How to fill cracks in concrete fireplace wall?

Hello @Innov8tive

I agree, renovation costs do tend to pile up after a while. I suggest using Earl's 500g Concremate Expanding Cement to fill in all the gaps in the concrete. My best advice is to remove as much of the loose concrete bits before using the filler.

If you need further assistance, please let us know.

Eric

@EricL

This was the product I was thinking of getting so will get it. I'm wondering if I can just use the applicator for what I use to fill the holes in my walls with spakfilla. I'm thinking that would be ok to apply this on the concrete that needs fixing.

If you're referring to the small plastic spatula that comes with Spakfilla, then yes, that would work just fine.

If not, you could always use a small plastic scraper like this Pro Renovator 50mm Plastic Scraper or a metal one, like this 100mm Sharp Edge Paint Scraper.

Let me know if you have any further questions.

Jacob

That plastic scraper is on my list anyhow as that is going to be used for attempting to remove water based paint from the hardwood floors. (Already posted about that)

@EricL @JacobZ

I purchased it. I'm just wondering how much water I need to add for the right consistency after I put what I need in a seperate tub?

I couldn't give you a specific amount of water, as it will all depend on how much you are mixing.

The instructions, which can be here - CONCREMATE® – Timbermate Group say - "To achieve PLASTIC CONSISTENCY (TROWELLABLE) for trowelling add about 300ml of water per 1kg of Concremate. Work the mix to a putty-like firmness, kneading it with the hands if necessary. If too fluid, add Concremate sparingly. It is always advisable to wear gloves."

You could use this ratio to work things out, or you could just grab some powder and slowly add water while mixing. You're aiming for something with a little bit of body to it that won't slump off your mixing utensil if lifted. If you accidentally add too much water, just add a bit more of the powder.

Let me know if you have further questions.

Jacob

Ok will give it a try. Not done it before so will post pics of how it turned out

I'm also wondering what grit sandpaper I should use when sanding back? It all came out pretty dark and wondering if it will lighten when I sand it back a bit? We bought Taubmans 1 litre paint to paint the wall surrounding the fireplace so don't want it blending in with that.

Sanding is not going to lighten the colour, but it will lighten as it dries.

I wouldn't usually recommend sanding a cement-based filler. These surfaces are textured anyway, so you shouldn't really need to and it would make the patch look different to the rest of the wall.

Once it is dry, have a look and see what you think. If you absolutely have to sand it, make sure you wear a mask and use 80-grit.

Let me know if you have any further questions.

Jacob

Well this was my first time doing this sort of job and mixing in concrete. I don't think it turned out too well but I feel I'm going to need to sand it back. I knew it lightened as it dried but this was a particularly difficult job for the less experienced.

Hello @Innov8tive

Thank you for the update, the patch job looks very good. I suggest following @JacobZ's suggestion of using an 80grit sandpaper to level the surface. I recommend using a UNi-PRO Cork Sanding Block for a nice uniform finish.

Eric

@EricL

Thanks for the compliment.

Is the unipro cork sanding block the same as 80 grit sandpaper? Apparently Bunnings does not sell single sanding sheets anymore so it's pretty much down to blocks now.

Hi @Innov8tive

The sanding block provides a flat surface for the sandpaper to wrap around on. Therefore, when you sand the surface, it will provide a flat even surface which you won't be able to get when sanding with just your hand. The sanding block itself is not sandpaper but there are sanding blocks that have sandpaper attached to it. Please just keep in mind that you'll need a low number for the sandpaper grit so that it works on the filler. I suggest looking for the Flexovit 115mm x 1m 80 Grit No Clog Sandpaper Roll, it's a close equivalent to the single sheet you are after.

Eric

@EricL

Understood. I do have a sanding pole. Will that roll you suggested fit the sanding pole I have?

Hello @Innov8tive

Yes, the roll I suggested should fit a standard sanding pole. However, I suggest double checking the width at the store by placing it over the sample sanding poles at the store.

If you need further assistance, please let us know.

Eric

@EricL the rolls actually come in plastic packaging so unless they have samples of unpackaged rolls there that would be hard to do