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Michaela
03-07-2006, 08:42 PM
Hi all, I have to break up some concrete in my basement inorder to run some plumbing lines underneath it. About 2 by 10 feet of the slab needs to go or more. Over this is going to be marble. Does all this sound ok.

1) How do I break up the concrete. Would just a 20 lb sledge do or should I get a jack hammer. The thickness of this concrete is 4".

2) I will have to drill holes and epoxy in rebar inorder to prevent vertical movement. I was going to use a 9/16" bit on a hammer drill to drill a hole 6" deep spaced about every 12" on the concrete.

3) before I fill in the hole I was going to pack the dirt underneath with a ram rod, go over with sand (no need to pack this), and then pour my concrete.

4) Over the whole area I will use the schluter ditra mating to help prevent any cracked tile from horizontal movement.

The only thing that I am really not sure of is how to get through the concrete alright and fill it without any problems. Everything else I am pretty ok with. Thanks

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Davy
03-07-2006, 08:53 PM
Hi Michael, Look into renting a big electric chipping hammer or Jack hammer for this job. Your plan sounds good to me. :)

Rob, P.E.
03-07-2006, 10:35 PM
Concrete. My favorite subject. Too bad just a basement slab and not a 10,000psi slip-cast liner. :tongue:

OK. First you want to rent yourself a concrete saw and saw cut your slab so you do not make your project worse with uncontrolled stress cracking of the adjoining slab to remain. Get a trolley/cart mount if you've never handled a German saw (a.k.a., cut-off saw) before, especially if your trench line is long. You should be able to cut full-depth, but since this is messy work, a half depth score will suit. Keep it all wet while you work if you can... You can demo between the saw cuts with a sledge if you're up to it, or rent a small chipper, or better yet, a small electric jack hammer if 220V is within reach.

For your bar, you have no need to use epoxy on the dowels. It will not serve you any purpose in this scenerio and only adds a significant $ to the work. Based on your indicated drill size, #4 deformed dowels are a bit overkill, but cheap enough. #3 would be fine. Also, don't span dowel the trench unless you will be installing a reflective crack mitigation system (I'll let the Ditra gurus address if it is truely such). Span dowels mean drilling opposing sockets and pockets and having the bar slip into the slightly deeper pocket and then pulled forward into the shallower socket, which is common on structural doweling. Instead, alternate shorter dowels in a side-to-side fashion would be sufficient for you.

Reality is, if you properly prepare the disturbed subgrade, dowels really aren't necessary, but a smart idea to temper the unknown. However, whomever told you not to compact the sand needs some serious lessons in elastic settlement theory... Definitely compact the subgrade and the pipe bedding material before laying the pipe. If this is a shallow cover install (less than 12" over the crown of the pipe), toss the idea of sand and get yourself some pea gravel. No compaction required with it, but make sure you control the slump of your patching concrete so not to run excessively into the gravel voids. If there's more cover, by all means use sand and compact. A jumping jack will save the shoulder and back for a small rental fee.

dan stark
03-07-2006, 10:52 PM
I did flat work for long long time before moving to tile. I have to say busting up concrete can be a lot of fun but very tough. what rob said is spot on: get a wet saw. If you don't feel comfortable with a free weilding one you can get one on rollers. If you don't saw it first you rish cracking more of your basement floor than you bargained for. the saw creates a controled joint for you to break the concrete away from. It also helps to have a partner in crime with a shop vac to suck up all the excess water from the saw. After that you can either rent a jack hammer or try it with a sledge and a pick.

Oh and like rob said tamp down everything that goes below your mud I like to put gravel down instead of sand but to each there own.

make sure also to compleatly cover all the metal that you put in the floor with concrete. Sometimes if a part of the rebar or mesh is sticking out from below the slab the rust that occurs can travel through the entire rod even though most of it is embedded.

have fun. have some beer in the fridge for afterward

NVC
03-07-2006, 10:53 PM
What Davy said re: a jack-hammer.

Pnuematics are fastest, but require a trailer type air compressor(Ingersol Rand). A large electric Bosch or Hilti will be fine for the small sq.footage you have.

Code here requires epoxy on the dowels, but if you have an engineer he can dictate otherwise. :D Check with your local "authorities having jurisdiction" (bldg. dept.)

What Rob said re: Saw cutting your slab first. It will make the tear out easier, and won't risk breaking/cracking/stressing the rest of your slab. For the compaction of your subgrade (dirt) rent a "whacker-packer" with a "shoe" narrow enough to fit in your trench. (find available sizes before you saw cut, and go a bit wider.

Lastly, wear goggles and a good resperator, as the concrete dust is . . . unhealthy. A search on-line on "silicosis" will explain why. I'm not a doctor, I just play one with the Mrs. ;)

Have fun, it's a dirty job, but somebody will save some $

hope this helps,
Mark

Tool Guy - Kg
03-08-2006, 12:56 AM
Of course the gas exhaust in the basement my be slightly objectionable......I can't help not posting a picher of the coolest tool out there. A gas powered diamond chainsaw (http://www.constructioncomplete.com/ConcreteMasonryEquipment/Saws/DiamondChainSawsGas.html). For a few extra bucks, you can get a hydraulic version (http://www.constructioncomplete.com/ConcreteMasonryEquipment/Saws/DiamondChainSawsHydraulic.html). :tup2:

tap
03-08-2006, 06:19 AM
Another and cheaper possibilty is to chuck up a masonry blade in a circular saw and set it at a say, 1/4 inch cut, snap lines for where you wish to break out and carefully cut to the lines increasing the depth of cut with each pass.
At a depth of say, 1" or 3/4" you can begin cracking out with preferably a jack hammer of some kind but i've had success with a sledge hammer.
The first breakthrough is the key, from there you can nibble away.