casting semi-decorative concrete bath base

[actionhand]

hi, i want to cast 2 concrete blocks to support my roll-top bath in a modern decorative style...

i was thinkin of using conti-board for the mould as it would leave a smooth, though matt, finish and i can't afford to get the finished blocks polished...

can anyone suggest what mix i should use as i'm concerned aggregate may show itself at the surface and spoil the look..? i could inset timber blocks to gain structural rigidity and lightness so as to reduce need for aggregate..?

would i need release agent in the mould..?

 

[noseall]

shuttering to the precision you are talking about isn't easy.

don't add timber to the mix it will only weaken it.

concrete is heavy and has a mind of its own. you could line the shuttering with conti but the structure will have to be much stronger.

the corners will have to be precise or else the concrete will find a way out.

you will also need to remove the trapped air. using a hammer drill may help.

i would use pea gravel aggregate, sharp sand and plenty of cement.

prepare for a disappointment as it is not easy to achieve perfect results with shuttered concrete unless you are experienced at it.

 

[actionhand]

thanks v. much, that is plenty of good advice- sounds a bit more to it than i thought but reckon i'm up for it taking onboard all those precautions...

cheers,

 

[gday2uk]

Don't forget the photos of the finished article

 

[Thermo]

when my father has done it, he does the filling of the mould in two stages. he first lines the mould in a sharp sand mix well worked into all the corners and the face etc, to get the fine finsh and then fills the rest of the void with a bit more aggregate mixed in. As noseall says vibration is the key (ask the wife!) A palm sander or similar aheld against the side of the mould is very good at achieving this.

You can get a smooth finish on the sides of the mould if you cover them with a smooth plastic covering first, something along the lines of fablon (i think thats its name) sticky back plastic. corners are the bugger, so if you can arris the corners in the design it casts a lot easier.

definite with the oil on the mould as well

 

[actionhand]

more wise words, thanks... the 2 stage fill makes a lot of sense...

i will definitely get photos of every stage- will look great if it works...

cheers