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Location: Visitation between Wal-Mart & Home Depot
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Quote:
Originally Posted by Wilson513
Spalling on horizontal surfaces is caused by too much water in the mix preventing the formation of the crystal matrix that makes concrete strong.
On vertical surfaces, water migrates through tiny cracks and leeches out soluble material from the vertical wall.
Porous peebles in concrete absorb water and explode. As I said above, one can choose an aggregate that is porous with which to make concrete. or not. I'd recommend not.
I agree about a cause of spalling being too much water in the mix, but that's not really what I was getting at.
Assuming that we're still talking about the porosity of concrete, portland cement (as an example of no aggragate) still has measurable permeability. There can be no permeability without porosity.
I agree about a cause of spalling being too much water in the mix, but that's not really what I was getting at.
Assuming that we're still talking about the porosity of concrete, portland cement (as an example of no aggragate) still has measurable permeability. There can be no permeability without porosity.
Granite is porous too. It is sealed just like concrete. And once sealed, the argument becomes theoretical.
Location: Visitation between Wal-Mart & Home Depot
8,309 posts, read 38,768,892 times
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Quote:
Originally Posted by Wilson513
Granite is porous too. It is sealed just like concrete. And once sealed, the argument becomes theoretical.
I'm with you there. If you put a flame spreader over a concrete countertop to get it nice and hot and then rub some beeswax over it, the wax gets drawn into the concrete thereby making the argument theoretical.
I really hate to get all "science teacher", but folks might look up this thread.
There are three basic classes of stone. Sedimentary rock, like sandstone & limestone, which is useless for kitchen countertops, has porosity of 35-31% at the high end . Metamorphic rock, like marble and quartzite, which has been formed when sedimentary rock like limestone or sandstone are subjected geologic pressure / heat causing recrystallization. Porosity is about 3.9%-2% Finally igneous rocks are formed under high pressure and heat -- that is why granite typically has porosity of less than 1.5%, often around 0.2%. That tremendous heat and pressure cooks out other minerals.
Best case scenario, a high quality Portland cement (roasted limestone & clay mixed with gypsum) might approach the porosity of limestone, but pure cement will shrink and fracture as it cures. If you dump in a ton hydrated lime it'll be more fragile than plaster. Instead an aggregate is added. If the aggregate chosen is non-porous, and added in sufficient quanities to be evenly distributed but no so much as weaken the recrystalized of the calcium you MIGHT get something about on par with marble.
These are not theoretical problems. Look up the info from any geology site or even the Cheng info sources -- if you don't mind / like the "patina of use" (also known less politely as "staining") then go ahead an use concrete as a countertop. It'll be more susceptible to damage than any true granite, and probably in the range of some quartzites / marbles.
No one should EVER directly heat any concrete, marble, quartzite or even granite. Thermal shock can fracture he surface and potentially cause surprisingly large fragments to stress shatter in a VERY dangerous way...
Location: Visitation between Wal-Mart & Home Depot
8,309 posts, read 38,768,892 times
Reputation: 7185
Quote:
Originally Posted by chet everett
I really hate to get all "science teacher", but folks might look up this thread.
There are three basic classes of stone. Sedimentary rock, like sandstone & limestone, which is useless for kitchen countertops, has porosity of 35-31% at the high end . Metamorphic rock, like marble and quartzite, which has been formed when sedimentary rock like limestone or sandstone are subjected geologic pressure / heat causing recrystallization. Porosity is about 3.9%-2% Finally igneous rocks are formed under high pressure and heat -- that is why granite typically has porosity of less than 1.5%, often around 0.2%. That tremendous heat and pressure cooks out other minerals.
Best case scenario, a high quality Portland cement (roasted limestone & clay mixed with gypsum) might approach the porosity of limestone, but pure cement will shrink and fracture as it cures. If you dump in a ton hydrated lime it'll be more fragile than plaster. Instead an aggregate is added. If the aggregate chosen is non-porous, and added in sufficient quanities to be evenly distributed but no so much as weaken the recrystalized of the calcium you MIGHT get something about on par with marble.
These are not theoretical problems. Look up the info from any geology site or even the Cheng info sources -- if you don't mind / like the "patina of use" (also known less politely as "staining") then go ahead an use concrete as a countertop. It'll be more susceptible to damage than any true granite, and probably in the range of some quartzites / marbles.
No one should EVER directly heat any concrete, marble, quartzite or even granite. Thermal shock can fracture he surface and potentially cause surprisingly large fragments to stress shatter in a VERY dangerous way...
I may have seen a recently poured frontage road (at the time) violently spall when some high school friends built a bonfire on it in Fort Bend County, but I don't remember any names...
But, when I say good and hot I don't mean "scorch your hand" hot. Maybe 120 degrees. With a 1.75" slab of countertop I don't think that's very dangerous, but - sure, use a penetrating sealer.
You guys are cracking me up. Seems you are all right in your scientific answers. In the end, no one cares about moisture inside a cement top. The consumer don't give a damn really. Their only concern is how that new counter top looks.
I've seen marble chips, computer circuit boards, nails and screws, nuts and bolts, sea shells and broken bottle glass.
Yes! One of my contractors was telling me about the cement countertop he & his dad did for his mom as a gift - their time together and how they included some heirloom glassware & pebbles from vacations, I almost bawled on the spot
Yes! One of my contractors was telling me about the cement countertop he & his dad did for his mom as a gift - their time together and how they included some heirloom glassware & pebbles from vacations, I almost bawled on the spot
Cement is an ingredient- used in the making of concrete (or mortar)- they aren't interchangeable, just sayin'.
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