New concrete slab on top on old thin slab

[Mike]

My workshop has a lower floor level at the far end. It was a single car size garage with a 2.2 m long extention added to the back. When the then owner build the extension he only laid a 30 to 40 mm thick (if that) concrete floor with a 60 degree slope up to the existing floor slab. As i have a few machine tools that really need a thicker ( and more flat) floor, what is my best option for pouring more concrete over this thinner floor. The area is 2.5m by 2.2 m and to make level with the rest of the workshop needs 75mm extra depth. It has also broke about 20 cm from the end of the workshop about 3/4 of the way across and must be dipping about 20 mm. Can i just pour extra concrete on top of the old floor to bring it up to height and tamp it down an smooth off. I did use a floor paint a few years ago which is still mostly there. Thanks for any answers

Mike

[Cash]

Mike,

Generally new concrete won't stick to old - and in your case, things are even more difficult with the existing concrete starting to break up, which could seriousl affect the new stuff.

In my experience I really would advise that you break the old stuff up and relay the whole floor (presuming the garage has separate footings and not build on top of old floor). That way, you eradicate any future problems, you can lay any electrical (or other connections) under-floor in conduit, make it non-slip - and you know the floor is level and safe to use.

Cash

[NT]

If 3" is enough, you could pour 3" on, but 4" is stronger. 3+1 is not

4 in this case, its just 3.

NT

[Tim Watts]

If the original concrete really is 40mm thick and covered with paint, I would agree. I'd have a different opinion if the original was 4"+ thick, but there's so little of the original it would be relatively little effort to remove it.

[Londonman]

My workshop has a lower floor level at the far end. It was a single car size garage with a 2.2 m long extention added to the back. When the then owner build the extension he only laid a 30 to 40 mm thick (if that) concrete floor with a 60 degree slope up to the existing floor slab. As i have a few machine tools that really need a thicker ( and more flat) floor, what is my best option for pouring more concrete over this thinner floor. The area is 2.5m by 2.2 m and to make level with the rest of the workshop needs 75mm extra depth. It has also broke about 20 cm from the end of the workshop about 3/4 of the way across and must be dipping about 20 mm. Can i just pour extra concrete on top of the old floor to bring it up to height and tamp it down an smooth off. I did use a floor paint a few years ago which is still mostly there. Thanks for any answers

Mike

decide where the relevant machinery is to be installed. Dig out an area of the existing floor about a foot larger all round. Install a 1" thick rubber "case" for the new floor and make it whatever thickness you need. This will provide a good standing for the machinery and a non-vibration isolation to the rest of the existing.

[Andrew Mawson]

My workshop has a lower floor level at the far end. It was a single car size garage with a 2.2 m long extention added to the back. When the then owner build the extension he only laid a 30 to 40 mm thick (if that) concrete floor with a 60 degree slope up to the existing floor slab. As i have a few machine tools that really need a thicker ( and more flat) floor, what is my best option for pouring more concrete over this thinner floor. The area is 2.5m by 2.2 m and to make level with the rest of the workshop needs 75mm extra depth. It has also broke about 20 cm from the end of the workshop about 3/4 of the way across and must be dipping about 20 mm. Can i just pour extra concrete on top of the old floor to bring it up to height and tamp it down an smooth off. I did use a floor paint a few years ago which is still mostly there. Thanks for any answers

Mike

Whip out the 40mm thin slab, then re-lay to height. This gives you a reasonable thickness at the height you want.

AWEM

[Mike]

Thanks for the answers thats what i will be doing then

Mike