick, and filled every core. I also placed 4 inverted U-shaped rebars into the cores (one at the front, one at the back and two between) which tie the two sides together as well as to the support slab (see photo's). The cores of the concrete blocks I used were designed for retaining wall applications, and had large cutouts in the internal webs for longitudinal reiforcement. This meant that the concrete used to fill the cores could flow from one core to the next, so I really had no choice but to fill them all.

Remember when you come to pour the concrete to ensure that the cores are moist, otherwise the dry blocks will suck moisture out of the wet concrete and it will not flow and fill up the cores as easily. It will also result in a weaker concrete strength. Neither do you want water puddling down the bottom of the cores, so I'd suggest a fine spray applied quickly to each core several times before concreting. Rodding - ramming a piece of 1/2" rod with a bullet-shaped tip up and down repeatedly in the poured concrete - is also effective in getting the concrete to fill the cores properly and minimise porosity.

Cheers, Paul.

[telehort]

Re: Pouring Hearth Question

Thank you all for the info, I will take pics and log my info as I being this in the next week or so. I like the idea of leaving a few feet of rebar out the top and bending it down for for the mesh support for the hearth.

Thanks!

[CanuckJim]

Re: Pouring Hearth Question

Red,

Funny how these traditions develop. While working underneath my mid-19th C house (balloon framed with a thick fieldstone foundation) I uncovered several whisky bottles in the rubble of the crawl space. Hand blown, too, very cool. Later, when I got seriously into masonry and took some lessons from a true master, I learned he always tossed a few coins, a newspaper, magazine, whatnot, into any enclosure he built. The one thing that did not vary was a wine bottle. The interior fireplace I built in the house has exactly the same traditional acoutrements, ditto the roof space of my outside oven. I also sign and date wet mortar with a pointing trowel in various places. Who knows, we might all end up in an archeological display some time down the road.

Jim

[telehort]

Re: Pouring Hearth Question

I may just have to create little "time capsule" in one of the cores before I fill it up.