Laying flags directly onto existing concrete

[Mutley56]

Hello all and happy bank holiday!

I would really appreciate advice on whether I can lay flags DIRECTLY onto this area of 10 foot x 10 foot concrete, which is just outside of the back door of the house. The concrete is disintegrating somewhat and I did manage to stabilise it a bit last year to keep the levels of dust and grit down; (the subject of a previous post in this forum).

The flags will be concrete measuring approximately 44cm x 44cm x 3cm. The patio will only be subjected to light foot traffic.

The area already appears to slope away from the house walls and water does not pool on its surface at all. I would endeavour to ensure that the flags would have an appropriate slope away from the house when I lay them onto a bed of mortar.

OR, would it be a waste of time doing the above and instead should I break up the concrete, use it as hardcore and cover with sand prior to laying the flags on a bed of mortar?

Many thanks for taking the time to respond.

Cheers.

Mutley56


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[^woody^]

If you lay them on a solid mortar bed yes.

Sand will wash out or stay soggy. Mortar spots can let water stay in the voids and break the mortar bond when it freezes. Big voids are homes for rats and mice

 

[JohnD]

do you need a fairly wet mortar mix so you can tap them down flat? or do you use a notched trowel like for tiles (I have a similar job to do)

 

[Mutley56]

Thanks for the advice ^woody^ (I think JohnD's reply was meant for ^woody^.

I will lay them on a solid mortar bed, can you let me know the thickness please, perhaps 2cm?

I have read that spots of mortar are not a good idea and you confirm this too.

I will post a picture when I have completed the project this week - weather permitting!!!

Cheers.

Mutley56

 

[Mutley56]

Hi ^woody^,

I have just thought of another question, should I paint a layer of dilute PVA onto the existing concrete to aid bonding of the mortar bed when I put that down?

Thanks for your thoughts.

Mutley56

 

[^woody^]

Spots are good because you can easliy tap the slabs down to level/align them, but would only be OK if the existing concrete drains well and has no dips to collect water, and would not leave masive voids under the slabs

A solid bed 2" thick will take a lot of mixing and work. thinnner would be better. And it does not have to be completly solid, but the concept is not to have massive voids, so a bit of solid with slightly raised spots may be better for DIY

Also building sand tends to be better and more sticky and is better than sharp sand for spot laying

A semi wet mix is good for spot laying, but not quiet as wet as for bricklaying, but not crumbly either

You don't have to lay a bed like wall or floor tiling, but another option is a semi-dry bed of screed sand/cement tamped down and levelled off and the slabs dropped straight on. This only works for slabs with a parellel front and back as otherwise they are a pain to get the top level

For spots, don't tread on the slabs for a day or so or they will tip. A solid bed will allow you to step on them lightly (in the centre) soon after being laid. So this may determine which is better

 

[^woody^]

Hi ^woody^,

I have just thought of another question, should I paint a layer of dilute PVA onto the existing concrete to aid bonding of the mortar bed when I put that down?

Thanks for your thoughts.

Mutley56

I wouldn't bother for outside work. Just brush any loose stuff off

 

[masona]

I will lay them on a solid mortar bed,

This is the best picture I can find, like bricklaying, do a few V shape lines on the solid mortar allowing easy tapping down.

 

[Mutley56]

^woody^ and masona,

Thanks a lot for your valuable advice. I'm on the project now.

Cheers.

Mutley56

 

[^woody^]

Go for it ... have the Radox ready for your back later though. LOL

 

[Mutley56]

hi ^woody^,

Got delayed on project - fa,ily birthday celebration, but I'm starting today though.

When laying the flags, I will lay them out dry to check the layout. Then I will put down small sections of mortar and start re-laying the flags starting from a straight line from the house and working outwards. Generally, as soon as the flags are laid on a bed of mortar, can I put a plank across them and kneel on the plank if necessary?

Thanks, all necessary painkillers are on standby!!!

Cheers.

Mutley56

 

[Mutley56]

Finished the project last Friday. Not too bad, in my opinion, for a DIYer.

Thanks again fro your advice.

Mutley56