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Old 02-25-2007, 06:50 PM   #16
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Originally Posted by concretemasonry View Post
The hammers for measuring the apparent strength are only for professionals (not contractors) since you have to interpret the hammer results.

They only give you the compressive strength (within 10 to 30%), but what good is that? You still have to know the minimum slab thickness for it to mean anything. The concrete can have any compressive strength, but if you do not know the minimum thickness, it is worthless.
Used with other tools such as a drill to find the depth and by an experienced engineer it is a great tool. No one tool can give you all the information you need. And most contractors are professionals where I live. Most have a very strong knowledge of engineering principles I would hope. The hammers we use have a chart on them to convert the reading to PSI. If you can read directions you can figure it out. Or if in doubt call an engineer. Engineers specializing in structural inspections are more likely to have one than a contractor.


Last edited by Jeff4Sun; 02-25-2007 at 06:55 PM.
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Old 02-25-2007, 08:32 PM   #17
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Well so let's say the car lift spec says the customer needs a min 4" of 3000 PSI

First, what's a "normal" thickness for garage floor concrete?

If the guy found out he's got 6" of concrete, wouldn't it be a pretty safe bet that he'd be fine? It'd have to get tested before the lift goes in, but at least the customer would know it's worth the cost of bringing a pro out to get it certified.

---- can the floor get "certified" or how would that work?
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Old 02-25-2007, 08:52 PM   #18
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As an experienced engineer, you are trying to beat a dead horse with details. The hammers are fun toys to play with, but I would not stake my life on the results.

It is difficult to get old concrete less than 3000 psi, but you have no idea of the minimum thickness unless you drill enough holes, when you eventually weaken the slab. - The minimum, not the average is what will control any failure.

There is no such meaningful thing as an average floor thickness. It could have been installed correctly or it could have be a "DIY week-end special" that was made trying to keep the cost to a minimum and fool the inspector for a shallow victory!

If you or someone else will be working on a vehicle held up by the lift and are injured you will get no satifiaction from a manufacturer's guarantee or an insurance company.

Just put in the lift according to instructions - it will be cheaper, easier and safer.
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Old 02-25-2007, 08:58 PM   #19
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