Filling the gap between concrete slabs

[BloodyIrishman]

I recently moved into a house with a rather large concreted back yard and want to do something about the weeds that grow between the joints between the slabs. It seems that over the years the ground has settled and the joints between the concrete slabs has become a gap of around 2+ cms  and many CMs deep. The original filler material is a tar sheet material which has degraded and is practically non-existent in some joints. 

Can anybody advise what is the best way fill in these gaps and thereby prevent weeds?

Thanks in advance.

[Jason]

Hi @BloodyIrishman,

Could we please trouble you for a photo so members can more easily visualise the problem? Let me know if you need a hand with uploading a photo or getting the most from the Workshop site in any other way. 

Let me extend a very warm welcome to the community. We trust that you'll receive loads of helpful information, advice and inspiration for your projects around the house and garden from our clever and creative members. Feel free to post anytime you need a hand or have something to share. 

Jason

[BloodyIrishman]

This one is probably the biggest of the lot

[Mathy]

Hi @BloodyIrishman (great name btw) - what you do depends on how many gaps there are to fill, and how much time/money you want to spend.

You could use a flexible adhesive/filler such as SikaFlex Pro, which comes in a “sausage” - but it’s about $20 per unit, plus you need a sausage gun. Selley’s also make a similar product “Selley’s Flexiseal” -  Polyurethane Sealant, also in a sausage but about $15.00. These are both 600ml products, you’d have to do some rough math to work out how you need etc. Both of these should last a while, but no product like this is going to be permanent.

You could contemplate some sort of grout, which would be a hard filler, so will crack and fail eventually. I have seen this done using an icing piping bag arrangement (I kid you not!) to speed application up.

Alternatively, I got rid of my recurring weeds in my pavers in 2 years by applying Roundup - so, a bit of work for a couple of years, but this year - no weeds. Hope this helps, cheers Deb

[Jason]

Following on from @Mathy's point about weed control, you might be interested in the tips on these previous discussions. Something simple like boiling water might be worth a try....

• Best way to control weeds

• How do you get rid of weeds?

Hope that helps.

Jason

[Ishan]

One question, can't we use mortar or render? If the gaps are outdoor under patio, what are the options?

[JacobZ]

Hi @Ishan,

A warm welcome to the Bunnings Workshop community and thank you for your question.

Typically you wouldn't use mortar or render as they are not flexible and will crack easily.

Have a look at How to fill a joint in a concrete slab as an example of a more appropriate method.

If this is not like the gap you are dealing with, please upload some images so I can assist further. Let me know if you need a hand with this.

Jacob