Mortar on creasing tiles won't stick

[Joe Shmoe]

Got a garden wall built 6 years ago, with creasing tiles and bricks on edge for the top.

Within a few years, the angled mortar pointing around the bricks on edge has cracked and came away.

I made up some mortar myself and redid it, only to find within a year or so, its done the same thing.

What gives? How do I point on top of the tiles and around the bricks on edge, so this never happens again?

 

[Old.bodger]

Would lime mortar be more flexible and not crack away?

 

[Lorenzl]

First photo mix looks a bit sandy to me.

 

[PerryGunn]

Mortar often cracks if it dries too quickly, if the bricks are dry they can suck the moisture from the mortar. If the mortar has cracks water gets into the cracks and freezes during the winter. When water freezes, it expands which increases the size of the cracks - repeat a few times and the bond breaks.

Try soaking the bricks with plenty of water, repeat and give it time to soak in, before repointing. In addition, some SBR in the mortar promotes adhesion as well as making it more resistant to shrinking/cracking.

 

[ChrisWiduWood]

First photo mix looks a bit sandy to me.

I would agree, whether its the cause of the problem I'm not sure, but more cement wouldn't hurt ,i think normal brick mortar is 6/1 but id say either 4or 5/1 for that... but thats a guess

 

[Bingy man]

Mortar often cracks if it dries too quickly, if the bricks are dry they can suck the moisture from the mortar. If the mortar has cracks water gets into the cracks and freezes during the winter. When water freezes, it expands which increases the size of the cracks - repeat a few times and the bond breaks.

Try soaking the bricks with plenty of water, repeat and give it time to soak in, before repointing. In addition, some SBR in the mortar promotes adhesion as well as making it more resistant to shrinking/cracking.

I’m definitely a fan of washing down with water to get rid of any loose mortar dust but good results can be obtained as you say with sbr in the mortar mix but in addition paint along the tile crease with neat sbr one or twice before pointing up , don’t attempt it on a hot day as perrygun says if the mortar dries to quickly then it will shrink / crack . You could cover the fresh mortar with damp hessian sacks to slow the drying process down . Also consider running an angle grinder into the mortar just above the crease tile to get better adhesion and wash as above + neat sbr brushed into the joint.

 

[Stigmorgan]

Clean everything off thoroughly, don't use mortar it isnt strong enough its designed to be compressed, use a sharp sand and cement mix at roughly a 3:1 ratio with an adhesive additive such as PVA, mix to a toothpaste consistency and apply with a pointing trowel.

 

[Stigmorgan]

I would agree, whether its the cause of the problem I'm not sure, but more cement wouldn't hurt ,i think normal brick mortar is 6/1 but id say either 4or 5/1 for that... but thats a guess

More cement doesn't mean stronger, it will be more brittle and prone to cracking more. The issue looks to me more that soft sand has been used instead of sharp sand.

 

[Joe Shmoe]

Cheers folks.

Some excellent replies here. I shall do as you've suggested.

Thanks kindly for your knowledge. Wonderful.

 

[Adam W.]

Don't bother with lime mortar either, as it will just get destroyed by the frost.

I agree with @Stigmorgan about the sharp sand, but I'd add hydrated lime to make the mix more plastic and workable.

 

[John Hall]

Also make sure you are using fresh cement…Look for Blue Circle Mastercrete cement…it has additives to help stop cracking and is more resistant to frost damage.Wicks B&Q, and most building supplies stock it….Thoroughly clean the area with a stiff brush and hose down..brushing a weak mix of PVA and water onto the surface just before you apply the cement may help, as well as adding a small amount to the mix…as already mentioned…Don’t make the mix too strong 4-1 is about right….don’t do it on a hot sunny day especially if it’s in direct sunlight. Covering it for 24 hours will slow down setting.

 

[davethebb]

You should clean the area really well (wire brush), remove the old mortar, and then as previous posts have highlighted soak with water the day before, then an hour or so beforehand. Cover after when pointed for at least a week and keep the cover damp. Using lime in the mix will certainly help but take care with it as it will burn you if you leave it on your skin.

 

[Jonm]

As others have said, damp hessian on top then cover with polythene to keep the moisture in.

 

[pe2dave]

I think I now know what a 'creasing tile' is! Thanks.

 

[Richard_C]

We had a professional rebuild of a bit of wall an oil tanker knocked down, similar tiles. Not sure what mix the builder used but he left wet hessian on top, weighed down with a few bricks, and came back a week later to take it away. Been fine for years. I guess a slim fillet like that will dry far too quickly unless covered.

I have also had repeat poor results pointing between slabs, last year I used a mix of sharp sand 4:1 plus pva and its lasting well. Sharp sand seems to perform very differently from soft sand and any of the bagged ready mixed repair stuff.

 

[Woody2Shoes]

As others have said: - The existing failed because it was soft sand not sharp sand and too weak a mix.

1) Clean back to basre masonry with a stiff/wire brush;
2) Use a strong mix (follow manufacturers instructions, but with masonry cement [rather than OPC] probably 4 sharp sand to one dust);

This is an exposed situation, so a strong mix is the only answer. There is unlikely to be much differential thermal movement, so cracking should be unlikely - if you get the mix right. If you use masonry cement, you shouldn't need any other additives, but you could perhaps add waterproofer - but this doesn't last, and I personally wouldn't bother.

 

[rafezetter]

Mortar often cracks if it dries too quickly, if the bricks are dry they can suck the moisture from the mortar. If the mortar has cracks water gets into the cracks and freezes during the winter. When water freezes, it expands which increases the size of the cracks - repeat a few times and the bond breaks.

Try soaking the bricks with plenty of water, repeat and give it time to soak in, before repointing. In addition, some SBR in the mortar promotes adhesion as well as making it more resistant to shrinking/cracking.

^^ This, oh and throw over either old towels (most people don't tend to have long sections of hessian lying around ) and keep them damp or those cheap thin polythene paint thingys that for the life of me I can't remember what they are called! - *blank*, utterly blank.

edit: oh jonm said it as well.

 

[Jonm]

or those cheap thin polythene paint thingys that for the life of me I can't remember what they are called! - *blank*, utterly blank.

Dust sheets?
And as you say, damp towels, or any cloth which soaks up water will do.