Rendering over concrete lintels

[Mr M]

I have replaced the external brick soldier courses over my windows with 150mm deep, precast concrete lintels and I am now ready to have the external walls rendered in sand and cement and then tyroleaned with Cullamix.

Is it ok to just go over the precast concrete lintels with the sand and cement or should they have anything applied to them beforehand

Anyone got any views on the use of PVC beads as opposed to stainless steel

 

[roughcaster]

Always PVA a concrete lintel before you scratch coat onto it. Some precast lintels are made with a rough surface which are ideal for coating onto, but others are fairly smooth. I PVA "both" types though just before the scratchcoat goes on, so the cement is straight onto it while the pva is wet. Use an "external" PVA.......My thoughts on plastic beading? I would never use them, others might, but I prefer stainless steel at best, although a good quality galvanised bead is a good second. Most plasterers/builders would not use beading of any kind on external corners for rendering/tyrolean. but along the bottom of the wall or over a window, a bellcast would be used, or a render stop bead. Plastic beads,,,apart from ones that form the radius of an arch,,,,,, not for me.

Roughcaster.

 

[roughcaster]

Forgot to say that external PVA is "waterproof", so it's more expensive that ordinary PVA. You can mix it with cement as a slurry, and stipple it on to a smoth surface to form a key for render etc as well.

Roughcaster.

 

[Mr M]

Thanks roughcaster, you mention the bellcast. What is the correct height to locate this in relation to the existing DPC level

 

[roughcaster]

Always FIX the bellcast just above the DPC,never below it. I fix the bead so the bell shape itself allows the water to drip off below the DPC. Hope you know what I mean. Although the bellcast is fixed to the wall "above" the DPC, the actual shape of the bell is below the DPC level, but the DPC has not been bridged.

Roughcaster.

 

[Mr M]

Got it. Thanks

 

[roughcaster]

No problem,,,, use galvanised nails ( 1inch) to fix them with as well, too long, and they'll bend.

Roughcaster.