Difference between interior and exterior grade slate?

[bolst3r]

I have slate tiles in my kitchen (Nero Riven 600x600x10) and want to continue them out into the garden. I've prepared my patio base which consists of 4-6" of hardcore with another 4" of concrete on top. I was just about to order tiles but when looking at them the exterior versions are 30mm thick and twice the price of the ones used in my kitchen. So my question is what's the difference apart from thickness? I wondered if I could use the interior ones on my patio as the base is a similar construction to an interior floor or is this asking for trouble?

 

[tpt]

Assuming your talking about real slate and not a slate effect then any slate is fine for external use providing the base is solid. the 30mm pavers would be offered for use over a normal compacted hardcore base - i.e. an equivalent product to a garden paving slab.

If you are laying them onto a slab, using a tile adhesive then providing its laid properly it will be fine.

Like i say though - i'm assuming your talking about real slate

 

[bolst3r]

Hi and Thanks,

This is the Slate used in my kitchen, I have about 25-30 tiles left so would be a shame to waste them when I can just add what I need to make up the difference.

http://www.mandarinstone.com/products/slate/classic_nero_riven

Would you say this is good enough quality/real enough?

I've got about 13 tons of concrete going over my shuttered hardcore base (10x6 meters) so i'm hoping this will give me a sturdy enough base.

 

[tpt]

yep its real slate.

make sure its laid properly following adhesive manufacturers instructions, and make sure you leave the concrete to dry out properly - guide is a week an inch but you'll need to allow for the english weather!

 

[bolst3r]

Ha financial constraints will make me wait a few weeks anyway, had that issue inside and had to use ditra but am not going to do the same outside. So I should used proper tile adhesive rather that mortar? that's another 50 bags of Dunlops finest... ca-ching

 

[tpt]

Yep use a tile adhesive. Granfix do a product called slatefix just for this kind of thing.

Mind if i ask how much your paying for a bag of dunlops finest?

 

[bolst3r]

Certainly not, think it's about £21 but this was a year ago so I need to find a pallet of new stuff. I'm going to need quite a lot so want to find a decent adhesive that doesn't break the bank!

 

[tpt]

This would be my choice http://www.tileadhesive.co.uk/PDF files/Slatefix.

Once i have time later i'll give you a quote based on 55 bags or more. i know i can knock spots off that price!

 

[tpt]

just got my calculator out. for a purchase of 55 bags or more i could do this at £14.50 a bag including VAT.
not sure where you are but delivery would be dependant on postcode and is normally 20-30 quid.

you can get full contact details from my profile if you want to discuss further.

 

[bolst3r]

Ok, so just called Mandarin Stone in Marlow and asked the difference between their interior and exterior slate and they said "Frost resistance". They said they wouldn't suggest anything below 30mm as there's a chance they might crack in a harsh winter – really I said, roof tiles are only 5mm thick and they tend to last pretty well! So are roof tiles made from a better quality slate?

I followed this up and asked them about laying the tiles and they said they would lay the interior ones with proper tile adhesive but the 30mm exterior tiles should be done with sand and cement like traditional pavings.

Rough cost break down

EXTERIOR
Tiles = £2290
Sand and cement = £100
Extra Time (laying & mixing adhesive) + tile cutter blades £300
Total = £2690

INTERIOR
Tiles = £890
Adhesive = £800 (55 bags)
Total = £1690

So there's about £1000 saving using interior tiles that are 8-11mm thick but is this a silly thing to do if the shop says they will crack?

FYI, I have about 30 tiles left over from my kitchen and they have sat out doors for 18 months and through some pretty harsh weather, recently used 6 in a porch extension and they were fine and the rest that are still outside haven't crumbled yet!

 

[tpt]

i sell 10mm slate all the time for external use, i have it on my own patio and after 6 years its fine. i only sell brazillian slate but ive sold thousands of metres of it and my supplier marks it as external grade - i'd hang my hat on these products but can only advise on mandarin as i dont deal with them.

spose the issue is if you buy from mandarin and you get an issue they wont back you up.

have a look at the black brazillian slate either on my site if you like (link on my profile). i'll happily confirm its suitable for external use and beat mandarin's price.

for the record thickness wont help a jot with frost resistance, damage is cause by absorbed water freezing and expanding causing cracking. whilst you wont get this issue with slate in theory the thicker the less frost resistant

 

[bolst3r]

All very interesting, I shall do some more research

Thanks.

 

[tpt]

of course. and by no means feel you have to use me - even if you buy elsewhere i'm happy to help on the advice front.