The Brew Cabin

Posted: **Sat Nov 22, 2008 9:53 am**

Dear Brew Cabin,
I would like advice on the most appropriate mortar class for laying paving slabs on a sound concrete base.

The position of the concrete base would allow for a 10mm mortar bed plus slab thickness without compromising the recommended 150mm slab top to dpc height.

I propose to use a 15 -20 mm deep U notched floor tilers trowel and lay the slabs on a 10mm thin mortar bed and joint with a class III mortar.

The general recommendation is for a class III mortar bed but could I use a class IV or V mortar instead?
This weaker mortar would save money but does have the added advantage that the slabs would be more easily cleaned for relaying, if they need lifting in the future, as I suspect a class III mortar would be practically impossible to remove.

Would weaker bedding mortars fail in freezing conditions?

Regards,

Posted: **Sat Nov 22, 2008 11:10 am**

i personally would go for the correct mix and make the bed 40ml. i have laid on a 10ml bed before using 10 ml rebar then screed off those. that was because it was unavoidable, was upgrading the flags in brighton so the levels were fixed because of kerb heights and below was cellers.

Posted: **Sun Nov 23, 2008 8:47 am**

"Bending The Rules
The Building Regulations require at least 150mm between the dpc and the ground or any paving. This is what is known as 'Best Practice'. However, there are situations where it is just not possible, or practical, to maintain this regulation. On professional work, and new build projects, every possible effort should be made to ensure the 150mm rule is not breached, but, for small, domestic projects, such as a driveway or patio, there are cases where keeping the paving to 150mm below dpc would involve a huge amount of work that cannot be justified. In such cases, the 150mm rule can be 'bent' a little, but with the following provisos...

* The rule should only ever be 'bent' on private property, never on public or commercial properties.
* The property owner must consent to the breach.
* The paving/ground level should always be at least 75mm below the DPC. Anything less than that is just asking for trouble.

It should be noted that breaches of the 150mm rule are the sort of thing that is noticed by Surveyors when valuing a property and it can lead to a reduced valuation or a requirement for remedial work to be undertaken."

Posted: **Sun Nov 23, 2008 8:52 am**

the above post is from the main index under DPC. bending the rules.

Posted: **Wed Nov 26, 2008 2:39 pm**

The cost saving that comes from using a class Iv or class V mortar as opposed to a class II is meaningless, unless you happen to have several hundreds of square metres to pave. The strength really shouldn't be an issue, as even a class V at 8:1 is more than adequate for residential foot-traffic-only paving and, assuming it's properly mixed, there should be no problem with frost resistance.

The Brew Cabin

Mortar class for 'thin bed' laying of slabs?