The Brew Cabin

we live in a very cold climate with major frost heaves and we wanted to create our slate patio (about 240 sqft) without using concrete but it seems the base of compacted crush topped with 2" of sand isn't allowing the 2" slate pieces to set - we are still experiencing some of the slabes lifting/shifting when they are walked on - we have wet the sand repeatly and have swept on new sand to fill to no avail...

is it not possible to lay on sand only - does it have to have a concrete component?

thanks for your help

It is possible to lay on a sand bed, but you will have to accept some movement of the paving, if you live in a country that experiences frost heave in winter.

We in Britain and Ireland are lucky in that we don't get any frost heave worth mentioning, otherwise the national rail network would use it as yet another excuse for not running any trains. Consequently, I don't have much experience of pavement design in contionetal climates, but, from what my colleagues tell me, a flexible construction (sand only) is expected to move, but a rigid construction (cement-bound) has to be of sufficient thickness to withstand significant heave, which can be as much as 600mm, I'm told. So, the short answer is that, if you want a non-moving patio, you need to use concrete as a bed. :(

thanks - we do have to worry about frost heaves here in northern alberta, canada

i'd really like to reduce the amount of "movement" and i'd like to reduce the "dusting" from the sand between the joints - is there any thing you can think of that we might introduce to the sand e.g. soil, much lighter amt of dry concrete, shale dust etc. that might help "set" the stones and reduce the dust?

thanks for your help -

while i'v never had the pleasure of visiting your country, i have vicariously through my wife - :} she leads designs, markets and leads tour groups to gardens throughout england and europe.... maybe someday i'll get to go as well ...

regards

The reduce 'dusting' of the sand joints, you might want to consider using a stabilising compound or a polymeric sand. I can't tell you the name of products that are available in Canada, but a good place to start would be with Envirobond, based in Ontario (I think!) as they are one of the biggest manufacturers of polymeric stabilising compounds in N.America and their CEO is a damned nice bloke (He's actually over here at the moment, allegedly on business!)

These products work by 'glueing' together the sand grains, preventing them being blown or washed out.

Their website is at www.envirobond.com and I'd be glad to hear how you get on. :)

Thanks - i've sent an email to the Cdn head office outlining my dilemna - if you are talking to the CEO would you mind mentioning my query - he might want to check out the results when done at www.icangarden.com/pix/backyard.cfm

by the way, do you think i will have to replace the underlaying sand (about 2-4") or just the joint sand?

thanks again for your help

I'm hoping to meet up with Mr Envirobond this coming week, so I'll take him a print out of one or two of your photos and see what he suggests.

The first thing I'd say is that joints between your slate pieces are awfully wide. When constructing what we call Crazy paving, the trick is to keep the joints to a minimum width, filling in wider joints with additional stone pieces as required. I've nicked one of your images, shrunk it, compressed it and reproduce it here for the benefit of other readers....



Where wide joints like these are unavoidable, they're normally filled with concrete/mortar, and then topped with a surface dressing or gravel or grit, so that it doesn't look like concrete but has its strength and prevent the jointing being scuffed or kicked about everywhere. If this were mine, I'd seriously consider using an Exposed Aggregate finish concrete in the joints, because I know I could make it look really good.

Nice garden - You can take a peek at my garden and see how it contrasts with the gardens in your part of the world. :)

Here's an image of crazy paving from a derelict garden I frequent on the outskirts of Bolton, Lancashire.....



...notice how 'tight' are the joints, compared to your project.

The joints are the weakness in a pavement such as this, so, by keeping them to a minimum, you maximise the strength and longevity of the paving. The example above was paved around 1906 and has never been relaid!

the widest joints shown are actually going to be covered by our stairs - we just finished cutting up an old 60' power pole for the stair "legs" - the balance of the gaps are only a few inches at best - would you suggest we make them tighter before we try and do the "bonding" - i worry about the concrete as we get a fair bit of frost heave in this part of the country ( our winters can get down to -30+C )

If you have to lift or re-lay the paving, then I'd definitely re-lay them with minimal joints. I'm not sure what effect severe cold/frost would have on the polymeric sands (but I can ask) but from an aesthetic point of view, it's the stone you want to see, not the jointing.

thanks - as the joints in the other areas are quite a bit smaller i may not move them immediately - besides my wife donna wants to plant between the joints with wooly thyme etc.

by the way i enjoyed "wandering" around your garden - nice to meet another gardener from across the pond

my wife has been visiting your country leading garden tours for over 6 years and every year she comes back wound up again about how great the gardens are in the UK - maybe next year i'll get to join her and see for myself

i'd be really interested in the poly / frost question - also, i'd like to know whether he feels we need to remove all the sand or just the sand in the joints ....

thanks again for your answers - they are appreciated

hi tony - did you ever hear from the person from envirobond - i sent a couple of notes to their head office but i haven't had a response yet

He's just returned to Canada after a couple of weeks over here in Europe, so I'll jog his memory for you. :)