MGW-Fla

Thanks Jeff for yours & others' valued input on this. I still haven't installed mine yet. Friend who is a CGC helped me last fall start with the planning & we stopped after drilling pilot holes & found the slab was just 3 1/2" thick. More concern was when we blew out one of the pilot holes with a compressor & muddy water sprayed up. The fun of living in Florida & the nearby water table. We stopped at that point. I called Gabe at GES & he sold me the 5 3/4" Power Serts with the epoxy. He assured me they would work, since one anchor alone is supposed to have enough holding power by itself.

It is discomforting thinking about the longer lengths of the two different anchors GES sold me and using them in just 3 1/2" of slab. The biggest concern wasn't the holding ability of either the Power Drop or Power Sert anchors. The major concern is the stability of the concrete. Especially with the 3 1/2" thickness & the known potential for the concrete to "cone" on the underneath when the hole is drilled.

The CGC has a friend & former co-worker who is an engineer that is supposed to stop by & look at my slab in the next week or so to give his thoughts. We had already considered cutting out two 2'x2' areas and pouring a thicker slab, and of course tying it in to the existing slab with rebar. I like the idea of just making it one 2'x13' area to allow for a multiple width set up in mounting on one side. The time, cost, & mess with the concrete dust the cutting will create in my garage was the apprehension there. Also sounds like with the high water table, I might will need a hydraulic cement.

We also wondered about just getting either two 2'x2', or one 2'x12'-13' by 1/2" thick steel plate(s) made & installing those under where the posts would go. This to add stability, spread the weight distribution, & add to the overall thickness. I'd appreciate yours & others thoughts on that possible solution?

Thanks!
Mel

depami

Anticipating your CGC's opinion on 3 1/2 thickness.

That was a good write-up but I question the relevance of the epoxy if the anchors move after cure. Or is it mainly a filler to prevent loosening through movement over time?

Also, I was taught to never vacuum concrete dust. It is fine enough to go through filter and then you breathe it.

dr bob

Hmmmm.

I gave serious though to embedding steel plates in the concrete under my current garage, with threaded inserts welded to the steel, but quickly decided that wouldn't help unless it was under the concrete, and I'd still need reinforcing in the concrete above the steel. The other option I am now considering is replacing a 12x24 porcelain tile in my new garage with a steel tile where the lift will mount. All the serious experts say it is't necessary, that I can just diamond-bore the holes in the tile where the bolts sit. I can decide after a tile fails I guess.


The situation with the water directly under the slab needs more pro attention. Depending on where you are in Florida, the high water plus the various minerals may be leaching something important from the concrete you have. My dad's house sits in an area that used to be a dairy farm 50+ years ago. The concrete pads there are more like plaster these days with the damage done by water in the contaminated soil all those years. Meanwhile, the too-regular CNN features on sink-holes in Florida would cause me to do a most-careful survey of soil conditions under the slab.

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The instructions with the lift tell you to drill and set the first anchor, then place the post and drill the other holes using the baseplate as a guide. My new 7/8" SDS bit would not fit through the holes in the baseplate, either on my lift of on Rob's. We did some careful measurement, double-checked said measurements, and set cross-marks in the floor for drilling. I used a sacrificial center punch to dimple the concrete where the lines indicated centers, drilled a shallow pilot hole, then the full-depth holes with the 7/8" bit. Keeping the drill vertical is a challenge, but the biggest concern is drilling a straight hole. If the top of the drill is moving around, the holes won't be straight or round. Any wobbling at the top of the drill motor only makes the holes bigger wherever the cutting tips happen to be in the hole, so you get odd muxhrooms mid-depth that you can't see from above. You can watch the progress from above, though, and make sure that the barrel of the drill bit stays centered in the top of the hole as you pressure the bit. The anchors take a bit of effort to set in the holes, and if they pass through with less pressure than my 3# sledge will deliver, the hole may not work with the supplied anchors. Looking at the anchor, there's a ring around a slightly cone-shaped section. As the anchor is drawn up, friction on the concrete hole wall causes the ring to tighten around the cone. Utimately, pulling up on the bolts is trying to expand that ring, which is restrained by the tensile strength of the concrete. Meanwhile, there's 1800 lbs pressing down on the baseplate, testing the compression strength of the concrete. Garage floor concrete specs start at 3000 PSI cabability these days, plenty enough to hold the car sitting on four little tire contact patches. The baseplate size for the lift is probably greater than the two tires worth of contact area, so it's fair to suggest that a floor that will hold the car up will probably hold the car on a lift. Better to suggest that a floor that will hold half the car weight on the two front wheels of your floor jack should be able to safely hold the same weight distributed over the area of a lift column baseplate.

Others in other places (GarageJournal among others) have done the bolt (and anchor) loading calcs. I won't draw a conclusion for you, other than saying I feel perfectly safe working under the car on the lift, perhaps much more so than working on jackstands at higher extension lengths.

Rob Edwards

I think that the risk of contracting cement dust pneumoconiosis due to a couple of minutes exposure to cement dust is a heck of a lot lower than the crush injury resulting from crappy hole prep when mounting a maxjax. I brought home a few large bottle brushes from the lab, and thoroughly brushed out the drilled holes in conjunction with compressed air and the shop vac for cleanup.

Murphy's law being what it is, we also ran into some rebar about 3" down in the 10th and final hole we drilled. I therefore have a very low mileage Bosch SDS 7/8" rebar cutting bit if anyone ever has need during their Maxjax install.

the flyin' scotsman

can a test hole be drilled with a regular drill and concrete bit or do we need the heavy duty drill?

Im placing the lift order tomorrow as the special is still available through Costco Canada.

oups59

I need one....I want one....

MGW-Fla

Interesting, so do you think having a 1/2" steel plate on top of the concrete would not solve the problem if they were permanently anchored to the concrete?

I'm in Jacksonville, northeast corner of the state, bordering the Atlantic Ocean, one county south of the state line with Georgia. Sinkholes do happen here, but not nearly the same frequency or magnitude of those in the central & west central parts of the state. Those areas have a base of limestone beneath, which is why it erodes more easily & in larger areas, to result in the scary big sink holes. The ones you see on tv are almost always from those parts of the state(Ocala, Orlando, Tampa).

The part of Jax I am located in, there is clay hard pan really close to the surface(typically 6'-15' I've been told). The hard pan does not percolate very well & not nearly as fast as the surface dirt does. The result is like a river running under the surface with the water that has drained through the surface dirt, but not yet through the clay hard pan. With the amount of rain we have here, I've done lots to enhance drainage away from the house, but its still always something to keep an eye on.

I realize that the description of a river running under the surface paints a picture just as likely for things on the surface to sink, crack, degrade, leak, etc. The driveways in my subdivision held up well the 1st 15 yrs, but most, including my own, have lots of cracks in them now. I can't think of any worth any real concern in my garage slab though. I have reached out to a company that specializes in concrete foundation repairs. Waiting to hear back from them. I'd like to get their expert opinion & see what they suggest. If its cost effective, I'd like for them to do the cutting & pouring for a thicker slab area to mount the posts.

Had some of the same thoughts of the hole drilling process. Most homes built here in the past 40 yrs had specs for 2500 psi concrete. But after 28 yrs, I'm certain mine has hardened to the 3000 psi level. The bigger concern is the thickness and the resulting potential for instability at some point.

I'm encouraged by your comments regarding the comparison of the tires & a floor jack being able to hold the car without the concrete cracking versus the lift column base plate. That's a great comparison.

Calgary Ole

Best is a good heavy duty hammer drill but up here where you and I live this is what you will probably find.
- 3 1/2" to 4" 32 mpa concrete
- 10 mm rebar on a 24" grid drilled in to 8" foundation walls that are a minimum 4' below grade
- 4" to 5" gravel on either 'compacted soil' or a series of Sonotubes if not compacted. Probably 4 or 5 tubes for an average size attached garage.

You will also have approx. 2% slope to the door

dr bob

You can use anything really. Just make sure that, if you intend it to be a pilot hole for one of the MaxJax anchors, you drill it straight. I've used thise little 1/2" percussion/hammer drills to drill small holes and set smaller wedge anchors. It takes a while in serious concrete though, and the holes tend to be large from the bit dpoing more bouncing than cutting. Flip side is that you can rent and SDS drill and buy the 7/8" bit for not a pile of money, and be sure the holes are pretty straight. Plus you'll likely finish the drilling the same day you start. One thing you quickly realize is that you only get one chance at each hole. If you miss on location, wallow out a hole accidentally, drill at an angle or end up with a hole that isn't straight, your only fall-back is to drill larger and set the anchors in epoxy.


I decided to buy an SDS drill on sale at Harbor Freight years ago, and it did the job just fine for my floor and for Rob's. The kit from H-F doesn't include a 7/8" bit, and considering the failure mode I deided to buy a real Bosch bit from Home Depot for the actual installation. As Rob mentioned, we found rebar on the tenth (last) hole of his installation, so a rebar cutter was added to the mix for his floor. As far as the H-F SDS drill, it's not quite as zippy/powerful as the rental Bosch drills I'd used previously, but it's been more than adequate for the occasional lift installation. I've also used it to set anchors for eyes in the south retaining wall below the house here, so I can practice my rock climbing skills while wearing a backpack tank of brush killer, a chainsaw, brushcutter, or a bag of tools to repair a drain pipe or three. It's 50-75' down to the public road below. I'm still here.

dr bob

Malcolm-- I suggest that you order extra anchors with your lift, so you can add some column placement options. It takes three more anchors to move the column 5" in or out. I bought ten extras, used some for extra spacing options and kept spares to install where the columns live when not in use. The ground moves here, so bolting the columns down even when stored seems prudent.

Rob and I both decided to mount the power unit on the wall, (as have oters who inspired us) and get extension hose to reach the columns. The unit comes with a couple ~~10' hoses, which are just long enough to put the power unit in the mid front or rear of the car to be lifted. I added a single 10' hose, with quick-disconnects redeployed strategically. The hoses hang on a hose hanger over the power unit on the wall when not deployed. Rob added some black PE drain piping in the ceiling during construction, and has the hoses routed up that way to keep them completely off the floor. If you do route the hoses up, you MUST bleed the system completely with the hoses low, and only then put them up in whatever overhead hanger system you use.

the flyin' scotsman

thx Ole.......would you have an opinion on how our frigid weather affects the concrete? ok to drill when -20c or wait 'till spring?

the flyin' scotsman

thx doc Bob.....the garage roof is open so the hoses could be strung in the rafters until its enclosed which will have to be done to extend the garage work season; too cold otherwise.

Calgary Ole

No problem drilling in the cold weather. Check to make sure the fill under the slab has not settled leaving a void. It can be re-enforced if needed to properly support the hoist but can be a little tricky in our freeze/thaw climate.

dr bob

Rob can share some of what he did for the hose pass-through in his garage ceiling, which is directly under living space in his house. For our new house, I looked at what kind of room would be needed to pass the QD connectors through, but I have storage/crawlspace access directly above where the lift will go so no need to embed a pipe in the ceiling as Rob did. His garage-build thread includes some details like power and air connections above the columns too. His lift does full-time duty with the race car on it, so having permanent power and air plumbed above the columns for drop-down stations is very convenient.

Rob Edwards

Yeah, I used a 10' length of 2" ABS pipe with large-radius 90-degree ends on it, and just strapped it to the side of the joist. The blue tubing is Rapidair, for compressed air.

Neither the builder nor the city inspector had any problem with the ABS pipe.




Per Dr Bob's suggestion I bled the hydraulic lines and got the system running with the hoses on the floor, to avoid trapping air in the overhead lines. Then I removed one of the quick disconnects, placed the hose end in a ziplock sealing sandwich bag, and pushed it through the overhead tubing. Ended up losing almost no fluid that way.

Bleeding hoses:



FWIW, the sealing plug on the reservoir is crappy, I got a replacement from Danmar but you might get lucky. Best to wrap it with some PFTE tape.

Pump mounted on wall. You can see the opening of the ABS pipe for the hoses in the finished ceiling: