What's the best product to fill cracks in plasterboard walls?
I have some cracks that appeared in the drywall of my living room after summer. I already tried with caulk but it didn't finish well. What's the best product for this to be invisible?
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The thing that makes the difference is preparing the crack properly first - run a wire brush or even a vacuum over it to get all the loose dust out, otherwise nothing sticks right. After that, acrylic filler or gypsum filler (the powder kind) work well, but the real secret is applying it in thin layers instead of trying to cover everything at once, because that way it dries better and doesn't crack again. A final pass with fine-grit sandpaper at the end makes it completely unnoticeable.
Try using drywall joint compound (the powder kind you mix with water) instead of caulk, because it adheres better to drywall and dries much smoother. After that, just sand it well with fine-grit sandpaper and paint over it and it'll be invisible.
Caulk by itself is way too weak for that, it leaves you with a pretty uneven finish! The trick that actually works better is using acrylic spackle (not the powder kind, don't do that) because it comes ready to use, dries faster and you can get really smooth panels with it. The key is applying it with a spatula that's bigger than it seems necessary, going horizontal and then vertical so it gets really embedded in the crack, then once it dries you just need a light sanding with 120 or 150 grit sandpaper and it becomes invisible!
Drywall that cracks like that after summer is almost always due to temperature and humidity fluctuation, so the crack will come back if you don't fix the cause first. I agree that prep work is essential, but the product that actually works is polymeric spackling compound (like Spackle or similar) - it has more flexibility than regular acrylic joint compound, so when the wall moves again, it won't crack along with it. Apply it with a putty knife, let it dry, sand it well with fine-grit sandpaper and then just paint. If the crack is too deep, put down one layer, let it dry, then another.
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