Product Review of the Roof Repair Mortar from Rizistal

Why do we Need Roof Repair Mortar?

Felt roofs, whether laid on a flat roof or a sloping roof, very rarely stay intact up to their (usual) 10-year guarantee period.

The range of UK temperatures, from zero degrees, to huge heats in Summer ensure that the felt covering expands and contract continuously getting very brittle in cold temperatures and all but melting in the Summer.

This movement causes splits and cracks in the felt that the water soon exploits. Finding the cause of a leak is all but impossible and most of the time the only way to repair a flat roof was to strip it off and start again.

Rizistal say that their roof repair mortar can be spread over the existing felts splits and cracks and a waterproof surface will result. The following on-site test will show this is exactly the case.

On Site Test of Bitumen Roof Repair Mortar

Repairing one or two splits in a leaking flat roof does not stop the rest of the roof moving about and splitting and cracking elsewhere! This is why Rizistal make two further roof repair products which are the subject of further reviews: The Bitumen High Build Roof Repair Coating and The Acrylic Polymer Roof Repair Coating.

The idea of these two coatings is that, once the Repair Mortar has been applied and allowed to cure for 24 hours, the entire roof surface can be covered with these excellent coatings giving the entire roof a new, lasting waterproof covering….But it is important that the cracks and splits are fixed in the first place, so first things first, lets apply the Roof Repair Mortar.

On our flat roof, some years ago, someone had cut a huge hole as a skylight. They had then stuck down some Polycarbonate sheeting, on some sealant, to keep it waterproof. It leaked almost from day 1!!

We removed all the Polycarbonate, built a 3-inch upstand around the hole. We covered the upstand with some mesh (usually used when tanking bathrooms and shower rooms) and prepared to waterproof the new skylight with the Repair Mortar.

Timber is one of the substrates that Rizistal say the Repair Mortar will adhere to but because of the likely excessive movement of the timber skylight on the flat roof we used the mesh to ensure that the repair mortar would not be compromised in any way. The mesh was fixed to the new skylight with galvanised clout nails to ensure they did not rust.

Having laid the mesh we started to build the upstand with the repair mortar. As you can see from the image and the video, the mortar went on really easily and because it does not sag we were able go put it on in a nice thick coat.

The repair mortar was laid on and feathered out to meet the existing surface so the upstand, in effect, was one with the roof.

At this stage, before it had even cured, we were incredibly impressed with the way the product handled itself.

It’s obviously very messy and all of the correct protective clothing should be worn, but it is simple to trowel on, simple to level and it even feels like it’s going to work when it’s being applied as the plasticity of it, together with the sight of the bonding fibres it contains, give a great sense of confidence to those of us who have been involved in roofing repairs before.

It’s important to note that for the Repair Mortar to do its job properly the roof must be absolutely clear of things like moss, fungi, leaves etc. If there is any chance of the moss and algae returning then a fungicide should be used on the roof before applying the mortar.

One of the excellent things about this repair mortar is that it can be applied in damp conditions. It is very rare for a felt roof to be completely dry because the felt usually dries with a slightly rippled finish, leaving a few hollows here and there which retain water and stay damp even after a bit of sunshine.

It took no time at all to work all the way round our skylight and as you can see from the video there was no effort involved at all.

The mesh bound the repair mortar together even better that it would have done on it’s own and when we returned 48 hours later we had created a great upstand.

Working Time, Mixing and Stirring Roof Repair Mortar

It takes about 6 minutes to stir a full, 5-litre tub of repair mortar. It starts out very thin, like paint, then gets thicker and thicker the more you stir. It obviously needs to be thick to stay in the self supporting state necessary for upstands etc.

In the tin, the product has an indefinite shelf life, the curing only starts when it is applied to the sub base.

Surface Preparation and Installation

We swept the roof clean and cut off the overhanging branches to reduce the number of leaves falling onto the roof. We then spent a lot of time with a scraper and stiff broom making sure there was no moss or algae on the roof. That done, we used some Everbuild Fungicidal Wash to clean and protect the roof thoroughly.

Coverage of the Roof Repair Mortar

This is a difficult one to asses. Rizistal say that 1kg of mortar will cover 0.1 sq m at a thickness of 10mm. Our skylight was 2.1m square with an upstand depth of 75mm.

We feathered the mortar out as we came from the vertical to the horizontal and would say the average width was 125mm. This gives us an area covered of just over 1 sq m which we did with 1 x 5 kg tin. This exceeds the stated coverage by quite some way and, as you will see by our product reviews on the Rizistal Tarmac and Asphalt Restorer, we believe Rizistal’s coverage statement are very honest indeed.

Curing Time of Bitumen Roof Repair Mortar

The repair mortar will cure, at normal temperatures and a thickness of 2 – 3 mm, in 24 hours. However, we used a thick coat for our upstand which took a full 48 hours to cure as we laid it in late October when it was very cold indeed.

DIY Doctors Opinion of the Bitumen Roof Repair Mortar From Rizistal

Excellent. This product really did exceed our expectations. Getting a skylight or roof vent waterproof is never an easy job but the repair mortar from Rizistal made it ridiculously easy.

The mortar feels robust yet very pliable and it’s elastic qualities make it almost impossible to not get the surface waterprrof as long as the instructions are followed and the roof has been cleaned and protected against moss and algae as described here.

It is a solvent of course, and care should be taken. PPE should be worn and no naked flames should be used when applying the repair mortar.

After finishing the roof we cleaned all of the tools with the Rizistal Safer Solvent This did the trick perfectly.