Mastic to fix plastic render beads

[jsmac]

We will be rendering the parapet wall with Best of Lime's Rendercote. The cement render that was covering the bricks previously made such a mess that re-rendering the top 800mm or so of this section of the front of the property is the best solution (completely rebuilding the parapet wall was not a viable option).

I will be fixing the drip bead and stop beads to the wall with stainless steel coach screws and plugs but may need to use a small amount of mastic to get the beading in place above a window arch before fixing with screws.

Can anyone recommend a suitable mastic for this purpose? As I'm sure you're all aware there is almost a limitless number of these grab adhesive products so if anyone can point me in the right direction it would be most appreciated.

Many thanks.

 

[Cubist]

I'm a big fan of Burnt Sand Mastic and have frequently used it around our place. Having said that though it can be difficult to prepare properly and it dries exceptionally slowly and can also be delicate until the curing process is well advanced. For your intended use I suspect it would be an expensive and perhaps wasteful material to consider. How thick/heavy will your render coat over the beading be? Once that cures do you not feel that it would be strong enough to resist the beading pulling away?

 

[jsmac]

The render will be approximately 20mm but thicker in places because some sections of the wall are so knackered.

Fixing the straight sections of the beading is straightforward enough but the arched area around above the window is going to be tricky. I can drill some holes in the brick but it will quite close to the edge of the brick so that's why I was thinking that holding the beading in place with a mastic might be the way forward before the render goes on.

 

[Cubist]

Faithfully following an arch with almost any kind of beading suitable for external render would be extremely difficult I think and I would be considering alternate approaches. Have you considered using a flexible/bendable plywood to make a form that fits within the arch and allowing you to apply the render to the face of the wall before finishing the inner face later?

 

[Stevers]

There was a time when rendering was done without the aid of any beads at all!

 

[stuart45]

When I plastered the inside and rendered the outside of our extension I didn't use any beads.

 

[stuart45]

What type of arch is it e.g. Camber, segmental?
To render an arch without beads you need to do the soffit and reveals first.
Make a plywood template to the exact shape of the arch, then fix to the wall. Same with straight edges for the reveals.
Once the soffit and reveals are done you remove the timbers, and then do as cubist suggested with an arch former and straight edges wedged into the reveals.

 

[stuart45]

This gives you a rough idea of setting up the reveals.

 

[stuart45]

These are the reveals 14 years later.