[Strawbale] PEX, Concrete Slab, Fear of Death (by contractor)

[Greg Haas]

"Do you have the details as to how you dealt with the substrate 
properly?"

It is exactly this concern that my contractor (I'm *so* possesive! 
wow!) has as he considers the use of XPS under the slab as improper 
substrate.

I've found the responses from list to be exceptionally helpful.  It 
might be easier for me to attempt my 18'x24' slab on my own so I can 
communicate directly with the truck operator about the mixture without 
telling the concrete contractor how to do his job. And without going 
'behind his back'.

He had the walls up on our foundation 5 days after they poured.  
Several of those days (and nights, of course) had sub-freezing 
temperatures.  He's very fast, I'll give him that! And our foundation 
walls were covered with insulated tarp-like things.

I was reading through the Reader's Digest DIY book from 1973 and they 
said minimum of 6 days with keeping it moist and/or covered with 
plastic.  Has concrete improved since 1973 such that this requirement 
is no longer in place?  It would seem not, from what I've read here and 
elsewhere on the web.

The guy that sold me my PEX tubing and manifold told me to prepare the 
insulation and substrate *exactly* the same way as Rob *and* the woman 
I spoke to at the XPS manufacturer.  They recommend plastic (not just 
taped seams) between the XPS and the super compacted gravel as the XPS 
needs a moisture barrier.  Does the XPS absorb moisture from the 
concrete? I don't know.

If it weren't for the snowy and rainy car I'd be parking in the garage 
I'd probably just have a dirt floor in it.  The dirt that is there 
packs so hard you can "burn rubber" on it.  But it is super dusty too, 
so concrete it shall be.

Anyway, I didn't mean to revitalize the discussion on efficiency and 
proper floor materials (although it always makes for interesting 
reading).  And I really appreciate all the comments in response to my 
note.

Thanks to all!

-greg

On Sun, 30 Dec 2007 19:04:07 -0700, John Paul Ogden wrote:
> "Of course, the lack of cracking is due in part to proper preparation 
> of the sub-strate."
> 
> Do you have the details as to how you dealt with the substrate properly?
> I've often wondered what is the best way to deal with preparing the
> substrate.
> 
> Thanks,
> John Paul
> 
> -----Original Message-----
> From: strawbale-bounces at listserv.repp.org
> [mailto:strawbale-bounces at listserv.repp.org] On Behalf Of Dion Hollenbeck
> Sent: Monday, December 24, 2007 7:29 AM
> To: greg at izzaboo.com; strawbale at listserv.repp.org
> Subject: Re: [Strawbale] PEX, Concrete Slab, Fear of Death (by contractor)
> 
> At 10:05 PM 12/23/2007, Greg Haas wrote:
>> What I've not found though is something to help me with the fear of death
> my
>> contractor is trying to put into me about impending cracks we'll get
>> using XPS insulation (2"x4'x8') under the slab in our garage.
> 
> 
> I did my workshop exactly this way.  It has NO signs of cracking 
> except where the slab had purposeful crack control joints installed 
> (vertical metal strips embedded in the concrete).  The workshop is 
> 30'x40'.  It has a 6" slab with PEX radiant heat embedded in the slab.
> 
> Of course, the lack of cracking is due in part to proper preparation 
> of the sub-strate.  If you have disturbed the sub-soil and it starts 
> settling, then whether or not you have XPS underneath, it will crack.
> 
> Add crack control joints on purpose, and bury them underneath 
> interior walls if possible so that they do not show. Crack control is 
> meant to allow stress relief in the places where you want it to happen/
> 
> And, bottom line, so what if it cracks in the garage!!  Get a little 
> cement repair mix and seal the cracks back up.
> 
> Disclaimer - My experience is from only one building, I am not a 
> contractor or an architect.  Your circumstances may be different from mine.
> 
> regards,
> dion
> 
> --
> Dion Hollenbeck
> Email: hollen at woodsprite.com    Home Page: http://www.woodsprite.com
> Brewing Page: http://hbd.org/hollen   Toys: 98 4Runner, 86 4x4 PU
> 
> 
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