Extra Rapid Cement

[hudd09]

Hi,

A couple of summers ago I refixed a driveway manhole cover frame using Extra Rapid set cement as the cover is slap in the middle of the tyre track with no space to get around it.

After the recent snows had melted all this concrete has lifted and literally crumbling like pastry.

As this is the only area I have used the Rapid cement on, all surrounding standard concrete being ok, I wondered if I had done something wrong ?
I primed the area with PVA and used a small amount of colourant - would these affect the cement in any way ??

The Rapid cement pack says its designed for jobs just like this so wondered why if failed so quicky when the previous cement had lasted 25 years.

thanks.

 

[DCC]

PVA and Colourant shouldn't cause any problems. The repair has failed now because water has penetrated around it and frozen I would guess. Perhaps the previous job took longer to set and had time to settle and more effectively block the spaces water could penetrate? Whenever you make a patch its always going to be weaker and prone to disintigrate (which is why on big concrete construction jobs they are so careful to get the pouring just right so that its all one continuous bonded lump of concrete). How large an area did you repair (and how deep)? small patches disappear quicker than larger ones - you might end up having to remove a proper size area and fill that.

 

[Deluks]

Maybe you didn't use enough to do a proper job, was the cover fully embedded in a good depth, or did you just dab it round the edges?

Rapid set should not be used where steel is present, although I believe this is more to do with corrosion of the steel itself.

Don't forget that ice is expanded water, so any small gaps or cracks would be forced apart by the freezing action.

Did you use sharp sand or building sand, or was it a ready mix pack?

 

[hudd09]

Hi,

It was a plastic frame as supplied with the new metal cover, and I did use sharp sand at the correct ratio etc.

Am limited to the depth I can bed it as it sits on the precast ring.

Think you have answered my question though in that the Extra Rapid stuff has no special conditions.

thanks.

 

[LooPrEvil]

i have just been looking at using rapid cement and note that additives, ie colourants / normal cement etc should not used with it.