workshop concrete replacement

[Matthew Hills]

I'm planning to replace about 70% of the slab in my garage/workshop area do to some large/unstable cracks in the original (70 years old).
I wanted to sanity check what to expect during curing -- whether it is viable to keep my big tools in the 30% remaining area, or if there will tend to be too much humidity during curing. Also, how long I should be expecting concrete to cure before the tools can be moved onto the new slab.

Thanks,
Matt

[roger wiegand]

You might want to consider, as an alternative, laying down sleepers (treated 2x4s, on the flat 12" OC) then a 3/4" plywood subfloor, with a vapor barrier if you like. You'll end up with a more pleasant surface to stand on and you won't have to look at the cracks. It gives you a place to run wires to the middle of the floor if you like as well.

If you don concrete keep a window open and run a fan, in CA in the summertime you won't have excess humidity.

[Michael Burnside]

Put myself through college pouring concrete and setting forms. Probably poured miles of the stuff. For a typical 4" slab I would recommend no foot traffic for 36-48 hours (some say 24 but we always said at least 36). For lighter tools, etc. you can start to move things back in after 4-7 days. Closer to 7 on the super heavy tools, especially anything that has to be dragged/slid into final position. This will mitigate surface scaling. For for lighter vehicles 10 days at least and any heavy trucks, etc. twice that if you can manage.

After about 24 hours, even with light calcium, the concrete should be generally surface cured so I wouldn't worry about "extra humidity" but if you're worried, throw a desiccant pack on a couple of the sensitive tools.

[Cameron Wood]

Presumably you'll be covering/wrapping the tools for splash- that should be enough for rust IMO, maybe run an oily rag over sensitive parts.

AFAS curing, what Michael Burnside says above, but there is also drying, which takes longer depending on slab thickness, vapor barrier, air flow, etc..

When you put equipment back, I would set everything on waterproof pads and don't plan on any sensitive woodwork for over a month.

A sealer is a good idea to cut dust and generally make the concrete behave better.

[Charlie Velasquez]

Demolition will create dust. That dust is caustic wrt to iron/steel. If you choose to keep your tools in there while cutting the bad concrete out, be aware the dust needs to be controlled.

[Jim Becker]

Relative to your question about the curing time, there is indeed a "yuge" amount of moisture that comes out of the new pour and it lasts for a long time. I had to borrow a dehumidifier from a friend (a big one) and I was dumping it daily for a few weeks. That gradually tapered off to every other day and then every three days, etc. (My shop is 24x36) Now my floor was poured in early October so there was no real opportunity to force air outside to wick off moisture, but I did have the heat on.

I share the concern with demolition. You may want to consider a temporary shelter outside the space for your tools during that phase of the process.

[Jack Frederick]

My first thought before reading the posts was why not pour the whole thing. Certainly more work getting the tooling out and secure, but then you move back n to a nice new FLAT & LEVEL work surface across the space.

[Bob Cooper]

Also don’t you normally want to keep concrete moist for a while?

[Charlie Velasquez]

ok, something else to consider
My previous workshop was concrete slab on grade, with loamy type soil; the freeze-thaw cycles played havoc with it, leaving the cracked sections disjointed and at different heights making rolling tools and cabinets a significant issue. I remediated the problem by cutting out the cracks (needed to go about 14” wide… that is how I discovered the caustic nature of the dust) then making expansion joints bridging the gaps with 1/2” treated plywood that smoothed out the differing edges and heights of the sections.

However, another problem remained, my knees, hips and back hurt after standing on the concrete for long periods.
When I moved I built a workshop with a raised floor of 2x joists covered with osb. What a difference! I will never do concrete as a finished floor again.

Your current slab is badly cracked (age doesn’t crack concrete too much, but rather ground movement) and Silicon Valley is near fault lines. You can expect your new concrete to crack also.

Consider this… ditch the concrete altogether.
Google concrete less slab on grade. Your location and situation seem like a match.

Remove concrete
Compact soil (probably optional as soil has been “compacting” for 70 years.
A bed of compacted crushed rock
A layer of Foamular xps insulation
Covered with Advantech osb as the finished floor.

Will not crack, can accommodate a few rumbles, legs will thank you.

[Matthew Hills]

Thanks for input.
The garage/shop will be used as a garage for one care in between projects, which has deterred me from looking further into the sleeper+osb workshop floor option, or even the heavy horsemat tiling. I'm assuming that I need to think about car weight, runoff (car coming in from rain), and not wanting any significant level changes.

The part I was not planning to replace had been a 10x9 laundry area at the back of the 19x21 garage.

I have been thinking about where to keep the big tools while the garage concrete cures -- whether the moisture during curing would be too much. (While silicon valley isn't terribly humid, I'd expect condensation on the tools if left outside)

Matt

[Michael Burnside]

It would be a code violation if the floor did not have grade if intended for automobile storage or, in most cities, a larger door access is available on the premises.

You can have the concrete company do the pour in two shots. Plenty of times I did this, especially around here when we would replace garage floors in the dead of winter and the customer didn't have anywhere else to store their tools/etc.

[Lee Schierer]

It appears that you can rent a PODS for about $800 a month. Your tools would be out of the way and protected while the floor is demolished and poured. Your tools would be safe and secure and away from the dust and moisture.

[Charlie Velasquez]

Thanks for input.
The garage/shop will be used as a garage for one care in between projects, which has deterred me from looking further into the sleeper+osb workshop floor option, or even the heavy horsemat tiling. I'm assuming that I need to think about car weight, runoff (car coming in from rain), and not wanting any significant level changes.

Matt

Not an issue.
Foamular panels come in compressive strengths of 25 psi to 100psi.
Your vehicle tires are probably 36 psi. The tires will not be on the foamular directly, but on the advantech osb. Advantech comes in various thicknesses. Just a wag, but I would guess the vehicle weight on the advantech would distribute at about maybe 150% before getting to the foamular. So, a 5,000# Toyota Highlander would have about 140 in² of contact on the osb and maybe 200 in² on the foamular after any osb defection. Even the lowest rated foamular would handle that. Go up one grade and the 40 psi foamular would handle imost vehicles without even considering deflection of the osb. Additionally, you could add thickness and go with a 1” or 1.5” osb.

Just about waterproof. I had just erected my shed walls before hurting my back in the fall. Snow…thaw, snow…thaw, snow… all winter. Spring rain…rain… discovered I had a low corner- water pooling, rain… Didn’t get roof up till May.
No effect on the advantech, swept it off and all good. No bubbles, no puckered seams, nothing.

Whatever you think best, but didn’t want you to decide thinking vehicle weight would be a prohibitive issue.
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