epsilonGreedy

Brick/Mortar Adhesion, low tech explanation needed.

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Posted (edited)

The following advice from http://www.source4me.co.uk/calculate_brick_block_mortar.php says...

Quote

 

  • Adhesion - Strength of bond is affected by the suction rate of the brick, the mortar constituents, water content and the weather. Where the suction rate of a brick exceeds the optimum value of 1.5kg/m2/min, it is recommended that the bricks are wetted prior to laying, particularly in hot & dry weather conditions.

 

 

 

I assume that adhesion is a good thing, so why is it bad above the stated threshold?

 

Furthermore in dry weather I would have thought that the stickyness between newly laid brick & mortar would reduce and that lowered adhesion could be counteracted through moistening of bricks.

 

I am thoroughly confused by all of this as the advice contradicts my intuition.

Edited by epsilonGreedy

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Ok feeling stupid now, I think what they are saying is this.

 

When bricks are very dry too much water can be sucked out of the newly laid mortar into the brick leaving the mortar/brick bond interface dry and thus lacking in long term adhesion. I suppose this problem is more prevalent as a mortar mix drys before use and/or the brickie delays leveling taps as these could break the bond if it is drying too quickly.

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I suffered from this laying thermalites, when dry they just sucked the moisture from the mortar and did not “ stick” I had to soak them with a hose before laying.

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Yep if the bricks are too dry the motar won't stick to the bricks. You can put some water on the bricks but not too much as then you can get the white efflorescence that will stain the brick work.

I was the same as Joe with my lightweight block. They take a lot of water and even more when you go to plaster them.

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It’s down to experience as I’m not sure there is any practical way of measuring that in the field as it would require measurement of a state of change in a built wall..!

 

Most brickies know when mortar is too wet or too dry, and when bricks need a wet or perhaps the mortar needs more liquid but it is down to experience and the mortar mix used. 

 

I’ve now got to the point of not allowing onsite mixing of mortar unless it’s for very small jobs and we use ready mix as I get a guarantee on consistency and mix. It’s also cleaner on site and - being considerate to neighbours - it’s also quieter than having a mixer running all day. Cost wise it is around 10% more than dry mixed including labour, but if you have to pay for mixer hire and fuel etc then it becomes about equal which for a standard product with less waste and mess it’s a significant saving in my book. 

 

I also think laying rates are better with ready mix as the labourer is only loading out so I’ve got no waiting for the mixer. 

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4 minutes ago, joe90 said:

I suffered from this laying thermalites, when dry they just sucked the moisture from the mortar and did not “ stick” I had to soak them with a hose before laying.

 

 

Good to know this is more than a theoretical problem. I suppose that in mid summer weather it would be difficult to oversoak blocks, whereas in the case of facing bricks too much wetting could lead to mortar sticking to the face and a poor cosmetic finish.

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9 minutes ago, PeterW said:

I’ve now got to the point of not allowing onsite mixing of mortar unless it’s for very small jobs and we use ready mix as I get a guarantee on consistency and mix. It’s also cleaner on site and - being considerate to neighbours - it’s also quieter than having a mixer running all day. Cost wise it is around 10% more than dry mixed including labour, but if you have to pay for mixer hire and fuel etc then it becomes about equal which for a standard product with less waste and mess it’s a significant saving in my book.

 

 

I might follow this advice, would I be correct in thinking that with ready mix you apply water to the readymix on a board and so dispense with the mechanical mixer entirely?

 

Is it possible to buy readymix suitable for below DPC use? I ask because I understand that for frost protection mortar below the DPC should have a higher cement ratio.

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It comes pre mixed with a retarder in it so will last a day or 2 depending on what you want. It won't need much water added to it at all unless it's windy and it dries out slightly on the board. If you keep the board wet this stops it sucking water out of the motar.

For frost you can get additives like kill Jack or a rapid hardener added which make the mix go of quicker.

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20 minutes ago, Declan52 said:

For frost you can get additives like kill Jack or a rapid hardener added which make the mix go of quicker.

 

 

My brickwork should happen over the summer months so overnight frost is not a concern right now. The reference to frost was in relation to suitable mix for longterm frost protection of below DPC brick courses. Since starting this thread I have been reading about trade standards for mortar mixes M2, 4, 6, and 12. I need to research further but it looks for M4 (iii) for regular above DPC brick/block laying and M6 below the DPC?

 

One manufacturer site indicates 2 hours before a mortar mix goes off, that feel right for pedestrian brick laying rates in June.

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49 minutes ago, Declan52 said:

It comes pre mixed with a retarder in it so will last a day or 2 depending on what you want. It won't need much water added to it at all unless it's windy

 

 

Are you saying that readymix is supplied to site wetter than the constituent ingredients would be? I'd have thought that supplying pre-moistened readymix would be inefficient in terms of transport costs.

 

Can anyone point me towards an introduction on mortar and readymix?

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It turns up pre mixed in a usable condition, you hire large plastic tubs and the truck tips it into the tubs, just like readymix concrete. 

You then cover the tubs with thin plastic to keep it damp. 

It should last 3-4 days

so you need to plan your brickies and make sure they have a good run of work in front of them. 

Obviously you don’t order it on Friday. 

If you have a local plant you can go with a tub and collect if you have a couple of little jobs to do. 

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It comes like whipped cream. The chemicals it is mixed with just means it won't harden quick. A 24hr batch will last 48 hrs but it will need water added and mixed with a shovel.

If you are going for having brick it will be much better as every mix will be the same. You won't get any colour differences in the beds. Plus you can also get coloured motar which looks good.

Check your area and see if there are any lorries doing deliveries to sites near you and call in and speak to the foreman or the brickies themselves and they will let you know if it's good stuff.

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1 hour ago, epsilonGreedy said:

Can anyone point me towards an introduction on mortar and readymix?

 

I use Breedon for mine - Tarmac

do one too as do others. 

 

Tubs can be heavy and you need decent access for the wagon as it side loads the tubs or is like an oversize concrete mixer. 

 

https://www.breedongroup.com/products/ready-mixed-concrete/breedon-mortar

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Posted (edited)

Thanks guys, this wet readymix delivery concept has been an eye opener. The Breedon web site says a standard 1/3 m3 delivery is enough for 500 to 600 bricks. For most of this thread I thought you were talking about bagged readymix e.g. 20kg Blue Circle examples on sale at TP.

 

As I digest the significance of this product it does not feel like a win-win option even putting aside the £££'s. It must create scheduling problems, e.g. weather, no-shows by the brickie team or construction gotchas that need an adhoc meeting with an architect or conservation officer.

 

The nearest Breedon mortar mixing site is 26 miles away.

 

Consistent mortar colouring is an attractive attribute of wet readymix, I guess when I review the prescriptive demands of the conservation officer in my detailed planning permission I will find something about matching mortar colour to the period style buff handcut bricks.

Edited by epsilonGreedy

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There's got to be a batching plant closer to you that offers the service. I think we have four or five within a five mile radius here.

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52 minutes ago, epsilonGreedy said:

As I digest the significance of this product it does not feel like a win-win option even putting aside the £££'s. It must create scheduling problems, e.g. weather, no-shows by the brickie team or construction gotchas that need an adhoc meeting with an architect or conservation officer

 

You should be block scheduling tasks with amounts of slippage or slack in them. Start with a 7 hour working day and the tasks by hour and it will be closer to the actual. Start with 8 hour days and you are up against it already. 

 

Weather is something you cannot predict, or manage, unless you build a very expensive scaffold roof over your build and even then it’s only rain you protect from. I forecast losing 1.5d/mth to weather and we lost 3 days in total over 5 months.  

 

No-shows from a brickie is an issue for you to manage but I would get them to tell you when they will be there and what they need a week in advance. That way you are prepared and the stoppages are less. That’s a day to day plan rather than a block schedule so it’s about managing the site. 

 

On wastage, I lost a tub in total out of 18 so just shy of 5%. That’s a cost of £50 to me, which tbh is lost in rounding on a £100k project. 

 

Balance that against the fact that is less than 1 day labouring charge, and now tell me it’s not a win win ..? I had a labourer ill for a couple of days but the brickie laid nearly as many on his own with me labouring (just fetch and carry) which would have not been possible if I was having to hand mix everything. 

 

On your last point, if you have planned properly then there should never be a “construction gotcha” on a new build as you build to the plan. Get it ironed out on paper, and in writing, and then build to the spec - no exceptions. Change is your only big enemy on a build, and planning is the key to minimising change. 

 

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3 hours ago, PeterW said:

 

On wastage, I lost a tub in total out of 18 so just shy of 5%. That’s a cost of £50 to me, which tbh is lost in rounding on a £100k project. 

 

Balance that against the fact that is less than 1 day labouring charge, and now tell me it’s not a win win ..?

 

 

This is persuasive, reckon I am won over to the idea of copious amounts of readymix souffle being delivered onsite.

 

To mitigate the risk of brickie no-show I will build up say three courses of inner wall block a couple of days prior to readymix delivery then I could solo lay and consume the readymix delivery on the mortar hungry facing bricks.

 

Was £50 per delivery a special price?

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3 hours ago, dpmiller said:

There's got to be a batching plant closer to you that offers the service. I think we have four or five within a five mile radius here.

 

 

It's a bit rural out here, there are 4000 tons of chipping potatoes in store 200m down the road from me if you would like a bulk deal.

 

The closest Breedon mixing plant is 15 miles from the newbuild site but the web site does not mention mortar being available from that location. 

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1 hour ago, epsilonGreedy said:

 

This is persuasive, reckon I am won over to the idea of copious amounts of readymix souffle being delivered onsite.

 

To mitigate the risk of brickie no-show I will build up say three courses of inner wall block a couple of days prior to readymix delivery then I could solo lay and consume the readymix delivery on the mortar hungry facing bricks.

 

Was £50 per delivery a special price?

 

I’d lay blocks and leave the facings to a brickie but maybe that’s me ....

 

Think it was £52 plus the Vat per tub, min 2 tubs on a drop and we only had 3 tubs total. £100 deposit on the tubs though and got that back at the end. Got to know the batching plant manager really well and the drivers who would sometimes drop before 7am so would ring to get the gate code - only had one driver who was an issue in 5 months and only had him once. 

 

We had a drop too that ended up being placed in what is like a half height bulk bag with the usual plastic liner and that was fab - bag is still being reused on site as it was very sturdy !

 

Batch plant was 30 miles from us but had no issues at all - I was flexible with them and they helped me including pulling in a couple of drops where I’d really missed the cutoff time. 

 

Plants do both types of mortar too - above and below ground 4N so you just ask for what you need. 

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9 hours ago, PeterW said:

It’s down to experience as I’m not sure there is any practical way of measuring that in the field as it would require measurement of a state of change in a built wall..!

 

Most brickies know when mortar is too wet or too dry, and when bricks need a wet or perhaps the mortar needs more liquid but it is down to experience and the mortar mix used. 

 

I’ve now got to the point of not allowing onsite mixing of mortar unless it’s for very small jobs and we use ready mix as I get a guarantee on consistency and mix. It’s also cleaner on site and - being considerate to neighbours - it’s also quieter than having a mixer running all day. Cost wise it is around 10% more than dry mixed including labour, but if you have to pay for mixer hire and fuel etc then it becomes about equal which for a standard product with less waste and mess it’s a significant saving in my book. 

 

I also think laying rates are better with ready mix as the labourer is only loading out so I’ve got no waiting for the mixer. 

Sounds good. Do you find you ever have too much and gets wasted or not enough and blokes waiting round for delivery? I understand it keeps for a day or so?

 

quantites wise are you just converting dry weights or I suppose you get a feel for how far it goes?

 

What do you do about mix strength? Different for facing bricks and lightweight blocks? Or do they just do a one size fits all job?

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Sorry hadn't read thru thread. Mix strength question still applies re blockwork/brickwork

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6 minutes ago, Oz07 said:

Sounds good. Do you find you ever have too much and gets wasted or not enough and blokes waiting round for delivery? I understand it keeps for a day or so?

 

quantites wise are you just converting dry weights or I suppose you get a feel for how far it goes?

 

What do you do about mix strength? Different for facing bricks and lightweight blocks? Or do they just do a one size fits all job?

 

Breedon tell you how many bricks and blocks on average you get from a tub so you work it up from there. 

 

Mix was all 4N above ground and used everywhere - it lasted a good 3 days and if it was wrapped to keep the air out we had tubs from Thursday still good on Monday morning but it soon went off. 

 

Trick is to work what the brickies need and get it “just about there” as a delivery could be anywhere from 7am to 2pm. I ended up with weeks of 2 Monday and 1 Thursday, with the odd week with none or just the one when we got onto gables etc and working round the roof. 

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27 minutes ago, PeterW said:

 

I’d lay blocks and leave the facings to a brickie but maybe that’s me ....

 

 

I might end up agreeing with you on that. My plan is to practice corners & window frames in a local agricultural shed which has a smooth concrete floor just like they do at brickie school on YouTube videos. Just need to source some budget practice bricks. If that goes well I will progress to a practice cavity wall with insulation batts.

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Just now, epsilonGreedy said:

 

I might end up agreeing with you on that. My plan is to practice corners & window frames in a local agricultural shed which has a smooth concrete floor just like they do at brickie school on YouTube videos. Just need to source some budget practice bricks. If that goes well I will progress to a practice cavity wall with insulation batts.

 

Why.....?? Are you planning to do the place yourself ..?

 

tbh you would be better saving on labouring and loading out to keep them moving - that’s the costly and time consuming bit. As soon as they stop laying they are costing you money - a bit like chickens ... 

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5 hours ago, PeterW said:

 

Weather is something you cannot predict, or manage, unless you build a very expensive scaffold roof over your build and even then it’s only rain you protect from. I forecast losing 1.5d/mth to weather and we lost 3 days in total over 5 months.  

 

Depends on the time of year - Although it is not my problem as have a main contractor and fixed cost for standard build.  We have lost 7 full days out of the last month

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