Pointing Around windows keeps falling out

[couldidoit]

Hi,

I live in a stone built house, built 1998, and the pointing around the windows between the stone Jamb (or is it mullion ?) and the stone block work constantly cracks. I keep raking out and repointing every couple of years but it keeps cracking. What am I doing wrong?

The Jambs aren't loose, they don't move so how do I stop the mortar from cracking and falling out. I've tried painting the stone work in the joint with PVA Feb bond to adhere the mortar but it didn't help. Can you suggest a solution.

Thanks

 

[gregers]

i would use expanding foam,once dry cut back and then repoint.

 

[rooferpro]

put some plastering sand in with the soft it goes off alot harder

 

[ColJack]

window frames expand and contract with varying conditions, so pointing them with something solid is a daft idea.. you want silicone / caulk or whatever they call it..

 

[couldidoit]

i would use expanding foam,once dry cut back and then repoint.

Hi Gregers, When I last raked out, just a couple of months ago, I cleared the mortar all the way through and then inserted expanding foam the length of the seam. The following day I did cut back and then repointed. That was in March but over the last days I've noticed some very fine airline cracks appearing, perhaps due to all the sunshine that we have had over the last month or so.

put some plastering sand in with the soft it goes off alot harder

Hi Rooferpro, I've not heard of plastering sand before, I'll check this out at the builders merchants. Do I reduce the quantity of normal sand and replace with plastering sand? Also will it effect the colour of the mortar?

I have considered mixing fibres in with the mortar but whereas the mortar will be less prone to cracking within its volume I don't see how that could stop the mortar cracking against the blockwork or the mullion/jamb but I'm getting to the point where I try anything.

window frames expand and contract with varying conditions, so pointing them with something solid is a daft idea.. you want silicone / caulk or whatever they call it..

Hi Coljack, Thanks for your suggestion, Unfortunately whereas Silicon would be an excellent solution to the problem, and I have to point out that the window frames are totally surround by silicon between the frames and the mullion/head and sill, it would spoil the aesthetics to substitute silicon for the mortar between the stone mullions and the block work.


C.

 

[ajrobb]

Would it be a daft idea to increase the amount of non-hydraulic lime and reduce the amount of Portland cement?

 

[r896neo]

Is it lime mortar or Cement? And you don't want to be using PVA in that situation as its not waterproof. You'd need to use SBR. Are the jambs are reconstitued or are they cut stone?

 

[couldidoit]

Would it be a daft idea to increase the amount of non-hydraulic lime and reduce the amount of Portland cement?

Hi ajrobb, Thanks for your question. The mortar mix has just been made up of sand and cement. I am unsure of the effect of adding non-hydraulic lime.

Is it lime mortar or Cement? And you don't want to be using PVA in that situation as its not waterproof. You'd need to use SBR. Are the jambs are reconstitued or are they cut stone?

Hi r896neo, Thanks for your suggestions and questions. As mentioned above the mortar is a sand and cement mix. I don't know what SBR is, can you explain? With regard to the Jambs they are cut stone.

 

[ajrobb]

I am unsure of the effect of adding non-hydraulic lime.

From what I have read, non-hydraulic lime putty or hydrated lime powder will have similar effects. The putty is more traditional and improves with age as long as it is protected from carbon dioxide in the air.

The lime mortars they produce help draw moisture from the masonry to prevent spalling (frost damage). Lime mortars can also 'self heal' micro cracks. Portland cement seems to be the normal 'hydraulic' component added to pointing mortars to make them set quickly (other additives have similar effects, including brick dust). Otherwise, non-hydraulic lime needs to react with carbon dioxide from the air in order to set and can take months to harden and years to reach full strength. In your window's case, this might be a good thing.

 

[r896neo]

Lime mortar is used on old solid walled stone buildings which need to breath and as ajrob said it doesn't harden like cement based mortar. You problem though will be matching the colour if you use lime mortar as it is typically very light. I am not sure whether or not it takes colouriser too well either but i honestly don't know much about it.

As for SBR i think it is a latex based primer but you can effectively think of it as waterproof PVA. Suitable for use as a primer to improve adhesion on low suction backgrounds.

Your best bet might be to post a new topic asking for specific advice on making and using lime mortar. Most people would buy it ready made as its not particularly pleasent stuff but if you need to match a colour you may need to have a go yourself.