Rendering chimney

[philp]

Hi

The render of the chimney on my bungalow parted company with the brickwork. I believe that this was due to the chimney getting damp (it was unused and had no air holes at the bottom). I have now added air bricks and now must re-render the chimney. I have removed all the old render and gouged out the cement between the bricks(1/2 inch). Because I am a novice I intend to add battans to the chimney to help gauge the thickness of the render. I am aiming at a thickness of 16 Mil. The first coat will be 10 mil.

My first intention was to use a lime mix. However I spoke to a builder and he told me to use a straight forward 1:3(Cement:sand) mix using a special plasterers sand. He told me to add PVA glue and treat the brickwork first with PVA. I asked him if 1:3 could cause cracking and he said that it would not.

I want to do things his way because it makes my life somewhat easier, I can stick 16mil battens in place and approx render the first 10. Fill the rest in later and take the batttens out and fill them in all with the same mix.

Should I really be using lime to do this job(I dont like using lime because its pretty nasty stuff).

On the other hand I dont ever want to go through the pain of rendering the chimney again, so I would like it to last the next 30-40 years.

Thanks for reading this, any comments appreciated.

[PaulK]

IMO sand cement is always the best way to go.

If it were me i would do this..

NB dont use neat PVA !! dilute it with water so it looks like milk.

PVA walls as its going tacky,

PVA Second Coat

use a 4:1 mix (Fist Coat)

Key the surface horizontally

Allow to Set

Wet 1st coat Render down

use a 3:1 Mix (Second Coat)

Reason i would use 2 mixes is that for the first coat, a 3:1 wont have as much suction as a 4:1 its still a good strong mix You could well use 4:1 for the second coat also your call.

You can easaily make a little keyer take a bit of 2x2 tack in some narrow gauge nails 5 or 6 then cut off the heads and LIGHTLY run it over the render first coat.