Leaking Roof

[RBH]

Hi, finished my oven a few years back and it worked great. Over winter, however, cracks appeared in all the mortar between the stone paving slabs I used to roof it. We get a lot of rain here and it took a while to dry out next year. Fixed that and the same happened, the mortar just breaks up and disintegrates. Any ideas how to fix this for good?

[MarkJerling]

Could you post some photos?

[RBH]

Hi, thanks for taking a look. Hope these will give you some idea. The slabs are bedded in mortar only along the joins so you may see gaps for ventilation, particularly in the corner pic. which is intentional, not fallen away mortar.

[NCMan]

When installing masonry on a horizontal surface, it's important to plan ahead for water infiltration. Normally, you'd want to make the joints as small as you can and make sure it's packed in and not too wet, as that just promotes shrinkage of the mortar. Instead, caulking is preferred to minimize this from happening. At this point, it may be best to remove any loose material and caulk it w/a good masonry caulk. Bottom line, is to try to avoid any masonry on a flat surface, as it just invites issues like this. Using a good quality sealer helps, but is not sufficient to do as a stand alone method. You should be able to find a good exterior grade caulking suitable for this. I personally like the Sika products and have had good results w/them. There are others, also.

[MarkJerling]

When installing masonry on a horizontal surface, it's important to plan ahead for water infiltration. Normally, you'd want to make the joints as small as you can and make sure it's packed in and not too wet, as that just promotes shrinkage of the mortar. Instead, caulking is preferred to minimize this from happening. At this point, it may be best to remove any loose material and caulk it w/a good masonry caulk. Bottom line, is to try to avoid any masonry on a flat surface, as it just invites issues like this. Using a good quality sealer helps, but is not sufficient to do as a stand alone method. You should be able to find a good exterior grade caulking suitable for this. I personally like the Sika products and have had good results w/them. There are others, also.

I came to say the same thing. Could not have put it better myself!

[MarkJerling]

Hi, thanks for taking a look. Hope these will give you some idea. The slabs are bedded in mortar only along the joins so you may see gaps for ventilation, particularly in the corner pic. which is intentional, not fallen away mortar.

Thanks for posting the photos. As NCMan has said, you need some good quality masonry caulk and yes, Sika makes great products. Ideally, you'd like to pick one that is both waterproof and can handle some movement, as is typical with masonry. You could use a good (again Sika) construction silicone. I would start by removing the mortar, placing backing rod and installing the caulk in the join above the backing rod.

[RBH]

Many thanks for that, I'll give it a try.

[RBH]

I found some materials, perhaps someone could confirm they are up to the job. Polyethelene foam backer rod seems straight forward https://www.dortechdirect.co.uk/back...acker-rod.html but there are numerous Sika products. Is Sikaflex EBT+ sealant any good for this?

[MarkJerling]

I found some materials, perhaps someone could confirm they are up to the job. Polyethelene foam backer rod seems straight forward https://www.dortechdirect.co.uk/back...acker-rod.html but there are numerous Sika products. Is Sikaflex EBT+ sealant any good for this?

I'd think that would be perfect.

[RBH]

Thanks again.

[MarkJerling]

You're most welcome.
Kind regards,
Mark