I have a 50m2 roof terrasse. The grout has become permeable and rainwater is leaking into the cellar below (this is because the original builder "forgot" to put any sealant on top of the concrete base??).
I can't remove all the tiles and start from scratch, so I simply need to renew the grout. Is it favourite to remove ALL the old grout? What is the best way of doing this? What is the most effective water resistant grout on the market? Thankyou.

im afraid the best fix is to remove the lot and start again hope this helps

thanks but afraid this is not possible; 50m2 is a a big area and the thickness of the cement between tile and terrasse floor is almost 15cm.
However, if you fancy quoting for the job I can send you a photo?

dont think you would like my quote as traveling would cost a bit

you can advertise your job on here and someone more local can quote it if you like

re grouting will not solve your problem

Could he tank existing and tile over?

Originally Posted by easyt

Could he tank existing and tile over?

thats not a good move as it will creat more issues and finding a waterproof membrane that will garantee over tiles will be hard you may have weight probs


job realy needs to be viewed but the only grout that is waterproof would be epoxy but the job needs to be seen by a qualified tiler to make the call on weather it can be done and i recomend epoxy be installed by a tradie hope this helps

if the substrate has been soaked and all the grout is cracking and letting in water to the point its coming through to the cellar below re grouting will not solve this issue i would say it needs to come up you may also have to sort the substrate again

Grout isn't waterproof. Water will just soak through it. So your problem isn't the tiles, or the grout, it's the substrate behind all that.

You really do need to pull the lot up, then waterproof the substrate, then re-tile if you want to just from an aesthetics point of view if it you want to see tile there.

Re-grouting would just be a waste of time and money. I don't think you'd get any professional tiler suggesting you should re-grout to solve the problem.

If the tiles are well and truly solid then you can waterproof the surface and re-tile... my recommendation would a Tanking membrane like Ditra.

But you will also need to prevent any water ingress at the sides/edges as well..

This is hard to say without actually seeing the lay out etc at face value..

where abouts are you..?

Would an epoxy grout not sort it?

Depends on how wet the substrate is.. Ditra would allow moisture to vaporise over time.

And provide a 100% true tanking.

I'm very impressed & appreciative of all the advice. Thankyou. Removing 50m2 x 15cm. is a pretty hefty job & I would then have to purchase new tiles. The terrasse is integral to the house and extends from the living room. If there is any way I can resolve this other than a complete re-hash I would prefer to do so. If the seepage is not filtering through the grout then where is the water coming from? There are no holes in the tiles and there are 2 drains at the balcony/terrasse front which discharge most of the rainwater so it must be entering the grout & working its way down through the substrate to the concrete roof/floor of the cellar? We took out one complete line of tiles at the front and the substrate was very wet.

where abouts are you..?

Epoxy can work but needs dry joints to adhere, so if the substrate is wet then that could be a problem.

Hi Branleur, I have just read through this thread. I would like to know what is the substrate?is it tiled directly onto concrete? I have done quite a lot of balconies, and agree with comments above. Tanking is advisable, better still a decoupling membrane. Balconies are subjected to the extremes of weather, intense heat / frost etc. Expansion, contraction is always a problem. I am concerned if this installation is leakiing, how much damage has been done to the adhesive. Prolonged water ingress will destroy most adhesives over time, leading to de-lamination eventually. I hope there is a easier fix for you, I can't think of one sorry