Plastering over KA tanking slurry

[phil.davies]

I took out my kitchen and found damp behind the floor units.
I have hacked off the plaster.
Do I plaster the wall and then apply the tanking slurry, or should I apply the tanking slurry first?

[Surveyorman]

Plastering always comes last. When plaster has been affected by rising dampness, salts originating from the soil particularly chlorides and nitrates are deposited within the plaster. These salts are termed as “hygroscope”
This means that they have the ability to absorb water from the surrounding air and cause additional dampness, even though a new chemical damp proof course may have to be installed.

The correct specification for re-plastering is as follows:

• Existing plaster should be removed to at least 300mm above the last sign of dampness.

• Mortar joints should be raked out to provide a key for the new render.

• 2 coats of a 1:4 SBR render mix (waterproofing slurry) are then applied to the wall. Sand should always be of a washed river sharp variety and should be free from sulphates and should conform from BSS 882. Cement should be sulphates resisting.

• A gap of at least 25mm should be left between the render and a solid floor, this will prevent dampness bridging from the floor.

• The finish coat should be a non sulphate type plaster such as multi-finish. This coat should not be over-toweled to allow for evaporation of moisture from the base coat.

• Always use clean water in the mixing of materials.

[Surveyorman]

How old is the house? If it is post 1875 it will have its own DPC therefore no need to consider any injection - just "tank" away!

[wes56]

find the cause of the damp before doing anything else.
it could be penetrating damp.
it could have a variety of possible causes, such as, solid walls, render, solid floor, bridging, ground level and inside floor level?
post some pics of outside and inside the kitchen.
its best to use a sand and lime mix for replastering. no cement.

[Surveyorman]

The OP was asking about the application of a Tanking Slurry not lime based mixes.

But yes, let's look at the bigger picture here.

OP: As Wes56 has pointed out, it is important to pinpoint the source of the moisture and knowing more information regarding all of the points Wes has mentioned might be able to help us help you.

How old is the property? What type of property? And then if you can try to offer us some info regarding the areas Wes56 has highlighted, particularly internal floor level vs external ground level. Photos are always good!

[wes56]

I know what the OP was asking about - do you?
If you do then why your extensive list for replastering ?
Why your mention of an injected DPC?
Most but not all post 1875 houses have a DPC.
Cement slurries and cement renders can be causes for further problems not remedies for existing damp issues. "Water proofing" a damp affected wall, or any wall for that matter, will also give further difficulties.

[Surveyorman]

Wes56 - I’m not really sure how to address your last message except to say that it’s quite defensive.
Let’s just leave it at that.
OP has enough info from the both of us now which has hopefully answered his original question.

[wes56]

Why dont you deal with your errors - the ones i pointed out?

Nothing defensive at all.
If you wish to make large statements then expect responses.
You now say, for instance, that you dont know what to say but then go on to say it for three sentences.
If you have nothing to say then why even say that I'm "quite defensive"?

[Surveyorman]

I haven’t the time nor inclination to enter a discussion with you on this Wes.

Let’s move on.

[wes56]

Then why not be more careful with your remarks?