styrofoam inside concrete form boards?

[mclausen]

Hi Everyone....I am two weeks away from pouring my slab for my 24x32 cabin.   I have my forms leveled and in place for the concrete.  I live in Northern Minnesota and therefore need to insulate the exterior walls to reduce heat loss from the heated slab.  My question is as follows.  Can I install the 2" styrofoam to the inside of my form boards before i pour the slab?  I started doing it this way, but I have not found a good way to attach the styrofoam to the 2x8 forms I built.  I was considering using duct tape every 1 foot to secure it to the top of the form to prevent it from moving during the pour.  Does anyone have any better ideas or warnings?  Any help would be appreciated.

[Amanda_931]

You are re-inventing the insulating concrete forms (ICF), leave-in-place jobs that pretty well take the place of forms--keeping away from blow-outs is the big challenge, I understand.  You do have to stucco or something the styrofoam once you're finished.

Five years ago there were a couple of dozen different systems, probably much fewer by now.

I'd think what you want more than holding the styrofoam against the forms is holding to the concrete.   One of the store-boughten versions had plastic spacers that hold the two parts of the form together at the right distance, or odd shapes or....

Even little pieces of wood stuck into the styrofoam on both sides would work--one if that's what you're using.  where | is the styrofoam and --- is the brace.

|---|
|    |
|    |
|---|

[Dberry]

Maybe screw thru the outside of the forms to the inside and into a small block of scrap wood every few feet.  I'd use long screws and keep them proud or spray paint where they are so when it comes time to remove the forms you an find them all and unscrew them.  

Might want to put a dab of construction adhesive between the wood and foam so it acts as a retainer to keep the insulation attached after the forms are off?

Maybe someone else will have a better way.... or the right way

[mclausen]

I like the idea of using some pressure treated wood scraps.  that would definetly work.  I will see if i get any other suggestions, but i think i will run with that for now.  Thanks!

[jraabe]

Since you are going to have to protect the foam after you pull the forms anyway, how about using 1/2" or 3/8" PT plywood as a liner or slip joint between the form boards and the foam. You can probably stagger the joints and tack the foam into the ply and get it all to hold together for the pour. You could even use double headed nails (from the foam side into the ply) and these would key into the concrete.

[bil2054]

Maybe a line or two of construction adhesive, too.
I like the image of the staging nails keyed into the concrete!

Of course that is why John gets the big bucks. [smiley=wink.gif]

[spinnm]

Here in the land-of-the-slab, insulation is required.  If inside, no one uses anything.  The concrete holds it in place during the pour.

Amanda's idea is good, but sounds like you've already built the forms.  Various names.  I always just call it "foam form".  The styro is the form.  Comes in various depths and heights.  Here we use it as the stem wall and pour the slab at a later date.

[peg_688]

It's nice ,if you can, nail it or if you planned ahead put a small 1x2 cleat above it , if you can rip it on a tablesaw nice and straight and your gentle / good you can screed the concrete using that as a guide .

   If not so good or gentle make sure it a bit low so it doesn't grab your float / screed / trowel when your pouring/ finishing .

 The mud will try to float it up,  so the cleat to hold it down helps I've found, it ( the concrete)  will push it into the form  but the last thing you'll want to do is fight that foam all day , if it shifts / floats up,  as you finish your slab    

 One word of warning on the foam forms , in hot weather they get softist , want to move , wavie etc . So a guy who sells them told me , a lumber yard / trade contact friend , cool / cold weather he said they work good. How warm ?? is to warm?? He didn't say but we seldom get over 90 ° weather around here so about 85° would be my best guess.  Insider info MTL = ( More  Than Likely) not mentioned in any hand out stuff.

           

[peg_688]

  I like the image of the staging nails keyed into the concrete!

Of course that is why John gets the big bucks. [smiley=wink.gif]

 Quite a image   key wayed foam  

 So that's why architects get the big bucks   I some times wonder that , generally out loud when I'm , ah , adjusting a detail so it really will work  

[MikeT]

This probably should go in a separate discussion of ICF's, but I though I would relay a cautionary note from our local fire marshall and a local builder.  They both reported that they recently witnessed an interesting ICF foundation "issue."  It seems that a DIYer used ICFs for the basement and garage on his house.  The house later caught on fire and burned to the ground.  The foundation was left standing but the ICF's melted away and left a scary sight-- concete that was essentially honeycombed and not settled throughout the form.  The builder then noted that he had trouble with ICFs and running a vibrator to property settle the concrete-- the vibrator caused blowouts in the sides of the ICFs.

I ramble, but you get the cautionary gist.

[Penny Ford(Guest)]

Not certain where to post this, but I guess it goes here.
Does anyone have experience using DURISOL ICF? This uses rockwool, not foam, as insulation. We are building in the area of Austin, Texas, most likely on sand (We also have sandy loam soil, which is supposed to be equally buildable in the type we have on our ranch land.) We are building the Grandfather Cottage.

I am especially interested in the "blowout" issues and general issues of ease of construction. Also, we want to use beadboard put in horizontally for our walls, in keeping with very local construction -- Durisol seems to think we can just attach the bead board directly to the concrete forms. I assume we would need a moisture barrier or something (?)

If this stuff works well enough, we would like to construct our sheep barn of it, as well, or at least use it for the bottom half of the structure.
Penny

[Amanda_931]

No experience whatsoever.  And I don't remember that one when I did some research on them.

But I can't resist trying to say something about (rock) wool and sheep!

[mclausen]

Well, it is done...I ended up using left-over Ultra Decking as blocks on the inside of the stryo to hold it to my forms, and in turn to hold it to the concrete when I remove the forms.  The decking is not solid, so the concrete was able to "seep" into the inside cavity of the decking board.  I used 4 inch screws to hold the "form-stryo-decking sandwich" together during the pour.  I used liquid nails to attach the decking pieces to the stryofoam.  I have removed one form wall thus far and it seems to be holding as planned.  Thanks for the ideas everyone.

[Billy Bob]

Congratulations, mclausen!  Sounds like a winner. [smiley=thumbsup.gif]

And.. congratulations to ever'body who posted an idea!  Sounds like most everything was used, and that it worked.

Huzzah for teamwork. [smiley=vrolijk_26.gif]