what are the pro’s & con’s of re-bar vs. wire mesh for a 350sq. ft. garage slab poured 4″ thick? are they even necessacary? am also doing a 750 sq. foot great room with stained concrete & radiant floor heating…what are my best bet’s to prevent the inevetable cracking of the concrete (would like to avoid cutting the slab if possible)? get a different answer from each concrete sub I talk to about these issues…would anyone be kind enough to lead me in the right direction? thanks!
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as you know just about all concrete slabs crack... some swear by fiber... rebar is always good placed correctly... and wire does very little... i'm sure if it's placed right it helps but i've torn out 100s of tons of slab work and better than 90% of the wire i see in tearouts is still lay'n between the concrete & base...
p
for u i'd use fiber
we have this discussion about once a week. so again from the top.
Rebar , wire, and fiber are not the same thing. They each have their own job. Rebar does nothing. Rebar is for load factors, it will not stop cracking ( whoa, hang on, not finish yet) rebar will control failure when a load is applied to the structure, whether its the building itself or an automobile in the garage. When a load is applied it bends the concrete on end, this is how the crack starts, the point of failure. Rebar counteract this force. concrete is good in compression but not tension. Rebar will hold a force in tension.
Fiber and welded wire are only used for shrinks cracks, non structure cracks, cosmetic cracks. They cannot hold a load factor. So now everybody in the room repeat after me. "REBAR AND WIRE ARE NOT THE SAME THING"
If you are placing a normal room slab like a bedroom, living room, there is no load in the center of the room, just people walking. You are wasting your money on rebar. Also for rebar to work properly its needs concrete thickness. 4 inch just aint going do it, not enough coverage. Ok you in the back, you claim you do it all the time. "YOU'RE WRONG, go back to sleep"
fiber, best thing since slice bread, no labor, no excess material, no cutting, no hauling to dump. 100% in there, like Rago. Its not laying on bottom, no poking out. I wish they would outlaw welded wire,its a joke. Concrete finisher not going pull it. " What you say in the back again, no you're wrong again, no matter who job it is, finishers do not pull wire, they walk on it" so why used it.
So you want to control cracking. couple maybe three #5 in footing, fiber in mix, I like super P. Control your slump to no more than a 4. The hell with finisher, all they are , are laborer with DUI's. as soon as you can walk on it, very important. flood with water, cover with plastic, keep wet and covered for seven days. and also don't use that cheap five sack 3000 mix, get a good six sack. I like pea gravel mixes.
Ok that's it, I'm done, go play.
Edited 5/23/2006 9:17 am by brownbagg
I get it that you don't like wire... but let me ask you a Q: Somebody told me that WWF helps evenly distribute heat generted during the hydration process. Ever heard that?
Another Q: What advice do you have for keeping the plastic from leaving marks on the slab? When I say marks, I'm referring to areas of different colors, not really imperfections in the surface....
if you wait till th etime you can walk on it without leaving marks, the platic will not leave marks. as far as marks on stain concrete, it makes it better. But lets not get into stain concrete. I'm also a pro on that and I need to get productive today, cant surf the web. If you search my name here for stain concrete, I have pictures. about six months ago.
'Bagg, I think that is the longest post (and one of the funniest) you have ever typed.If I went back through the archives and took all of the times you and I have answered this question we could get you published in FHB.
If I'm mixing concrete by hand, is fiber something I can add along with the portland cement and aggregate or is fiber a ready-mix only option? If I can add it myself, what kind and how much should I use?Thanks,
Tim
yes you can but mixing by hand will cost you at least double than ordering a truck load. a bag of sackcrete is $4 you will need 27 bags for a yard. times 7 yards. 189 bags $850 with tax, without hauling, throwing or mixing compare to a mixer truck of $644. already mix and then you got a weak 1800 psi at that.
Thanks for answering, but cost was not what I was wondering about. If I want to mix portland cement, sand, and gravel to make my own concrete, is there a "fiber" that I can add myself?I know that ordering mix in that quantity is cheaper, but I am interested in situations where it is not practical to do so, ie places with inadequate access for a truck or not enough labor to place the mix fast enough. Thanks,
Tim
OH BOY - I GET TO CORRECT BROWNBAG ON A CONCRETE ISSUE :-) !!!!!
>> a bag of sackcrete is $4 you will need 27 bags for a yard. <<
Around here we get 80# bags that are 2/3 of a cubic foot... That would be ~40 bags per yard.
Or, maybe you are getting 120# bags? I guess those bags are for the young men :-)
I do agree though, mixing any more than a small amount of concrete from bags is ridiculous. Learned that the hard way....
Edited 5/23/2006 7:54 pm ET by Matt
to a properly compacted base ... rebar will add just about nothing in a slab but cost you for the steel..
not compacted you might need it because then you have a large concrete float that you don't want to break apart... prestressed cables with tension would be fun...
fibers stretch and they will not keep concrete from cracking.... even the manufactures do not claim they do or will
pea gravel mixes should usually be your last choice not your first... they are useful in thin pours and i use them for such... that and for casting ... pea gravel in a generic term for small rocks bigger than sand but usually less than 1/2" most are rounded... NOT good... angular are better.... in all mixes you want your rocks to fill all voids between themself so you want a mix of sizes, sand being the smallest stones... the sharper the edges of stone the better the portland is the binder...
I cast alot of concrete and yes you can mix it yourself i buy 10ton loads of sand (the finest they have they refer to it as "golf course sand" i pay about $12 a ton and haul it with my dumptruck, I also keep a piles of U M and O rock... I use as large of rock as i can get away with for each pour... I pay on average $10 a ton for rock...
I have aprox 80,000lbs of portland in stock (all white)
and i still can't make concrete as cheap as i can buy it premixed
i have a mixer that makes 1/3 yard per batch... i have a bobcat that i place my material as close to the mixer as i can... and it's still alot of hard work...
if i need even 1 1/4 yd for small flatwork or form work and don't need white, i'll go get u-cart for $120 vs mix'n it myself
what i will do is play with my mixes for different results and effects you can make concrete look like many natural carved stones... i design alot of my projects around what i can cast for effect...
no matter what you pay for concrete there isn't much you can do cheaper it's like drywall... what else are you going to use for the price?
i get finished fire rated floors stained & scored for under $2 a sf
i get counter tops for kitchen & baths & bars for maybe $3sf
cool stuff that concrete
if you just like work'n with it go for it...
p
Edited 5/23/2006 8:01 pm ET by ponytl
EXCELLENT POST!!! THANK YOU FOR TAKING YOUR TIME.
one more thing, from past expriences. On garage slabs, no thinner than six inches, true six inches. also compacted subsoil. we use plain red sand clay but I like the rock idea. #4 foot each way will work good in a garage on chairs
Edited 5/23/2006 9:08 am by brownbagg
It's hard to argue with logic like that!
another point, compacting subsoil. Jumping jack. vibrating sled are not compaction equipment. they are used to make asphalt look pretty. to vibrate sand bewteen pavers. thats all their good for. They are a waste of money for compaction. remember your building depends on compaction to stand up and you are relying on a joke of a equpiment to get it.
Are you saying that 1) neither a jumping jack nor a vibrating sled is real compaction equipment? Or, are you saying 2) a jumping jack is, but a vibrating sled is not. If you meant #1 then what do you consider real compaction equipment?
#2and yes you can add the fiber yourself. its come in a bag per yard, so half a bag, half a yard. too much no big deal
Edited 5/23/2006 7:54 pm by brownbagg
I'll jump in here on the compaction equipment.There is a lot more to compaction than one might expect. The proper choice of equipment depends upon the soil type.In general, the more granular a soil is, the better it will respond to high-frequency/low amplitude, the more cohesive, the better it responds to high amplitude/low frequency.There are exceptions, however. Some granular soils are sensitive to travel speed, and it is difficult to hit good values with what you would think is the right equipment because the lift shatters behind the roller as you travel.So a jumping jack is good for cohesive soils, and sometimes the best choice for poorly-graded but confined granular soils with some cohesive properties.The vibratory plate that 'Bagg is refers to is indeed worthless for compaction. We're talking about those 200-lb. asphalt tampers.Not to be confused with a reversible plate, which is about 800 pounds or more. This is a serious piece of compaction equipment, again, useful for granular soils at or near optimal moisture content, with low plasticity.
got a pic or a link for the >> reversible plate << ?
I knew brownbagg would answer! He's our resident concrete expert.
A couple of other points that others might have said if they had the time: For a garage, you'll want to thicken the slab at the vehicle door to 6 or 8 inches. Wire mesh does have an application where it is useful, that is, when installing radiant floor heat. It provides a convenient structure to which to tie off the tubing. It's really the only good way I know of to do that.
I want to emphasize the criticality of compacting. If you don't compact well it will be like making peanut brittle on a waterbed. No matter how many nuts you use it will crack when you lie on it. The support for a slab must be unyielding for the slab to be dependable.