Pillar formwork

[Rick Hughes]

I have several US construction books, they recommend creating pillar foundations .. using SONOTUBE forms. Have job coming up that would suit this method of construction .... there are UK equivalents such as

are basically cardboard tubes ... you dig a hole as close to tube diam as possible, fix tube so as top is about 2" above ground and cast your pillar.

concrete is set you cut cardboard form off down to ground level ...

In my case I need to cast 12 of these about 24" long. Then setting in something like these:

I will have to get them made up to suit the 5" x 5" posts I intend using.

Was going to buy 9" cardboard forms ...Just been offered a load of 9" uPVC pipes offcuts. Thinking about using these, can't think why leaving the plastic pipe in ground would be any inferior to leaving cardboard tube in ground.

[NT]

iam

Why do you need tubes at all? Usually one digs the hole and pours concrete in.

NT

[Dean Heighington]

What's the load on the deck going to be?

[Jules Richardson]

In some ways - there's certainly a lot of "that's the way it's always been done", which probably applies to foundation work. Sometimes the techniques seem primitive because they don't need to be any better, though, assuming that you're building a timber-framed house (as most in the US are) rather than brick.

Don't get me started on US wiring and heating, though :-)

cheers

Jules

[Phil L]

Yes they are perfectly adequate for the job, I mean we never see the balsa wood huts blowing into the sea everytime a 'hurricane' passes by....I don't know why they don't just build them out of cardboard.

[Rick Hughes]

Not a deck ... setting up lots of 5 x 5 posts that I don't want to be in contact with ground ...

[dennis]

I doubt if a traditional brick house would survive a hurricane, and certainly not a tornado. Maybe a reinforced concrete wall cast in situ or prefabricated and fixed to piles might.

[The Natural Philosopher]

Both certainly CAN survive both.

Weakest part of a house is the roof. Walls are actually pretty good, especially if tied together with steel. .

[Dean Heighington]

By 'deck' I didn't literally mean 'decking'. I meant floor, building, frame, construction - whatever! Or are you doing this for fencing? If yes, then just dig holes, dip timber posts in blackjack and then fill holes with postcrete.

[dennis]

So when the roof gets ripped off and the timber gets blown through the walls you call it a survivor.

[Grimly Curmudgeon]

I'm reminded of a coastal house in Donegal - the wind blew in a gable end window, got under the attic wood and lifted the roof right off. I thought at the time it was probably a builder who'd been more used to building inland.

[Rick Hughes]

This is a combination of 12 Pergola posts (5" x 5") giving me a 7.5m run of Pergola, then at end is a 3m x 3m pergola combined with raised deck area.

I did put some posts here a couple of weeks back and the consensus ... was absolutely no to putting posts in concrete ..

Doing it this way ... i.e. casting short pillars, with post base plates on top .... to keep all post ends clear of the ground.

[NT]

They do use cardboard as insulation

NT

[Jules Richardson]

Yes, things with big slab sides and hurricane-force winds don't tend to mix very well, no matter what the structure. As TNP says, even if the walls do manage to take it, the roof's usually toast.

I've heard of dome-shaped dwellings being developed in areas of high tornado activity, but I think anything box-shaped with windows and doors is at risk, no matter what you build it out of. We get a few tornados where I am - I think the closest one this year touched down about 13 miles away.

cheers

Jules

[Dean Heighington]

Dipping the ends of the 5x5's into a tub of black jack (liquid dampproof) would help protect them from ground water penetration and you could put some metal studding through them to act as rebar in the concrete. But if you're prepared to go to the effort and expense of the pile method then you're certainly not undercooking it :)

As for the use of pipe for the form work as opposed to cardboard, I can't think of any reason why this isn't ok. Unless the cardboard is meant to dissolve over time leaving concrete against surrounding subsoil? Maybe there's some risk of slippage with plastic? Or water being trapped but then your diagrams show inclusion of DPM around inside of formwork and so plastic pipe would do same job as that! You could always line the inside of the pipe with olive oil or lard- then polythene sheeting to try and allow you to pull out the plastic pipe once the concrete has set, leaving a column shrouded in DPM and then you could reuse the pipe when you need to do this again!

Just musing.

[Rick Hughes]

I saw the DPM ... and the forms are impregnated to prevent rot (for how long I don't know.)

I have been given offcuts of 9" ribbed drain pipe ... so looks like I will use these .... will probably only use 12" lengths as that is enough.

Your idea of sliding off ... might be good ... would not have the hassle of trimming 2" off the top ... if I can just slide them out of the ground.

[Rick Hughes]

might.

wasn't it pressure was the problem ... if you opened the windows the pressure did not knock down the wall as it could spill out.

[Dean Heighington]

don't know.)

Hmmnnn, if the plastic pipe is 9" 'ribbed' (French drain?) the concrete would find the ribs (or is it smooth on the inside?) and make sliding off problematic! Unless you fill the ribs with wet sand/soil and/or line the insides with a couple layers of very thick DPM. heavy greasing will also help the removal.

[Rick Hughes]

This is drainage pipe ... not French drain it is standard underground 225mm ribbed .. there are circumferential ribs on outside of pipe, smooth on outside:

used on d-i-y often, so probably people not familiar with these - used on civils projects as storm drains.

[Dean Heighington]

Yep seen em on road and shopping centre builds. Those ribs'll help you pull the pipes off when concrete has set :)