Hi, I am going to do some test cement mortar mixtures soon, but I bought the wrong type of lime; hydraulic instead of the usual hydrated. My aim has been to get a traditional, whiter mortar. Does anyone think that I might be successful by creating a mixture with both portland and NHL in it? I am guessing that this is not done, but I thought I'd ask here first. thanks -Elliot
I quote the following extract: The essential feature of a lime mortar or plaster is that it needs to carbonate in order to cure. A transformation takes place within it as calcium hydroxide changes to calcium carbonate, a process that requires moisture, as carbon dioxide in the atmosphere has to be carried into the lime plaster in solution. A hydraulic lime has the extra feature of also having a chemical set, so that it can feel hard to the touch within a few hours to a couple of days, depending on the strength of the hydraulic lime. It can remain workable for several hours or days, but it still needs to carbonate after it has set. Lime strengths vary greatly depending on the type of lime used, but it takes about 28 days to reach full strength. Cement does not carbonate. It hardens because of a chemical reaction with water, usually setting within half an hour to an hour, after which time it cannot be re-worked. It takes about 28 days to reach its full strength, and is generally very much stronger than lime
I've done another hour or two's searching, and I think I might be fine with some kind of portland & hydraulic lime mortar. It turns out that this is what was used to restore Hadrians's Wall! If anyone wants to know more about this then just google "The hydraulic lime pointing mix contained a 'trowel full' of ordinary". Some tables of info are here: https://content.historicengland.org...drians-wall/hadrians-wall-appx-refs-indx.pdf/
May I ask what you need the mortar for? I've done concrete testing in a previous life and it's not just about getting the colour correct.Hadrians wall may have been fine but it didn't have lots of weight on it or doors slamming,if it's just a bit of mortar for pointing then go for it,however if it's for actual bricklaying then be careful,its pointless having a mix that matches the existing perfectly but has no strength in it. We used Snowcrete on a job at my mate's house a couple of years back as we were dealing with portland stone,it dried nice and light. Incidentally did you know that the type of sand used also has an effect on finished colour? Traditionally a lot of older houses near seaside resorts used beach sand to build with,this gave a lighter mortar than red sand,although I believe it's use is frowned upon these days,it was common years ago.Up here there was a lot built using something called Mersey Grit,again a light mortar resulted,go to inland areas where the sand was dug out of the ground and it's more of a reddish colour,boring maybe,but there's a lot more to it than meets the eye.
I was in Wickes a couple of weeks back and it said on a poster that 'Snowcrete' doesn't have an expiry date?
A lot of manufacturers have improved the packaging now,it used to just be a paper bag but now it has plastic in it which keeps out the moisture,it used to be terrible,you'd have to get a bag of plaster on a weekend from the big orange shed and it was going off before you'd finished mixing it.
Just spoke to Tarmac technical and it would seem that J T is correct,apparently there is a chemical in all cement which causes it to go lumpy,this is called chromium 6,incidentally it also causes dermatitis in some people.I was assured by technical that as Snowcem has extremely low levels of this then it doesn't "go off"! However another interesting thing I was told was that if you could grind down the lumps in a bag of ordinary cement then it would be ok to use,apparently it isn't degredation of the product just a sign of incorrect storage.
I'm going to send a sample to conserve to get the mortar matched (lime mortar). they need a size of a thumbnail to match.
It's funny because I have bought a bag of snowcrete from Wickes just two weeks ago. Last weekend I opened it up and it was nothing but lumps. I looked at the expiry date and it was almost a year out of date. I have now been waiting for 2 days for them to call me back about this so that I can exchange it. Really bad!
Hi, thanks for the informative reply. The mortar is for patio pointing. The pavers don't have a great bedding (dab bedding...damn) but will only be walked on. For sand I have bought sharp sand and soft sand from Wickes. Neither seem very red. My plan is to try using 50:50 sharp:soft if the applicator gun can take it. I will probably have to sift the sharp sand. For the cement, my current plan is to try 1:1:1 portland:snowcrete:NHL . I will probably add a dash of Febmix for the applicator gun.
Hi again, I went ahead and used the NHL in the cement mixture, as one might usually use hydrated lime. It seems fine, I was probably only worried due to ignorance but I have learned a huge amount since. I used the following mixture on the patio: binder: 2 parts mastercrete, 2 parts snowcrete, 1 part NHL 3.5. sand: 2 parts sharp sand, 1 part soft sand (both from Travis Perkins). Here are some pics. The last one is a the house joint; it joins to a stone wall. I used NHL-only here with the same sand mixture. I didn't even try using the pointing gun. I bashed the mortar into the joints as well as I could, and then used trowels and finally a sponge technique.