Concrete Questions

[hawkman]

I had a pad poured last year and almost soon after I noticed some hairline cracks coming from under the tub and out the sides. They haven't gotten any wider that I can see. I am having the tub replaced at the end of the month so I will be able to see what it looks like underneath.

I got a good deal on the concrete but if I was to do it again, I would have put down a nice base of crush and run. There is sand under it. When they pour driveways around here they dont put anything down and they seem to be fine.

My pad is 4" thick and was the same PSI as the drive way.. I think 3500 or 4500.. no rebar or anything in it and no fiberglass was used.

My question is should I have it replaced or let it run it's course until it gets bad (and I mean like wide cracks). I think it is stable enough for the tub for sure.. all concrete cracks some..

I've heard others using those pads.. maybe that is an option??

[Vinny]

How soon after it was poured did you place the tub on it? I've read that you should wait at least a week if not longer to get it to be close to cured hardness as possible.

Is the concrete still level?

It's probably OK but I would make the assesment after the tub is removed ... you only see the visible cracks, there may be bigger ones or there may be none.

[hawkman]

I waited about 4 weeks. The pad is level and it just seems like stress cracks.. nothing has shifted.

[Vanguard]

Concrete tends to get hairline cracks.  There really is not much you can do about it.  If they start getting bigger, then you have an issue underneath the concrete like shifting soil.  If they just stay hairline, that is fairly normal.  If your home has a concrete foundation, you'll see the same kind of cracks.

[Drewski]

I had a pad poured last year and almost soon after I noticed some hairline cracks coming from under the tub and out the sides.... My pad is 4" thick and was the same PSI as the drive way.. I think 3500 or 4500.. no rebar or anything in it and no fiberglass was used.

Unfortunately, you will continue to have problems. Stress fractures are usually caused by environmental heating/cooling combined with load. If a small void caused by a root or shift in the base appears, the concrete will crack. Most of the time, contractors put in "relief" cuts (a small gap with a filler material, also called expansion joints) that allow large concrete slabs to "float" and move slightly. The FOOLS that put in my driveway at my new house apparently didn't understand this principle which is why they now refer to me as "plaintiff."

If you are using a "small" slab (say 8'X8') you shouldn't need relief or expansion joints BUT, if you did not have a well prepared base AND wire mesh reinforcement, your slab WILL crack.

I generally recommend digging down and leveling to 10" for a 4" slab. Add 4" of sand, compact until hard, add 2" of fine crushed stone paver base, wet, compact until hard, dry 24 HRS, drive small sections of rebar (2ft or so) into the base to form 2 squares inside each other, tie in the wire mesh elevated about 1 1/2" from the base, pour your slab. The fiber treated concrete really DOES hold up better, it is especially good for resistance to cold cracking caused by micro water intrusion during the winter. Cure for 1 week or rapid cure by covering with plastic and treating with water.

As far as other base methods go, I'm currently using a paver base framed by 6X6's. This is working well, staying nice and level. My only issue is that feet (especially LITTLE feet) pick up quite a bit of sand from the paver filling and transfer it to the tub. This is a pain to clean out. If I had to do it again, I'd pour a slab where my tub now sits. BUT, that's just ME....

Drewski

[hawkman]

I read somewhere if you use rebar you need to ground your concrete pad before putting the hot tub in.

Under my concrete, we just had sand.. no gravel.. It pays to get a good contractor first!

The pad is part of a larger pad and there are joints cut into it..

[Brewman]

I'd check on the rebar grounding thing with your local inspectors- not sure how that rule is being interpreted or enforced.  Local authority could clarify.

[mattNY]

The FOOLS that put in my driveway at my new house apparently didn't understand this principle which is why they now refer to me as "plaintiff."

Lol Drewski.

I just had a 4" slab put in, 12x16.  They excavated, tamped the area, put down 2" of crushed stone, and had wire mesh throughout the slab with additional rebar where the hot tub was.  I covered the slab with plastic and watered occasionally for the next 3 days, then they came back and cut the expansion joints (one down the middle, in each direction, so 4 8' x 6' rectangles) and caulked the joints.

I called several contractors for estimates, one told me the wire mesh was essential, another told me I could get a fiber mat instead, and yet a third told me nothing was required, but all of them recommended crushed stone as a base.

To answer your question, if the cracks are small, I would get the tub removed, smooth them over with some concrete patch, and set the new tub in place once it's dry.  It'll most likely be fine for quite a long while and only cost you $20 instead of $2000.

[Jack_L]

I had a 15'x20' slab poured.  The only prep done was that I removed all of the sod then the guy poured the concrete over top the dirt.  There was one crack that appeared about 1 month after the pour but it really doesn't matter because we are going to put slate tiles over top of the concrete whenever the weather gets better so that I will have a week or more of guaranteed dry, warm weather.   I'll post photo's when done.

[hawkman]

I had thought about putting tiles over the slap to make it nicer as well. MY dad did that to a porch.. One warning.. it becomes slippery.. Maybe you can find some that don't get too slippery when wet. When I walk on his porch, I need to go very slowy as it is very slippery.

Good Idea on the concrete patch stuff.. I might try that out.

[Brewman]

I had a 15'x20' slab poured.  The only prep done was that I removed all of the sod then the guy poured the concrete over top the dirt.  There was one crack that appeared about 1 month after the pour but it really doesn't matter because we are going to put slate tiles over top of the concrete whenever the weather gets better so that I will have a week or more of guaranteed dry, warm weather.   I'll post photo's when done.

You had that large of a pad installed without any prep other than stripping off the sod?  No gravel base or other support?
If that slab shifts and cracks more as the months/years go by, your tile job will very likely suffer.  The tile quality will suffer if your slab moves.  
In this area- that slab would be a mess after one harsh winter- hopefully you live where the ground is more stable.

[hawkman]

Im going to resurface the concrete tomorrow using Quikrete resurfacer. I only have hairline cracks and this will fill them in while giving a new surface.

It the damn thing cracks again, the hell with it. These fly by night concrete contractors piss me off. Next time I will have a contract of my own waiting for him and if he doesnt sign it, no work for him.

I have sand underneath and then a hard ground. There hasnt been any shifting of the concrete other than the hairline splitting. Resurfacing will cost me $200 so we will see. I will post some pics.