# Forum Home Renovation Concreting  Point load on 600x600 tiles

## jacy_m

I've just posted this in the tiles section but as the concrete hasn't been poured yet, I'm wondering if there is anything else we need to do to the concrete to prevent the tiles/concrete cracking when the load is applied. Extra strong reo is going to be used with footings poured - that is about all I could gather. The slab will be about 5m x 6m, with the fish tank on one side and a built in bbq on the other.  
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We are planning to place a 6ft fish tank, which holds up to 900kg, on  our soon to be tiled area. The tank stand is welded out of square tubing  and has 6 legs approximately 20mm in width. So this is 150kg per leg. I  am concerned about the tiles cracking and wondering what type of load  distribution would prevent this. We were considering putting the tank on  wheels as the 6 legs are already taking the load ok and the wheels will  enable the tank to be moved (after it is mostly drained as I am aware  of the force the water has against the glass). Would nylon castor cups  under the wheels be enough to distribute the fully laden load? Or would  we need to put down sheeting or rails or something else?  
The 600x600 tiles will be on a concrete base which has a thicker piece  of concrete directly under where the tank is to be (sorry not sure of  the correct term). 
thanks for any advice

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## Master Splinter

I'd spread the load over each pair of legs with a chunk of MDF covered in a scrap of carpet or rubber or something on the underside - it'll take up any irregularity in the tiles and prevent the face of the tile getting damaged from metal to tile contact. 
As long as the tiles are good quality, and bedded in well, they will take a compressive load (structurally, they'll survive stilletto heels, and these have an estimated load of over 10,000kpa/1,400 psi) but the greatest risk is that of damage to the glazed face. 
Don't worry about the concrete. A standard slab will happily take that sort of weight.

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## jacy_m

Thanks for your reply 
If I put wheels/castors on, then this would stop the metal/tile contact. From what you have said, it seems possible that I could get away without using anything to spread the load because I have selected high quality tiles - have I understood correctly? The way the tile layout has worked out is that the load will be on 6 tiles - but within 100-200mm of the edge of each of the tiles.  
I guess it would still be better to spread the load if possible. I couldn't use MDF as this will be in an area that will be hosed out every now and then. I'm trying to think of something thin enough that getting the wheels up onto it will not be a problem if the tank has to be moved, but strong enough to distribute the load. And that still looks attractive  :Smilie:

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## Master Splinter

The key word is 'structually'.  Surface damage such as glaze fretting and cracking are cosmetic only and are not structural defects.  They can look like crap, though. (Reinforced concrete with cracks in it is still just as structurally sound as uncracked...it just doesn't look as nice). 
I'd be hesitant about wheels for two reasons - firstly, it's an even smaller contact area and secondly, grit getting embedded in the material of the wheel and then getting crunched and dragged over the tile surface when you move it. 
No tiled surface is going to be perfectly level and even (especially not across a 6 foot span) so you will need to place something with some compliance under each leg to help even things out.  Personally, I'd go for a dense 3-4-5mm thick rubber layer between the bottom of the leg and the tile.   
With your current 6 legs at 20mm square each, your loading is about 300psi, which is well within the compressive strength limits of tile (10,000psi or more), but if you want to make sure you don't damage the tile surface, you really want to spread the load as much as possible.

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## jago

As MS said;
Not a fan of the wheels either, but more to do with stress loads on the glass if you started to move it when full of water. 
With regard to the suggestion to the rubber. Have you thought about welding some square plates to the bottom of each leg and then fix some vulcanized rubber to the bottom of each plate to stop the scratches. 
What is the volume of the tank?

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## jacy_m

I've had another look at the tank and discovered it actually has 10 legs. I swear i only saw 6 when I bought it. Oh well  :Smilie:  10 makes it better 
The reason for the wheels is that we cannot complete the finish on a particular wall the tank will butt up against until a DA goes through (not even submitted yet). The approval/denial of the DA will decide what this room will be used for and the window size. Anyway, the tank will only have to slide out of the way about 50cm to give access to the corner of the wall. I was planning to empty about 1/2 of the water out when the tank has to be moved.  
It holds about 670L plus the 2ft sump tank, plus weight of glass, gravel and stand. 
I cannot think of any other way of moving it when the time comes unless it is emptied completely or it has wheels.  I like the idea of the square plates and rubber pads though  
Any other ideas?

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## jago

Use a removalists Skate I seen 2 tonne safes be moved (pushed  along) by a single guy on these.  Try a hire shop . 
I would still remove alot of the water as even 300 kilos moving backwards and forwards against the glass well I dont like your chances .  
I am sure you know but 1 litre of fresh water is = to 1 Kilo and saltwater will weigh approx 1.027 kg per litre. :2thumbsup:

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