Sunday, November 12, 2017

Is your concrete flat?

How to get a flat concrete garage floor? I posted the information below on a forum when I was researching how to specify a flat garage floor and what standard of work could be expected:

What does flat mean? First of all, flat does NOT mean level.

Flat: smooth and even; without marked lumps or indentations. No concave or convex areas. A vertical wall, sloped surface or level floor can be flat (a flat surface can be sloped).

Level: a perfectly horizontal plane with respect to the distance above the center of the earth. A bubble level will show this to be level in all directions

On the high end of concrete floors, you can have "super flat" concrete installed, they do this particularly for warehouses that have high lifts and robots that run in the isles. However, this requires laser guided machines than smooth and flatten the concrete. I don't think many of us are going to do this for our relatively small backyard garages or shops.

There are some standards for flatness and levelness and these are measured in FF (flatness) and FL (levelness) numbers. And these are not easy things to measure. The sell special gizmos to do the measuring. Essentially, measuring with a long straight edge isn't really acceptable, because each person who measures will measure differently. The other obvious problem with using a straight edge is that what you really want to do is hold that edge just above the plane of the floor and then measure below it, you don't want to just lay it on the floor. Companies make cool gizmos to actually measure FF and FL, and they are pretty sophisticated (see

I called a bunch of concrete guys. Essentially, none were willing to commit to a standard like "less than an 1/8" dip below 6' straight edge anywhere on the floor". After my floor was poured and I wanted to make it flatter, I also spoke to a couple grinding and polishing companies that sounded interested in "flattening my floor and they said "oh we can definitely make it flat", but as soon as I mentioned my 6 foot straight edge they lost interest. No one had a plan or a method to make the floor flat. No one said anything about flooding the slab and marking high spots, or anything like that. No one owned an electronic dipstick to measure flatness. I suspect this stuff just doesn't happen in standard residential construction.

I did find one company that seemed pretty competent at flattening concrete floors and their info mentioned they do "slab correction". This guy does lots of work including warehouses that use high lifts that really need flat floors. Essentially, he said my floor was "normal" for work these days (sadly). He could make it better and wasn't wildly expensive, he'd charge just somewhat more than a regular floor polishing for the extra time and effort. But he questioned making an effort to get it really within 1/8".

I found this chart online:
"Although there are no direct equivalents between F-numbers and straightedge tolerances, ACI 302, "Construction of Concrete Floors and Slabs," gives the following table of approximate values:

F-number Gap under an unleveled 10-foot straight edge
(fraction of an inch)
FF12 1/2
FF20 5/16
FF25 1/4
FF32 3/16
FF50 1/8

Apparently typical concrete floors are in the FF20 to FF25 range. I did find this statement: "Although "1/8th inch in ten feet" has been used to specify billions of square feet of concrete, it was seldom, if ever, achieved. The typical industrial floor, for example, is closer to a 5/8th inch deep envelope, rather than a 1/8th inch deep envelope."

A big issue is that typical concrete guys never check their work. How many visit the site 30 days after the pour and measure the surface with a proper dipstick style gauge according to the standard? So essentially, your residential concrete guys do not really know how good or bad their work comes out!

I'm a geek, so when my concrete cured enough to walk on, I went out and tried a 6' straight edge all around the floor in a grid pattern. I really tried about 40 placements. Only one area was out of whack. Mine may not be that great, but I also suspect very few people have garages that would really meet the FF50 (1/8") standard.

On contracts. I've been around the track a couple times and I understand these things. It sounds great to have everything specified in a contract and to have it be enforceable. In my case, I didn't know enough to ask the details about flatness, let alone specify something. But at least around here, it wouldn't be easy to even find a residential contractor with a dipstick gauge who would commit to an FF number. The other problem is that the residential finisher is usually a subcontractor who makes a modest wage. Even the head contractor , unless he is a big outfit, isn't in a financial position to "replace your foundation" if it doesn't work out. Certainly, the finisher, who is maybe making $250 to $1000 is going to disappear before buying you a new slab. I personally think you are just far better off trying to understand what you can get, checking references, and looking at similar work than expecting the contract to make it "all right". In my case, yes, I wish the floor was better in one spot, but I can live with it and I'm not going to make others pay for something I didn't understand well enough to demand better.

So, in conclusion:
I'm no expert on concrete, but having done this once, and read some others advice; here are my recommendations:
- You aren't going to get a "perfectly flat" floor, especially with high PSI concrete poured on a warm dry day.
- It seems harder to make a floor with a curb (stem wall) around the edge flat (especially with just one pour) than a slab without a curb, as the finisher cannot use the top of the form as a guide when there is a curb. If you are going to have a curb/stem wall, perhaps look into doing the floor as a separate pour.
- Talk with the actual finisher, not only your general contractor, about what he can do. Make sure he knows this is going to be your "pride and joy", not just another lousy garage. Make sure he has a wide bull float and will run it both ways, North-South and East-West. Is there enough room to run the float both ways or are other buildings in the way? Go see similar work he has done and if it matters bring a dipstick or at least a straight edge. Does he own a dipstick? Has he ever returned to a job after it has cured and tested the floor's flatness?
- During the job, have him show you it is flat, while it is wet. Maybe they can go out with skis and show you a straight edge on the surface.
- Don't let any of the finishers hang out on their skis on the floor. If they stay in one spot too long they will make a depression. (My low spot just happens to be were a finisher hung out playing with his phone while he waited for the concrete to get a bit dryer.)
- Lastly, If you can get it close to a 1/8" gap under a 10 foot straight edge, you are doing amazingly well. 1/4" is probably more reasonable.
- Be present during the pour and finishing, ask questions, and make them do it right.

PS: On sloping the garage floor vs making it level: 
Most people slope the garage floor so liquids will drain toward the car door opening. This can be particularly important in places where it snows or rains significantly, and it maybe part of the building code.
Often, concrete finishers who slope the concrete significantly care much less about flatness. The more the floor slopes, the less likely water will puddle! Typically, builders who slope floors do at least 1/8 inch per foot (1 inch in 8 feet). If the floor is sloped sloped significantly, many people will want to level things like workbenches, shelves, and floor mounted tools with leveling feet. And if you must have leveling feet for the sloped floor anyway, flatness may not matter as much to you.
But be careful with floor slope; some builders will slope the floor as much as 1/4 inch per foot or more. That would be 1 inch of slope in 4 feet. It's also 4 inches in in 16 feet. Many would consider that too steep for many garage uses.

Wednesday, November 1, 2017

Proto, SK, old Husky USA (and Tekton) Combination wrench comparison

Proto, SK, Old Husky USA (and Tekton) Combination wrench comparison

(Top to bottom: SK, Proto, old Husky USA; 7, 14, 22mm)

It was my birthday recently, and after a beer I decided that maybe I should upgrade my old Husky USA metric combination wrench set. Now I love my old Husky's and have had no issues with them. The only negative thing that comes to mind is that on some heavy pulls the narrow beam can dig into my hands a bit. But otherwise I really like the almost dainty, jewelry like feel of the polished Husky USA wrenches. (I also have heard that some older Husky tools had some issues with the "made in the USA" mark, but regardless, the quality of mine has been fine.)

I should also say I work on old vintage stuff and I do some restoration work. I cannot really accept wrench damage to my fasteners. I typically use 6 point sockets on everything I can get them on, and I use box end wrenches occasionally and only use open end wrenches when necessary or it doesn't matter (like spinning an already loose bolt or working on something that I don't care as much about). I don't want any special ridges or teeth on the open ends that could "bite-mark" the nuts and bolts, so that eliminated Wright tools' WrightGrip and some of the other options.

Also, all my work is metric, but recently I ordered an inexpensive Tekton SAE set for those rare occasions I need a wrench with inch markings. (I won't reveal the horrid tiny open end wrenches I had been using when necessary before that!) So I have those Tekton wrenches for comparison too.

After finding I had a couple different brands of wrenches in my hands I thought other people might be interested, I decided to take a couple minutes and write this review comparing the sets.

First I ordered a full set of SK, the "SK 86224 SuperKrome 19 Piece 12 Point 6-Millimeter to 24-Millimeter Combination Wrench Set", $244.74 from Amazon. This arrived promptly, but I was surprised that this ships from SK in a brown cardboard box with the wrenches jangling inside a plastic bag. No individual cushioning or packing material at all. Also included were two plastic rails to hold the wrenches in your toolbox, but they were nothing special. The wrenches themselves seemed properly made (I saw a previous garage journal poster had some issues with his set). Some had a tiny bit of marking, possibly from shipping or storage, but nothing they wouldn't get with some light use. They seem to have a fatter beam, and that may be more comfortable to some in the hand. But, I was surprised how short they were, especially the small sizes! I don't think my old huskies were "long", but as I said, I was surprised. Short wrenches can be a great thing as they can help prevent over-tightening, so maybe that is good. I would think that being fatter in the beam would make them heavier than the other brands, but being shorter seems to even things out. I noticed that the open end's aperture is a bit less deep than on my old Husky USA wrenches. That seems functionally fine, just different. The SK size markings are only on one side of the wrench, which can be could be an annoyance. Very nicely, the set includes all the full millimeter sizes from 6mm - 24mm.
For me, in summary, I wasn't thrilled by the hand feel / extra thickness of the larger SK wrenches, the small ones looked tiny to my eye, and I just wasn't convinced I preferred them to my old Husky USA wrenches. Now, I should say, if you like a fatter wrench, without any open end gimmickry, you may love the SK wrenches. I do particlualy like the sweep of the wrech up to the box end.

So then, not being perfectly happy with the SK set, I ordered a set of Proto wrenches: "Proto J1200RM-T500 17 Piece Full Polish Combination Wrench Set, Anti-Slip, 7-24mm", $239.66 shipped from Zoro. These arrived in a colored cardboard box in a red cloth tool roll. I must admit I preferred this to the way the SK's clattered in the box. To my surprise, the Proto's are VERY similar to my old Husky USA wrenches. A quick bit of research showed the old Husky USA wrenches were likely made by Stanley/Proto. Hmm. The new Protos seem to be the same as my old Huskys except for the antislip design of the open end and they are just a bit longer and some have with a bit more angle on the closed end. To my eye, the "antislip" design seems to be just a bit of relief where the outer corner of the nut would be, so that most of the force falls away from the corner. There are no sharp ridges or teeth. For me, working on restorations, that seems good. Below size 10mm, the wrenches have normal open ends (no antislip design). I note the Proto, like the Husky, conveniently have size labels on both ends of both sides. It's dissappointing the Proto leaves the 23mm wrench out of this set. (Interestingly, my old husk set from 7mm to 22mmm skipped the 20mm! Who makes thses silly decisions?) Adding the 23mm and 6mm to the Proto set so it has the same sizes as the SK set would cost an additional $58 on Amazon.

Frankly, all of these wrenches seem good. Even the Tektons look nice next to the higher end wrenches. On the SK side, for the very close to the same price as the Proto, the SK set is more complete including the 6m and 23mm sizes. Personaly, I prefer the familiarity of the feel of the Proto (so very similar my old Husky) and I want to try this Anti-Slip Design" stuff. I'm hoping it will be a bit better than standard, and won't mark my fasteners.

On the other side of all this, I've found my old Husky USA set looks pretty good compared to these new sets. Frankly, when I place my first order, I had expected a bigger difference from the SK and Proto sets. If it wasn't for a little interest in this Anti-Slip design stuff, I would not not bother with anything newer.


(Top to bottom: SK, Proto, old Husky USA; 7, 14, 22mm)

(Top to bottom: old Husky USA 14mm, Proto 14mm, SK 14mm, Tekton 9/16")

(Same as last picture, other side of wrenches. Note SK has no size markings on this side)

(Proto Anti-Slip design on 14mm wrench)

(Proto Anti-Slip design on 14mm wrench, other face)

(SK above Proto; 7,14, 22mm)

(Proto above old Husky USA; 7,14, 22mm)

(SK above Proto; 7mm)

(Proto on left, SK on Right; 7mm. Note deeper aperture on Proto)