Saw cut(s) on garage floor

[grabeb]

Trying to find best spot(s) visually and functionally for the saw cuts. 26' wide x 32' long garage floor. They are pouring tomorrow.

I will be installing a 4 post lift on the rear corner. Plan is to place the lift 3' off the sidewall and maybe 2' off the rear wall. It might go closer to rear wall, because I plan to eventually tie it to an existing garage and will thus have 3' extra when that happens. The footprint of the lift is 17'7" long and 9'6" wide.

The stuff I read says don't place posts within 6" of saw cuts. I am installing a drain 10' off the overhead door and the pipe runs parallel to the front of garage at that 10' mark, so builder says 1 cut goes over that area as it'll 100% want to crack where that pipe runs. That'll leave 22' for the rest of the length. I believe if we come 10' off the rear wall or even 11' off rear wall, that might look best. 11' would be hard visually for anyone to notice and leave two 11' sections and one 10' section. I'm also thinking 10' off rear wall, matches 10' off front and leave a 12' center section. I also don't think either would interfere in any way with the lift lengthwise. Trying to visualize what might be best ???

For the width, what's best? If we divide the slab in 3 (2 cuts along the length) equal would be 8.6'. What about 9' from each side wall, so the center section would be 8 (again shouldn't be noticeable). I also don't think this would interfere.

Part of my reason for questioning is another builder says he prefers to place all his cuts within 3' of edge, then 1 down middle. That just doesn't work for my situation, but he says they all crack there. Haven't noticed that on similar sized neighbor garage, who has a 4" slab I believe and he didn't saw cut his and it's barely cracked at all. Mine slab is minimum of 5", most will end up being close to 6" because he was tired of building up the grade. We are going with 4000psi concrete and 1/2" (#4) rebar 2' OC's. The lifts require 3.5" of concrete 3500psi.....I wanted overkill just to be safe as I'll be lifting a 6000lb yukon xl at times and the added cost for 5" 4000psi wasn't that much. I think some 2 posts require thicker as well and if I ever want to change things up....

I've had various concrete guys quote various ideas on these cuts, so I'm asking some more to get my final thoughts. And yes, I'm very OCD, so if it doesn't look good, I'll be bothered by it!

 

[Leaflessshadetree]

10' x 10' squares are about ideal. At 26 wide either one down the center (13') or 2 spaced (8'8").
As far as the length 10'8" would be even spacing. Might work out with the drain or maybe move the drain so it does.

 

[wssix99]

I will be installing a 4 post lift on the rear corner. Plan is to place the lift 3' off the sidewall and maybe 2' off the rear wall. It might go closer to rear wall, because I plan to eventually tie it to an existing garage and will thus have 3' extra when that happens. The footprint of the lift is 17'7" long and 9'6" wide.

You should think this out more. Even with a 4 post lift, you still need to center the load. Your car or truck may overhang the footprint of the lift once centered...

The stuff I read says don't place posts within 6" of saw cuts. I am installing a drain 10' off the overhead door and the pipe runs parallel to the front of garage at that 10' mark, so builder says 1 cut goes over that area as it'll 100% want to crack where that pipe runs. That'll leave 22' for the rest of the length. I believe if we come 10' off the rear wall or even 11' off rear wall, that might look best. 11' would be hard visually for anyone to notice and leave two 11' sections and one 10' section. I'm also thinking 10' off rear wall, matches 10' off front and leave a 12' center section. I also don't think either would interfere in any way with the lift lengthwise. Trying to visualize what might be best ???

Most of your bed is already made...

You have to put a cross of cuts through that drain, as your builder pointed out. From there, your cuts should not be greater than 10 feet unless you specially reinforced the slab and planned for longer cut widths.

You can space the cuts closer together or space two close together so that you end up with a pattern that keeps your post feet far away from the cuts. (You should assume each cut will house a crack and the crack is what you have to keep the post legs away from IF YOU ARE BOLTING the lift to the floor.)

Part of my reason for questioning is another builder says he prefers to place all his cuts within 3' of edge, then 1 down middle. That just doesn't work for my situation, but he says they all crack there. Haven't noticed that on similar sized neighbor garage, who has a 4" slab I believe and he didn't saw cut his and it's barely cracked at all. Mine slab is minimum of 5", most will end up being close to 6" because he was tired of building up the grade. We are going with 4000psi concrete and 1/2" (#4) rebar 2' OC's. The lifts require 3.5" of concrete 3500psi.....I wanted overkill just to be safe as I'll be lifting a 6000lb yukon xl at times and the added cost for 5" 4000psi wasn't that much. I think some 2 posts require thicker as well and if I ever want to change things up....

There isn't anything related to engineering for your builder's preference. If he was getting cuts along the edge, it was probably because he was cutting the 22' dimension in half, which it a bit too much. (So, I would expect a chance for cracks along the edge in that situation.) Your builder's crack problem can be solved wtih 3' cuts along the edges or cutting the 22' section into even thirds. It's an asthetic decision.

The cracks some from shrinkage stress. If the cut sections go over 10', the chances of an out-of-control cut go up. If the cut sections are under 10', you get additional insurance.

 

[grabeb]

You should think this out more. Even with a 4 post lift, you still need to center the load. Your car or truck may overhang the footprint of the lift once centered...



Most of your bed is already made...

You have to put a cross of cuts through that drain, as your builder pointed out. From there, your cuts should not be greater than 10 feet unless you specially reinforced the slab and planned for longer cut widths.

You can space the cuts closer together or space two close together so that you end up with a pattern that keeps your post feet far away from the cuts. (You should assume each cut will house a crack and the crack is what you have to keep the post legs away from IF YOU ARE BOLTING the lift to the floor.)



There isn't anything related to engineering for your builder's preference. If he was getting cuts along the edge, it was probably because he was cutting the 22' dimension in half, which it a bit too much. (So, I would expect a chance for cracks along the edge in that situation.) Your builder's crack problem can be solved wtih 3' cuts along the edges or cutting the 22' section into even thirds. It's an asthetic decision.

The cracks some from shrinkage stress. If the cut sections go over 10', the chances of an out-of-control cut go up. If the cut sections are under 10', you get additional insurance.

Trust me, I've been thinking this out since about March. The lift I am buying is about as large as I can go in the 9000lb load rating. The Yukon XL Denali trim is about 6500lbs. The lift is 17'7" in length. The Yukon XL is 18.5'. I know there will be some centering but not much there. Most of the time it will be home to my 1960 Suburban, which is 16' long and only about 3500lbs.

No moving the drain for the previous reply, concrete is showing in the morning. We thought a lot about it's location. It's not near the lift.

Yes, the bed is made, so to speak, but the cuts aren't placed yet. I was wrong about the drain, It's 6' off the front wall, not 10'. We located it so the vehicles won't be likely to park a tire over it and block it. We also needed it away from the lift posts and ramps.

So with the drain at 6', that leaves 26' left to figure cuts. I think we're planning on splitting that into 13', though it is a bit over 10', hoping it is fine. I'll discuss more with him if needed....it isn't cut yet! Then we decided 7' from side walls of width might be best. That would leave a 12' x 13' section uncut in the very center and the back of garage. If that's unwise, we could go 8' from side walls and make that 10'x13', but if I ever needed to slide lift to center of garage that makes it a bit tricky.

I'm unsure if I'll ever bolt it down, but I might. I was told what concrete anchors to use if I do, to where I can easily unbolt if I want to move it. I know a lot of people don't bolt them down.

As for engineering....the concrete specs for the lifts are 3500psi 3.5" thick. I'm not only adding 1/2" steel on 2' centers, but adding at least 1.5", if not 2.5" of thickness and another 500psi to the concrete.....ohhh, you're saying his decision isn't an engineered one! Should I go with more cuts? Maybe 6' off both ends then and then split the middle? That would be 32-6-6 for 20/2=10'? For the width I could maybe do the same 26-5-5 for 16/2=8'? Largest slabs would be 8x10 then....hmmm! Would that look bad? Is that too much? That's 16 section!!!

 

[wssix99]

I would go with more cuts to get under 10'. Your personal challenge here is that you have gone thicker on the slab but are staying with the same rebar as a thinner slab would have. What that does is eat up some of the margin you would otherwise have to work with. (The thicker concrete cross section creates more shrinkage stress for that rebar to fight against.)

Cracking in concrete is a game of chance. The shorter your saw cut spacing, the more in control you are of your chances of having all your cracks in those joints. I've commonly seen guidelines for spacing of 10-12' on normal slabs, but since you have gone thicker per unit of rebar - I would err closer to the 10' mark. I defintily wouldn't push to 13.

The other great thing about the control joints is that you can fill them in after the slab cures without penalty. Let the slab cure, let it crack in those joints, and then you can fill them in with Ardex products or flexible fillers, depending on how you are going to condition the space. You can then epoxy the floor and it will look like a flat surface.

 

[grabeb]

Thanks, that helps a bunch!!

 

[Bucko]

Best to draw out your ideas so you then have a plan on paper. Also can he run a groover instead so you have a rounded edge. I think it looks cleaner but some guys have a hard time maintaining a strait line on a large slab. I've seen them lay a 2x4 down as a "fence" and then the finishers touch it up as they work the slab out. You can also come back and saw cut after the groove for a deeper relief area as long as they can follow the seam left by the groover.

I've done enough concrete to know that the professionals are magicians and I will never be as good as them.

 

[ConCretin]

Good luck with your pour. A couple final points; make sure he cuts the control joints 1/4 the depth of the slab and as quickly as possible after finishing preferably with an early entry or soffcut saw.

 

[glentre]

I was also OCD with my saw cuts and all my worries were unnecessary. Once you are in the garage and you have vehicles, tools, machinery and "stuff" on the floor, the saw cuts become much less noticeable and disappear to the eye as they kind of fade into the background. And, I didn't even fill mine because I thought the filler would make them more visible. Main thing as others have mentioned is to not get them too far apart. Even if not symmetrical, you will not really notice them once you are up and running in the garage.

Glen

 

[racecougar]

I was also OCD with my saw cuts and all my worries were unnecessary. Once you are in the garage and you have vehicles, tools, machinery and "stuff" on the floor, the saw cuts become much less noticeable and disappear to the eye as they kind of fade into the background. And, I didn't even fill mine because I thought the filler would make them more visible. Main thing as others have mentioned is to not get them too far apart. Even if not symmetrical, you will not really notice them once you are up and running in the garage.

Glen

Agreed. It might seem like a big deal at the moment, but as long as the cuts are made in nice straight lines, you won't pay them any mind once you start filling up the space.

 

[grabeb]

I handed my paper over to the concrete guy, but i think i finally decided on 6' from each end then split the middle.... on the 32' length. Then 5' from sides and split middle.... width wise. I'll have 5x6, 8x6, 5x10 and 8x10 sections. Hope that is good.

Same number of cuts but smaller sections. I'll likely fill before epoxy if for no other reason than to keep dirt and saw dust out.

 

[wssix99]

Sounds like a great plan!

 

[WarDamnEagle]

If it's poured with the right slump and kept wet for a week or two after the pour then you could get by with one cut in each direction down the middle. My 40 x 40 shop only has two cuts, one in each direction, and I have no other visible cracks. But the concrete guy knew what he was doing.

 

[wssix99]

If it's poured with the right slump and kept wet for a week or two after the pour then you could get by with one cut in each direction down the middle. My 40 x 40 shop only has two cuts, one in each direction, and I have no other visible cracks. But the concrete guy knew what he was doing.

Slump in itself has no impact on the shrinkage cracking we are addressing. (Having the wrong water content can cause problems, but that's a different thing.)

If you were able to get away with 20 foot spacing without visible cracks, then your contractor put other variables into play than the OP has put on the table. (You could have more reinforcing, a lower cement content, etc.)

I have some large slabs that have no cuts at all, but they are designed and reinforced for that. Odds are that your concrete guy knew something about slab design in order to space out the cuts.

 

[WarDamnEagle]

Slump in itself has no impact on the shrinkage cracking we are addressing. (Having the wrong water content can cause problems, but that's a different thing.)

If you were able to get away with 20 foot spacing without visible cracks, then your contractor put other variables into play than the OP has put on the table. (You could have more reinforcing, a lower cement content, etc.)

I have some large slabs that have no cuts at all, but they are designed and reinforced for that. Odds are that your concrete guy knew something about slab design in order to space out the cuts.

Agree slump has no direct impact, per se, but the finishing guys like to get the concrete truck to add water which lowers the slump, which increases shrinkage cracks. I probably could have explained that a little better. Keeping the mix as designed and wet curing the slab are as important as the the control joints in my opinion which was the point I was trying to make; albeit perhaps poorly.

I also agree that 20 foot spacing is above the norm and won't work for everyone.

 

[grabeb]

Well, I'm not going to pretend i know everything that went into the pour. It went very well and it's finished out nicely, the sun didn't hit it much and the day was fairly cool, so drying was slow. Not sure how slow in relation, but they opted to cut the concrete first thing in morning. They explained how the footing was a different 'dryness' than the slab and i think they did add an additive to the slab mix to give them working time. Don't recall what they said, but it's poured.

If adding cuts is a good thing, and this slab is way above the normal garage slab in the area and way more than spec for the lift, then I'll add more. Especially if i can hide them with a product that can be smoothed out prior to applying a finish such as epoxy.

 

[WarDamnEagle]

Good to hear that it went well for you. I would try to keep it wet for at least a week. Set up a sprinkler; use burlap bags and keep them wet; anything along those lines will help prevent shrinkage cracks.

 

[ConCretin]

Congrats on a successful placement!

I realize it's a moot point now but just for the record, slump absolutely affects shrinkage. It's the reduction of concrete volume due to water loss that causes shrinkage. The more water there is to lose, the more the concrete shrinks. Another good reason to limit mix water in concrete.

Curing is important. It doesn't change the ultimate amount of shrinkage but it slows it down to allow your concrete more time to gain the strength it needs to resist it. Btw, I'd avoid using burlap. It will stain the concrete.

 

[grabeb]

Congrats on a successful placement!

I realize it's a moot point now but just for the record, slump absolutely affects shrinkage. It's the reduction of concrete volume due to water loss that causes shrinkage. The more water there is to lose, the more the concrete shrinks. Another good reason to limit mix water in concrete.

Curing is important. It doesn't change the ultimate amount of shrinkage but it slows it down to allow your concrete more time to gain the strength it needs to resist it. Btw, I'd avoid using burlap. It will stain the concrete.

I plan to keep it wet. I won't use burlap, i don't have and am not buying for that big of slab. Concrete appeared to have very nice slump.

 

[wssix99]

I realize it's a moot point now but just for the record, slump absolutely affects shrinkage. It's the reduction of concrete volume due to water loss that causes shrinkage.

I think you mean that water content, which also often affects slump is a driver in shrinkage. (We can add things to concrete like fibers and admixtures that will change the slump but don't necessarily have a proportional effect on shrinkage.) I point this out because we can't really grab a slump cone and make cracking predictions from a reading. As pointed out earlier in the thread, one really needs to plan ahead, avoid taking short cuts, and engage a competent finisher to get the job done right.

I plan to keep it wet.

Where are you located? Certain parts of the country need to guard against fast evaporation and other parts - not so much.

What did your finisher tell you to do? For example, if they applied a curing compound to seal the slab, you may not need to do anything. There are also web tools that you can use to check your zip code and see if you are in an area where water might evaporate from your slab too quickly. (If that's a concern.)

 

[ConCretin]

I think you mean that water content, which also often affects slump is a driver in shrinkage. (We can add things to concrete like fibers and admixtures that will change the slump but don't necessarily have a proportional effect on shrinkage.) I point this out because we can't really grab a slump cone and make cracking predictions from a reading. As pointed out earlier in the thread, one really needs to plan ahead, avoid taking short cuts, and engage a competent finisher to get the job done right.

I guess I could have been more clear but you are correct. I was replying to comments specifically referencing slump, which to most is still an indicator of water content.

 

[grabeb]

I live in south central Kansas. I can't find any websites taking about specific areas where keep wet or not. I've kept it wet all day. Concrete guy just returned to grab his saw, he said no need since he cut it this morning. Hmmmm...... I've always heard to keep wet for several days. He did cut 1/4 of thickness he said, about 1-1/4". He speaks pretty good English, but I'm not great with heavy accents so hard to get all the info needed.

I'll add my Brother In Law, who I've been friends with for about 25yrs, which is longer than he's been family is from El Salvador and i still can't always understand him.

 

[ConCretin]

The purpose of 'keeping the slab wet' is simply to prevent the premature evaporation of the mix water in the concrete, which will slow the chemical reaction that results in strength gain. Some climates and weather conditions are worse than others but concrete always benefit from proper curing. Seven days is the generally accepted period for curing but longer is better.

 

[grabeb]

The purpose of 'keeping the slab wet' is simply to prevent the premature evaporation of the mix water in the concrete, which will slow the chemical reaction that results in strength gain. Some climates and weather conditions are worse than others but concrete always benefit from proper curing. Seven days is the generally accepted period for curing but longer is better.

So i should keep it wet until next Tuesday!??? Thanks

 

[charbar]

Im late to the party here so obviously it doesn't matter, but I honestly would be worried a single bit with a FOUR post lift close to, or even on, a cut.


**** one of my two post has one column sitting ON a cut, and the other side is with in 3 inches of another cut. Only place I could fit that one. Been that way for years and it gets used daily with mainly 3/4 and 1 ton pickups on it. Zero issues....Im sure most people would freak.

 

[ConCretin]

So i should keep it wet until next Tuesday!??? Thanks

Honestly, if you have low wind, cool temps, overcast skies, etc., I probably wouldn't bother. I don't recall where you are located but curing is less critical this time of year up our way. You won't ruin your slab either way.