Replies

1. 
   LFred | Mar 14, 2002 03:57am | #1

   *
   You're still going to have to use a release agent on the formply and it will cause you pain with any flooring you try to cover it with. Tile won't stick to it and it will bleed through forever.

   BUT you wouldn't be the first to do it.

1. 
   Stan_Foster | Mar 14, 2002 04:05am | #2

   *Van: When I built my house years ago, I poured my basement walls using my subfloor as forms, and hundreds of feet of 2x4's for the walers.It worked real nice,, any tile was layed over concrete board.Also, I poured my garage foundation using my 5/8 roof sheathing for its forms. No problems.

1. 
   Jonathan_Bush | Mar 14, 2002 04:12am | #3

   *VanWe built a house 10 years ago, used the 1/2 cdx for forms w/ lots of whalers, the used the ply for ext. sheathing, it worked fine, some small flecks of concrete stuck, but could be chipped off.JB

1. 
   IanDGilham_ | Mar 14, 2002 06:39am | #4

   *--- or you could use a bit of common sense and put the side with the release agent on to the joists.

1. 
   jim_"crazy_legs"_blodg | Mar 14, 2002 08:23am | #5

   *If it's not t&g, what would you do, block under all the joints? I've used plywood from forms lots of times for roof sheathing, but we always use t&g for subfloors.

2. 
   xJohn_Sprung | Mar 15, 2002 11:18pm | #6

   *How about lining the forms with 6 mil black poly? It would keep concrete off of the plywood, and keep the plywood from absorbing water from the concrete and changing the mix.-- J.S.

3. 
   Dave_Richeson | Mar 16, 2002 02:11am | #7

   *Back in the old days when we used 1X for forming, it all got use for sub flooring and roof sheating. Tile areas always had the joist notched down 1 inch and mortar bed tile set. We never paid any attention to which side went up. Shrinkage in the 1X after being used for forms meant all the boards had a cracks between them. On 16 inch centers, I would not think that 3/4 inch plywood would need blocking along the edges. Now with the reduction in acctual size of plywood from 3/4 to something less, it is probably necessary to block the edges.Somebody explain to me why I may be wrong on this.Dave

4. 
   jim_"crazy_legs"_blodg | Mar 16, 2002 05:18am | #8

   *All the 1x subflooring I've seen was either t&g or shiplap, Dave. I never could figure out why they used to run that stuff diagonally, which increases the span between joists, but it was real common here in Western Washington. I wouldn't think of using square edge subfloor without blocking it, but maybe that's just one of those unnecessary techniques I use. Truth of the matter is, I can't remember the last time I didn't use t&g (osb nowdays).

5. 
   Dave_Richeson | Mar 16, 2002 02:14pm | #9

   *Must have been a regional thing Jim. The last house I worked on that i used the form boards for subflooring was in the mid seventies. I jumped to commercial work then, and by the early eighties when I went back to residential everyone was using T&G plywood. Sometime durring that period hardwood floors dissapeared also. At least on the starter houses I worked on. The local code had also changed and we could no longer single form basements either. That one was a welcome change. Single form 1X concrete walls are scarey when they start to blow out.

6. 
   4Lorn | Mar 16, 2002 06:33pm | #10

   *I'm no expert in form work but a long time ago I worked as a carpenters helper on a large 6 story building. The job shut down one day when a fire broke out in loose stack of form plywood. The firmen thought that a cigarette set the stack on fire. A fire inspector told us that it could have been spontainious cumbustion caused by the 100+ degree summer days and the pile being on in a confined spot with a southern exposure and the decomposition of the form oil. He claimed that lumber that had been repeatedly reused and resprayed with form oil was more highly flamable than either the oil or the lumber alone.I don't know how well I would sleep in a house constructed with oil soaked lumber. The newer silicon based form compounds might not be so flamable. An additional thought is that the form oil we used smelled like kerosine and diesel fuel. Not exactly what I want my house to reek of.Be safe. Take care and have a little fun.

7. 
   George_Roberts | Mar 17, 2002 04:14am | #11

   *This is an interesting thread because I am going to use 3/4" T&G plywood for 30" high concrete forms and then use them as subflooring.I am pouring a footing and slab in one pour so the whole area is covered by black plastic for a vapor barrier but ...6 mil black plastic works well on the plywood (wrap each piece individually if you wish with staples or tape on the back side. 2x6 stringers (roof rafters) at the top, 2x4 stringers (treated plates) near the bottom.I need 11 sheets for the forms. I will use 8 for sub flooring (if I leave T's on half of the pieces and G's on the other half.

8. 
   Americandownunder | Mar 17, 2002 06:31am | #12

   *Jim,our old house(1954 Cape)in Connecticut had 1x8 t&g doug fir subfloor layed diagonally.This acted as a bracing element.The 2nd floor was usually layed in the opposite diagonal direction. Regards.

9. 
   Mike_Willms | Mar 17, 2002 05:47pm | #13

   *Why not just rent the forms? Oil up or oil down, house would smell worse than codfish insulation.