Bradstone over dolomite - Bedding thicknesses.

[Rich Payne]

Hello, My first post and typically wading in with a query.

I'm based in Belgium so my problems have a slightly foreign tint to them.

I am intending to lay a patio of 4m x 10m in Bradstone Old Town (which is available here) and have an existing surface of compacted fine dolomite chippings. It is a bit of a typical thing here and whilst it looked good when first laid 5 years ago it is impossible to keep clean and walks in badly. Whatever, it has allowed the ground around the new house to settle without any problems.

The subsoil is a heavyish loam and the 75mm of dolomite was laid over 100mm of compacted road planings.

I see reference on the main site to laying slabs on a coarse sand bed. Bearing in mind that the pointing on "Old Town" will be fairly wide, am I asking for trouble if I remove the dolomite to depth (this will leave me with about 30 - 35mm of bed) and lay the slabs directly on it? The slabs would be at the smaller end of the scale as the 750 and larger sizes are not offered here.

If I use a bed of sand /cement (They call it Rhine sand here), how deep would it need to be to ensure stability and would it be a problem if any dolomite remained above the sub-base ?

It rather goes without saying that I would prefer to use as much of the existing material as possible but on the other hand I don't want to do it all again next year.

Thanks in advance for your help.

[Tony McC]

Lay the flags on 30-40mm of your Rhine sand with 10% added cement and they will be fine. It's identical in construction to what we use in Britain and Ireland.

[Rich Payne]

Thanks for that Tony, much appreciated. I suspected that sand/cement was the way to go but if an expert had said "bang it down on the existing" then I was prepared to do less digging !

Your bedding calculater is based on 50mm and suggests 3t sand for 40m² so I'll work on 33mm bedding and order 2t.

Is a fall of 1:100 OK for "Old Town" ? That's what I've got at the moment to the existing pavé edging. I won't be going out as far as that and I'd prefer to leave it.

I'd rather not come higher on the house wall because it's already a bit high. Round here they go to one brick under the DPC and don't seem to worry about splash. It worries me a bit but they all do it and say it's OK because the DPC comes up two bricks higher on the inner wall ??? No problems so far.

[Tony McC]

1:100 is not adequate - way too shallow. You need 1:60 as a minimum with that type of riven-effect flag

[Rich Payne]

1:100 is not adequate - way too shallow. You need 1:60 as a minimum with that type of riven-effect flag

Glad that I asked then

I've now managed to get hold of a Bradstone brochure and they talk about 1:40 - I should have thought that a fall of 1" across the average table would be enough to tip a pint glass over ! Do people really work with that sort of fall on a patio ?

My next serious question is relating to the pointing. I am quite tempted by the Romex option particularly for its resistance to shrinkage. Is the permeability not a problem with freezing temperatures ? I assume not but can't find it mentioned anywhere.

As there is no buttering involved, should I be expecting to space the flags and remove the spacers as I brush in ?

By the way, is Bradstone reasonably OK regarding colour-fastness and weathering ? I don't expect it to look new for ever.

[lutonlagerlout]

sadly rich its a payoff,you can have a flat level patio that looks great in the summer but gets covered with algae and puddles in the winter ,or you can have a slight fall 1:40 is too much
i like to go for about 12-15 mm per metre,which isnt noticable drinks wise but get the rain water heading the right direction,but you may get localised puddles with riven slabs/flags
first patio i ever laid in 1985 i did 1:35 fall,absolutely shocking i had to cut 2 inches off the guys back gate
at least the only way was up after that
cheers LLL

[seanandruby]

had to jet wash some old flags once. as there where bushes on the side i didnt relise they were on top of a reinforced garage roof. next day got called back there, the side wall had not long been painted white. aaarrrggghhh!! i had to buy some paint and do the lot again. on reflection it, maybe, wasnt my fault. but i redone it out of goodwill. learning curves a? :p

[Tony McC]

1:40 for a patio is a tad excessive, but with riven and riven-effect flagstones, the manufacturers/distributors are concerned to cover their arses and that's why the recommend what is, in effect, the degree of fall we build into public highways. Somewhere around 1:50 to 1:60 will be adequate.

Romex and freezing: not an issue. Romex was first developed for the German market and is more than capable of dealing with the continental levels of frost.

Spacers: you could use them if you really wanted, but, in all honesty, they're more bloody trouble than they're worth, especially when laying random layouts (because of the need to balance joints)

Colour-fast: Bradstone are better than most but you can;t really call any dyed concrete product "colour fast".

[Rich Payne]

I've pretty well decided to use Rompox Easy which the Belgian importers tell me is also sold in the DIY chains here as "Fugli" !

How do I begin to calculate requirements /m² using the six smaller Old Town flags ?

[Tony McC]

Ask Romex - they have data on coverage for all sorts of different paving materials