Concrete floor, liquid DPM and trenches - advice needed!!

Hello all,

This is my first post so please go easy on me...

We moved into our current house a few years ago. The ground floor has wooden flooring on a concrete base. A few weeks ago we discovered a leak in the central heating system and discovered the pipes have been buried directly in the concrete.

Cut a long story short insurance is covering the replacement of the wooden flooring but having located and fixed one leak another one has occurred! (Apparently copper and concrete don't like each other)

I have therefore been advised that I should replace all the groundfloor pipework by digging trenches laying down a galvanised steel box and laying the pipes with insulation inside them before the new floor goes down.

Looking at the plans of the house it mentions the following for the floor construction:

1.5" sand & cement screed
3 coats of synthapruf
4" concrete 1:3:6
6" hardcore well consolidated & blinded with sand

I have two questions:

1. By digging to locate the initial leak we have gone down 3.5 odd inches. Can I assume we have already breached the DPM layer?

2. If we dig trenches to say 3.5 inches deep assuming we have breached the DPM - how do we re-establish it?

Hi

You will know if you get to the dpm: if it's as per the spec, then you will come across a black painted finish on the top of the structural slab. You will see a difference between the slab concrete and the screed, it should be obvious which one you are going through.

If you have to go through the dpm into the slab to form the duct at the required depth and it is indeed a painted one, then cut back the screed by about 4" from the side of the little "trench" that you are forming and apply 2 or three coats of synthapruf over the existing dpm, into your "trench" and out the other side. Then install your ducting.

Hi,

Thanks for that! I'll take a closer look and let you know how I get on.

Hi,

OK had a close look last night. It doesn't look like there is a DPM layer as specified.

There is no distinction in the concrete (layering) - in fact it all looks the same 3.5 inches deep

So it appears its not as specified in the plans - how do I know if there indeed a DPM layer?

"wooden flooring on a concrete base"

Is there a gap between? Joists etc? Or is it a floating wooden floor? Looking at the floor concrete spec, it seems theres no insulation - is this between the concrete and wood?

If there's a gap, use it for your pipework.

If not, cut the pipework into the insulation?

As far as I know it's a solid concrete floor. As for insulation it appears it is non existent.

We've never had any problems with the original flooring so there must be a barrier preventing moisture coming up - but where

What I am worried about is if we have the new floor laid after cutting the trenches we don't compromise what seems as yet an invisible barrier.