Help, what is a Firming liquid for turn of the century crumbling mortar!?

[jimtmcdaniels]

Hi I need help on this subject please,

I'm searching for the definitive answer as to whether or not there is like a spray on liquid which will firm up house stone foundation/wall mortar.
These are turn of the century 1900, which the mortar is very crumbly. It is constantly slowly falling out.
I know home improvement books say to scrape out some of the old mortar and repoint the grooves with new mortar after wetting the surface with sprayed water.

*BUT I have seen some old 1900 walls in restaurants where the mortar seems firmed up and no longer crumbly as if it was sprayed with some kind of firming agent.

Otherwise is repointing the only treatment for such walls?

Thank you for your time and knowledge!

Jim

 

[jamest]

How friable and crumbly the mortar is depends upon multiple factors, so the fact that some walls have more crumbly mortar than others is hardly surprising - it's what you would expect. I assume that it's lime mortars we're talking about, given the age (but not necessarily) and how do you know that the mortar that's crumbling is the original one? Perhaps the mortar in the different walls is of a different age.

It's highly unlikely that the difference in crumbliness is a result of the use (or non -use) of a consolidating agent. Traditionally, consolidating agents were sometimes used, but usually on renders rather than on pointing (where application would be nearly as tedious and time consuming as re-pointing). All sort of things have traditionally been tried, including lime water and barium water (weak solutions of calcium and barium hydroxide respectively), but they are of limited effectiveness. If you're interesting you can read this:

https://www.sciencedirect.com/science/article/pii/S1296207414001150

Interestingly, Vitruvius recommended the impregnation of friable mortars and stone with wax in the first century B.C., so you could try that!

There are modern polymeric products that could work, but they might compromise the vapour permeability of the wall structure. You could even use glue. From what I've seen, there is no one recommended method/product and there never has been. Someone else may know different or be able to recommend a product.

 

[jimtmcdaniels]

How friable and crumbly the mortar is depends upon multiple factors, so the fact that some walls have more crumbly mortar than others is hardly surprising - it's what you would expect. I assume that it's lime mortars we're talking about, given the age (but not necessarily) and how do you know that the mortar that's crumbling is the original one? Perhaps the mortar in the different walls is of a different age.

It's highly unlikely that the difference in crumbliness is a result of the use (or non -use) of a consolidating agent. Traditionally, consolidating agents were sometimes used, but usually on renders rather than on pointing (where application would be nearly as tedious and time consuming as re-pointing). All sort of things have traditionally been tried, including lime water and barium water (weak solutions of calcium and barium hydroxide respectively), but they are of limited effectiveness. If you're interesting you can read this:

https://www.sciencedirect.com/science/article/pii/S1296207414001150

Interestingly, Vitruvius recommended the impregnation of friable mortars and stone with wax in the first century B.C., so you could try that!

There are modern polymeric products that could work, but they might compromise the vapour permeability of the wall structure. You could even use glue. From what I've seen, there is no one recommended method/product and there never has been. Someone else may know different or be able to recommend a product.

Thank you
What about the bonding agent they sell at hardware stores which allows new concrete to stick to old concrete? Might that have a bonding effect on the old mortar if sprayed onto it?
The stuff kind of smells like Elmer's glue ha

 

[jimtmcdaniels]

Btw why are these turn of the century mortars so poor and crumbly when the roman's mortar is still going strong?

 

[stuart45]

Exposed brick walls in restaurants and pubs are often given a few coats of sealer to stop mortar and brick dust coming off.

 

[jimtmcdaniels]

Exposed brick walls in restaurants and pubs are often given a few coats of sealer to stop mortar and brick dust coming off.

Do you know what kind of sealer?

 

[stuart45]

Silane Siloxane.

 

[stuart45]

Btw why are these turn of the century mortars so poor and crumbly when the roman's mortar is still going strong?

It's to do with seawater in Roman concrete.

 

[aockenden]

Would a drying oil like linseed or tung work?

 

[stuart45]

Years ago a mix of linseed oil and turps was sometimes used on brickwork.
Walls in restaurants when they have all the plaster hacked off, are often repointed with either lime mortar, or white cement mortar to tidy them up, but still look original.

 

[Toby Newell]

PVA is used to stabilise raw mortar but normally only to reduce dusting. Siloxane is just another word for silicone (siloxane is the monomer, silicone is the polymer, silanes are very small silicone polymers that only react with alkaline mortars whilst siloxanes react with moisture and work on all masonry, timber etc, silanes are used more commercially to protect from chloride salt degredation whereas siloxane which is more forgiving to use is more common in the domestic / DIY market, both are breathable) these are primarily waterproofing agents, being breathable I don't know how much consolidation power they have. PVA might have some limited use as it is an adhesive, a weaker solution to impregnate deeper then a more heavier coat for the surface. The inorganic chemical method is interesting. Often there is a crossover between stone / masonry and timber. To stabilise friable timber the two main chemicals are a moisture curing solvent PU or a one, two or three part epoxy. The issue is not whether these would work in a limited capacity (they would) but the difficulty in vertical application. Try contacting Bencon, the old boy there is an expert on repair epoxies for wood, if anyone knows he would. As has been said applying any consolidating medium would seriously reduce the porosity.

I think Roman mortar is so long lasting due to a possible happy accident wherby they hotmixed the lime, the extreme temperatures formed tiny, brittle, unreacted limestone 'clasts' (small inclusions). Subsequently when the mortar cracked these clasts would split, react with moisture and bond the crack together. It is quite amazing that effects like this, the use of pozzolans and animal hair fibres, which is really an early composite material were so effective that their analogues are all still used today 2,500 years later in the most high performance technical concretes.

 

[jimtmcdaniels]

Silane Siloxane.

Thank you
I searched which led me to a dry lok company product. They have many products so I called their tech number 1-800-845-5227.
Their tech recommended their "Protect" dry lok product. It will help the problem but of course not as much as the ultimate solution, time consuming repointing. It's like $176 for 5 gallons and can be sprayed on using a garden pump sprayer on a low pressure.
They said they have another product where you encase the wall in their stuff, but I said I'd rather repoint and save the stone wall appearance too.

 

[Toby Newell]

That might help a little, its basically a finish.

 

[a twig]

Limewash does a good job of healing lime mortar and plaster

 

[Toby Newell]

Just to add to the above, Drylok appears to be a transparent latex sealer, so really an exterior latex masonry paint without the pigment. It will stop dusting but not sure how much consolidation power it would have. Also consider that it will probably reduce the breathability of the wall somewhat, if that is a consideration of yours.