concrete garage sub base

[bobho1]

I'm replacing a concrete garage base, after digging up the original concrete, the base under is constructed of red ash. Is red ash a suitable material to lay concrete on or does it react with the concrete and cause cracking ?.

[tradeaway]

red ash or 'red death' as it has come to be known, is sulphate rich and reacts with concrete causing it to expand and bow away from the ash.

i would dig it up, or at least use a gas dpm if you are going to leave it down.

[dents]

just lay a dpm