Ask Andy “Add 30mm Bonded Screed Over Liquid Dpm”

I am Andy Parkin Managing Director of the Multi-Award Winning Speed Screed. Thank you very much for your question, Mary.

Your question is:

“I need a liquid radon DPM over an existing concrete slab of unknown thickness in a project in a three-level porch and WC utility space. Head height is limited, not looking to add floor insulation. Can I add 30mm bonded screed over liquid radon DPM?”

Watch Andy’s video to find out his answer:

Indeed, a liquid DPM is OK. You can use it depending on the screed. You can actually sand scatter the liquid DPM. When the liquid DPM is still wet, you sprinkle over with some kiln-dried sand onto the surface. The next day you would go, and then you hoover the kiln-dried sand excess. Then you are left with the kiln-dried sand embedded into the liquid DPM. What that does is it gives a key to the screed that you are going to place on top.

At 30mm, several products will bond to the substrate so you can use them. Besides traditional screeds, traditional sand and cement screed would need 40mm, so at 30mm, you can use polymer-modified sand and cement screeds. There is quite a wide range of products on the market that you could use.

There are certain smoothing compounds that you can be laid to 30mm. So, depending on your particular requirements, it may be a drying time requirement. You may need a fast-drying screed. Most of the polymer-modified screeds that will go down to 30mm are already, by nature, faster drying. But you may have a specific requirement on how quickly you need to get your floor coverings on that might determine your choice.

But certainly, I would say, sand blinding of the liquid DPM and then bonding. Apply a primer and then bond, whichever is the preferred screed, and we can again advise based on the other factors relating to the project as to which would be the most suitable screed to meet your needs.

I hope that helps Mary!  I’m sure you’ve got some other questions, and we would be only too happy to help!

We love to help!  Contact us.