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Probably due to the age of the house (~30 years old), a lot of weeds now grow in between pavers in my backyard. I read that I can use polymeric sand to fill in that space, but that sounds like something that I may need to redo every a few years and would also not apply for the places with larger spacing (please see pictures below). Can I use quick set concrete instead? And are there other good ways to deal with this? If possible, I would like to avoid using chemicals like glyphosate as there is a pool nearby.

Also anyone recognize the weeds in the pictures?

Weed01 Weed02

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Your photos show two different types of paving; the top photo shows block paving, which is laid on sand with the blocks closely laid and then infilled with polymeric sand using a whacker plate. Whilst this type of paving is helpful to the environment because it's semi permeable (allows water to dissipate between the cracks, reducing flood risk from heavy rain generally) it does inevitably, over time, get weeds growing in between. It won't be possible to use a mortar mix to seal the gaps, particularly as it is not laid on hardcore beneath. In the UK, it's usual to apply a long acting path/driveway weedkiller such as Pathclear to the cracks in mid to late spring annually - this prevents growth for up to 4 months. This is done to avoid having to blast out in between gaps and reapply polymeric sand with a whacker plate (vibration plate), though this latter provides a much longer lasting solution.

The other paving looks as if its laid on soil, with large gaps between, If it has no harcore or concrete beneath, consider deliberately planting low growing plants in the gaps to prevent weed invasion. It depends on the climate where you live what type of plant you can use and to some extent how much foot traffic the area gets - clover will tolerate being walked over quite often, as will Soleirolia (or Helxine, sometimes known as mind your own business, see here https://www.rhs.org.uk/plants/17471/Soleirolia-soleirolii/Details) but there are other plants which can be used for lower traffic areas - see here for some suggestions https://www.flowerpotman.com/plants-for-soil-type-and-conditions/plants-for-pathways/.

UPDATE: GailD has not actually suggested just concrete, she is talking about a dry mortar mix, which is just sand and concrete well mixed together in a particular ratio. I have used this method myself with ordinary pavers spaced about quarter to half an inch apart, brushing it into the gaps, then gently pouring water over and it works well, assuming weather conditions are right. However, it's not clear whether you think you want to do that for the block paving, but bear in mind block paving is meant to interlock closely leaving a wafer thin gap in between each block which is not intended to have mortar between. The other answer suggests using a funnel to get the mortar mix in the gaps, but as I said before, a vibration plate is normally used because it's very difficult to get anything to go down in between the blocks.

As for the larger paving slabs, I would not use a dry mortar mix method there - the gaps are so wide that a wet mortar mix is fine. Regardless, wet or dry, I fear the gaps are so wide that the mortar, once set, will crack, especially as the material in between the slabs looks like loose, small chippings which presumably have not been compacted.

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  • Thanks for the very good information on both types of paving! What's the problem with sealing gaps with mortar mix? GailD suggested concrete -- is there a difference between the two? I guess gap size in the brick case may be mildly problematic. I now also found that in the bottom photo, the stone pavers were laid on top of the same small rocks/sand as those in the gaps (which is why I waited a bit to reply as I was going to put in a downspout extension pipe beneath those stone pavers).
    – Roc W.
    Dec 3 '20 at 23:19
  • See updated answer
    – Bamboo
    Dec 4 '20 at 17:59
  • Very clear explanation and it makes sense to consider cracks down the road. Thanks! Difficult to battle nature.
    – Roc W.
    Dec 4 '20 at 21:51
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If you have just a few weeds, you can kill them by pouring boiling water on them. Of course in larger numbers this quickly becomes very time consuming, as you keep having to return to the kitchen, refill the kettle, and wait for it to boil again. This will work for shallow-rooted plants. If you have deep-rooted weeds, boiling water will kill the leaves but not the root, so they will regrow from the root. I don't know what weed you have there, but it looks to me like a shallow-rooted one.

A weed torch is perfect for killing weeds growing between stones. You can use a basic blowtorch, or get a specialized wand that attaches to a propane tank. Various models are sold as weed torches or as ice torches (intended for melting ice from steps or a walkway). The trick is not to actually light the weed on fire, but to hold the flame several inches away until the leaves loose their glossiness. This way, you destroy the outer coating of the leaves, so the plant loses all its moisture to evaporation, which kills off the stems and roots as well as the leaves.

Or you can use a vinegar weed killer, which is just highly concentrated vinegar (usually about 20% acetic acid, much stronger than the usual 5% stuff used for cooking and cleaning). Keep in mind that the concentrated stuff is hazardous to your eyes and skin. So make sure not to apply it on a day when people will be walking around the area barefoot. It will also make the area smell like vinegar for a while (this article says the smell will linger for a couple days). The good news is that if any of the vinegar does migrate into your pool through rainwater runoff, it will get diluted along the way.

Of course, there's always hand-weeding. With weeds that spread out really flat along the paving stones like that one, it can be helpful to first sweep the area with a push broom. That will pull some of the stems up away from the pavers and make them easy to grab.

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  • Thanks for the various suggestions! I was mostly pulling the weeds, which is often a time-consuming and/or losing battle in the more beautiful seasons. Is there anyway to deal with the dirt/soil that is forming in between the bricks and stones?
    – Roc W.
    Nov 7 '20 at 5:03
  • @RocWhite A pressure washer would help with the dirt building up between the bricks, but would probably dislodge the gravel between the pavers (unless that gravel is fused together; in that case, perhaps a pressure washer on the lowest setting, but try it in an inconspicuous area first). I think Bamboo provided a good summary of other options in their answer.
    – csk
    Nov 7 '20 at 19:26
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Once you get weeds cleared out, by whatever method, you can do any of several things to help prevent regrowth.

  1. Spray your pavers with water, making sure to get the sides facing the void good and damp. Then use concrete bagged with sand (not with rocks, gravel or "aggregate" in it. Using a large funnel, fill the voids with dry concrete. Use a household broom to gently sweep any excess off the pavers and into the voids. Gently sweep and level voids. Using a garden hose set to a fine spray gently wet the surface of the concrete-filled voids, being careful not to wash out the filling. Continue to spray the concrete to keep it moist for the next 3 days. If the surface sinks lower than the pavers, you can add more concrete.This will fill the voids with a thin but fairly tough skim of concrete that can be easily taken up if you decide to change the pavers.
  2. There are products made of ground corncobs (Preen is one I've used) that prevent seeds from germinating. Filling gaps between pavers with Preen or similar and tamping it in until gaps are filled should prevent growth for some time. Although longer than manufacturers claim, I've seen this technique prevent germination for over a year. You will eventually need to add more to top it off as it breaks down and returns to the soil underneath. Preen does not prevent regrowth from the root, so be certain you've cleaned out the unwanted plants completely.

Fortunately, both concrete and Preen are relatively inexpensive, non-toxic, and removable.

I have personally used both methods with pavers laid on soil and/or builder's sand and found them very effective. I recommend getting a stool or something low to sit on while pouring concrete through a funnel in order to save yourself a backache...just scoot along and fill the voids.

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    Would the fact that the bricks are laid on loose base (soil/sand) present problems for concrete, as Bamboo mentioned for mortar mixes?
    – Roc W.
    Dec 4 '20 at 0:12
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    No, you can use concrete with no problems. You're not trying to construct a concrete slab, just something to fill the cracks that weeds won't grow through. Because you will be walking largely on the bricks and putting very little weight or stress on the concrete filler, it will hold up well. Yet, should you decide to change your yard layout at some future time, you can lift the bricks, break up the minimal concrete fill with the back of a garden rake or shovel edge, rake the pieces into a scoop shovel, and completely remove it. I've done this with both sandy loam soil and pure sand.
    – GailD
    Dec 5 '20 at 1:12
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The space between your pavers is a perfect place for wind to blow in some soil and seeds and something will start to grow. Removing existing weeds is simple, but keep in mind that this process will repeat itself. You can try to prevent accumulation of soil by removing any gaps that can trap soil, but that seems like a lot of work, pulling out a weed when it just emerges is easier, I do mine after a rain - weeds slide right out of moist surface.

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I mix 2 parts distilled vinegar to 1 part water into a 2L spray bottle. Then I add ~3/4 tbsp of salt and mix. (Sometimes I also add a little dish soap, too, but have found success without it).

I spray the weed leaves and make sure I soak the base of the stem where it comes out of the ground with the squirt bottle mixture. Most of the time the plant is dead in a day or 2. Sometimes, I need to follow-up with 1-2 additional squirting sessions to knock off any remaining living tissue.

I've found a lot of success with this concoction on weeds growing in various substrates (rock gardens, soil, cement cracks, and lawn). It has worked on dandelions, plantains, purslane, bindweed, and even poison ivy growing rampant in a window well!

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