Reinforcement mesh above doors and windows - good practice?

[kingandy2nd]

Hi all,

I bought some strongboys from a builder during the week, and he was giving me some helpful tips. One of which was that I should put reinforcing mesh in my mortar beds above and below door openings as I was rendering the property.

He called it exomesh I think, but I’m guessing it’s this sort of stuff.

https://www.toolstation.com/galvanised-reinforcement-coil-20m/p18233

I’m just at the point of putting in lintels, so is this good practice to use as well?

Thanks
Andy

 

[23vc]

Yeah it’s that stuff. I put it in recently on a bit that was going to be rendered. Slight faff but not too bad.
@noseall has posted pics in the past where it’s featured.

 

[tony1851]

If it's for reinforcing rendering, or mortar joints in an external skin, galvanized mesh (eg Expamet) is not a good idea. Over time, cement renders and mortars loose their alkalinity and become slightly acidic in the presence of damp. This then attacks the galvanising and the steel begins to rust, leading to brown staining.
Metal liable to be used in potentially damp positions should be stainless steel, as wall ties are now.

 

[^woody^]

Was he a builder or a bodger?

You can't successfully insert mesh retrospectively, and neither will it do anything anyway if the existing wall has already set and compressed.

 

[kingandy2nd]

Thanks for the input. The mesh is 63mm wide so lives within in mortar bed I guess to prevent transfer of and rust too far out.

@^woody^ by the looks of his house he is a very skilled builder. There was no suggestion to retrospective fit anything. He was saying that if rendering, especially if using a monocuse render, that expamet (thanks @tony1851) was a good idea to prevent cracking around windows and doors that could open.

Id just never heard of doing that before, so I thought I’d ask here. Sounds like it’s not commonplace and might risk discolouring unless I can find a stainless steel version.

 

[23vc]

The one I used was 100mm so look forward to rust one day as I doubt it was stainless, however they’re outdoor planters so will probably look terrible by then anyway due to the great British weather

 

[^woody^]

Oh, you bought the strong boys and he randomly mentioned using exmet above openings. Me and my putting 2 and 2 together.

You should be using concrete blocks externally which don't crack, so mesh is a waste of time.

 

[cdbe]

I used to use the stuff internally - nail it on timber that's built in the wall as a key before rendering/plastering - my last house was full of timber - vertical lumps of 4x2 to nail tall skirtings to, waist hight to nail old wainscoting to, just below ceiling height as timber wall plates for first floor joists. It provides a key for the render. This was before before the fashion for sticking plasterboard over everything, now I just tend to span any timber with board.