My driveway (which is built with paving slabs) has been somewhat neglected
over the past year, and as a result has a major problem with weeds (some as
big as triffids ;) ) growing up between the slabs. I'm planning on tackling
it in the near future, and wanted to get some advice.
My plan is as follows:
1. Remove the bigger clumps of weed
2. Lift the slabs
3. Put down some very strong weed killer
4. Check the level of the base (allowing for run-off) which I think is
currently just sand on hardcore.
5. Re-lay the slabs, and 'grout' them.
Any advice on what weedkiller to use, and the best (read easiest) way to
'grout' the slabs to stop anything growing back for as long as possible?
I had similar triffids in full flower in our back yard (concrete slabs)
earlier. I adopted the following strategy.
1. blitz them with glyphosate, blitz them good and proper, wet them all
2. Wait a week for the glyphosate to kill the roots then get a tool like
I have. It is basically a flat piece of aluminium in a strong hook shape
and a handle. You insert said tool between slabs and scrape out both
plants and accumulated soil.
3. Sweep it all up regularly.
4. scrape the gaps regularly to prevent soil buildup and especially at
the start of spring.
School of Life Sciences, University of Dundee, Scotland
Other than the weeds, is the drive ok, or could it do with relaying
If it is otherwise ok I wouldn't bother with lifting the slabs, as
someone else has said, glyphosphate (such as Roundup) will do the job of
killing the growing weeds - this is a systemic weed killer - it is
translocated through the plant and kills the roots as well. So it kills
perennial weeds such as Dandelions etc.
Most of the weeds that are going to grow in this situation will be
killed with one application. sometimes a big old Dandelion root may
take a couple of goes.
It doesn't stop new weeds growing of course, but a further application
is easy enough.
You could use Sodium Chlorate as this is a persistent weed killer, but
I don't think ti would really get down into the ground- but note that if
it gets into the soil where you want to grow anything else then it can
take 6 months of more before stuff can grow there.
As for 'grouting' if the slabs have been tight laid (like pavements)
there is little to do. You can try brushing in the sand they use for
block paving, but I don't think it's make a lot of difference.
You need say about 10mm gap between the slabs so that you can mortar in
between them. This will stop pretty much all of the weed growth as long
as it stays sound.
If you do lift the slabs and relay them I wouldn't bother weed killing
the ground. The weeds don't come up through the slabs, they germinate
in the gaps and grow down into the soil.
For advice on the paving see Cormaic's site:
In my experiance all weedkillers that are selective, or 'specially
formulated for your driveway' are expensive and crap. I relaid my patio
after moving in as year ago as it suffered the same problem. I ripped up the
weeds, lifted the slabs, chuned the base, levelled it, poured loads of
sodium chloate down and then put down bin liners (covering the whole area
with no gaps) and relaid the slabs on top using some sand where necessary to
level. "Grouted" with a sand / cement mix. I then oiled my spurs and went
off into the sunset on my horse.
It does take a while, for me it was something like 8 slabs an hour but I'm
slow, get bored doing things like this and it was hot... It is hard work but
you only do it the once.
Nothing has grown back in over a year now and I've not done anything to it
since either. I guess the bin liners stop any water getting to the roots
(and washing the nasty weedkiller away).
Spray with a weed killer sprayer every 3 months using a Roundup copy
(much, MUCH cheaper, usually more concentrated and just as good) and that
should sort it, or even get some Dairy Hypochorite from a farm supply
place (bleach) and water the slabs with that, diluted. Cleans the slabs
like new, stops green mould and stops weeds growing. Be careful with it,
but it has a multitude of uses, IMO.
There are better thungs than Glyphosate for totall kill. Sodium Chlorate
is one, and there are others (2-4 summat?)
Agreed totally., Just scrape out the much, or use a pressure washer as well.
Or, as in my case, mae a 6:1 sand cement mixture and brush in to the
gaps. tamp down hard.
It goes off eventually.
Now tyou can simply pressure wash the area any time it gets 'seedy' :-)
After a few years rain frost and cars, it needs doing again. But not as
often as weeding if you don't...
That sounds like a good idea. I thought of regrouting with sand on my
slabs but being a biologist I realised it wouldn't take long for the
sand to become an ideal growing mix. But with cement it would take a lot
How hard would it be to scrape this out and redo after a few years?
School of Life Sciences, University of Dundee, Scotland
I know I'll regret asking but... couldn't sodium chlorate be added to the
filling mix or would it just get washed away? Only asking as I have the same
problem on the patio but the gaps between flags are too small to use a
traditional "grout" - 3-4mm so a dry mix brushed in would seem ideal.
Speay the interstices once a year with Simazine weedkiller. Unlike
Roundup which works on growing weeds, Simazine lays on the surface and
remains active in stopping weed growing.
Alternatively Jeyes fluid can be sprayed more regularly and will also
help control moss .
Paul Mc Cann
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