epsilonGreedy

Engineering bricks with through frog holes, a bit daft?

Recommended Posts

Posted (edited)

The standard grey engineering brick in these parts at the BMs features three finger size holes right through the brick. Given the moisture resistant qualities of an engineering brick I am troubled by the thought these holes will be filled with moisture conducting mortar.

 

I appreciate that the DPC is the ultimate moisture barrier but it feels wrong to undermine the essential quality of an engineering brick with a fast path for moisture.

Edited by epsilonGreedy

Share this post


Link to post
Share on other sites

Mortar is reasonably good at keeping water out, which is why cement rendering works as a weatherproofing layer. 

Share this post


Link to post
Share on other sites

I think the holes make them easier to lay and help stop the mortar going everywhere.  You can get solid ones but youstill have perps anyway

Share this post


Link to post
Share on other sites
10 minutes ago, Mr Punter said:

I think the holes make them easier to lay and help stop the mortar going everywhere.  You can get solid ones but youstill have perps anyway

 

 

Ah ha, that makes sense. The parting comment from a brickie on the subject of grey engineering bricks was "don't ask me to lay them in wet weather or the finish will be messy".

Share this post


Link to post
Share on other sites
Posted (edited)
1 hour ago, JSHarris said:

Mortar is reasonably good at keeping water out, which is why cement rendering works as a weatherproofing layer. 

 

 

Good point, NHBC standards dictate stronger mortar below dpc which as you say is more effective at keeping water out.

Edited by epsilonGreedy
  • Like 1

Share this post


Link to post
Share on other sites
46 minutes ago, epsilonGreedy said:

 

Good point, NHBC standards dictate stronger mortar below dpc which as you say is effective at keeping water out.

 

Never knew that! Got any mix ratios? I'll need to consider this for my gate pillars.

Share this post


Link to post
Share on other sites
4 minutes ago, Onoff said:

Never knew that! Got any mix ratios? I'll need to consider this for my gate pillars.

 

 

An easy to digest lookup table of recommended mortar mixes here: http://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2011/Part6/section1/appendix.htm#61C

 

Thanks for asking because in responding I noticed that my future chimney stacks will require a below dpc strength mortar.

Share this post


Link to post
Share on other sites

In over 15 years of filling a mixer I just kept the mix the same strength. It was always 1 bag cement to 3 sand. Why would you want to skimp on a few bags of cement over the cost of a build.

Share this post


Link to post
Share on other sites
7 minutes ago, Declan52 said:

In over 15 years of filling a mixer I just kept the mix the same strength. It was always 1 bag cement to 3 sand. Why would you want to skimp on a few bags of cement over the cost of a build.

 

I think the dilution of mortar strength and the involvement of NHBC was a result of mass housebuilders cutting corners/costs by reducing the cement ratio in their on-site batch plants.  One consequence was that several new builds have suffered from premature mortar failure, with the stuff just crumbling away after a few years.  https://www.bbc.co.uk/news/business-46454844

 

 

My guess is that NHBC may have picked up the tab for this and so have tried to mitigate it whilst still allowing a weaker mix to be used in some areas, in order to keep the hand that feeds them happy.

 

It's completely bonkers for any self-builder to agree to reduced strength mortar, IMHO.  The cost saving is trivial in the overall scheme of things.

Share this post


Link to post
Share on other sites

We could do a full lift on most houses, seven course of block and either the brick or block on the outside each day, so it was in our interests to use good motar as we had to build on top of it the next day. If you had used weak motar then no chance you could keep the wall above plum if the one below was still moving about.

 

Share this post


Link to post
Share on other sites
12 minutes ago, Declan52 said:

In over 15 years of filling a mixer I just kept the mix the same strength. It was always 1 bag cement to 3 sand. Why would you want to skimp on a few bags of cement over the cost of a build.

Cause you'll catch a cold on thermals!

6 and 1 for those bad boys

Share this post


Link to post
Share on other sites
Just now, Oz07 said:

Cause you'll catch a cold on thermals!

6 and 1 for those bad boys

I built mine using lightweight blocks and mixed it all 3 to 1 . Why would you mix 6 to 1.

Share this post


Link to post
Share on other sites

the way i was told -long time ago was 

3-1 is a pointing mix  ,very very strong 

4/5-1 brick laying mix ,depends on sand type as well

yes plenty use 6-1  no problem -

-but the problem with mega builders was I think

it wasn,t even real portland cement ,but a cheaper type mixed with other stuff,then made weaker cos it laid up easier

not the right thing for all weather building

why would you use 6-1 --half the cost --thats why  

Share this post


Link to post
Share on other sites
1 hour ago, epsilonGreedy said:

Thanks for asking because in responding I noticed that my future chimney stacks will require a below dpc strength mortar.

 

That depends ... if they are exposed and have a pot and concrete liner then you should really use a sulphite resistant cement too. 

 

1 hour ago, Declan52 said:

In over 15 years of filling a mixer I just kept the mix the same strength. It was always 1 bag cement to 3 sand. Why would you want to skimp on a few bags of cement over the cost of a build.

 

Using old reclaims we use 5:1:1/2 OPC:Sand:Lime to get something a bit softer but still strong enough to hold. 

Share this post


Link to post
Share on other sites
15 minutes ago, PeterW said:

 

That depends ... if they are exposed and have a pot and concrete liner then you should really use a sulphite resistant cement too. 

 

 

Using old reclaims we use 5:1:1/2 OPC:Sand:Lime to get something a bit softer but still strong enough to hold. 

Yep but the lime helps this. 

Share this post


Link to post
Share on other sites
Posted (edited)
3 hours ago, JSHarris said:

I think the dilution of mortar strength and the involvement of NHBC was a result of mass housebuilders cutting corners/costs by reducing the cement ratio in their on-site batch plants.  One consequence was that several new builds have suffered from premature mortar failure, with the stuff just crumbling away after a few years.  https://www.bbc.co.uk/news/business-46454844

 

My guess is that NHBC may have picked up the tab for this and so have tried to mitigate it whilst still allowing a weaker mix to be used in some areas, in order to keep the hand that feeds them happy.

 

It's completely bonkers for any self-builder to agree to reduced strength mortar, IMHO.  The cost saving is trivial in the overall scheme of things.

 

If you mean it is "bonkers" to use any mortar less than 3:1 in strength then that would be bad advice.

 

For hundreds of years mortar mixes have traditionally been far softer than current NHBC standards. Above dpc there are two competing considerations, on one hand a 3:1 mix is too brittle for a whole masonry wall and age old brickie lore is mortar should be matched to the strength of the brick or block. A wall built with a softer mortar can accommodate movement without fracturing. The 150 year old cottage next door to me has experienced obvious movement in its walls as the foundations have moved, had a modern house with brittle 3:1 mortar throughout its elevations been built on the same Victorian standard foundations it would have been condemned by now because a modern wall would have fractured under the movement stress.

On the other hand a strong mortar is more weather resistant and so different regional regional practice evolves.

 

The mortar failures in mass built houses that routinely hit the news are attributed to gross transgression of elementary building standards, nothing to do with dodgy modern standards that specify use-cases for softer mortar.

Edited by epsilonGreedy

Share this post


Link to post
Share on other sites
15 minutes ago, epsilonGreedy said:

The 150 year old cottage next door to me has experienced obvious movement in its walls as the foundations have moved, had a modern house with brittle 3:1 mortar throughout its elevations been built on the same Victorian standard foundations it would have been condemned by now because a modern wall would have fractured under the movement stress.

 

That’s irrelevant ..!! The reason your neighbouring house hasn’t cracked is there will be a lime mortar not a cement mortar in the brickwork. The benefit of lime mortar is that it remains “flexible” and can also “heal” over time. 

 

19 minutes ago, epsilonGreedy said:

The mortar failures in mass built houses that routinely hit the news are attributed to gross transgression of elementary building standards, nothing to do with dodgy modern standards that specify use-cases for softer mortar.

 

No... just read the actual reports and then comment ..! Some of the lab samples are showing 8:1 and worse - these are being site mixed using silo products which are pre-blended prior to even getting on site, so there is nothing the site can do. Add into this that there is a move to reduce OPC and replace with GGBS at up to 50% and you are now in the realms of big issues. 

 

If you build a house at 3:1 then it will crack as it’s far too strong, and more than likely will also cause block failure especially with lightweight blocks. 

 

The key is to use an OPC of known provenance and one that isn’t half full of GGBS or other pozzolanic material and then mix on site with a gauged mixer if you’re wanting to be sure of the mix. 

 

I suggest starting with this as light reading - a useful guide to mortar

 

https://www.brick.org.uk/admin/resources/mortar-for-brickwork.pdf

 

Share this post


Link to post
Share on other sites
Posted (edited)
41 minutes ago, PeterW said:

That’s irrelevant ..!! The reason your neighbouring house hasn’t cracked is there will be a lime mortar not a cement mortar in the brickwork. The benefit of lime mortar is that it remains “flexible” and can also “heal” over time. 

 

 

It is entirely relevant to illustrate why using a 3:1 cement mortar throughout house walls could lower structural integrity, which is a point you confirm later in your post. Some people reading the@JSHarrispost might conclude they should use 3:1 for the whole of their house which could lead to cracking as your say.

 

All large structures are subject to stresses and movement. Their long term structural integrity is determined by how they flex in response to these stresses. By some measures cast iron is stronger than steel but a super tanker built from cast iron would break up in the first storm it encountered at sea. Houses and ships need to flex and using the right hardness/strength of mortar or grade of steel is part of the engineered solution.

 

To impune that modern houses are suffering structural failure because the NHBC permits a variety of strengths of mortar is misleading.

 

41 minutes ago, PeterW said:

No... just read the actual reports and then comment ..! Some of the lab samples are showing 8:1 and worse

 

 

Indeed and what else should that be called other than the phrase I used above = "gross transgression of elementary building standards". My point is that modern houses have not been condemned because builders used NHBC specified softer mortar mixes.

Edited by epsilonGreedy

Share this post


Link to post
Share on other sites
13 minutes ago, epsilonGreedy said:

Some people reading the@JSHarrispost might conclude they should use 3:1 for the whole of their house which could lead to cracking as your say.

 

Nope. It says a self builder shouldn’t reduce the strength based on cost. House builders are using 8:1, 6:1 is the correct standard and this was the quote :

 

4 hours ago, JSHarris said:

It's completely bonkers for any self-builder to agree to reduced strength mortar, IMHO.  The cost saving is trivial in the overall scheme of things.

 

20 minutes ago, epsilonGreedy said:

To impune that modern houses are suffering structural failure because the NHBC permits a variety of strengths of mortar is misleading.

 

You’re misquoting and wildly off the mark here. NHBC will have picked up the tab and if you read the table in the linked document you would see the different classes for different purposes. The issue is that the stated M4 mixes are not meeting the strength classifications and that is causing problems, but given NHBC is entirely funded by the industry it’s not really going to bite that hand is it..??

Share this post


Link to post
Share on other sites
Posted (edited)
12 hours ago, PeterW said:

Nope. It says a self builder shouldn’t reduce the strength based on cost. House builders are using 8:1, 6:1 is the correct standard and this was the quote :

 

 

If you took the time to review the thread timeline you would note:

  1. Someone asked me for a reference to clarify a below dpc stronger mortar mix.
  2. I provided a link to an NHBC table which illustrates the prescribed range of mortar mix/strengths in different use cases.
  3. Declan immediately countered saying he used 3:1 throughout and then questioned why would anyone try to save money using a weaker mix. I thought this an odd comment but then concluded his house was built using entirely of blocks in Northern Ireland hence his decision must reflect local building convention.
  4. In a direct quote of Declan's 3:1 recommendation, Jeremy seemed to reinforce this view by equating weaker mortar mixes with a questionable desire to save money.

At this point I felt is necessary to point out that use of prescribed NHBC spec weaker mortar mixes where recommend, leads to improved structural integrity. 

Edited by epsilonGreedy

Share this post


Link to post
Share on other sites

Sod it. I'm going to go with whatever my 1980s Reader's Digest DIY bible says! 

 

😁

  • Like 1

Share this post


Link to post
Share on other sites
7 hours ago, epsilonGreedy said:
  1. In a direct quote of Declan's 3:1 recommendation, Jeremy seemed to reinforce this view by equating weaker mortar mixes with a questionable dire to save money.

At this point I felt is necessary to point out that use of prescribed NHBC spec weaker mortar mixes leads where recommend, leads to improved structural integrity. 

 

"Seemed to" is entirely your personal misinterpretation.  This is what I wrote, have a go at reading it again:

 

Quote

I think the dilution of mortar strength and the involvement of NHBC was a result of mass housebuilders cutting corners/costs by reducing the cement ratio in their on-site batch plants.  One consequence was that several new builds have suffered from premature mortar failure, with the stuff just crumbling away after a few years.  https://www.bbc.co.uk/news/business-46454844

 

 

My guess is that NHBC may have picked up the tab for this and so have tried to mitigate it whilst still allowing a weaker mix to be used in some areas, in order to keep the hand that feeds them happy.

 

It's completely bonkers for any self-builder to agree to reduced strength mortar, IMHO.  The cost saving is trivial in the overall scheme of things.

 

The point I was making was that there had been a lot of cases of mass built houses suffering from mortar failure, as a consequence of corners being cut to save money.  The last sentence I wrote is the key one.

Share this post


Link to post
Share on other sites

I have been using 4:1:1 sand cement lime for years, but This is for repairing my old stone walls and it’s the mix I used in Australia for my walking track construction. It amazed me at how well this mix lasted when repairing or building with sandstone, it never cracked, was hard wearing - could be walked on by hundreds of thousands of people without visible wearing and could withstand extreme heat and temperatures below zero. I have been using this mix on my property for six years and so far it’s all 100% as a general DIY mix i think it’s great. I have never laid a brick in my life so can’t comment on this aspect  but just wanted to pass on my experience. 

Share this post


Link to post
Share on other sites

‘The mortar should be the weaker element of the wall’ (I.e. not as strong as the material it’s bedding) was a fundamental passed down to us at college. 

Another was the question ‘is the mortar there to keep the bricks together or to keep them apart?’

Bit of a trick that one as it has to do both to carry out its function properly,but it was intended to stimulate a different train of thought. 

When I was a hoddie/improver in my late teens/early twenties it was all mixed on site (except maybe jobs in the city where space was an issue so they might get ready mixed delivered.)

We used to do different ratios for the external & internal walls. 

I think some issues arise due to building on unsuitable land (or not building with the correct system for the land.) 

I’ve worked on two flood plains in my time on site. 

One of them I know had issues with cracking before the job was even finished. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now