Concrete Slab Expansion Board

[n74tg]

I'm pouring my basement slab in two pours; so there will be an expansion joint in the middle.  I've always heard you should use redwood (I think) as the expansion board.

Why is this?

I don't really want to drive all the way to the building supply for just one board; SO, would 3/4" OSB work as the expansion material.

[glenn-k]

Redwood naturally resists decay and bugs.

I'm wondering if you really need a board in there at all except to screed off of.  It seems that the ground being fairly stable in temperature wouldn't cause much expansion or contraction so just a key joint of some sort should work - a 2x4 with 1/2 of a hex such as a 1x2 cut with about a 15 degree angle on each edge to release from the concrete when you remove the form. Nail the 1x2 about centered on the side the first pour is on.  They make metal key joint in this configuration - may be hard to find.  6x6 10-10 remesh can go under the form to tie the two slabs together - as I recall you had rebar in there - you could notch the form bottom  for it to continue to the next slab- commercially they use steel dowels with half in a plastic tube or steel plates in a special plastic pocket on one side diagonally.

[peg_688]

     Redwood / cedar / Pressure treated rot resistant,  

   3/4" OSB will be gone / rotten in a few years even inside.

 

   Concete has some water in it the ground under your slab will have some water in it the OSB will suck that up and turn to mush  

   At that point you could shop vac it out( the rotten / decomposed OSB ) and pour a epoxy like seam filler into the joint  

 The redwood is spec'ed for it decay resistance ,IMO.

 They sell a tar like black expansion joint material as well. Generally 4" wide like most concrete slabs.  It also decays as will the wood they just do it slower than the OSB will.

 That epoxy like  filler is really cool , it crush's and then stretch's as the slab moves with weather changes . It is pricey $$$ thought

G/L , PEG

[peg_688]

Glenn yous fast

[glenn-k]

I didn't mention but PEG is right about the OSB -- It swells like crazy under damp conditions -- under Bituthane it swelled so much we couldn't get steel frames over balconies without smashing it with a sledge hammer.  

[glenn-k]

Thanks PEG --tonight I am -- other nights I'm only half fast. :-/

[peg_688]

PEG is right   

 I love that line   Don't go fergetin it , EH

[glenn-k]

I'll bet you've forgotten more than I'll ever know, PEG. :-/

[peg_688]

I'll bet you've forgotten more than I'll ever know, PEG. :-/

 Doesn't matter how much a guy forgets , what important is what ya remember

 Or was that a slam :-/ :-/

[glenn-k]

I forgot what I said now. :-/

[peg_688]

I forgot what I said now. :-/

 CRS?

[Rover]

Unless you have a large concrete slab project, I doubt that you really want an expansion joint.  You want a construction joint just as Glenn described.