New mortar is crumbly

[Don1357]

I sure hope this is normal, I don't want to spend the day undoing all the work I did yesterday...

I started the 3 runs of cinder blocks for my shop (2' tall, framing from that point on). On the 24' wall side I did the corners plus two runs of blocks. I came out this morning to continue my work and all the mortar is crumbly. It still look dark grey and I can pulverize it with my hands.

This is the Quikrete Mortar Mix, I think is the type N.

 

[gunguy]

This help at all?

https://www.lime.org.uk/community/lime-mortar/troubleshooting-guide-crumbling-or-failing-mortar.html

Jim

 

[Don1357]

Not really. Brand new bag of premixed mortar. Mixed to the recommended consistency.

Is Quikrete mortar mix supposed to be crumbly a day after?

 

[ConCretin]

Not really my area of expertise but 24 hours isn't very long for any cementitious material to gain strength. If you used a pre-packaged mortar and mixed it properly, I doubt you have a problem.

 

[Don1357]

That's what I'm hoping for but I'm not familiar with mortar. I have used premixed concrete and that seems to solidify a lot faster than this.

I just don't know if this is normal.

 

[Leaflessshadetree]

From the few jobs I did I remember the mortar being "soft" the next day. (Not sure I'd describe it as crumbly but I never tried to crumble it). I did keep it damp for the first week.
I never used premixed mortar, but when I use bagged concrete mix I usually add some additional portland cement.

 

[Dan in Pasadena]

Not really my area of expertise but 24 hours isn't very long for any cementitious material to gain strength. If you used a pre-packaged mortar and mixed it properly, I doubt you have a problem.

Sorry but your comment about cementitious material not achieving much strength in 24 hours is incorrect. I'm not talking about mortar specifically but about structural concrete. Ordinary production mix (NOT a "high-early" mix or specialty mix) should achieve a significant percentage of its intended design strength in 24 hours. The specific numbers escape me already - retired for 17 months, ha ha. But 70% in 7 days is easily achieved and mostly exceeded.

The OP is saying his mortar mix is "crumbly" which to me connotes the mix was dry and is now brittle. Something ain't right. Strikes me like insufficient cement content in the mix or poor/insufficient mixing is possible. Crumbly seems to me like it would have poor adhesion properties which is after all the entire purpose of mortar.

 

[mcbane]

No idea where you are and what the weather may have been like but it may have dried out and not had enough moisture to cure properly. Dry blocks and/or hot dry weather would require extra efforts to maintain moisture during the cure process.


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[Dagny]

I think all those bagged mixes are short on portland . My dad was a bricklayer and he and I put 12000 bricks on his home he used portland unslacked lime and sand.

 

[mz44]

Type N has less portland than a type S. The type S quikrete we have been using works way better with a shovel or 2 of portland added per bag.

 

[Hilltopmasonry]

Describe crumbly




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[TRWham]

Be sure which product you used. Quickrete Mortar Mix (yellow bag with green stripe) is ready to go as Type N if you mix per instructions, but Quickrete Type N Masonry Cement has no sand in it. If you used that, did you add sand? We typically use Type S Mason Mix (white bag with green stripe) which includes sand and is much stronger, but that is mostly on foundation walls.

 

[Don1357]

Just to follow up on this. Looks like it was a temperature issue. Here at night it is dipping in the low 40s and according to the cinder block supplier mortar has a tendency to 'go dormant' and not harden. It took two days for the initial chunks of mortar to start behaving like cement. I also switched to Sakrette Type S, I like the consistency a lot better, I find it easier to work with.

 

[Leaflessshadetree]

It also may help to wet down the blocks before placing the mortar on them and the block going onto the mortar. Keeps them from sucking the moisture out of your mortar.

 

[rustyjames]

Wetting masonry units prior to placing them is not permitted on government projects.
https://www.concreteconstruction.net/how-to/pre-wetting-brick-masonry_o

 

[NUTTSGT]

Sorry but your comment about cementitious material not achieving much strength in 24 hours is incorrect. I'm not talking about mortar specifically but about structural concrete. Ordinary production mix (NOT a "high-early" mix or specialty mix) should achieve a significant percentage of its intended design strength in 24 hours. The specific numbers escape me already - retired for 17 months, ha ha. But 70% in 7 days is easily achieved and mostly exceeded.

The OP is saying his mortar mix is "crumbly" which to me connotes the mix was dry and is now brittle. Something ain't right. Strikes me like insufficient cement content in the mix or poor/insufficient mixing is possible. Crumbly seems to me like it would have poor adhesion properties which is after all the entire purpose of mortar.

I'm going to go out on a limb here and say that Doug knows exactly what he is talking about when it comes to concrete.



However, your advice on the mortar, I'd tend to agree with about it being dry or possibly the beginning or end of a lot where something wasn't mixed correctly/proportionally.

 

[Milton Shaw]

I know from experience when I was a teenager that you cannot lay wet block. I was a helper on a job that block had been rained on that morning. The masons laid up a shower wall with all the cutouts for pipe, knobs etc. They got it about 4 foot high and the whole thing collapsed. We spent the rest of the day cleaning off mortar mix from the block so they could be relaid when dry a few days later. Cold does effect concrete strength and curing as there was a deadly accident building a cooling tower for a power station. They moved the attached scaffolding up too soon for the wall to have enough strength to hold it. Seems like 6 or 8 died in that accident. Use the better grade stuff and you won't be sorry about the small amount more it cost to do the job right the first time.