Can You Caulk Over Caulk? Will It Stick?

If you are doing some renovation, the temptation to cut corners can really be strong. This includes applying new caulk over old caulk. But is this something that you should do?

The answer is somewhat more complicated than you might think.

Can You Put Silicone Caulk over Old Caulk?

In general, you should not put new caulk over old caulk. The reason is simple in that the old caulk may have shrunk or otherwise be compromised. The result is that applying a new layer of caulk will not fill in all the gaps. And instead of creating a better seal, you instead only have the same openings that let in the moisture, mold, mildew, and other unwanted elements.

This means that in most cases you will need to dig out the old caulk, remove all the dust and debris, then apply a new line of caulk. This is time-consuming, but well worth the effort as it will ensure that the crack or gap has been fully sealed.

Of course, this may lead you to believe that under no circumstances should you keep the old caulk in place. However, the truth is that there are certain instances in which keeping the old caulk around is fine. This means that you can apply a new layer without having to remove the old caulk.

When Can You Caulk Over Caulk?

In the case that the bottom layer of the old caulk is still sound, then you can apply a new layer over the top. This assumes that the old caulk is not compromised.

Caulking over Cracked Caulk

The existing layer of caulking should not be cracked, damaged, or moldy. In such cases, the old caulk will have to be removed. Otherwise, it will not stick properly and is a waste of effort.

So, if the bottom layer of the old caulk is still in good condition, you can cover it up with a new layer.

How to Re-Caulk?

If you believe that covering the old caulk with new caulk is the best option, which is normally based on time, budget, and the condition of the old caulk, then you can do it if you follow these steps.

1. Preparation: Type of Caulking

First, let’s decide which type of caulk to use, acrylic or silicone.

Silicone is the superior caulk because it is watertight and prevents rot, mold, and water damage. However, silicone is much more difficult to apply over old caulk compared to acrylic latex. Because silicone is more rigid and less adhesive, it may not stick.

Acrylic caulk does work considerably better on old caulking, thanks to its flexible and adhesive qualities. For applying a second layer of caulk, you probably want to go with acrylic latex. If you need a watertight seal, then you should remove the old caulk entirely and replace it with silicone.

2. Process

The re-caulking process consists of three steps.

1. Cleaning the old sealing
2. Applying new caulk over the old layer
3. Curing

Soap & Water: If the old caulk is acrylic latex, clean out the old caulk using soap and water and the surface on either side of the crack or gap. For surfaces that are well away from the old caulk, you can use denatured alcohol. However, if the denatured alcohol touches the old caulk it will start to dissolve it.

For silicone caulk, you will not want to use soap because it will leave behind a residue that interferes with the caulk’s ability to seal the crack or gap. Instead, use a mixture of 10 parts warm water to one part bleach. This will create an effective cleaning solution which will remove the contaminants without leaving a residue behind.

Let the old caulk dry for at least 24 hours. Make sure that the caulk and the surface is fully dry before you proceed. Now you are ready to apply a new bead of caulk over the old one.

Apply: When applying the new bead of caulk, be sure to cover the entire amount of the old caulk. This means that you will need to extend the line of the new caulk beyond the old layer. The goal is to allow the new caulk to not only bond with the old one, but also to bond with the surrounding surface as well. This will help improve adhesion and limit water penetration.

Dry: You should let the new bead of caulk dry for at least 24 to 48 hours. This will allow the new caulk to cure.

You can check the new caulk to see if the seal has taken hold. If so, you can shape the outside of the caulk by sanding and painting over it if you desire, but painting over silicone will not be effective. Instead, be sure to choose a color of silicone caulk that matches the surface.

When Not to Re-Caulk?

Despite all the advantages of putting new caulk over old caulk, there are times in which you should instead remove the old caulk entirely.

1. Cracked Caulk: You may think that by adding new caulk over cracked, old caulk that the openings will be sealed. However, the truth is that the openings will remain and allow the new caulk to be exposed to the outside air, elements, or moisture that caused the old caulk to become damaged in the first place.
2. Damaged or Worn Seal: The caulk may not be cracked, but it is clearly not in the same shape as new caulk. When this happens, it means that some of the elements that make up the old caulk have faded. Perhaps due to UV damage or simply age, once old caulk shows signs of being damaged or worn it is best that it be removed.
3. Mold: There are those who believe that covering up old caulk that has mold will cause the mold to stop growing. This is simply not true as the presence of mold indicates that something else may be going on well underneath the old caulk.

If you see any signs of mold on the old caulk, it will need to be removed. Furthermore, the area will need to be treated such as with the bleach to warm water mixture that will destroy any mold present in the gap or crack. Not removing all the mold before applying the new caulk will only lead to even more issues.