Mortar and dry warm air

[geraldthehamster]

I've just built a little dwarf wall in the eaves of my dormer bungalow (we're only talking about a 4 foot right-angled triangle), to close off a space behind a room. After three days the mortar doesn't look like it's gone off properly, but is sandy and crumbly. Central heating pipes run through this space and under the wall, and I'm thinking that the warm, dry air has caused the mortar to dry out too quickly and prevented it going off properly. I'm now considering removing the wall and rebuilding it. I'd turn the heating off during and afterwards, and possibly give the occasional mist of water to keep things wet for a bit.

My question is: how long ought I to plan to leave the heating off, to be certain I've given the mortar a chance to go off? A day? Two days? Longer? I know I can wait and see, but in the interests of domestic harmony I need to plan this against the weather forecast ;-)

Regards Richard

[Stuart Noble]

Maybe the bricks are too porous. Try a bit of pva in the mortar

[Phil L]

You don't ned to take down the wall, the mortar is just awaiting some water to complete the setting process - I've repointed walls and such likes and the sun has caused this same drying out - the mortar remains sandy until it's been wetted down a few times, then it sets as normal.

[Andrew Gabriel]

Also, mortar takes about 6 weeks to fully set. For the first couple of weeks, you'll easily brush sand off the surface.

[meow2222]

Just spray with water several times, no need to turn heat off.

NT

[geraldthehamster]

It wasn't just sand coming off the surface - a knife could be pushed right into the joints. The bricks could be removed from the wall by hand. Anyway, I've rebuil the wall now, and turned the heating off at least for tonight. Given these facts, would anyone like to suggest how long I ought to leave it off now, to give the mortar the greatest chance? It's all quite damp at the moment as I wetted everything down; it's my experience that if it's wet for longer it will set more slowly, but harder - there must be a point though when the chemical reaction becomes irreversible?

Cheers Richard

[meow2222]

thats normal

people have already said

its always irreversible with cement, all the way thru the setting and curing processes.

NT

[sm_jamieson]

Just been building walls last couple of days. 6 to 1 mix. Next day bricks are firmly "stuck", mortar getting hard, but could push a knife in if you tried. But I wouldn't give the bricks a yank for a week or so. You get that urge to "go on, push it, see how strong it is" ! By the way, if your loft is now cold, note that mortar takes longer in the cold ;-) Simon.

[Stuart Noble]

IME, if you can easily pull the brick upwards a couple of hours after laying, you haven't got a proper bond. It's all about the right consistency of mortar, suction, and tapping the thing to get it level rather than actually moving it. I'm a useless bricklayer but my joints don't usually fail

[geraldthehamster]

Well, I examined my second attempt this morning, and already the mortar was much harder than it has been after three or four days on the previous lot. As I made a point of ensuring the bricks were damp, I'll have had less suction as well, and a better bond, which as someone pointed out may also have been part of the problem.

I don't want to give the impression that this brickwork is merely "near" some heating pipes. It forms one side of a mainly enclosed void about 6 by 4 foot in the eaves, in which the main 22mm copper pipes run. Even with insulation on the pipes, it gets very hot and dry in there. It would have been more like laying some bricks, then using a hairdryer on them.

I'll inspect it again tonight, give another misting with water and put the heating back on.

Cheers richard