MaxJax Question/Maybe dumb question

[bdeutsch]

Jay Leno's website contains a video clip on the MaxJax and found that last year there was a group buy for this item. Think that in the next couple of months I am going to purchase these for my garage.

Here is the question. Based on what I heard on Jay Leno's video, the anchors used to secure the lifts to your garage floor must be set in a minimum of 4" of concrete (which given the weight they support makes sense).

I am wondering though whether your typical garage concrete pad is in fact 4" think. Suspect it varies from state to state, but 1) how do you find out the depth of your concrete garage pad (do you just drill a test hole perhaps?) and 2) if concrete pad is not the required 4" depth, is it just a matter of having a contractor come in, tear up a hopefully small portion of your existing pad, dig a little deeper, then pour the new area? I am guessing that it is a bit more complicated, but simply do not know.

As always, appreciate the help.

Bob

[bdeutsch]

Guess I needed more coffee...ughhhh

Bob

[rustyBob]

Dats ok Bob naut evrybdy iz a mornin prson.........
I say drill a test hole and see what you got.........
a friend of mine had to cut 16"x16"x12" holes in his floor
and fill them with rebar and high strength concrete to
put in his lift......and he did it himself....

[bdeutsch]

Bob, thanks for the response and now a bit more alert this end...

Anyway, perhaps a better way to ask my question is to poll all MaxJax owners to see how many had to repour a portion of their garage concrete pad in order to meet the 4" minimum?

Thanks,

Bob

[Silverback51]

If you do have to cut the floor and pour a thicker slab, be sure to tie it into the existing slab with rebar. If you don't, that new pour will float relative to the existing slab and you will have all kinds of problems. The rebar should be on 6 to 8 inch centers.

[madmaxx]

go buy a 4 post lift, they do not need anchored. I would think the whole floor or larger than 16x16 would have to be replaced. I imagine the bending moments on your bad can get pretty high. 2000lb times 4 feet? = 8000 ft-lbs of torque, it does not seam a 16x16 square would not pop out off the ground and let the thing turn over.

[Silverback51]

Originally Posted by madmaxx

go buy a 4 post lift, they do not need anchored. I would think the whole floor or larger than 16x16 would have to be replaced. I imagine the bending moments on your bad can get pretty high. 2000lb times 4 feet? = 8000 ft-lbs of torque, it does not seam a 16x16 square would not pop out off the ground and let the thing turn over.

As long as it's tied into the existing slab he will be okay. Otherwise you are correct. I would pull out of the floor.

Here is a link to how to tie into existing slabs.

http://www.finehomebuilding.com/how-...ete-slabs.aspx

Also, you need to maintain a 1 to 1 ratio between depth of the anchor to the edge of the slab to avoid break out. This means with a 4 inch anchor, you have to have a minumum of 4 inches to the edge of the slab, or slab joint.

[rustyBob]

He told me that he had to flair them at the bottom so they would not pull up thruogh the old floor and he did tie it into the existing concrete with rebar that he had to epoxy into the existing cancrete....

[Silverback51]

Originally Posted by rustyBob

He told me that he had to flair them at the bottom so they would not pull up thruogh the old floor and he did tie it into the existing concrete with rebar that he had to epoxy into the existing cancrete....

If you do that you are subjecting the concrete to tension loads without any rebar reinforcement. Concrete is very strong in compression, but it sucks in tension.

I would not risk my car, or my life by using a tapered cut to retain the new pour.

[bdeutsch]

Thanks for responses to my question.

Given that garage pad is likely less than 4", likely that I would need to find somebody what they are doing with high strength concrete (why do I suspect that this means $$ )

Just guessing, but suspect that after everything done and said, looking at least the cost of the lifts to get this type of work done...

Bob

[bdeutsch]

what Bob meant to say...

"that knows what they are doing with high strength concrete"

Bad day for me to be working a keyboard it seems.

[madmaxx]

You are putting your life in the hands of the concrete installer, usually not rocket scientist unless they are pouring slabs for lathes and other machine shop equipment and then you are talking $$$$$$ if the even touch it. All concrete is 3000 psig it is the rebar pattern, are they using a vibrator to ensure no air pockets, what about the anchors, epoxy very strong as long as you follow the instructions EXACTLY. Most drill the hole to large or rotate the fastner when installing.

Not worth it and I am one to take risk. In reality the only purpose for concrete is to maintain the spacing on the rebar!!!

[madmaxx]

An interesting side note, 99% of concrete cracking is due to the water permeating the slab and rusting the rebar. When the rebar rust it expands and cracks the concrete. Coated rebar, fiberglass rebar is just around the corner. i agree the mesh is a horrible option. Reviewed the email on tying in the slab, looks pretty good, i am no structural engineer though.

[slider701]

I think there are more stuff you need to take into consideration than just the thickness of the existing slab. The first thing I would be worried about is whether you have a tension slab foundation and garage floor. If you live somewhere that you have a basement in your house you probably don't, but if you live where you don't you may have a tension slab pad under your house.

In the photos below you can see the large red cables that span the foundation:





On my house new house in Texas they dug a ratwall about 3' feet deep around the perimeter of the foundation and also in a H pattern about every 8 feet that was 3' deep. Then they run tension cables across the foundation that is cable shielded in a plastic sheath. They also use a wire mesh which is not shown in these photos. When the slab is cured they tighten the cables up to pre-tension the slab to keep it from cracking. If you have a tension slab floor you have to make 100% sure you don't cut through them or you're screwed.

The other thing they did was place the plastic down as a water barrier to keep the water from making its way through the foundation since we have a high water table.

If you have a normal slab I would think of pouring a 24" x 24" pad that is tied into the existing foundation but you might want to think of digging as deep as possible (2 to 3 feet) and installing a 24" sonic tube over a bed of compacted sand/rock as a base material. From there tie your rebar on the top into a cage of rebar inside the sonic tube, essentially making a small pillar underneath the new section of floor you are pouring.

Might be way overkill but I believe that sometimes you can never over-engineer something, especially the footing for a hoist to hold a $50K+ car

Or you could just buy a 4-post hoist...............

[Bernica]

[quote=slider701;1019815]I think there are more stuff you need to take into consideration than just the thickness of the existing slab. The first thing I would be worried about is whether you have a tension slab foundation and garage floor.

This is a good heads up. You don't want to cut a post-tension cable (PT) if you have them.

If I was going to do this, and wanted to have plenty of peace of mind, I would cut approx 16"-24" squares at the two anchor locations, then dig a caisson (a round hole) approx 14" diameter and 3' deep with a post-hole digger. Then build a rebar "cage" that is 3" smaller than the hole on all sides, including the bottom. Make the cage with #4 (1/2") rebar running vertically resembling the shape of the hole, spaced approx. 3" apart with the top bent at 90 degrees and inserted all the way around the edges of the existing slab into drilled holes, approx 6" deep. Set these inserted "dowels" into the existing slab with epoxy made for this kind of thing (Hilti product). The cage should also have "stirrups" wrapping around it from top to bottom spaced 4"-6" apart. These are just more #3 or #4 rebar bent around the vertical cage. Use tie-wire to hold them in place. Next, find some good long anchor bolts (12" or more) and some threaded couplers with a size and thread pattern matching your MaxJac hold-down bolts. Make a template out of plywood with hole pattern matching the baseplate of the MaxJac and bolt it to the threaded couplers using spare hold-down bolts. Set the bottom of the plywood flush with the existing finished floor level and fill the hole with concrete (3,500psi or higher strength). After setting, when you remove the hold-down bolts from the template, you should have some sturdy and well-anchored inserts that will resist pull-out and tipping.
Overkill? Maybe, but like I said: If I wanted peace of mind.....

[Bernica]

After reading the above, I should have made it more clear that bottom of the threaded couplers should be threaded to the tops of the anchor bolts, which then extend further down into the caisson.

Hope that's all clear as mud......

[bdeutsch]

As always, appreciate all of the responses.

Coming to the conclusion, given I have absolutely no idea what kind of slab my garage sits on, that a 4-post lift such as a Backyard Buddy or something similar will likely be the one I end up buying.

Even if I knew of cement contractors who did this kind of work, suspect it would not be cheap plus, as mentioned in an earlier response, sight unseen I would have to trust that they knew what they were doing...

Bob