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Hi everyone,
Our house has subsidence (rising damp) and we’ve had the inside slab professionally waterproofed and are working on outside drainage etc to protect the house. Lateral damp also impacting. Found a massive hole in the stormwater pipe and another in an ag pipe up the top of our retaining wall / garden bed. All in same area where the subsidence is. We started digging and there’s SO much water in the clay soil.
We want to waterproof and backfill against the wall with gravel and put in a gravel path. Our plumber has redone the stormwater and will come back to do a new ag pipe by the house once we’ve waterproofed the wall. We didn’t have one there before but hoping it might help reduce water. I get the risks of having an ag pipe near your house which is why we’re getting professional help.
We’ve replaced the ag pipe up the top of our raised bed / retainer ourselves already as less risky.
BUT - because the wall is exposed and lower than the other ground, water keeps seeping on top of the footing.
We are proposing to waterproof the bottom 4 rows of the brick wall to be backfilled plus the top of the footing. The water from the clay and dirt in bricks won’t have helped the damp inside either but to get the right fall for the stormwater pipe has to sit quite high so means we have to build the fill levels back up again.
Questions
Repointing
i was planning to use a concrete mix and silasec waterproofing additive to first repoint the bricks where mortar is missing - surprisingly a lot of them look ok but the mortar is recessed back quite far and for waterproofing I’ve read it’s better to have a flush pointed wall. I’ve cleaned and scraped out the dirt etc.
Is there any harm in just redoing over the whole lot of the 4 rows flush pointing? I feel like that’ll be easier than faffing around doing bits, but I also don’t want to grind or remove all the mortar, I was just going to do the crumbly bits and go over the rest.
Should this be ok? Does the 7 day cure time apply to repointing mortar only as well?
Waterproofing
All the waterproofing products I’ve seen require it to be dry and those that can be applied damp need it be dry afterwards. The footing is constantly wet from random water coming from either within or underneath the retaining wall, despite several days no rain. The water is very clear. I’m nervous leaving the footing too exposed for long but need to try to dry it out to waterproof.
The water probably won’t resolve until we get the ag pipe but we need to waterproof the wall before we can get the ag pipe installed. Catch 22.
I was thinking of using the silasec / concrete as a paint on the footing, then something like Crommelin exterior waterproofing membrane on the brick wall. The crommelin bitumen can’t be exposed to UV and exterior is listed as preferable for ‘critical walls’ which I’m guessing my house is? I think exterior is better even though it won’t be exposed to UV so bitumen could work too.
We are real novices (but our job is a bit small for professional waterproofers who are busy people so we’re giving it a crack) so we need something that is easy, highly durable and effective.
Any recommendations for products and any suggestions to keep the water out while we do it? My thought is probably to dig the other side of the pipe / path lower so water finds somewhere else to go away from the house. It’ll make the gravel fall out from under the stormwater but we could always repack that. We do need to take the levels down anyway for our new roadbase and gravel.
I thought Sika komponent might also work but again needs several days no rain. I’m in Qld, it is always raining lately so cure time is a worry.
Getting the footing top clean is another thing - should we even bother with wateproofing it if we can’t do it properly? Or should we just cover the footing back over with earth to protect it and just do the bricks?
Also with backfilling is it better to replace the clay dirt beside the top of the footing with roadbase or just leave the clay there? Both are porous so maybe no difference?
Thanks for reading - this post is the same project as my other one about building a gravel path but is a slightly different topic so I’ve starred fresh. Any advice much appreciated! 😊
Hi @FernyG,
For the repointing, full flush repointing of the bottom four rows of bricks is fine — you don’t need to grind out perfectly good mortar if it’s sound, but since you’ll be waterproofing over it, a flush finish is better for adhesion and water runoff. Only rake out loose, crumbly, or damaged mortar. A stiff wire brush or a plugging chisel is sufficient; there’s no need for angle grinder work unless the mortar is truly shot. A cement-to-sand mix at 1:3 works well, and adding Silasec will improve water resistance, though it won’t make it entirely waterproof. As for cure time, even repointing mortar should ideally cure for seven days before applying a waterproof membrane, but in wet weather you can get away with three to four days if temperatures are warm and you’re using a cement-based membrane. Avoid bitumen until it’s fully cured to prevent adhesion issues.
To keep water out while you work, the simplest temporary diversion is a shallow trench on the “high” side of the work area to intercept water and send it elsewhere. Even a hand-dug channel lined with plastic will buy you time to dry the footing surface. Lay tarp or plastic sheeting over the footing overnight to keep rain off. If the seepage is from below — which is likely, given the constant clear water in the clay — the only real long-term fix is the ag pipe, so the waterproofing will always be working in a damp environment until that’s installed.
For waterproofing, if you can get the top of the footing wire-brush clean and surface dry, it’s worth painting it with a cementitious waterproofing slurry such as Crommelin Dampstop or Drizoro Maxseal Foundation (a Special Order item), as these can tolerate some residual damp. If you can’t get it dry enough, skip the footing and focus on the wall — applying membrane over a damp footing in poor conditions can trap moisture and cause blistering. Cementitious coatings like Maxseal or Dampstop work well for the wall because they bond to damp masonry, are UV stable, and are easier for DIY use than some bitumen products. If you opt for a bitumen product like Crommelin Exterior or Gripset Betta 2P, make sure the wall is completely dry first, as these can’t handle damp application. Apply at least two coats and protect the finished surface from damage during backfilling with something like Builder's Plastic.
When backfilling, free-draining material is essential. Drainage gravel without fines is ideal. Use geotextile fabric to wrap around the pipe to keep fines out. The top layer under your gravel path should be compacted roadbase for stability, but keep it separate from the drainage gravel.
This all ties into the “catch 22” problem: the ag pipe is the long-term solution, but it can only go in after the wall is waterproofed. That means you’re in temporary works territory. The best approach is to dry the wall as much as possible with a diversion trench and tarp, then use a cementitious membrane that can be applied to damp walls. Once the ag pipe is in, water pressure against the wall will reduce significantly, and your membrane will last much longer.
Please let me know if you have any questions.
Mitchell
Hi @FernyG,
In your circumstance, I would use it as a primer for a damp surface. It's a waterproofer in its own right, but I would use Crommelin waterproofer over the top for a complete system.
Mitchell
