Lobster wrote:
Harry Bloomfield wrote:
explained on 13/03/2005 :
Lobster wrote:

I've got an old brick shed with a concrete slab roof; watertight
at the
mo, but in one corner (external) the surface of the concrete has
broken
up under the influence of weather; probably an inch deep? in a
4-5 inch
slab.

3:1 is the strongest non-shrinking mix, and just a little pva
makes it
adhere better.

Thanks guys. Are we definitely 100% sure about the PVA thing? :-)
I
always thought it was a complete no-no outdoors. and wouldn't want to

cock this up...

The PVA I've got gives instructions for using it for this. It says mix
pva and water 50/50 and use that for the liquid in the mortar mix.

Yet it also says do not use in constantly damp situations.

I've come across this puzzle before, heres what I know:
1=2E its used in mortar for copings to increase adhesion and tensile
strength.
2=2E 3:1 sand:cement is used as a mix that is not water damageable, due
to its minimum permeability. Weaker mixes are much more permeable and
do get damaged by a wet freeze.
3=2E PVA is no good used alone as glue in damp, but in mortar it seems to
work.
4=2E Your wall mortar shouldnt be constantly saturated anyway, once its
set.


Then once properly dry, consider adding a waterproof membrane to
prevent
water getting into and freezing in the concrete again.

How do you mean, paint-on bitumen type stuff? Aquaseal? Or felt of
some
sort? Wouldn't just adding waterproofer to the cement mix do the job


it would, but for 3:1 nothing is needed.


(or would that interact with PVA?)

no idea, personally, dont use them. Why pay =A38 for what you can buy
for 13p.


NT