Hey everyone, Got a question.
I am building a sealed crawlspace house and I am trying to figure out the forms for my piers. I have these double walled corrugated pipe forms. (Used for culverts and all) I am wondering if I should leave them inplace in the crawlspace? The would certainly aid in keeping moisture form coming through the concrete. (Minimallyl I am thinking) But when I was an up and coming young concrete dude I was taught to never leave a form on the concrete!
So whatta ya think? Should I leave the forms on or not? (I think I should remove them)
Thanks. KD6
Replies
We use double wall drain pipe (corrugated outside, smooth inside) for embedded formwork, specifically when we are pouring a slab and need to carry a point load to a footing below. The inspectors here allow us to leave those permanently (obviously... it's under the slab). They would not allow cardboard form tube, of course.
I don't know that you're going to get a helluva lot of water vapor migrating thru a typical round concrete pier that's poured below grade and has minimal exposure above grade... but I guess you would get some. Leaving the pipe form in place would reduce it somewhat.
How would you seal your ground cover to the piers? Seems like you need to do a good job there to make it work. When I've seen it done well, the pier is poured flush to grade, the ground cover laid over the entire crawlspace floor, and the stirrups for the posts are poked thru the ground cover. Or maybe you're going to have a rat slab?
Hi Dave,
Hmmm.... You gave me cause for pause. I like the idea of placing the membrane over the pier. Hmm.. I'll have to percolate on that. But You are absolutely correct in your estimation of the difficulty in securing the membrane to the pier. Which is why I am wanting to pull the forms. That corrugation would be a mutha to mastic to.
Anyway, my piers are going to extend from below grade to the top plane of the stem wall. From 30" to roughly 50". (The crawlspace is sloped towards the drain.) I want to do this to make the floor real secure for tile. Its a bit of overkill but I really figure it best to do it now than try to fix it later.
Thank you for your input. By the way. Whats a "Rat Slab"?
Thanks,
KD
I think the easiest thing to do is to pour the pier to grade and then use a wood post from there up. That way you can lay the ground cover down and simply slit it where the post bases need to poke thru.
A rat slab is a ~2" thick unreinforced slab in a crawl space. It holds the ground cover down, protects it from damage, and can be more comfortable to work on when you're in there doing plumbing, electrical, etc.
Hey Dave,
I really like your idea. I have only one issue and I am puzzling on it now. Code requires 6 " from grade to the first wood. So pouring to grade would still require me getting another 6 " somehow I am thinkin. But maybe not. IDK. I like your idea and am gonna think about it while conducting "hydraulic sandwich" activities! Thank you!
I am gonna comment some more in another post reply.
KD
Several years ago, I was building a big house that required a bunch of sonotubes, but at the time, the cardboard tubes were more expensive than the plastic culvert you describe (with the smooth interiors).
Because we had a lot of columns to pour, we split the cut-to-length sections of culvert (as required by varying elevation) and strapped them in place with long plastic tie wraps.
As a result, removing the "forms" was just a matter of cutting the tie-wraps and pulling off the culvert.
As a result, I have a fair collection of plastic culvert lengths that I've since used mutiple times.
We had 4 columns that were 18' feet tall and I had some concerns about the structural limits of the culvert....but not to worry....those held just fine (they were to be buried in backfill so we didn't split them....they're still in place.
I just don't use sonotubes anymore.
Hey Notch,
Yea, I was thinkin about the "zip ties" too. What I have done though is to make only one cut. Thata way I can pry the form apart and hopefully lift it free. But I am sure you thought of that. Did it not work for you? Dave has given me a real good idea but I am worried about the inspector. Besides a good solid concrete pier is pretty much what I am lookin for. I looked at sonotubes and the idea is pretty cool. But I figure I'll use the corrugated pipe. (Though it is expensive!) I have decided I have to pull the form in order to get my membrane properly masticed to the pier. (Can I use mastic as a verb? Hmmm) Thank you for your response it was helpful
KD
Hi Notch, and everyone.
Thought I would zip this off to you all as a reference. I did my pour yesterday. It did not go well. So for those of you who do not want to pay the tuition I paid here is what happened. The corrugated culverts are great. Other than having a pretty huge investment in "half pipes" they are good. The problem is the zip tie deal. DO NOT use nylon zip ties. The are unsat. My shortest column was 34' and the form spread. Not real bad but it did spread. My tallest was 54' and it blew out. Being sober at the time I was able to think my way out of it and this is what I did. I/we took all the wire we could find and started wrapping forms. It only helped a little. The bottoms spread roughly 3' at the bottom. A real mess. So what I did was I poured only half the form and went on to the next form. This way the first half had a chance to set and then we came back and filled the rest of the form. (Standing back from the form of course. Those zip ties pop pretty hard!) That worked. So I have a "warm joint". As opposed to a cold joint. You can not tell where the joint is. (I have removed the forms) Summary? Well, if I do it again I am going to use metal strapping. (Like a dummy I had the tools but not the materials to do exactly that but did not) I would use the zip ties just to get the forms together and then metal strap the the bejesus out ub'em form there. So out of ten columns I have three that have wide bases and the rest with quarter to half inch visible vertical seams. So there you have it. Just want to pass on my experience.
KD
I"m sure it was stressful, and I don't want to discount your experience, but I could tell you some real form blowout stories. None of them were my forms, but I was there for the pours. Honestly it sounds like yours turned out pretty well.
Hey Dave,
Yea, it was a bit stressful. But we had a few laughs at my expense so that helped. But you are right it did turn out okay in the long run. I did a little clean up last night and it is fine. Not my best work but it ain't gonna fail! Thats for sure. I paid the tuition, took the test and now I have the knowledge!
KD
Ah, grasshopper, you have failed but only once. There are many more ahead of you.
Everyone,
Here is one more of the finished product.
KD
Walls look great, columns look fine too although I don't remember why you chose to pour them that tall. A little more vibration in a few of them would have eliminated the rock pockets. Vibrating tends to get forgotten when blowouts happen.
Thanks, Dave. Yea, but I really did not want to be movin and shakin anything when those zip ties were tighter than a banjo string! I feel lucky to have got what I did! It coulda been waaaaayyyyy worse!
KD
Oops! Sorry Dave somehow I sent my reply to Mike 2244 or sumthin like that. (My typing is starting to match my forms! arrrg)
I have some plastic sewer pipe I use.
Kinda light blue color, used to be covered with numbers but long gone. It has bell ends that seal with an o ring. about .20 wall thickness.
Anyway, ran it through table saw and over lap it about an inch.
Piffin screws about every 6". Screws come right out and peel it off.
I have a couple short pieces I can use to extend them if I need a taller form. About 4' to 5' is the average height of my columns, I have never had a blow out, but I mix pretty dry & hammer on them to settle the mix.
I bought damaged pipe from the supply house, it wasn't much more than sonatube to start with. No reusing sonatube.
This one got an extension, one of the bell ends fits over the pipe to get the height needed. Frost puts it 30" down and it's about 30" above finish grade.
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Joe H
What is a piffin screw?
Drywall screws.
Good for everything.........or not, according to some.
Joe H
What is a piffin screw?
Well sir it one of the finest screws made in USA by the Piffen company, the last of the totally owned and operated usa company. The Piffen family been in business since the early 1900"s piffen an orginal from Ireland that bring the go ole Ireland workmanship to United States.With Piffen you get screwed by the best. You can buy them only at the best lumberyard. It fact you can order them here at this site. Tauton press is in tight with the Piffen company. Just ask the Company itself, They go by the handle of "Piffen".Haga su trabajo de fricken
What was your spacing on the zip ties?"Poor is not the person who has too little, but the person who craves more."...Seneca