Building plinths to support filters

[Jon W]

Hi Guys

To get my filter bays to the right height for the water level I need to build a couple of plinths. One is for a CL3 (so needs to be about 1 1/2 meters square and one for a settlement vortex (about 70cm square) Both need to be about 60cm high. I'm quite sure how to go about building them so that they are strong enough, particularly the bigger one. Should I create a "cell" structure of smaller square piers and fill in with concrete, make a perimeter block wall and fill the whole thing with concrete and rebar or could I just build the cells and put paving slabs across the top as supports?

Thanks for any advice.

Regards

Jon

[MUTL3Y]

Hi,
why not use some 2x2 and form 2 rectandles 60cm high and run some decking over them to make the platform?

ian

[eds]

I'd go with wood forms and then fill with concrete. You can then remove the wood to leave the concrete plinth. I wouldn't bother with rebar if the base under it is solid.

[Jon W]

Hi Guys

Didn't read these posts until this morning. Being tight and having blocks left over from the pond build I opted to build 2-block width piers. A total disaster; whatever I did I couldn't get them level. In the end I only managed to lay 4 blocks. For some reason this seems much more difficult than building ponds walls. Then Fulham got stuffed 0-4 by that other London team Man U so crap day alround.
Does have any tips for creating level piers with blocks (or how to stop Hodgson buying Championship level donkeys for a forward line).

Cheers

Jon

[eds]

I only posted this morning and mis-read the height! 60cm would probably be too high for shuttering unless you really made the wood walls very strong!

Are you trying to make the whole plinth out of blocks? If so I'd lay them on their sides on mortar and then use a large spirit level to level them all in one go. Use a decent amount of mortar with enough give to allow you to level them out. I use a rubber mallet to tap them into place and you'll want a large spirit level or a very stright piece of wood and a shorter one. Thorny or other builders may have even better advice though!

No advice on the football sorry - I'm a rugby and cricket fan!

[vippymini]

my idea would be to build the base larger than needed out of blocks layed on their side (2" lower than needed). and then use shuttering on top to create the final level surface using a nice sloshy mix of cement.

[Jon W]

Hi Jane

It's trying to get 2 blocks laid flat and side by side that I've found difficult. Maybe I shouldn't worry about them being exactly level until reaching the required height then as you say using a pliable mix (I was going to use a paving slab or slate as the final base.

Cheers

Jon

[Thorny]

OK shuttering up and building concrete block wall to hold back 600mm of concrete seems a little on the drastic side to Me. Getting blocks level is a simple task if You have a gauge to work to. I would go with laid flat concrete blocks and bricks to get to Your required hieght. First thing to do is mark Your water level on the wall. Then measure down from that to the underside of Your filter. Basically the point of contact that Your CL3 needs to be to make it work. Then from that point now measure down to Your concrete floor. This will give You the amount needed to be made up. You say its 600mm. This will then need 4 courses of laid flat blocks each course is 112.5mm thats brickwork gauge so Your 4 course will add to 450mm. To save cutting blocks down and messing about now lay two course of brick each course equals 75mm so two course will give You 150mm, making YOu bang on the 600mm mark. The CL3 has four points of contact so I would build 4 individual 215mmx440mm piers. Materials needed is 16 blocks 32 bricks.
Little tip draw a level line around the area of Your filter bay where You need Your piers to finish. Then You can mark Your gauge marks from there down. ie 75mm, 150mm, 265mm, 375mm, 490mm 600mm to floor You will notice the beds differ very slightly just save messing about.
Dont wory about getting them all level from the first course as by the sounds of it Your floor is uneven, If You cant get to Your marks straight away dont panic You slightly increase Your bed joints each course until You do. Keep an eye on each course with a level, this will let You know how things are going.Then when You lay Your last course of bricks to the top of your marks You will be spot on level. Happy Days.
Hope this all makes sense I am not the greatest at explaining things and even worse when trying to put into words
Justin

[Jon W]

Hi Justin

Thanks very much for all the info. To be honest I have done just about everything you have suggested already. I even got hold of a laser level to make sure that the water level in the pond and that chalked on the side of the filters is completely accurate. I have drawn the position of the plinths on the floor.

My problem is that I seem to be completely unable to lay 2 blocks flat and side by side! The floor is a bit uneven but nothing very significant. Maybe I'm trying to be too accurate from the off. I'll give it another go and see what happens.

Regards

Jon