Hardening crumbly mortar ?

[clarkyboy]

I've just retiled an overhang above a window and it appears I used the wrong bag of cement ! (ie the old one that damp had probably got to).

I had to mix Snowcrete and normal grey portland cement to get the right colour mortar. I mixed 3 Sand to 1 mortar very carefully measured along with a squirt of plasticiser (9 sand , 2 Grey, 1 snowcrete). Surely these two different cements don't react ?

I placed a line of mortar about an inch deep and 2 inches wide along where the tiles meet the stone wall to finish the job. It's set and all feels fairly firm and secure but I can scratch the surface of the mortar with a finger nail.

Is there any chemical I can use to harden the mortar further ? Or am I best to strip it all off and redo it. It does feel solid just a little crumbly if scratched. Will it be secure if I just leave it ?

 

[Fluffster]

Sounds like a weak mix to me I would remove and start again esp given the location will be open to the elements.
If you decide not to replace a good pva will seal and bond it so it does not crumble followed by a water proofing agent.
Pete

 

[clarkyboy]

Sounds like a weak mix to me I would remove and start again esp given the location will be open to the elements.
If you decide not to replace a good pva will seal and bond it so it does not crumble followed by a water proofing agent.
Pete

Cheers. I'm a perfectionist so I'm not sure why I'm asking. Off it comes and I'll test a combined snowcrete and grey mix with the new stuff before restarting. The roof tiles I've already bedded feel very secure so I'm sure just s topping of good mortar to give a good bond and seal to wall will do the job. ( I was briefly tempted by the PVA and sealant option as I have both in the garage).

 

[JohnD]

It might also have dried out too fast. Cement really needs to stay damp for a few days to gain much strength. It takes a couple of weeks damp to near its ultimate strength.

Once it has dried out, re-wetting it will not help.

A nice dull, drizzly spell, and bricks that are moistened, will help a lot.

Buiding late in the day, when the sun has passed over, can also help. In some countries road concrete is never laid until the afternoon for this reason, and to prevent cracking, as it will have set before it gets heated again.

If you put a left-over sample into a yoghurt pot, and cover it to stop it drying out, you will see how strong your mix can get.

If cement has no lumps in it that cannot easily be broken in the fingers, it is generally still OK to use.

 

[diyisfree]

I agree with John,

BUT no one as asked the OP how long it has been since laying and then testing the strenght of the mix?

I mean was it the next day ? If so then give it chance. Concrete (ok its a cement motar) is tested after 21 day's or there abouts so if you scratched you pointing the day after you did the job then YES it will mark with your finger nail.


3.1 mix sounds ok to me... Tis what i use.

As many would say, MORE INFO REQUIRED. When, where , what, how, and so on

 

[clarkyboy]

I agree with John,

BUT no one as asked the OP how long it has been since laying and then testing the strenght of the mix?

I mean was it the next day ? If so then give it chance. Concrete (ok its a cement motar) is tested after 21 day's or there abouts so if you scratched you pointing the day after you did the job then YES it will mark with your finger nail.


3.1 mix sounds ok to me... Tis what i use.

As many would say, MORE INFO REQUIRED. When, where , what, how, and so on

When I mixed mortar samples (using new fresh snowcrete white cement)to match the colour most set very well within 2 days and did not break down under rubbing. I can crumble this between my fingers. The beauty is that it's such a shoddy mix I can remove it cleanly with little problem. Cooler and overcast today so I'll replace today.

We had two bags of cement. One old one new and a helpful soul removed all the lumps from where the old bag had hardened on the outside and I dove in without checking.

Mind you I did use the mixture on a South facing stone wall in bright mid afternoon sunshine which probably didn't help matters.

 

[Fluffster]

How often do you wish for a dark damp cold day eh

 

[diyisfree]

Sounds like it was caused by the cement then Out of date or had got damp

I once went to a plastering job to bond a few walls then skim and also patch an hole in a ceiling where the occupier of the house had fallen through the ceiling

I ran out of skim and didn't have enough to repair the newly boarded hole in the ceiling, The helpful lady said " I have a bag of plaster upstairs what the window fitter left for me, do you want it" I thought, brilliant, means i can finish the job.

I mixed up the plaster, carried it indoors had a sip of my coffee then tried to pick up my bucket trowel from the mix, The plaster had set rock solid in the space of about 5 mins.
I scratched my head looked at the lady then looked at the date on the bag of plaster, it was almost 2 years past its sell by date Serves me right for not taking enough materials i guess...

Opposite of your problem clarkyboy but it happens to all of us.