REINFORCING CEMENT RENDERS OVER JOINTS

[wildehond]

Its standard practice to create joints in the cement render at the junctions of brickwork and reinf conc. But I have a project where the Architects are insisting, for aesthetic reasons, on not having a joint. I'm investigating reinforcing the render over the joint in order to accomodate the movement in a series of micro-cracks. The concept would be to de-bond the render from the substrate for about 5" on both sides of the joint and then to reinforce the render for another 6" beyond that. Thereby creating a total of 22" of reinforced render. (the redner is typical 3/4" thick)

Comments anyone?

Thanks
Alten Hulme

 

[dik]

I'm not familiar with the term render. Is this the same as parging?

Dik

 

[wildehond]

Cement render also called plaster (is it called Stucco in the US?) is made of one approx 1 part portland cement to 6parts sand and is typically applied to provide a smooth surface to accept paint.

 

[minorchord2000]

I think your architect does not understand or chooses to not understand the concept of shrinkage cracking. I doubt your idea will work, especially where two distinct building materials come together as your brick work and concrete. It is up to you to educate your architect. I would insist on the joint.

 

[dik]

You can get a 'plastic' modified stucco that is often used with EIFS systems. I don't know about the availability of this in Europe but it has some ductility... Dik

 

[wildehond]

Dear Dik & Minorchord2000

Thanks for your replies. I'm in South Africa and I'm not aware of any commercially available "plastic"
stucco. We typically add hydrated lime to improve workability and to improve plasticity.

I was thinking of the waterproofing industry which routinely will torch on waterproofing over a joint by laying an unbonded section of membrane over the joint and then torching on over that. Obviously there are order of magnitude differences in flexibility between cement stucco and bitumen impregnated felt, but I'm still thinking that the concept is "worth a shout"

In Italy some years back, I noticed that they plastered over all their concrete/brick junctions using only a thin fibreglass mesh! I would love to get back there now and see how it all performed.

Thanks again

Alten

 

[dik]

The plastic stucco is an acryllic based modifier used for the stucco. It has the appearance of stucco but does have some ductility.

Dik