Fairy liquid added to mortar? Criminal or not?

Legacy_user

Is using fairy liquid in mortar considered bad practice?

phill99

As you said, 2 schools of thought. I imagine the walls with fairy liquid in the mortar are still secure and standing, so it's not a problem.

FreeBear

Dangerous, no.
Poor practice, debatable.

I have added a few drops of washing up liquid when mixing mortar, and it only needs a couple of drops per gallon of water. One wall I did is still standing 20 years later.

Does a plasticiser help - Most definitely, and worth using a drop or two in most mortars. But it does only need to be a very small amount, so measure carefully.

EachPenny

FreeBear wrote: »

Does a plasticiser help - Most definitely, and worth using a drop or two in most mortars. But it does only need to be a very small amount, so measure carefully.

This is the issue, too much plasticiser leads to poor quality mortar which can cause real and genuine problems with the brickwork. It is not just about whether the wall still stands up in 10 or 20 years time.

Mortar plasticiser is supplied with instructions on the correct amount to use and will provide consistent results.

Washing up liquid comes in variable dilutions with no instructions on use as a plasticiser, users tend to put a 'squirt or two' in Therefore it is very easy to put an excessive amount into the mix and end up with a wall with mortar which is not fit for purpose.

Given the cost (approx £1/litre) compared to the cost of other building materials, saving money by using washing up liquid can be a false economy - especially as washing up liquid can vary in price from £1 to £4 per litre.

The issue is really about quantity and convenience. Most places only sell plasticiser in 5l containers, which is a bit much if you are only doing a small job. So it is easy to see why DIYers might be tempted to raid the kitchen supplies. However if you are mixing and using mortar on a daily basis (or for a big project) then the 5l quantity is not an issue.

Therefore if a professional builder turned up with a bottle of washing up liquid I would not allow them to do the job (also thinking what other shortcuts they might take).

DigForVictory

EachPenny wrote: »

Therefore if a professional builder turned up with a bottle of washing up liquid I would not allow them to do the job (also thinking what other shortcuts they might take).

Me, I'd hope they'd make their own brews & wash up properly after themselves. Let alone bring & use their own hoover.
It's been so long since I could afford a professional whatever, I live in a fantasy world about how these folk might operate. (With the honorable exception of the NHS, naturally.)

EachPenny

ruhe wrote: »

Thanks for the replies. It seems that there's no real scientific reason that using soap suds somehow weakens the mortar so it doesn't make someone a bad builder which was what I was really trying to find out

Not sure I'd agree with that summary. Plasticiser is formulated to give the best results and using the correct amount generates the right amount of plasticity for working without creating problems with the strength and porosity of the set mortar.

Washing up liquid has a similar effect on workability of the mix, but with an uncontrolled impact on the mortar in terms of air bubble size and quantity. You may also introduce unknown chemicals in the washing up liquid into the mortar with unknown potential to affect hydration and final strength. You might get a good result, but it will be by luck rather than judgement.

There certainly is science which shows that incorrect use of plasticisers weakens mortar, which is why the instructions on the right stuff explain clearly about the correct amount to use.

If a professional builder uses washing up liquid instead of plasticiser then they are a 'bad' builder, there is no question about that.

If a DIYer uses washing up liquid in a small (non-structural) wall then they are not following best practice... and you have to ask why they'd do that when the correct product is relatively cheap, and easy to obtain.

AndyMc.....

ruhe wrote: »

Many thanks for that thorough and detailed reply. The builder in question only used fairy liquid when they an out of plasticizer so it wasn't or isn't a regular feature. This chap is a £50k per year tradesman in demand. The only reason I say that is to show that he's not a cowboy builder/odd jober who hasn't done proper training.

Why’s he carrying fairy liquid if he’s running low on plasticiser, why not just stick up?

Beenie

It depends what you are building.

We had a garden pond and waterfall feature installed at great expense about 15-18 years ago. The builders son used fairy liquid in the mortar for the waterfall.

The upshot is that we can't use it: every time the waterfall is on, it produces loads of bubbles in the pond at the bottom and looks stupid.

buglawton

EachPenny wrote: »

Not sure I'd agree with that summary. Plasticiser is formulated to give the best results and using the correct amount generates the right amount of plasticity for working without creating problems with the strength and porosity of the set mortar.

Washing up liquid has a similar effect on workability of the mix, but with an uncontrolled impact on the mortar in terms of air bubble size and quantity. You may also introduce unknown chemicals in the washing up liquid into the mortar with unknown potential to affect hydration and final strength. You might get a good result, but it will be by luck rather than judgement.

There certainly is science which shows that incorrect use of plasticisers weakens mortar, which is why the instructions on the right stuff explain clearly about the correct amount to use.

If a professional builder uses washing up liquid instead of plasticiser then they are a 'bad' builder, there is no question about that.

If a DIYer uses washing up liquid in a small (non-structural) wall then they are not following best practice... and you have to ask why they'd do that when the correct product is relatively cheap, and easy to obtain.

My understanding of traditional building with brick is that they are supposed to be joined with mortar, not cement. Mortar is meant to keep bricks apart, not to glue them together. Traditional mortar breathes moisture so can actually help to avoid damp problems. It also shifts with ground settlement so you dont get a nasty crack down through the brickwork. At some point in time builders switched to harder mortars or near-cement, I know not why. This is a potentially complicated topic.

Alter_ego

Other washing up liquids are available.

EachPenny

buglawton wrote: »

My understanding of traditional building with brick is that they are supposed to be joined with mortar, not cement. Mortar is meant to keep bricks apart, not to glue them together. Traditional mortar breathes moisture so can actually help to avoid damp problems. It also shifts with ground settlement so you dont get a nasty crack down through the brickwork. At some point in time builders switched to harder mortars or near-cement, I know not why. This is a potentially complicated topic.

Cement is just the name of the (usually) grey powder which mixed with sand and water produces mortar. There are other kinds of mortar, and traditional building used a mortar which was essentially just lime and sand. Cement mortar has the advantage it sets much faster than traditional lime-based mortar and is more durable because it has greater resistance to water.

Cement-based mortar has the disadvantage of being inflexible, so cracks easily. To combat this mortar mixes used to be specified with a portion of lime, the lime makes the mortar more flexible when set, and improves workability.

But lime is expensive (one of the reasons traditional mortar went out of fashion) so chemical plasticisers became popular. These have a similar effect to adding lime. The plasticiser helps facilitate the entrainment of air (little bubbles) which makes the mortar easier to work with. When set the mortar will contain tiny cavities where the bubbles were, and these cavities help make the mortar flexible and resistant to freeze/thaw effects.

But as I mentioned earlier, it is important to get just the right amount of 'bubbles' of the right size, otherwise the mortar can be weakened. Washing up liquid has a similar effect on mortar, but not exactly the same.

In terms of function the purpose of mortar is to make the masonry units (bricks/blocks) adhere to each other, so in that sense it is a kind of glue. If walls only carried vertical loads then mortar wouldn't be essential (e.g. dry stone walls), but in most buildings the walls also carry horizontal and shear loads. For a brick wall to resist horizontal loads it must have something resisting the bricks sliding over each other. This is the purpose of mortar - it fills the microscopic pores in masonry units in the same way glue does and effectively 'locks' the bricks together.

Cement-based mortar undergoes a process called hydration which results in the formation of mineral crystals with jagged shapes. These crystals enable the mortar to bind very firmly to the masonry - but only if there is sufficient water available for the hydration process to complete. That's why mortar which isn't fresh is no good for brick laying (the hydration process is too far advanced already) and why mortar which is too dry doesn't properly hold the bricks together.

It really is a complicated topic