How To Repair Concrete

If you have a concrete path, patio or garden wall that is generally in good repair but does have a few knocks and cracks, and you don’t want to go to the trouble or expense of replacing it – here are a variety of quick fixes

Each method is for a different type of repair, and is explained separately. Before purchasing materials, check the various methods and images to find which is most appropriate for your repair

Before using any of the repair materials make sure the cracks and surrounding surfaces are clean, dry and free of dust or debris. Oil, grease, paint, other stains or chemical cleaning products must be removed prior to using any of the materials, as they may affect the bonding or curing processes

1) For cracks up to 1/4inch (6mm) width (Horizontal surfaces only):

CONCRETE CRACK SEALANT

This is ideal for long skinny cracks, and involves very little labour.

The crack sealant is a latex-based liquid, concrete-coloured, and comes in an easy to apply bottle

Pour the sealant from the bottle, overfilling the crack slightly to allow for settling and shrinkage
Multiple layers can be built up in deep cracks, as the sealant levels. Pouring too much into the crack is not a problem as it will spread and self level on the concrete surface

Because the sealant is applied directly from the bottle, and is self-levelling, you don’t have to mess about smoothing it over with your finger or a knife

2) For shallow holes and dips less than 1/2inch (13mm) depth (Horizontal surfaces):

CONCRETE PATCHING MIX

Patching compounds come in various forms from dry powder you mix with water to ready mixed

If using dry powder, check it already contains hardener and bonding resin

Follow the manufacturer’s instructions and mix to a thick soup-like consistency

Pour into the hole, wait for it to thicken and start setting then smooth with a wet trowel

3) Cracks up to 1/2inch (13mm) width (Walls & Floors):

CONCRETE REPAIR CAULK

This caulk comes in a tube and is applied with a standard caulking gun.

Cut the tip of the nozzle on an angle with a sharp knife to match the width of the crack and load the tube into the gun

Slowly draw the gun down the crack, forcing the caulk deep into it

Concrete repair caulk is latex-based and blended with sand. Unlike regular caulks, this means you can apply it in multiple layers, allowing each layer to dry inbetween. However, for deeper cracks it’s a good idea to use foam backer rods to fill the crack first. Push the rod into the crack with a screwdriver. Do not use caulk to fill expansion joints (see section 7)

Smooth with a trowel to match the surrounding surface immediately on completing filling the crack, as it will begin to form a skin within 20 minutes and will harden completely in 1 to 2 hours

4) Cracks over 1/2inch (13mm) width, and holes, edges, remodelling (Walls & Floors):

QUICK-SETTING CEMENT

Mix quick-setting cement with water to a thick clay-like texture that you can push into cracks.

It’s a good idea to add an acrylic fortifier. This will help to strenthen the cement and increase bonding

Quick-setting cement can also be used for to rebuild chipped edges, corners and missing pieces of steps, slabs and walls, holding them in place with wooden boards until set if necessary

5) Cracks and holes in very wet areas and concrete water features:

HYDRAULIC CEMENT

Hydraulic cement is extremely quick-setting and can be used to plug cracks and holes while very wet, if water is pouring through, or even underwater!

Mix to a thick putty, closely following the manufacturers instructions, push into the fissure, wait 5 minutes, then slice off the excess with a trowel or knife

Hydraulic cement actually stops water so is ideal for sealing cracks and holes to stop leaks in any concrete construction, sealing holes around water pipes, and to repair concrete water features, fountains, ponds, pools, bird baths and planters etc

6) Cosmetic surgery for unsightly or repaired surfaces (Floors & steps):

CONCRETE RESURFACER

For concrete paths and patios where the surface is essentially sound, with minor repairs, a skim layer may be enough to improve it’s overall appearance. This is only suitable for a thin resurface of upto an absolute maximum depth of 1/4inch (6mm)

Make sure old expansion joint sealant has been removed, as further on in this article (section 7), insert foam backer rods into the joints pushing them in with your fingers or a screwdriver/putty knife

Mix the resurfacer as per the manufacturer’s instructions, to a pouring consistency

Resurfacer starts to set in approx 20 minutes so you have to work fast

Spread the resurfacer out with a trowel to ensure the whole area is covered. Resurfacing compound is self-levelling so you don’t have to worry about it being too even.

After 5-10 minutes you can use a broom to sweep over the surface in one direction if you want to make it more anti-slip, this should be across the direction that foot traffic will take

After 15-20 minutes remove the rods from the expansion joints as you will need new ones when you reseal

The skim layer should be ok to walk on after 5-6 hours, but obviously the longer you leave it the better

7) Filling expansion joints:

FOAM BACKER RODS & FLEXIBLE JOINT SEALER

Large areas of concrete have expansion joints, long thin straight gaps between large or differently shaped concrete slabs. This is because concrete expands and contracts with varying temperature and moisture levels. Keeping expansion joints watertight prevents water from seeping under the concrete causing the slabs to lift or sink

Because of movement, expansion joints should always be sealed and filled with a flexible joint sealer and never be epoxied, coated or covered over with other materials except latex-based paint

The need to read this article shows that chances are, along with your concrete needing a facelift, the original filler in the expansion joints is worn out and needs replacing. One of the reasons for cracks is movement due to water seepage, as mentioned above

The old sealant will need removing first to ensure a watertight seal. You could try to do this with a sharp utility knife, but an angle grinder will be quicker and easier to separate the sealant from the concrete. You will also have to dig out the old backer rods, then use a vacuum cleaner to clear out any debris from the joints

Foam backer rods are used to save on the amount of sealant you would require without them. When purchasing the rods, they come in rolls or strips depending on size, make sure you choose ones which are approximately 1/8inch larger in diameter than the width of the joint. This is to ensure a watertight fit

Moving along the joint push the backer rod into the gap using a screwdriver, putty knife or piece of wood if necessary, but making sure not to damage it. The rod should be slightly lower than the surface of the concrete so there is no hump when the sealant self-levels on top

Apply the sealant using a caulk gun, but don’t cut too much off the nozzle of the sealant tube or it will flow out too fast and be messy and difficult to work with (you may have to pierce inside the nozzle with a strong piece of wire to break a seal inside the tube).

Squeeze the sealant along the joint filling the expansion joint, the sealant is self-levelling but you can top it up or fill in gaps as it settles. Have old rags handy to wipe off any sealant that goes where it shouldn’t on the surface of the concrete

The sealant takes 3-5 days to fully cure

Sealant can be painted after a few hours