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Slab thickness with Ampex

Joined
Mar 4, 2017
Messages
14
Hi everyone,

Well, after a large tree took out my barn this past fall I thought the hard part would be rebuilding. But it turned out to be a bunch of arguments with the insurance company. Glad that is finally over with…

Anyway, my 60X40 design is done and I have received the requisite height and area variances from my Town offices. In the next couple months I will be breaking ground and I couldn’t be more excited. The front half is a two stall garage and the back half is an RC Airplane shop that will double as a woodshop. The planes I am building these days are way too big for my current basement space. The wings are 116” and the fuselages are around nine feet; 170cc twin engine, performace exhaust…fun!

The replacement building will be stick built and sit on a frost wall. The interior wall detail at the floor has a ledge all the way around where the perimeter of the slab will be supported. The overdig will be filled with stone; the woodshop floor will be flat, the garage section will pitch to a trench drain. I will do pex in the floor; one zone for the shop one zone for the garage. I will spray foam everything and have a conditioned attic space.

I’d want to use Ampex R16 under the slab which is 4 7/8ths thick to the top of the nub. I am seeing from the spec sheet that the nubs are 1 3/8ths. I have a couple questions on details for those inclined to weigh in:

1. The panels have shiplap sides to lock together. I have seen some references to also using an adhesive (which I kinda like) but I also can’t seem to find when using an adhesive is recommended.

2. Ampex says their foam is the vapor barrier but some jurisdictions require poly regardless. I believe it is an option for me in my area, but I am thinking if I used an adhesive on the shiplap I can probably eliminate poly under the foam. Thoughts? Maybe I am overthinking it and it’s not an appreciable difference either way. What do you guys think?

3. With a 1 3/8ths height on the nub, I am wondering what the slab thickness should be. The concrete calculator for Ampex works off slab thickness measured from the top of the nubs. So does a floor with Ampex need to be thinner when compared to a floor over plain foam? In other words a 4” slab over plain foam is different than 4” over the nubs on Ampex, because in the foam voids in the Ampex floor will be 5 3/8ths. Does this get adjusted at all? The garage will have cars, a boat and a New Holland tractor during the winter months. I always thought a 4” floor would be good. Do I just go with 4” from the top of the nubs and call it a day ? If I use rebar it will sit on top of the nubs and I would hate to have rust bleed through 2” expansion cuts because the rebar will get nicked by the saw in spots.

That’s it for now. Thank you in advance for your comments!

Tom
 
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ratflinger

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Jul 7, 2016
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South Central Texas
I was going to say to call Ampex, but looking at their website there doesn't seem to be a support line. Guess you'll have to depend upon the dealer for these questions.
 

Mr onetwo

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Apr 6, 2011
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Coastal Maine

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ConCretin

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1. The panels have shiplap sides to lock together. I have seen some references to also using an adhesive (which I kinda like) but I also can’t seem to find when using an adhesive is recommended.
I don't see any benefit to the adhesive. The panels fit tightly together and stay put pretty well.

2. Ampex says their foam is the vapor barrier but some jurisdictions require poly regardless. I believe it is an option for me in my area, but I am thinking if I used an adhesive on the shiplap I can probably eliminate poly under the foam. Thoughts? Maybe I am overthinking it and it’s not an appreciable difference either way. What do you guys think?
If you are planning on epoxy or similar adhered floor covering, I wouldn't depend on the Ampex as a vapor barrier. If you simply want to limit moisture intrusion into the space, it would probably be fine. Not to contradict my previous answer but I suppose sealing the joints with adhesive would improve moisture transmission.

3. With a 1 3/8ths height on the nub, I am wondering what the slab thickness should be. The concrete calculator for Ampex works off slab thickness measured from the top of the nubs. So does a floor with Ampex need to be thinner when compared to a floor over plain foam? In other words a 4” slab over plain foam is different than 4” over the nubs on Ampex, because in the foam voids in the Ampex floor will be 5 3/8ths. Does this get adjusted at all? The garage will have cars, a boat and a New Holland tractor during the winter months. I always thought a 4” floor would be good. Do I just go with 4” from the top of the nubs and call it a day ? If I use rebar it will sit on top of the nubs and I would hate to have rust bleed through 2” expansion cuts because the rebar will get nicked by the saw in spots.
I'd want 4" of concrete over the nubs. If you use rebar, you'll want to support it at mid slab and cut 1" control joints.

Take a look at my Guide to Floor Slabs in the link below for some additional thoughts on slab construction.
 
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thammel

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Joined
Oct 3, 2005
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Location
Maryland
Whenever I see the word Ampex, I immediately think of the high end reel to reel tape recorders of the past. Ampex made great stuff!
 
OP
R
Joined
Mar 4, 2017
Messages
14
I would look at Heat-Sheet heavy R10 https://heat-sheet.com/heat-sheet/ I'm going to be using it in my new shop this spring.As too your questions. I would use 10mil Steego underneath, no glue and figure concrete from top of nubs. I am using Element ICF's https://elementicf.com/ to form my alaskan slab and Helix micro rebar in 4000psi concrete https://www.helixsteel.com/products-services/helix-micro-rebar/
Ok thank you. Some good links there too, I appreciate it.

My soil conditions aren’t great for an Alaskan slab but also, there is a “Code Compliance” coverage in my insurance policy that will pay for a 4’ Stem Wall. My new building is a bigger footprint, but I will at least be able to recover the cost of the linear feet of foundation on the old building.

Thanks again for the information and good luck with your project !
 
OP
R
Joined
Mar 4, 2017
Messages
14
I don't see any benefit to the adhesive. The panels fit tightly together and stay put pretty well.


If you are planning on epoxy or similar adhered floor covering, I wouldn't depend on the Ampex as a vapor barrier. If you simply want to limit moisture intrusion into the space, it would probably be fine. Not to contradict my previous answer but I suppose sealing the joints with adhesive would improve moisture transmission.


I'd want 4" of concrete over the nubs. If you use rebar, you'll want to support it at mid slab and cut 1" control joints.

Take a look at my Guide to Floor Slabs in the link below for some additional thoughts on slab construction.
Perfect information…thank you. I hadn’t thought about epoxy coverings; it might be worth the small effort to use the additional vapor barrier as there seems to be no downside to it.

I will look at the link you provided. Thank you
 
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