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Posted: Sun May 03, 2009 2:47 pm
by Jamie in france
Hello
First post so please forgive any errors. I have read most of the info on the forum re catchpits and have three questions.
First is very basic I'm afraid... what is a C30 mix for the base?
Second I hope is less obvious... if I construct a catchpit from brick (or maybe even block), does the pit require a waterproof render to prevent seepage through the wall material?
If a render is rerquired would there be an advantage to use a harder (engineering?) brick and not bother with the render?
Last... would it be a better idea taking into account time/cost to buy pre-made concrete manhole sections (either round or rectangular) and cut the two pipe holes through at the appropriate points?
Many thanks
Jamie
Posted: Sun May 03, 2009 4:46 pm
by msh paving
I would not mess with building a brick chamber quicker and as cheep to buy a pre-cast concrete ring 1050mm dia. then cut the pipe hole in it, C30 is the concrete mix strength
http://www.pavingexpert.com/mortars.htm#mixos
MSH 
Posted: Sun May 03, 2009 8:41 pm
by seanandruby
A nine inch brick built catchpit if laid correctly should be waterproof. You have to consider how to lift a concrete ring into place. You would'nt render the inside of a brick manhole, although it would'nt hurt to render the outside or concrete surround it. The other option is to shutter it up, you may have to use a puddle flange, or wrap hdydratite around pipes.
Posted: Sun May 03, 2009 8:59 pm
by flowjoe
Not sure what the project entails but for a domestic find yourself some cheap 450mm plastic manhole sections, a plastic manhole base with all inlets/outlets capped and a good quality sealant. You will just need to core drill or stitch drill for your inlet/outlet.
You will have to way up the cost of materials against your time constructing it but there are plenty of cheap plastic suppliers on the web.
HTH
Posted: Sun May 03, 2009 9:15 pm
by seanandruby
Then why use a base at all ??? just set the raising pieces in the base. the only thing with the 450 is the depth your allowed to go with them, i think it is a metre?
Posted: Sun May 03, 2009 9:23 pm
by flowjoe
Just trying to keep it simple Sean, you could pretty much construct it above ground in half an hour, let it set and drop it in as one unit.
1200mm depth for 450mm rings which should cover most domestic land drainage jobs, they do manufacture 450mm rings for 3mtrs deep chambers if required
Posted: Sun May 03, 2009 9:40 pm
by Jamie in france
The maximum depth is 1100mm or a tad under so I guess the plastic option isn't a problem, but, what does occur to this groundworking novice is the ribs on the walls of the plastic manhole sections will make it difficult to seal the outlet pipe in a satisfactory manner? Also some of the added height rings are quite shallow with the outlet pipe having a 235/250mm outer diameter. This week I am not where I'm doing the work and where the pipes are, so can't give accurate dimensions.
For this reason the use of concrete rings or a build on site appealed as I can seal both of these very easily.
I have a 1.5T mini digger to lift with, so I guess that individual rings are no problem but not sure about it all assembled?
Thanks for all the info so far
Jamie
Posted: Sun May 03, 2009 9:45 pm
by flowjoe
The ribs are not a problem, put one in this week for a pump chamber on the outlet of a septic tank.
Likewise 24 x 18 (600mm x 450mm) concrete sections can be man handled easily enough you will have to make sure that you bed the rings with a slurry mix or again a good quality sealant.
Edited By flowjoe on 1241383583
Posted: Mon May 04, 2009 7:33 am
by seanandruby
As i work on mostly large construction sites, i'm used to deep drainage and the correct materials ie concrete rings, shuttered manholes etc: The only thing i would be worried about with the 450 option if it were in a awkward place like a back garden, without access to clean the silt out. Visions of being held upside down by the ankles with a bucket and trowel spring to mind 
not trying to blow holes in your idea flo' it's just what i am used to. Would'nt the large diameter of the two pipes ( assuming there are only two ) with 100 ml on each inside the manhole make it difficult if not impossible to clean ??? Also as you need a smooth base for a cathpit, then the base, channels etc would be a waste of money. I agree that sometimes we have to think outside the box on domestics to keep the cost down. Just my two penn'orth :;):
Posted: Mon May 04, 2009 10:18 am
by flowjoe
Horses for courses Sean, i suppose it comes down to access to the site for plant and machinery and the capabilities of whoever is installing.
Must admit its a while since i have seen a guy lowered into a chamber by his ankles to clean out, but i have seen it. There are plenty of long reach gully shovels and grabs on the market but again it all adds to the cost i suppose.
Posted: Mon May 04, 2009 10:26 am
by Jamie in france
Where we are situated it would only be my petit wife available to hold my ankles... probaly we would both end up in the manhole with only our ankles showing!
The site is on a hillside with good access. Under heavy rain water skims the surfaces as well as permeates through the top layer of a loam type soil. About 400mm below the loam there is clay and sandstone rock mixed. The french drains will be uphill behind, above and to the side of the house, I will be using a solid 100mm perforated pipe.
The pipework will end up at this catchpit before crossing a drive to run into another catchpit about 10/12m further down the hill, and then into a lower grassed/trees area (at this point I was going to create a close to surface soakaway until a pond is dug in about 2 years time). The other side of our lower grassed/tree area is a boundry hedge then a field with cattle. About 80m beyond/downhill of the second catchpit is a stream in our neighbours field. The pipe for crossing the drive is a 235/250mm? ringed pipe, sorry don't know the name of it but see it used in various sizes in major building and civil engineering sites. I was advised this was the best to use if bedded correctly. The top of the pipe will be about 600mm below drive level.
The catchpit will have 100mm in and 235/250mm out. The manhole cover will sit about 300mm above the drive level.
I understand the logic for a flat smooth base to the catchpit but I have to say that I will be using a handmade tool that looks a bit like a 90o hoe to clear the silt out with, didn't like the idea of getting into such a confined space.
Is there a named product to seal concrete/plastic rings with? and I guess to seal the pipes into the wall too. I did run a rain water down-spout into an existing concrete underground cistern and used a waterproof cement. That appears to have held ok but prefer to do it the correct/professional way.
Sorry about such a long posting, just thought it may help to get all the detail into this thread.
Thanks
Jamie
Posted: Thu May 07, 2009 1:45 am
by Jamie in france
After considering the input of everyone, I have decided for simplicity to use rectangular manhole sections (450 x 600 x 229) seated onto a concrete pad of 150mm thick.
The inlet pipe hole of a 100mm will be cut into a 229mm panel side with a hole saw, but the 235/250mm outlet pipe will be cut in two halves using 2 semi circles into 2 panels.
So the question is - as the panels are capable of cracking and using an impact chisel may do some damage, is there a recomended way to cut the semi circles out?
What springs to mind is drilling a number of small holes through the outline shape and then chipping it out, is this a good idea?
As this will be used as a catchpit and will retain water up to the bottom of the oputlet pipe, is there a good way to make a seal between the concrete sections?
I assume that to bed the first section on to the flat concrete base I will use motar?
As usual thanks for all the opinions.
Jamie
Posted: Thu May 07, 2009 5:09 am
by seanandruby
Good choice jif. stitch drill then tap out. a good strong mortar/grano around the pipe haunch it slightly around pipe prime concrete and pipe first with pva, also add some to mix. strong mortar for base and sections etc.