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Is Polyfilla Waterproof?

Polyfilla is a great filler and now a household brand, one of those brand names that has become synonymous with an entire product. But is it waterproof? Let’s have a look and find out.

Regular Polyfilla is not waterproof. However, moisture resistant and exterior (which is fully waterproof) versions of Polyfilla do exist.

Exterior Polyfilla

Not many people are familiar with the different variations of Polyfilla, but lots actually exist. While we are all used to seeing the regular stuff in stores there are specialist options available.

One such option is Exterior Polyfilla, which, as the name suggests, is formulated for use outside. Because of this it obviously needs to be fully waterproof.

It will set in 60 minutes and is then fully waterproof. This filler is great for water sensitive areas that require filling. Think window frame surrounds and other areas where water might otherwise leak in.

Fully Waterproof
Polycell Multi Purpose Exterior Filler 1.75 kg
£11.95
  • Durable weatherproof formulation for general outdoor repairs
  • Sets in 60 minutes to a grey, weatherproof finish
  • Accepts bolts and screws and will not shrink or crack
  • Waterproof and frost resistant
  • Fills up to 10mm


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This waterproof Polyfilla can be painted over and it can also be sanded like regular Polyfilla. Unlike the normal stuff though it dries grey rather than white.

Can I Use Exterior Polyfilla While It Is Raining?

No, you cannot. This filler is waterproof, but only once set. You need 60 minutes for the filler to properly dry, throughout this time it needs to be kept dry. So you cannot use it while it is raining.

Is it weather resistant?

Yes, exterior Polyfilla is frost resistant and rain resistant. This is obviously essential with an exterior filler that will be left exposed to all weather conditions.

Moisture Resistant Polyfilla

As the name suggests this is not a fully waterproof Polyfilla but rather a water-resistant variant.

This Polyfilla is made for bathrooms. It is intended to get wet and be fine but is not expected to be exposed to water for prolonged times. Think bathroom tiles as an area where this filler is designed to be used.

Made For Bathrooms
Polycell Moisture Resistant Polyfilla, 330 g - White
£5.29 (£16.03 / kg)
  • Water resistant formula
  • For flexible, crack-free filling between two surfaces where movement can occur
  • Easily controlled application for long linear gaps
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This filler is white so is perfect for filling gaps in the grout in between tiles. It is also flexible, so if you have some grout that keeps cracking due to movement then maybe consider using some of this stuff instead.

This filler needs a minimum of 6 hours before it can be exposed to water, so make sure it is fully dry or it may just wash out!

Can It Be Used Outside?

No, this Polyfilla is moisture-resistant not waterproof. if used outside it will not last, the constant exposure to heavy rain will damage it.

It is also not advertised as being frost resistant, so freezing temperatures will damage it leading to cracks and chips.

Can It Be Painted?

No this is more like a silicone filler than a regular Polyfilla. That is what gives it its flexibility but it also means it is not suitable for being painted over.

Can It Be Sanded?

Again like the painting, no it cannot be sanded. As I mentioned before it is a flexible filler. That means it is a bit rubbery, which then means it is not suitable to be sanded like normal Polyfilla.

More On Polyfilla

Interested in the good ol Polyfilla are ya? Well, you might find these related posts interesting.