Shuttering a raft foundation

Anthonyk2010

Anyone know if you can use shuttering pans on a raft foundation.

Seen them used on farm tanks and wondered if you could turn them on there side for a slab about 2' thick( at the perimeter).

Raft foundation is 11 m x 7 m

sydthebeat

forgive my ignorance, but whats a shuttering pan?

Anthonyk2010

sydthebeat wrote: »

forgive my ignorance, but whats a shuttering pan?

Rectangular sheets made from timber or metal, come in verious sizes. They can be assembled together to form shuttering for huge tanks on farms.

Only seen them once. Might be open to correction.

audi a4 2008

Anthonyk2010 wrote: »

Anyone know if you can use shuttering pans on a raft foundation.

Seen them used on farm tanks and wondered if you could turn them on there side for a slab about 2' thick( at the perimeter).

Raft foundation is 11 m x 7 m

hi i often taught about this option.but never went with it.
i think its safer and more trusting to go with the shuttering carpenter.
u must think of the pressure thats been held in with the concrete,with pans they dont come with right height and braceing it will be hard.
just my opinion im sure others will be on to have there say.

Anthonyk2010

audi a4 2008 wrote: »

Anthonyk2010 wrote: »

Anyone know if you can use shuttering pans on a raft foundation.

Seen them used on farm tanks and wondered if you could turn them on there side for a slab about 2' thick( at the perimeter).

Raft foundation is 11 m x 7 m

hi i often taught about this option.but never went with it.
i think its safer and more trusting to go with the shuttering carpenter.
u must think of the pressure thats been held in with the concrete,with pans they dont come with right height and braceing it will be hard.
just my opinion im sure others will be on to have there say.

It's the pressure that's worrying me too and thought the pans would be stronger.

What type was the timber shuttering you used.

Could you describe what you did please.

audi a4 2008

Anthonyk2010 wrote: »

It's the pressure that's worrying me too and thought the pans would be stronger.

What type was the timber shuttering you used.

Could you describe what you did please.

look at it this way did you ever see farm shuttering pans ever been used in a raft,i dont think so.

well the way we did it was in houseing schemes where we had the carpenter so it was easy for us.
and youre right the pressure is extreme and more when useing the poker.
is the raft on stone or have u a floor/base done allready.
pmme if u want i can ring u and talk true with u.
i can also post it here just take me time not that fast on pc

Anthonyk2010

audi a4 2008 wrote: »

Anthonyk2010 wrote: »

It's the pressure that's worrying me too and thought the pans would be stronger.

What type was the timber shuttering you used.

Could you describe what you did please.

look at it this way did you ever see farm shuttering pans ever been used in a raft,i dont think so.

well the way we did it was in houseing schemes where we had the carpenter so it was easy for us.
and youre right the pressure is extreme and more when useing the poker.
is the raft on stone or have u a floor/base done allready.
pmme if u want i can ring u and talk true with u.
i can also post it here just take me time not that fast on pc

There is no rush any description would help.
The slab I'm putting down I'd 11 m x 7 m and 16" deep.
Was going to use shuttering ply put not sure how to secure it in place. Low budget so cannot afford to get someone in. Anyway it not a huge job, it's making sure it's secure for concrete.
Around 17 m sq of concrete going in there.

Someone suggested using pans on there side because they can be easily clipped together and would be stronger.

Cheers.

audi a4 2008

area 11/7 raft so area of stone squared shoud be around 15/10
804 stone brought up in layeres and rolled with big roller every 2 feet
mark out raft 11/7
set pins top of raft at four corners
shuttering ply cut in strips and nailed to 3/2
put together like a jik-saw:D
every foot long steel pins in the back of 3/2 stand back of ply,like a l shape
remember have plenty of braceing,never enough and when pouring nice and handy never just fill as fast as u can .bring raft up even pokeing as u go:D

audi a4 2008

oops dont forget the steel silly me:D

ppink

what size are the pans?

are you sure about you're volume? 11x7x.406 = 31.262 cu m or am I going cross eyed:)

Anthonyk2010

ppink wrote: »

what size are the pans?

are you sure about you're volume? 11x7x.406 = 31.262 cu m or am I going cross eyed:)

16" deep at perimeter about 4"or 5" in the middle ( floor area).

Anthonyk2010

Cheers Audi, great help. When u say 3/2 nailed to ply like jic saw what do u mean?

audi a4 2008

Anthonyk2010 wrote: »

Cheers Audi, great help. When u say 3/2 nailed to ply like jic saw what do u mean?

every sheet of ply u will get 3 sheets in it.
nail to 3X2 top and bottom
you are now forming a pan
when u get to corners step back so one joins into another
that will make it stronger,u will be makeing a square
l brackets at back well strutted

Anthonyk2010

audi a4 2008 wrote: »

Anthonyk2010 wrote: »

Cheers Audi, great help. When u say 3/2 nailed to ply like jic saw what do u mean?

every sheet of ply u will get 3 sheets in it.
nail to 3X2 top and bottom
you are now forming a pan
when u get to corners step back so one joins into another
that will make it stronger,u will be makeing a square
l brackets at back well strutted

Lovely stuff. Thanks a million.

just do it

Worth searching on youtube. Post a link if you find something worth watching!

Another suggestion - ask around, particularly the digger man and supplier of the stone. They'll know where a raft is going up close by.

just do it

http://worthdesign.co.uk/crc/vle%20project/Assignment%201/foundations1.pdf

51 pages on foundations! It's big at 10mb and not too sure how much there is on how to set up the shuttering. But there ought to be plenty of useful info in it.

mickdw

Dont know what the edge detail of your raft is but around here, its always 9 x 2 timber thats used. The raft is 18" deep at the outside with a 9" deep step so this leaves a 9x2 board around the outide and the second 9" board stepped in 9" on top of that.
Very easy to hold in place too

Anthonyk2010

mickdw wrote: »

Dont know what the edge detail of your raft is but around here, its always 9 x 2 timber thats used. The raft is 18" deep at the outside with a 9" deep step so this leaves a 9x2 board around the outide and the second 9" board stepped in 9" on top of that.
Very easy to hold in place too

What do you mean by edge detail? Also you say 9" board stepped in, how much of a step and do u need a step?

Poor Uncle Tom

Anthonyk2010 wrote: »

What do you mean by edge detail? Also you say 9" board stepped in, how much of a step and do u need a step?

If this is a raft foundation, then all the insulation, radon barrier and reinforced screed will be laid on top of it. For the radon detail to be carried through it is usual to have it stepped at the edge. I'm sure mickdw was referring to it depending on what detail you intend for your raft corner in order for this to work.

BTW, the 1.5m x 0.6m shuttering pans mentioned earlier would be too cumbersome to set up right for a raft. They work best where there are corresponding pans on the opposite side of the wall they are working on and are usually secured with pins through the wall. That isn't possible here. The pans are usually shouldered with acros, which is overkill for a job like this.

Anthonyk2010

Poor Uncle Tom wrote: »

Anthonyk2010 wrote: »

What do you mean by edge detail? Also you say 9" board stepped in, how much of a step and do u need a step?

If this is a raft foundation, then all the insulation, radon barrier and reinforced screed will be laid on top of it. For the radon detail to be carried through it is usual to have it stepped at the edge. I'm sure mickdw was referring to it depending on what detail you intend for your raft corner in order for this work.

Ok trying to get my head around what your saying. Don't think it complicated just can't visualise it.

You have 9 x 2 on edge, pinned and supported all around perimeter, another row of 9 x 2 flat on top of first row and from there you lay barrier, insulation and steel. Right or wrong.

Poor Uncle Tom

Page 159 shows the raft foundation with the stepped edge. The 9" x 2" timbers mentioned would be at the vertical edges of the steps.

Max Moment

Shuttering pans would be ideal in this instance IMO. Think of all the wasted money, time and labour making up timber shutters and then this will all be skipped once completed.

To hold the pans in place you could use the slab reinforcement. Special nuts can be welded to the reinforcement and then the pans can be attached in the normal way using dividag bolts through the pans to these nuts using proprietary spacer blocks to achieve cover. The pans will be clipped together at the sides using the standard clasps. There will be no need for any propping. The pans are removed once the concrete has cured and the bolt holes are filled using a repair product.

Another option would be to use a permanent formwork system such as this. This would a quick, cheap and easy way to form the slab edge. This can be left in place. There are many other types on the market with this just being an example.

Anthonyk2010

Max Moment wrote: »

Shuttering pans would be ideal in this instance IMO. Think of all the wasted money, time and labour making up timber shutters and then this will all be skipped once completed.

To hold the pans in place you could use the slab reinforcement. Special nuts can be welded to the reinforcement and then the pans can be attached in the normal way using dividag bolts through the pans to these nuts using proprietary spacer blocks to achieve cover. The pans will be clipped together at the sides using the standard clasps. There will be no need for any propping. The pans are removed once the concrete has cured and the bolt holes are filled using a repair product.

Another option would be to use a permanent formwork system such as this. This would a quick, cheap and easy way to form the slab edge. This can be left in place. There are many other types on the market with this just being an example.

Have you used that frame work?

Poor Uncle Tom

Max Moment wrote: »

To hold the pans in place you could use the slab reinforcement. Special nuts can be welded to the reinforcement and then the pans can be attached in the normal way using dividag bolts through the pans to these nuts using proprietary spacer blocks to achieve cover. The pans will be clipped together at the sides using the standard clasps. There will be no need for any propping. The pans are removed once the concrete has cured and the bolt holes are filled using a repair product.

For this to work the slab reinforcement would also have to be welded together within the base to stop the pans from spreading as the re-bars are a maximum of 6m long and the shortest distance between the pans is 7m. All this welding together with the dividag bolts and proprietary spacer blocks would cost a lot more than the timber formwork. There is also the issue of protecting the insulation while any welding is being done near it.

Max Moment wrote: »

Another option would be to use a permanent formwork system such as this. This would a quick, cheap and easy way to form the slab edge. This can be left in place. There are many other types on the market with this just being an example.

That type of formwork is to reduce the amount of concrete lost to edge spoil. If the top of the raft is level with the ground the trench sides can be used to pour against, there is no need for that type of shuttering, imo.

Max Moment

Poor Uncle Tom wrote: »

For this to work the slab reinforcement would also have to be welded together within the base to stop the pans from spreading as the re-bars are a maximum of 6m long and the shortest distance between the pans is 7m. All this welding together with the dividag bolts and proprietary spacer blocks would cost a lot more than the timber formwork. There is also the issue of protecting the insulation while any welding is being done near it.

That type of formwork is to reduce the amount of concrete lost to edge spoil. If the top of the raft is level with the ground the trench sides can be used to pour against, there is no need for that type of shuttering, imo.

I have to disagree with you on this one PUT. The only welding that would be required would be a few spot welds locally at each nut; the rebar would not need to be welded IMO. The rebar arrangement which for a raft edge usually has a U-Bar at typically 300mm c/c restraining the main the longitudinal rebars would prevent any spreading (this of course depends on the reinforcement design). The remainder of the rebar would be tied as normal using annealed steel wire. Also, as you have said above the radon barrier and insulation would be placed on top of the raft therefore damaging these during welding would not occur.

A typical pan would be 2.7m long with two bolts to each pan. The dividag bolts would be part of the pan system and the OP would already have the spacer blocks as these would be required regardless of which way they shuttered. If the OP already has the pans or can hire them in my experience this is a far cheaper way.

I agree with you on your second point, if the top of the raft is level with the ground no formwork would be needed. However, in my experience due to the nature of a raft being required on poor ground, the raft edge invariably ends up above the existing ground level due to a stone formation being placed and is required to be shuttered. Also, pouring against the banks leaves a very rough edge for placing insulation against later if required IMO.

I have used this type of permanent formwork a number of times and has worked out very cost effective compared to shuttering with timber. Have a look at the image attached which shows the full raft edge detail formed using a similar product called 'Pecafil'. It is just another option for the OP to consider.

I suppose it comes down to price in the end. The OP could consider and price all options to see which is more financially viable.

Poor Uncle Tom

The only welding that would be required would be a few spot welds locally at each nut; the rebar would not need to be welded IMO. The rebar arrangement which for a raft edge usually has a U-Bar at typically 300mm c/c restraining the main the longitudinal rebars would prevent any spreading (this of course depends on the reinforcement design). The remainder of the rebar would be tied as normal using annealed steel wire.

Personally, I would have serious concerns with attaching pans to the reinforcement where it is just held together with tie wires. I have to say you could be right and it might hold, but there are too many variables for my liking depending on the workmanship of the Tier as well as the number and placings of the ties. Also just to note that the ties themselves add no structure to the reinforcement just a stabelising effect until the concrete is poured.

Using reinforcement to tie mould pans is not a new concept, it is used in almost every lintel manufacture where the reinforcement is prestressed to the mould while the concrete sets. In effect what we are talking about is a bigger and more complicated version of the same thing. I just have concerns that the reinforcement held together using tie wire would be enough to hold the pans in place.

Anthonyk2010

Was offered scaffolding planks at a good price yesterday.
Worked alot cheaper then shuttering ply.
Could I use them.

mickdw

Anthonyk2010 wrote: »

Was offered scaffolding planks at a good price yesterday.
Worked alot cheaper then shuttering ply.
Could I use them.

Long 9x2 boards would be better.