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anthonyl
1st Aug 2005, 09:37 PM
Hi

I have discovered a rotten stump (redgum) under the house. I am thinking about replacing it with a concrete stump. What I would like to know is how deep does it need to go? The height of the stump from the ground to the bearer would be about 50cm but I m unsure how deep into the ground it goes.

Thanks

Anthony

nt900
1st Aug 2005, 10:11 PM
Hi Anthony,

I am not a restumper, so take this advice as from an amateur. But generally speaking I would:
Dig a down at least 400mm, but I would go as far as you can reasonably dig before it get to hard. Solid is good. And if it is easier to dig, I would keep digging. Having said that, your existing sole plate, which should still be intact should already be sitting on a good firm foundation.

Make the hole 400mm x 400mm across. Although I think 350mm x 350mm is acceptable.

Drill a hole through your bearer and pass the rod of the concrete stump through the bearer. A threaded rod is better than just a wire as some concrete stumps have. If threaded, once through the bearer tighten it down with a washer and nut. If a wire, pass through bearer and bend over, hammer down snug. Hang your stump from the bearer in the already dug hole. Make sure there is at least 100mm clearance below the hanging stump and the bottom of the hole.

Make sure there is no spoil still in the bottom of the hole.

Shovel in concrete.

Let it set a few days.

As long as the concrete is 400mm x 400mm by 400mm minimum, it does not matter if this new concrete block around the bottom of the stump is way down a hole (shaft), you just backfill soil over it once cured. Personally, I would fill a deep hole with more concrete, without going crazy.

Hope this helps. But others may have more technical advice. Especially about soil types and what makes a good foundation.

Hope this helps.

johnc
1st Aug 2005, 10:55 PM
Anthony,

Just go down and dig out the old stump, generally its pretty dry and tough going, until you get to virgin ground which should be at the base of the old stump, then it is usually like iron. Don't use to much concrete under the new post, it has to move with the house otherwise it risks cracking over time. About 50mm or so of moist concrete under the stump and a similar amount above the base of the post is plenty then back fill with the soil excavated. Don't forget an ant cap otherwise as described, if one post has gone the others might be ready to follow but fixing the current problem is fine as long as you have everything blocked up nice and level at the point you are putting in the new stump.

I use an old spade blade with a bit of heavy steam pipe welded to it which seems to have the clout to cut the hole in reasonable speed.

John.

anthonyl
2nd Aug 2005, 09:17 AM
Thanks for all your advice. Would a car jack be suitable to support the bearer during the replacement?

ausdesign
2nd Aug 2005, 09:27 AM
Anthony the structural work is done by the concrete pad. The stump itself is the means of transferring the floor load to the pad. Pad sizes and depths are governed by the type of soil (depth of hole) and the amount of load or floor area (width of pad), having said that the existing depth, if firm, will be suitable - in most homes this will be a minimum of 500 down (sandy soils require less than clay soils generally). A pad width of 400mm square with 150mm minimum under the stump would suite most situations with stumps spaced at around 1800 centres. The pad size would need to be increased if there are any point loads directly above the stump - ie a post or column inside the house transferring roof loads. Any concrete up the side of the post acts as bracing for the stump not vertical support. Alternatively there are premade concrete pads available but Anthonys suggestion of 'hanging' the post is the easier method.

HavinaGo
2nd Aug 2005, 11:25 AM
Another amature response:

Restumping my place .. the sole plates were down 1 metre. The restumper charged extra because of the depth :( but he did remove all of the pieces of timber and was quite happy to show me around the work in progress .. all in all the best money I ever spent as the guys earnt every penny ! How they dug 1 m holes lying under a house I don't know .. but they did!!! (Some of the pieces of redgum have been useful .. most have not.)

Question on jack: given a car jack is only good for 2 tonnes at most I'd not recommend it under a house. I've used a 10 tonne jack to lift one bearer 1 cm to relevel a floor but would think much larger capacity if more than just adjusting packing.

echnidna
2nd Aug 2005, 12:23 PM
Its extremely unlikely to just get 1 stump rotted out and the others ok.
You will probably find if you dig down about a foot or so alongside all the other stumps that they are also rotted.

HavinaGo
2nd Aug 2005, 04:07 PM
I'd agree with echidna .. my place was an example where only 1 stump was bad, the others superficially looked OK. On removal, 50% showed significal thining just below the ground.

I have had them in a heap with the thought of using the good timber (there looked like 3-4' of good, above ground timber in some of them). Last week my better half packed them into the ute for a trip to the farm and it is amazing how little there is left of the below ground portions. I'll acknowledge that storage may not have been the best but I'm glad they have all been replaced. It is funny, that the sole plates are still sound.

I had heard it is the changing dry-wet-dry that kills a redgum stump .. maybe that fits as under my place it would always be wet down deep, but varying levels of dryness at the surface. (The joys of being at the bottom of the hill)

nt900
2nd Aug 2005, 08:21 PM
Anthony|

As for the jack, I use a relatively small hydraulic jack to lift bearers up a little so I can replace the occasional stump. Usually this is enough lifting power for bearers in the middle of rooms. Lifting bearers supporting walls would be different and bigger is better. Make sure it is hydraulic. Less chance of failure under load.

Good points raised here about checking all your other stumps. And if it is all going down hill, get a restumper. It's a horrible job. There's restumpers and there's restumpers.

Hope all goes well.

echnidna
2nd Aug 2005, 09:57 PM
And dont rely on a jack.
Use a jack to lift then put temporary blocks in for safety support as well as the jack.
Men have been crushed during DIY restumping

nt900
2nd Aug 2005, 10:37 PM
Yes

Bear
3rd Aug 2005, 07:47 AM
As mentioned it is really worth checking all the stumps. I have just done this myself, and now know I am up for a bigger job than first thought. I still intend to do it myself. After much researching I have decided to use treated pine posts (H5). They are lighter and all the reports that I have read and people (in the job) I have spoke too agree, they are more than adequate for the job


Regards

Bear

grinner
3rd Aug 2005, 10:27 AM
I've just had my place re-stumped, and also added an extension in the last 9 months. The engineering plans for the extension called for 400 mm diameter holes, dug down 600mm, with at least 50mm of concrete under the stump. The restumper said all he was requred to do was to dig down to and remove the original sole plate.

If your going to replace it with concrete stumps, make sure you get the ones designed for restumping, these have a wire loop coming out from one side of the stump, rather than a piece of reo down the middle of the stump.

nt900
3rd Aug 2005, 11:15 AM
As far as I know, there are three type of fixing to bearer mechanisms.

>Wire that passes through the centre of the stump - meant to pass through a hole in the centre of the bearer, bent over the top of the bearer.
>Wire loop coming out the side of the top of the stump - meant to nail onto the side of the bearer.
> Threaded rod that comes out the centre of the top of the stump - meant to pass through a hole in the centre of the bearer, fixed in place with washer and nut on the top of the bearer.

Although the wire loop version is meant for restumping where it is difficult to drill through bearers and position, the others can be used and threaded rod version would be preferred.

I had a house restumped and he the restumper specified threaded rod types for each replacement except for the perimeter of the building where they could not access the top of the bearer. There he used the wire loop version. Note that all threaded rods are not the same diameter, thicker is preferable.


Also, for anyone is western <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com /><st1:City w:st=Melbourne</ST1:place</st1:City>, I would be happy to recommend him. He did an excellent job at a fair price. And was quite happy to document the specifications of how the job would be conducted (diameter of holes, concrete under stump, threaded rod diameter, type of stumps, etc) before hand. He also suitably cleaned up the site afterwards!

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