Can I use cement mortar for bricking up an internal opening in a lime mortar house?

[phillymclee]

I plan on bricking up an unwanted door opening into our lounge in an internal brick wall in our 1930's semi. My Engineer has specified that the bricks need to be toothed into the existing as we are making other alterations in the house, removing a load bearing wall so a new beam will be bearing onto this wall and he can't get the masonry to work with the current opening. Anyway that is irrelevant. My question is, can I use cement mortar to brick up the opening? The rest of the wall is currently constructed using a lime mortar. Will this small area of brick and cement mortar create a stiff point in the wall that won't move like the rest of the wall and ultimately cause cracking? Or am I worrying about nothing. This will be my first time laying bricks so I don't really want the added complexity of using a lime mortar. Many thanks in advance.

 

[a twig]

An NHL3.5 mortar is similar enough to a cement mortar that you shouldn’t have any issues other than the “set time” being a bit longer, which often makes things easier from a DIY perspective as you get longer to fettle

 

[phillymclee]

Great thanks for the reply. Obviously another factor is the cost. So are you saying you think it’s definitely necessary?

 

[Flyfisher]

What do you think is the added complexity of lime mortar? Also, since you already have a (presumably structural) engineer designing this project for you, perhaps they would be best placed to answer the question.

Personally, I agree with a twig above. In fact, I suspect you'd be hard pressed to notice the difference in using NHL3.5 compared to cement (except for the colour).

As for the cost, yes NHL3.5 will cost more than cement but since you're only bricking up a doorway the cost difference will be insignificant - perhaps a tenner?

 

[phillymclee]

Ah ok I’m new to this so have very little knowledge on the subject. To be honest I just watched a YouTube video of a Bricky using lime and complaining about how it mixed but I’ll ignore that. I thought there was a bigger price difference but if it’s really that insignificant I will go with lime. I’ve been trying to work out how much I need for about 150 bricks but all I can find is a calculator for a premixed back of which it told me I needed 6 25kg bags which came to around £160 with delivery whereas it looks like I can do around 200 bricks with 1 bag of cement for £7 from Wickes haha so that’s why I was a bit put off. Any idea how many bags of NHL 3.5 will be enough for approx 150 bricks? Yeah my Engineer will give me a min. Compressive strength but I don’t think he will know the ins and outs of actually using each type. Thanks for the advice guys.

 

[phillymclee]

Ok I’ve found another calculator and it’s telling me I need one bag of lime so big difference. Thanks for your help chaps.

 

[Flyfisher]

Premixed bags of mortar is about the most expensive way to buy, it's the price of convenience I guess.

I'd say your estimate of around 200 bricks from a bag of cement is probably about right and, as you say, a bag of cement is going to be around £7. I haven't bought any lime for a while and I know it has gone up in price but I'd expect a bag of NHL3.5 to be around £20 and would do as many bricks as a bag of cement. That's why I said the price difference would be insignificant (OK, it might be a little more than a tenner, say £15) because either option still needs the same amount of sand.

 

[phillymclee]

Yeah that’s a no brainer than. Every days a school day. Now time to test out my brick laying skills.

 

[Stevers]

Personally I would never use OPC for anything other than concrete. I was also thinking a 25kg bag of NHL might do your opening. If you add hydrated lime to your OPC to improve workability, then that's quite expensive too. If you just use OPC don't mix it too strong - 1:4 or 1:4.5 so it is less likely to crack the bricks.

Re the cost of NHL, I've just bought two bags of NHL 3.5 from my local builders' merchant and was stiffed for £26 a bag +VAT! I queried this, but the guy behind the counter was a miserable s*d I'd not encountered before. It was five minutes before closing time, so not really the time to play hard ball over a couple of bags. I did a bit of research when I got home, and was staggered that Travis Perkins wanted £35.73+VAT! Feeling only slightly less stiffed by my usual mechant, I then found out that I can collect from Limebase in Isle Brewers (truly the centre of the middle of nowhere) for £16.40+VAT. Last year I think I paid £15+VAT from the local merchant, so something else that's shot up in price.

Whilst quite a bit more expensive than OPC, there are savings to be had by shopping around, and then telling your local merchant what you'll do if they don't give you a fair price for a decent quantity when you've a big job on. I've collected NHL from Lime Stuff on the other side of Salisbury too, at the time they were better value than anything locally, and were my previous go to bargaining chip. Only slightly more expensive currently than Limebase, but may be closer to you.

Not a customer yet, but Limebase have a good range of products that you can pay for on-line and collect. This includes a black grit aggregate that I've not seen anywhere else and will need to repoint part of my gable end.

 

[stuart45]

Cement mortar is more difficult to work with, unless you use a soft, building sand and plasticizer or an equal quantity of hydrated lime.

 

[paulc]

I’ve been trying to work out how much I need for about 150 bricks but all I can find is a calculator for a premixed back of which it told me I needed 6 25kg bags

If you are using modern bricks, you'll find they are a little smaller than 1930s bricks. This means you will need thicker mortar joints to tooth in with the old bricks. So more mortar.
If you can reclaim bricks from the wall that is being knocked down, that will save considerable headaches along with a few quid.

 

[phillymclee]

Yeah I was looking at Travis online what a rip off! Bradfords are a bit cheaper at £34.30 inc. VAT but still pretty pricey. I’m in Bournemouth so not to far from Salisbury so that might actually be worth the drive if Bradfords can’t do me a better price, thanks for the tip! Also thanks Paulc that’s a good point, they are 110mm wide but I thought they still measured 65mm high but will have to check again and might have to get a second bag. I was just going to use common concrete bricks to keep the cost down as it’s just going to be covered up with plaster anyway. Although I’m sure there’s probably a reason that is not a good idea haha.

 

[phillymclee]

The wall we are removing will be a bit further down the line unfortunately. I have a list as long as my arm of things I need to do before we move in and that’s quite far down.

 

[Stevers]

I've haggled with Bradfords over the price of NHL with some success and even had a cash account with them. It was faily hard work, and in the end it was much pleasanter to deal with my local independant merchant who doesn't reach Bournemouth (yet). I grew up in Wimborne, and in my mid-twenties I spent 18 happy months working for Wimborne Timber Company shortly before it turned into a Jewsons. You've got quite a lot of choice in the area still. Buildbase can be up for haggling, Sydenhams are a class act for timber, and you could do worse than try Elliotts as an independant. I'm not a fan of Travis Perkins - and particularly their gruesome Ferndown depot - avoid!

 

[stuart45]

As your house was built in the 30's it may well contain some cement in the mortar. When Portland cement was first invented it was.used mainly.for concrete. Using it for bricklaying mortar made a virtually unworkable mix.
However in the 20's builders started gauging small amounts of cement into the mix, as it was found to help harden up the mortar a bit quicker, without the loss of any workability. Gradually the amounts were increased until by the 50's a 1/1/6 mix was common. The staff at Limebase regard NHL 3.5 as the equivalent of a 1/1/6 and NHL 2 as a 1/2/9.
One thing to bear in mind when building a wall is that even when using the same mortar if different masonry units are used the wall will move at different rates, so cracking is more likely.

 

[phillymclee]

Oh wow Stevens small world, I’m actually in Broadstone so only a couple of miles away. All good suggestions thanks I will try them all. And thanks for the info Stuart, maybe I need to use clay bricks then after all.

 

[stuart45]

As it's only a short length it probably won't matter as much. Technically concrete blocks and bricks are different to clay in that they are at their wettest when first laid, and shrink in time as they dry. Clay bricks are dry from the kiln, and especially when used outside expand as they absorb moisture. Bricks can expand by 0.5 mm in the first 15 years. In a really long wall that adds up. Temperature changes also cause expansion and contraction.

 

[phillymclee]

Interesting. Hopefully the temperature changes shouldn’t be to much of an issue as it’s an internal wall and as you say it’s only a short length. I will have a look around and see if I can find some cheap clay bricks anyway.

 

[Stevers]

Our top flat had a reinforced concrete staircase up to a blockwork porch and 'front' door with access through a hole knocked through the 20" stone wall into what was the kitchen for the flat. The redundant opening was filled in by my builder with two skins of dense concrete block and stoned in using 1:1:6. Internally it was cement rendered and finished in pink gypsum plaster. I can confirm that concrete does shrink, as when I redecorated up there a few years ago there was a neat 2mm gap all round the old opening, not least because no attempt was made to bond old and new work internally. The wallpaper had torn all round so that you could see where the door had been even before I stripped the paper!

 

[stuart45]

In the building trade minor cracking such as thermal, shrinkage and settlement are accepted by builders and customers alike. Although they aren't normally serious issues, they can usually be avoided by using the correct methods. Out of the the different types of engineering, the construction industry is probably the one which takes the most short cuts.
School friends who went into factory trades like mechanical engineering seemed to be taught more about doing the work properly, whereas in the construction trade there was always an emphasis on speed, even in tech.
This is especially true in bricklaying. Been taken to another level in the USA, where they lay over 900 in a hour in the World championships in Las Vegas.