# Forum Home Renovation Brickwork  Laying blocks onto moist concrete

## surfdabbler

I've poured a slab a few days ago, and I'm keeping it regularly sprayed for the first week.  However, it would be nice to start building my walls on it.  Can I start laying the blocks down on the watered concrete, or should I wait until I can let the slab dry out first, and then start putting the blockwork on?  I'm not worried about the strength of the slab, as it will have had four days setting already, and the footings are 500mm deep, and the blockwork is only 1200 high, but I just don't want to compromise the first layer of mortar if the water will be a problem.

----------


## mudbrick

I would wait at least until you have finished spraying unless you get some specialist advice saying it's ok.

----------


## Marc

As long as there are no puddles of water, you want to lay the blocks on the wet concrete not dry. The mortar would be compromised if the concrete is completely dry and sucks out all the moisture from the mortar before it can cure.

----------


## cyclic

> As long as there are no puddles of water, you want to lay the blocks on the wet concrete not dry. The mortar would be compromised if the concrete is completely dry and sucks out all the moisture from the mortar before it can cure.

  So that means all the blocks must be wet when they are laid to avoid compromising the mortar, is that correct ?

----------


## Marc

No cyclic, you know that is not the case. Try helping the OP not confuse him in order to catch me out. I am a very unattractive target.

----------


## cyclic

Marc, you have confused the issue by stating something that is clearly not correct. 
OP, lay the blocks whenever you like, but don't wet the slab down or the mortar will squish out.

----------


## Marc

Rubbish, the question was if he needed to _wait_ for the concrete to dry or if he could lay the blocks on the wet concrete. Yes you can lay the blocks on wet concrete but not on water puddles. The OP never asked if he needs to wet the blocks, nor if he can use river sand or if the trowel can be round with a wooden handle.

----------


## cyclic

> As long as there are no puddles of water, you want to lay the blocks on the wet concrete not dry. The mortar would be compromised if the concrete is completely dry and sucks out all the moisture from the mortar before it can cure.

  And this is not rubbish I suppose

----------


## surfdabbler

> So that means all the blocks must be wet when they are laid to avoid compromising the mortar, is that correct ?

  Thanks for posting this question.  I actually logged on this afternoon to ask exactly this, but I saw that you had already posted it.  The blocks arrived today, and they are sitting on the slab, so they are going to get some moisture from there anyway. 
Good to know I can start working on the slab before it completely dries out.  I will just make sure there are no puddles around.  The blocks arrived this morning, so I may have time to start laying tomorrow afternoon. 
Thanks to all for your help.

----------


## phild01

Personally, I think it comes down to making a judgement call on the day as to how you go about mixing your mortar and whether the blocks should be wetted.  We are heading for 40 degree days which might need a different approach if doing it in the winter shade.  When I have laid bricks I find the weather, and the heat the bricks have in them, plays with how I think I should do things...just my opinion.

----------


## surfdabbler

I'm building a basement, so I'll be in the shade.  There is some heat forecast here, but hopefully will be OK down in my cave.   :Smilie:

----------


## r3nov8or

So the slab is in a basement. Is the air damp down there. Has it been getting any direct sunlight? Just wondering if it actually needed frequent wetting in the first place...?

----------


## surfdabbler

The air is exposed to outside, so the air is not overly damp, but there's zero direct sunlight.  It does dry out in spots overnight, enough that the surface will turn pale grey in spots, noticeably different from the darker grey of the wet.  I've covered most of it in plastic now, so it probably needs very little wetting from now on.

----------


## SkirlGHB

On a volunteer building project in the Philippines last January we dug foundation the afternoon before, laid foundations 1st thing in the morning, waited until after Merienda (morning smoko) and started laying hollow concrete blocks straight away, filling around reo as we went.  Seemed to work and it's still standing.

----------


## Marc

The time I build cinder block walls this is how I do it as a one man operation. Lay on fresh or one day concrete footings, and have mud and concrete mixed, the first to lay the blocks the second to fill the core as I go. As long as you clean out the mortar that falls on the concrete each row, this system works very well when there is no help nor pump.

----------


## sol381

One man operation. Dont you have any mates.  :Biggrin:

----------


## pharmaboy2

> The time I build cinder block walls this is how I do it as a one man operation. Lay on fresh or one day concrete footings, and have mud and concrete mixed, the first to lay the blocks the second to fill the core as I go. As long as you clean out the mortar that falls on the concrete each row, this system works very well when there is no help nor pump.

  also no inspection.....

----------


## Marc

Inspection?

----------


## pharmaboy2

> Inspection?

  q 
you know, that quaint Australian custom that provides for steel work to be inspected before pouring - often associated with getting a certificate for the works so you can sell it

----------


## Marc

Steel work ... you mean the footings? Inspected the week before or the month before or the year before pouring the footing. Block work and core filling needs no inspection.

----------

