[iknownothow]

For those not familiar, the secret ingredients are to do with the Lime Cycle [1]:

1) Quicklime/Slakedlime (Calcium Oxide, CaO)

2) Lime (Calcium Hydroxide, CaOH2)

3) Limestone (Calcium Carbonate, CaCO3)

To keep it simple, typically you start with Quicklime (CaO) and after construction you end up with some mix of all three and after hundreds of years, the masonry transitions to mostly Limestone with microscopic traces of the other two. The slow transition of the lime cycle upon exposure of the masonry to both air and water (rain) ends up making the structure "self healing" and "stronger over time".

Fun fact! Lime putty is anti-mold even in humid conditions because upon exposure to moisture, CaOH2 + H20 becomes too basic for mold to grow on.

Cement/Concrete (based on Portland cement) is water proof but Lime by itself is not. But Roman Concrete, made from Lime and mixing with ash or broken pottery or ceramics makes it water proof [2]. I beleive Roman concrete was used whenever contact with water was expected. Both concrete and Roman concrete have the same underlying chemistry (Pozzolanic reaction) to make them water proof [3].

The fascinating thing is that Lime is everywhere in ancient masonry. Lime is more breathable, workable and sustainable. The only thing is, it requires maintainance, which is why Portland cement has taken over the world.

Modern cement/concrete is amazing for large structures. I hope Lime makes a comeback soon at least partly as putty and for building smaller homes.

[1] https://en.wikipedia.org/wiki/Lime_(material)

[2] https://en.wikipedia.org/wiki/Roman_concrete

[3] https://en.wikipedia.org/wiki/Pozzolanic_activity#Reaction

[carlmr]

>Fun fact! Lime putty is anti-mold even in humid conditions because upon exposure to moisture, CaOH2 + H20 becomes too basic for mold to grow on.

Can we use this instead of grout in the bathroom somehow?

[iknownothow]

I'm not sure as I'm not a builder or plasterer and it does depend on the use case.

However I do know that some grout and some paints that say they are anti-mold contain Lime or calcium hydroxide as their primary anti-mold ingredient. I think pure Lime putty can be used as pointing material between bricks in humid basements. Lime plaster (lime mixed with sand) can also be used in bathrooms (with some considerations I am not familiar with). So, my best guess is that some mix of Lime can be used as grout. But I can't say for sure.

Something I plan on doing before this winter is to use Lime Wash. Take Lime (CaOH2 in powder form) and mix with water until it has milk like consistency and brush it on grout or on (white) bathroom walls. If it works, I expect it to be a yearly or quarterly ritual and not a one time solution.

EDIT: A fascinating historical material I recently learned about used in bathrooms is called Tadelakt [1] which uses Lime as one of its ingredients.

[1] https://en.wikipedia.org/wiki/Tadelakt

[eleveriven]

I like the idea of treating limewash as maintenance rather than a permanent cure. That is probably closer to how these materials were historically used anyway

[paulgerhardt]

I just restored an 1800’s house and we redid the paint in limewash as part of that process. (Effectively zero VOCs but pretty caustic when wet.)

Historically (for interior paint) you would use regular limewash in dry spaces and add casein/milk in high traffic/wet spaces. It works in a bathroom but wouldn’t hold up in a shower (for that you would want to use “tadelakt“ - especially if you’re going for that Aman spa look).

The contemporary solution with modern limewashing is to use “mineral shield” - it uses silicone instead of casein - it makes water droplets bead up but still lets water vapor breath through.

It also doesn’t flatten out the nice velvet texture one gets with limewash paint from the calcite crystals.

That said, it’s extremely obvious if one touches up a patch of wall with limewash. No two batches are the same color unless you’re going pure white and even then…

[jimnotgym]

Lime wash also discourages people from leaning against the wall, once they have seen the white marks on thier suit...

[psd1]

In my experience, grout doesn't go mouldy but silicone sealant certainly does. It's the caulk and the sealant that you want, i think, to replace

[whateverboat]

In India, people have used lime for all sorts of things in houses, including grout in places. It requires yearly maintenance.

[FuriouslyAdrift]

There is a variation of lime wash that includes a fatty oil as a sealant and has been around for 100s of years

https://en.wikipedia.org/wiki/Tadelakt

[IAmBroom]

Pure silicone caulk is mold-proof, even in the white variation. The various "improvements" in many caulks allow mold to get a foothold.

[bityard]

After decades of owning multiple bathrooms and only using products advertised as 100% silicon caulk, I can assure you that it is not mold-proof.

[fsckboy]

does "mold proof" mean mold won't grow on the surface, or that mold will not affect the silicone?

[jimnotgym]

Luckily mold is not chlorine bleach proof, but grout and silicone are

[tpm]

it's not waterproof

[gravypod]

Neither is grout. Grout is water permiable. You shower is water proof from the water proof backing we install the tile on top of.

Cement board + roll on or something like kerdi system.

https://youtu.be/B5DVpruLygw?si=jD8eMHHGQoWG4hI2

[Moto7451]

This is why you pay the premium for epoxy grout. When we redid our house we used only epoxy grout and cleaning it as as simple as using a foaming tile spray.

[gravypod]

This is not always a great idea. Especially if you have a water proofing membrane that allows drying out. You never want to trap moisture in a cavity. You want to be able to dry into the wet side.

[tpm]

right, but lime will be washed away by the water if no waterproof layer is added

[dredmorbius]

I suspect the term you were looking for in your original comment was insoluble, that is, a substance not (readily) dissolved into water.

Concrete is insoluble (it won't wash away, contrast with lime), but not water-proof.

[iknownothow]

It is not lime as in the fruit, it is lime as in the material (CaOH2). Lime the material is the binding agent in lime plasters. It is not likely to get washed away.

[tpm]

caoh2 is water soluble (slightly). the question was about anti-mold properties and it is commonly used for these properties in paint for example in cellars but it will lose these properties when too wet. so it's not used in bathrooms.

[DANmode]

My shower is waterproof because it’s a one-piece insert made of plastic.

Other shower materials that aren’t absolutely insanely stupid include glass, quartz, and other non-porous materials.

Because biology.

[meindnoch]

>Cement/Concrete (based on Portland cement) is water proof

That's patently untrue. Otherwise we wouldn't need concrete sealants.

[iknownothow]

You are correct.

I'm not sure why I remember cement to be water proof. Its possible I infered from how its been used around me. I have seen cement very often used where water contact is expected (bathrooms etc). I have also seen brick walls plastered with an extra layer of cement as putty considered to be rain proof and any leaks were thought of as poor workmanship rather than poor material choice.

P.S. I'm not a builder. I've taken an interest in the topic a few months ago.

[dnemmers]

Hydraulic cement is made for some of those occasions:

https://www.quikrete.com/productlines/hydraulicwaterstopceme...

But I wouldn't want to make any sort of building that only relied on it for waterproofing.

[Groxx]

Might be because it's water tolerant, i.e. it doesn't break down with exposure to water? Roman über-concrete stories are always full of "check out the concrete that's sitting in sea-water, it's still going strong! maybe it even helps!" cases too.

[DannyBee]

You can also just see it with cement board - if you pour water on top of it, it will eventually migrate through and drip.

[throwaway173738]

Also if you put a slab basement in a hillside in a rainy area. Water will percolate up through the slab unless you make good drains to divert the water around your foundation.

[amszmidt]

The key here is “based on Portland cement”, which is generally has water repellent added to it making it water proof.

Normal cement, concrete .. Is a different story.

[lazide]

Concrete is generally porous and definitely not micro-waterproof (aka lots of water vapor makes it’s way through). Including if using Portland cement.

It is generally macro-waterproof, however, unless there are large cracks.

[dnemmers]

I'm not sure exactly what you're saying is correct.

'Concrete' is a combination of sand, cement, water and aggregate, that cures together to form.

When the water migrates away from the curing concrete, it leaves open pores behind that future moisture can move through.

https://en.wikipedia.org/wiki/Portland_cement

[iknownothow]

I forgot another important reason why Portland cement is preferred over lime these days. Lime takes a while to set (a few days?), cement sets faster.

[_n_b_]

> Lime takes a while to set (a few days?)

Up to 30 days to set, and depending on the type of lime (hydraulic or non-hydraulic) and form/process (putty, hot mix, etc.) up to a year to reach full hardness.

[dnemmers]

Cement will still take many days to reach full cure time (measured in increasing PSI ratings)

https://www.ce.memphis.edu/1101/notes/concrete/section_3_pro...

[jimnotgym]

But it will be set enough to keep laying bricks tomorrow. Lime on the other hand takes a bit more thought. It is doubly true if the weather is cold

[IAmBroom]

You aren't contradicting anything. MOST of the strength is achieved in 24 hours or less.

[Fizzadar]

Victorian brick houses are all lime based, pointing (mortar between bricks), render outside and internal plaster. (Ours is 140 years old ish).

Lime is also more flexible (these houses have minimal to no foundation and constantly move), it’s breathable (no/less damp) and as such it also improves air quality indoors. It’s annoying to do because drying times are days/weeks not hours, but long run it’s a far superior material for small buildings.

It does burn though if you accidentally get it on your skin!

[ln809]

Spain stone buildings too... common problem modern plaster on those stone walls, folk have forgotten the wall needs to breathe

[cogman10]

> The only thing is, it requires maintainance, which is why Portland cement has taken over the world.

What kind of maintenance and why did roman cement survive without it? Or are we simply looking at ancient survivorship bias where the surviving roman concrete structures survived through the lime cycle without maintenance until it was no longer required?

[iknownothow]

I mentioned elsewhere that time taken for setting is also a major factor for why Portland cement is preferred.

Maintenance is probably less of a factor but it also depends on the use case. Take what I have to say with a grain of salt. Lime is a living material that slowly converts lime to limestone. For some use cases, the lime needs to be replenished often through applying lime wash on the plaster of external walls or wet interior walls.

As for load bearing walls or regular interior plaster walls I'm not sure there is much maintenance you can do and they are fairly durable.

As far as I know Portland cement sets faster and is a stronger but has a life span of decades and does not lend itself to be repaired or replenished.

I'd like to also convey some vibes I have about this topic as follows. Imagine having a 2 storey family home made of concrete that you want passed on for many generations. In 50-75 years, repairs/upgrades would require a lot of demolition as concrete with rebar is very strong. Much of the old material is trashed and hard to recycle. A similar house made of lime based products and some stone and wood would lend itself more easily for similar repairs and seamless upgrades and can maintain the same aesthetic look for longer. It feels like lime based products are appropriately strong and suitable for the smaller scale. The old material can be treated like any old dirt or rubble and is less polluting.

[eleveriven]

This makes me want to see lime used more in ordinary homes

[poelzi]

The trick was: Lime CHUNKS, proper volcanic fly ash, salt water + no steel. Self repairing and more flexible

[abdullahkhalids]

> Lime is more breathable, workable and sustainable. The only thing is, it requires maintainance

What sort of maintenance does it need?

[Fizzadar]

It wears down quicker than concrete (you can scratch it easily with a nail and minimal pressure). But we’re still talking 50+ years (before repointing brick, in my case). As long as maintained it’ll last forever (our home is 140 years old, I just re-did the pointing, should be good till I die).

[CGMthrowaway]

TLDR, use lime mortar not portland cement. And don't use rebar.

Also- modern concrete is not waterproof... requires sealant