How to seal a joint between PVC and concrete?

[wolive]

Hello, I have a retaining wall under my house that is solid concrete in PVC permanent formwork. Like Dincel or CSR Rediwall for example. It sits on a concrete slab and therefore forms a joint at the bottom of the wall where it meets the concrete slab. The problem is that when it rains, water seeps through under wall at this joint in several locations. This is causing water to get under my house where it runs across the concrete slab and then on to the clay dirt, which takes forever to dry. I need to have no rain for a month in order for it to dry. So I need to stop this water somehow. It is impossible to gain access to the back of the wall, so my only option is to apply some kind of seal to the joint at the front of the wall. I'm just not sure what to use.

I thought I could apply a thick undiluted coat of Gripset Betta Bitumen Membrane along the joint, but then I thought it might be better to use some kind of silicone in the joint first perhaps then paint the bitumen over the top? I wondered if something like this Crommelin Silicone would be suitable. It sounds like it would adhere to the concrete and the PVC in the joint. But then I read online that a hybrid MS polymer sealant is better as it bonds better to things like plastic and gives a stronger watertight seal than just silicone alone. Is that what Crommelin Hybrid MS Polyurethane Sealant is?

Can anyone provide any advice on this? Is my plan a good idea or should I be doing something else? Would any of the above products be suitable or should I use something else? Thank you.

[EricL]

Hi @wolive 

Welcome to the Bunnings Workshop community. It's sensational to have you join us and thanks for sharing your question about the joint in your retaining wall.

In order for our members to get a better idea of what the joint looks like, would it be possible for you to post a few photos of the area? We can then make recommendations on how to proceed.

Trapped moisture is the enemy of any sealant, I agree with your analysis that you would need to wait for all that trapped water to dry out before you seal the joint. Between the two, Crommelin Hybrid MS Polyurethane Sealant is rated for exterior use, whereas Crommelin Silicone is aimed more towards interior use.

If you need a hand posting the photos, please let me know.

Eric

[wolive]

Hi @EricL, here is a photo of the wall where it joins the concrete. It needs a good clean first before I apply any kind of sealant.

[EricL]

Hello @wolive 

Thank you for sharing the picture of your wall and concrete floor. I recommend cleaning the concrete surface and wall with a stiff bristle brush and detergent to remove any oil or grease contaminants on its surface. 

Once both sides are dry and you feel that the interior is dry as well, I suggest using Sika 300ml Grey Sikaflex 11FC Plus Polyurethane Adhesive Sealant. This is a very effective sealant and is rated for outdoor use. It is a 1-part, multipurpose elastic adhesive and joint sealant with very good application properties which bonds and seals most construction material substrates.

If you have any other questions we can help with, please let us know.

Eric