Rendering Around Chimney Pots

[keyplayer]

I have a few cracks on the horizontal face of a chimney stack that I would like to cure with a fresh layer or two of render. The existing isn't blown, but the cracks are letting in water. I was thinking of grinding a few cross pattern grooves in it before application of a fresh mix. Can anyone advise on mix ratios, whether to use lime, (the chimney is used for a real fire), and whether I should prime or just soak down the old render. A perfect looking finish is not required, just a weatherproof one! Here are a few snaps:

Untitled

• keyplayer
• 24 Dec 2009
• 1

Untitled

• keyplayer
• 24 Dec 2009
• 1

Untitled

• keyplayer
• 24 Dec 2009
• 1

 

[keyplayer]

Anyone?

 

[hotrod]

You could use a lime/cement render for the repair, but, considering aesthetics are not a primary concern, you may find using an epoxy mortar product quicker and easier as it will mean less surface preparation, due to the fact it will stick like sh*t to a shovel.

 

[keyplayer]

Thanks hotrod, I'm not familiar with these products. Would you be suggesting that the cracks are 'pointed' so to speak with an epoxy mortar product, or a whole layer spread over the top of the stack?

 

[Richard C]

Cracks act as a siphon & you would be amazed at the depths or heights they can suck water into. Covering cracks up is false economy & will only be a temporary cure for as long as “whatever” covering lasts; the only way to effect a permanent repair is to chisel the lot off (or at least 2 inches of it) & re-render.

You’re up there anyway so it’s not an awful lot more work to hack it all back & start again, if not you could well be back up there again within the next year or so.

 

[jeds]

Just for reference; the render around the pot is called flaunching. I agree that a coat of some sort of waterproofing compound is probably the best solution if you don't want to hack the lot off.

 

[hotrod]

Thanks hotrod, I'm not familiar with these products. Would you be suggesting that the cracks are 'pointed' so to speak with an epoxy mortar product, or a whole layer spread over the top of the stack?

I would just give the cracks a brush to remove the moss and any loose render and then point up as required. You would not use an expoxy resin to recover the whole stack, for one it would not be economically viable. I have used SikaDur for similar applications in the past with success.

As Rich and Jeds point out, this is only a remedial repair, although it will perform adequately if applied to MI's. If you want to carry out a comprehensive repair the only way forward is to hack the whole lot off and re-render - and ask yourself why the original render has failed - movement?

hth