i need to riase the level of a shed base by 150mm, i propose to concrete over the existing one there, which is also 150mm deep. Do i need to use a bonding agent and also put a membrane down, or literally just pour on top.[/quote]
JUst pour on top for a shed base Sid as long as the existing base is fairly sound and not cracked and wobbly. If it is it will soon crack the new one. See our project on building a shed base.
