Finish Coat Drywall Crack Repairs
When repairing drywall cracks, you must first eliminate unwanted movement and then tape the crack. If you have not done so already, please read our previous articles regarding these two steps. Once the drywall crack has been taped, you are ready to finish coat the repair.
Type of mud to use for finish coating drywall repair
You have a few more options for finish coat mud than you do when taping drywall. All-purpose drywall mud can be used though it is slightly more difficult to sand when dry. Lightweight-all-purpose drywall mud works very well for finish coating drywall repairs since it is easy to work with and much easier to sand when dry. The downside to both all-purpose and lightweight-all-purpose drywall mud is that they take up to 24 hours to dry before they can be re-coated. So a small patch can end up requiring several days to finish due to dry time.
Since most drywall repairs need to be done within a short time, Quick set powder drywall mud (also known as hot mud) can be used not only for taping cracks but also for finish coating the repair. Quick set drywall mud can be re-coated within a matter of minutes so 3-4 coats can be applied within a couple of hours. It also does not shrink when setting so it is a good option when you are trying to work quickly.
Benefits and challenges of hot mud for drywall repair
One challenge to working with hot mud is creating a smooth finish. Quick set drywall mud tends to be grainy or leave trowel marks that are not noticeable until fully dry. If you will be texturing the finished patch, this will not be a problem but if you are trying to match smooth wall, it could present some challenges. There are a couple of options that can help you create a very smooth surface even when using hot mud.
If you are using hot mud, the first option is to apply several very thin layers of mud instead of the traditional two to three coats. The first two coats can be done as normal, but then an additional 2 to 3 very thin skim coats can be added. This helps to fill in any pockmarks or even out any trowel marks. The benefit of this is that the entire repair can be completed within a few hours including taping and finishing.
If you are using hot mud, the second option is to finish with a skim coat of lightweight-all-purpose drywall mud. The first two coats of hot mud can be applied as normal. Thereafter a thin coat of lightweight-all-purpose mud can be floated over the surface. This will need to dry overnight before being sanded. The advantage to this is that the lightweight-all-purpose drywall mud is easier to work with and covers any imperfections left by the hot mud. Pockmarks or trowel marks left in the all-purpose drywall mud can be easily sanded away, leaving a perfectly smooth finish.
How many coats when repairing drywall cracks
When finish coating new drywall, two or three coats are enough to float over taped seams and butts. However, when repairing damaged drywall, three coats may not be enough. Finish coating over repaired drywall cracks is like finish coating drywall butt joints. The joint needs to be floated out at least 12 to 15 inches on either side. In general, finish coating creates a flat and smooth surface. Drywall butt joints are the most difficult to float out flatly since the tape is not recessed in a drywall joint of two bound edges.
Two or Three coats of mud may be enough to finish coat drywall crack repairs but if the crack was raised on either side, it will probably take more.
As is true when finish-coating all types of drywall seams, several thin layers of mud are easier to control than a few thick layers of mud. If you are new to drywall finishing, start out by adding thin layers and focus on creating a flat smooth surface. You can always add another layer of mud if the surface is not as smooth or flat as it should be. It may take a little longer but you will be happier with the result.
Once you have finish-coated your drywall repair your next step is to texture the patch to match the existing drywall texture. Matching drywall texture takes some imagination and a variety of skill sets. You can read our tips for matching drywall texture here.