Wet Mix

[Bahco]

Currently laying slabs on a concrete pad and am laying them on 5 sand to 1 cement mix.

Had to take 1 slab up today as it was not right and found that it was not firmly "stuck "to the concrete base even after 2 days. Am I doing it wrong or should I not worry?

Thanks

 

[PrenticeBoyofDerry]

How deep was the bed, should be about 5-8mm, for best results.
The fact that the mix has not started to set, could well be the addition of too much water to the mix.
5:1 ratio can be used but I would generally go with 4:1.

 

[Bahco]

Hi PD

The bed was about 20 mm TBH and was probably too wet .

 

[^woody^]

Building sand should stick no problem. If you are using a sharp sand, then you don't get a such a good bond

 

[Bahco]

Building sand should stick no problem. If you are using a sharp sand, then you don't get a such a good bond

Guess what I have 1 ton of

 

[Deluks]

Shouldn't matter if they're not 'stuck' down. Gravity will hold them there, and the friction between the base of slab and mortar bed, which will be moulded to the underside of the slab.
They won't slide about.

 

[hotrod]

should be about 5-8mm, for best results.

5mm? Shirley not PBoD?

 

[studips]

if there is dust or anything loose on the underside, or if the base drags the water out too quickly for the mix to go off normally then you may get poor adhesion.

laid some slabs called 'Regal' something or other that came from selco - had to wire brush every single one, as the backs had some sort of loose 'paint' on them. likewise some sandstone slabs can require a bit of prepping.

1:5 is fine and the bed of mortar can be as thick as you like, however that sharp sand is pants.............

 

[noseall]

Sharp sand or screed sand is ideal for laying slabs.

However, it will struggle on a non-porous surface like concrete, as there will be nowhere for the water to go.

As stated, don't worry too much about bonding. Be more concerned about laying a solid bed and use the same mortar to form a joint, i.e. tease a bit of mortar against the edge of the slab then but the next slab to this mortar joint (like a bricklayer would ).

This way all the mortar is connected and very solid.

...and it won't all wash out when you jet wash it either.

Anybody who five spots slabs then brushes in some dry rubbish pointing after, is a fool.

 

[Bahco]

Thanks for all the replies. I am half way through now and seems to be ok. Pics in my Projects soon.

That cardboard on the back of the slabs is a nightmare and I am soaking and scraping.

Is there a better way?