Concrete on concrete

[dazzmondo]

Hello,

Ive dug out loose material from the fireplace in my house and filled with a few inches of concrete. Due to the depth I need to do this in two stages, I have done one layer and need to fill the final few inches to get it level. I understand concrete wont stick to concrete, what can I do. The strength and stability of the concrete is not an issue as I am only filling it to get it level to put a hearth on it.

Any ideas.

Thanks

 

[ottosump]

Laying a few inches of concrete onto already existing concrete will pose no issues, If the concrete underneath is still green you could scutch the top layer off to give you a bond,however, its not structural. If your wanting a super smooth level then you could always pour in self levelling grout.
Regards Otto

 

[digdilem]

Is it going to be used as a fireplace again? If so, self levelling compound is right out, and the thermal issues might cause problems with a thin layer of straight concrete. Be interesting to see what the majority viewpoint on this is.

 

[foxhole]

Very little heat reaches the base.

 

[dazzmondo]

Thanks for all your help, I have two fireplaces, this one will not have any heat as its just for show so I have levelled the concrete so that I can level the hearth. The other will have an open fire, there is already concrete in there will a thick hearth be good enough to stop heat transferring to the concrete below or should I take other precautions?

 

[Burnerman]

I'm sure there won't be any problems with what you propose - concrete will stick to concrete no trouble if the surfaces are roughened (keyed) - if you want to help things even more a thin brushed layer of PVA adhesive won't do any harm either.
John

 

[Nige F]

Hello,

, I understand concrete wont stick to concrete, what can I do. Thanks

Have a look @ the Hoover Dam - That`s concrete - no pva needed

 

[Nige F]

Hello,

, I understand concrete wont stick to concrete, what can I do. Thanks

Have a look @ the Hoover Dam - That`s concrete - no pva needed

 

[PrenticeBoyofDerry]

Concrete will stick to concrete, but it depends on the depths we are talking about. If you intend to pour less than 2 inch it may not bond that well and shear away after time.
If it is only a few mm out, you could well get your level when you bed your hearth in.