Shrinking concrete?

[tomsmith]

Hello all,

Some of you might know that I'm running into problems with my maxjax install because my garage floor slab was only 3". I have an email from my home builder who stated the slab would be 4" and 4600PSI as per Ontario Building Code (their words)

This morning, I got an email starting the slab was indeed 4" when they poured it, but due to natural shrinkage and absorption by the dirt layer underneath, it shrunk to 3" and they have no further obligation.

my first thought was .. if it really shrank, wouldn't it have pulled in from the edges as well, rather than shrinking only in depth? And secondly, if Ontario Building Code states 4", wouldn't that be 4" AFTER any shrinkage - that is, when all is said and done, the slab would be 4" cured?

Can any concrete experts chime in with their thoughts on the shrinkage and any folks familiar with OBC, comment on the minimum thickness requirement?

 

[Chaznsc]

It shrank vertically 25%? LOL, thats magic concrete! They are, of course, lying to you. 4" means 4" not 3" and nothing is going to shrink 25%

 

[M17715]

Ha!! The only thing that is going to shrink that much......well never mind. But a 4" concrete slab shrinking down to 3"? I don't think so either.

 

[paulrey27]

It shrank vertically 25%? LOL, thats magic concrete! They are, of course, lying to you. 4" means 4" not 3" and nothing is going to shrink 25%

Echoing this. Concrete does NOT shrink that much.
Rough figure I've seen many times is 800 x 10^-6 in/in. ... so if I can math... .0002" total should be expected?

 

[djjsr]

They are lying to you and they know it.

 

[mayday0017]

Bet if you go measure on the outside it is 4"... Sounds like someone skimps where you can't see it

 

[tomsmith]

Hey,

Thanks for the feedback. this is pretty much what I expected so at least when I go back to them, I can stick to my guns.

I will however drill a hole near the edge to see if that's 4" deep .. even if it is though, the concrete should be 4" throughout.

I'm hoping they will be reasonable and cut out a 4x4x12 or even better a 4x4x16 section and repour rather than do the whole thing. I have a double garage with a 9'x8' workshop built into the back so I figured, the concrete they would have used pouring a 4" slab properly can be better spent on the 4x4x16 section. I'll let you know how it goes.

 

[Highbeam]

"This morning, I got an email starting the slab was indeed 4" when they poured it, but due to natural shrinkage and absorption by the dirt layer underneath, it shrunk to 3" and they have no further obligation."

That's almost the best line I've ever heard. I am a licensed civil engineer and can tell you that they are absolutely lying.

Absorption by the dirt layer.. ha!

 

[Daedalus]

Echoing this. Concrete does NOT shrink that much.
Rough figure I've seen many times is 800 x 10^-6 in/in. ... so if I can math... .0002" total should be expected?

You can't math. Lol.

 

[Nostraquedeo]

Just a guess, but the line along the edges was marked 4" above grade, however the grading was uneven where the MaxJack sits. I would want more than 4" of concrete under the lift anyway. Why not saw cut the floor, dig a good sized hole and then put in a good sized footing. That way you have an expansion joint around that footing, so you wont have any cracking in your floor.

 

[paulrey27]

You can't math. Lol.

https://www.google.com/webhp?source...Wc&fp=6ca84d98d48f74bf&ion=1&biw=1920&bih=979

 

[NUTTSGT]

A concrete floor shrinking from 4" to 3" . . . . . . . LMAO. . . . .lol . . . .

 

[rasit]

I have an email from my home builder who stated the slab would be 4" and 4600PSI as per Ontario Building Code (their words)

This morning, I got an email starting the slab was indeed 4" when they poured it, but due to natural shrinkage and absorption by the dirt layer underneath, it shrunk to 3" and they have no further obligation.

The good news is they put it in writing ( e-mail) so you have proof of their stupidity in case you have to show it to a lawyer...

 

[dadsEH]

Sounds like a job for Holmes!!!!!

 

[PugetDude]

Might just CC your friendly attorney and the specific individual at the appropriate Provincial agency responsible for overseeing construction compliance when you ask them what they are going to do about their out-of-specification concrete. That will show them you are serious, not going to roll over and are prepared to take this to the next level if they keep shirking their responsibility and lying about their specifications.

 

[PugetDude]

Sounds like a job for Holmes!!!!!

Holmes would tear out the entire garage floor, half the foundation, all the drywall, insulation, reframe the ceilings, rewire, re-plumb, install new drain tile , add radon monitoring and new roof vents to fix this issue... all in half an hour.

 

[mike_81]

If you closed more than two years ago you're hosed. Sorry.

 

[Rookie2]

did you call maxjac ? is it the portable one ?

 

[jhelrey]

Time to put a hold on the CC payment

 

[PoolGuy444]

Holmes would tear out the entire garage floor, half the foundation, all the drywall, insulation, reframe the ceilings, rewire, re-plumb, install new drain tile , add radon monitoring and new roof vents to fix this issue... all in half an hour.

Now that's funny. And true.

 

[Milton Shaw]

PudgetDude forgot the new kitchen, bath, roof, siding and deck that would be required by Holmes to fix this problem. Extreme makeover would require a two week vacation in addition and another 2000 sf of floor space in the house. Underground garage or bunker/mancave under in would probably considered to be over the top though.

 

[Daedalus]

https://www.google.com/webhp?source...Wc&fp=6ca84d98d48f74bf&ion=1&biw=1920&bih=979

That's not how it works. You don't divide by 4, you multiply by 4. Expansion/contraction is positively correlated to thickness since it's a %. Still, assuming the shrinkage coefficient is correct, the answer comes out to about .003, which is just less than the thickness of a sheet of standard copier paper.

 

[paulrey27]

That's not how it works. You don't divide by 4, you multiply by 4. Expansion/contraction is positively correlated to thickness since it's a %. Still, assuming the shrinkage coefficient is correct, the answer comes out to about .003, which is just less than the thickness of a sheet of standard copier paper.

derp mode here. You're correct. I did hit the /...when I meant the *. Again, you're right. my bad.
So what's the verdict on this?? op?

 

[KinzeMech]

I'd blame it on the metric system. They probably poured that slab to 4 metric inches, which is about 3 real inches...

 

[premierplayer]

You're drilling a hole with a hammer drill? Inserting a piece of wire with a "L" bent onto the end to measure thickness?

What's the possibility the slab is really 4" thick and the drill bit as it nears the end of the bore is blowing out a chunk which is skewing your measurement?

I'm not buying the shrinkage story, it's BS. I'm just questioning you have gotten an accurate measurement.

 

[tomsmith]

Maybe the drill bit is blowing out a chunk but a whole inch? And for three different holes?

Not saying its impossible but what would be the best way to measure thickness?

On the third hole, I wrapped some masking tape 3" on the drill bit and it was a tiny bit past the surface of the floor when it drilled through the bottom.

Update on the situation: the builder is sending someone out to take a look next week. I was floored by the response, they pretty much responded to my email the same day. When the guy comes out, I will explain how I determined the 3" depth but if there's a 'proper' way to do it, would love to know so I check before he arrives

 

[tomsmith]

PudgetDude forgot the new kitchen, bath, roof, siding and deck that would be required by Holmes to fix this problem. Extreme makeover would require a two week vacation in addition and another 2000 sf of floor space in the house. Underground garage or bunker/mancave under in would probably considered to be over the top though.

Lmao .. That would be awesome for me. Maybe I need to get in contacts with Holmes

 

[p_mori7]

I'd blame it on the metric system. They probably poured that slab to 4 metric inches, which is about 3 real inches...

Metric inches ?

I don't know if I should or if I should

 

[premierplayer]

Maybe the drill bit is blowing out a chunk but a whole inch? And for three different holes?

Not saying its impossible but what would be the best way to measure thickness?

On the third hole, I wrapped some masking tape 3" on the drill bit and it was a tiny bit past the surface of the floor when it drilled through the bottom.

Update on the situation: the builder is sending someone out to take a look next week. I was floored by the response, they pretty much responded to my email the same day. When the guy comes out, I will explain how I determined the 3" depth but if there's a 'proper' way to do it, would love to know so I check before he arrives

core drill, you should be able to lift the core out of the hole and have the proof in your hand

 

[tomsmith]

Hey

Sorry for the delay on posting a follow up. The builder did come out and look at the holes I drilled and concurred they were not the 4" I had asked for and was promised.

They offered to tear the whole thing up or just cut out sections. I know the 'proper' thing would be to rip it all out but 4" is still pretty shallow for the maxjax and waiting the 15 weeks or so for it to cure would be extremely tough - I need my garage

Instead, I opted to have two 3'x3' sections cut out and poured to 12". I would have gone for 4', but that would have put me close to the foundation wall on one side which I wanted to avoid.

The contractor came out the next day and got to work at 7am.

We covered up as much equipment as we could with plastic but the dust cloud was truly epic. Even now, I am finding dust in nooks and crannies. I asked if I should spray the blade with water from the hose but he said it'll make more of a mess that way - after the dust apocalypse, I wish I had insisted on wet cut..

After cutting the sections and using a sledgehammer to break into smaller pieces, this is what we're left with..

Definitely not 4"

We dug down to around 14" and covered with around 2" of gravel. Then he called in the cement truck to pour.

One thing he didn't do and I completely forgot about it as well was to rebar into the existing slab. He did however put 6 pieces of rebar in each section (3 and 3 in a tic-tac-toe pattern) and sank them around 4 inches deep.

When we were digging down, I did notice that we both removed gravel and soil a couple of inches under the existing slab so the concrete would have 'gone under' the existing slab and hopefully tied somewhat into the slab.

Here's the finished look

I'm waiting until the end of August before I drill again - that would have been 6 weeks.

 

[bobscogin]

One thing he didn't do and I completely forgot about it as well was to rebar into the existing slab.

I would have some concerns about that.

Bob

 

[Moose97]

Might just CC your friendly attorney and the specific individual at the appropriate Provincial agency responsible for overseeing construction compliance when you ask them what they are going to do about their out-of-specification concrete. That will show them you are serious, not going to roll over and are prepared to take this to the next level if they keep shirking their responsibility and lying about their specifications.

I agree. These guys are probably gonna clam up and not speak with you. Lawyer up!

Holmes would tear out the entire garage floor, half the foundation, all the drywall, insulation, reframe the ceilings, rewire, re-plumb, install new drain tile , add radon monitoring and new roof vents to fix this issue... all in half an hour.

.....and he would add a bathroom to the garage! Too funny!