I live in an apartment in a multistoried building. The building is assembled of huge enforced concrete plates - one plate is size of a wall of a room. One of the inter-plate seams has a crack in it due to a slight basement slump (the code allows that) that lets the cold from the outside (the atmosphere) into the apartment.

I need to choose some compound to seal the seam from the inside of the apartment. The crack is about two millimeters wide and I could use ordinary cement-based mortar, but the problem I see is mortar is not elastic, so if the building continues to slump the crack will surely reappear and I'll have to start anew.

I could use silicone-based sealant, but it is not fireproof and I don't like the idea of a fire suddenly bursting from inside a wall if there's a fire in some other apartment.

So I'd like to have something like a cement-based mortar (fireproof) yet flexible enough to compensate fro future slumps. Are there such compounds?

  • sounds dangerous. Apr 4, 2011 at 9:19
  • 1
    @Asaf Chertkoff: Not at all - we have entire cities of such houses and such cracks are considered "requires maintenance" class situations.
    – sharptooth
    Apr 4, 2011 at 9:28
  • where do you live?
    – warren
    Apr 4, 2011 at 15:29
  • @warren: Very Eastern Europe I'd call it.
    – sharptooth
    Apr 5, 2011 at 5:25

3 Answers 3


I'd opt for a fire resistant silicone sealant such as this one >> http://www.bostik.co.uk/construction/product/bostik/Fireseal-Silicone-Joint-Sealant/340

That's from a UK site, but I'm sure there are similar products in your part of the world.

When it comes to cement then flexibility is usually imparted by including lime in the mortar - although that's a slow process involving the exposed lime within a crack recalcifying over time so not really suitable in your scenario.


How about lime puddy? It's elastic and performs like cement You can use Hydrolic lime mix that's very simple - only use with caution! Toxic while wet but the next best thing to nature after dry...


i've just read about Polyurea, in hebrew but it says that as a sealing material for concrete:

  1. tensile force of 3500 PSI (suitable for filling concrete cracks) up to 3 mm
  2. can extend to 900% of its original state(!). very flexible.
  3. resistant to heat and even to direct flame (making it fireproof). when the flame Extinguished the Polyurea act as a fire repellent.
  4. and considered in some degree as a "green" material, because of some non-hazardous application characters.

i'm sorry that i don't have a recommendation of a specific product, or even experience with applying it, but it sounds so promising and i needed to share :)

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