When re-plastering after installing a damp proof course (dpc) good building practice says it must be carried out in accordance with BS6576 which is the British standard for dealing with dampness in walls of buildings. The paper says that when re-plastering after the contaminated existing plaster is hacked off a salt neutralising plaster must be used.
There are lots of companys selling damp-proofing products these days and they all have to come up to BBA standard with its third party testing to say if the product does what is says it does.
Some products just reach the standard set which can be priced on the cheaper end of the market and some go above and beyond what is required.
This week we were sent 10 bags of Safeguard Europes new Dryzone Damp Resistant Plaster by our kind rep Rob. We needed this amount as we needed to test a large amount on one of our many jobs.
What Qualifies Damp Sam To Test The Product.
I have been a plasterer for 33 years now and am in the top 1% to be qualified with a HNC in building management. I have used every type of plaster on the market over the years some not in use and some now in smaller bags.
The bags are 23kg which is a surprise because on the original sheets safeguard sent out it says they are 25kg. It is a striking blue colour bag and an orange one for the High Lime. The bags are made from paper and I know this keeps down costs but NatCem 35 has 2 plastic bags and can be kept outside when stored. This is such a great idea as a lot of users don’t have the resources for storage but a pallet can be dropped on the drive or garden and a tarp thrown over it. Buying a pallet brings the price per bag down and saves running to the merchant or ordering all the time making it a win win for both the manufacturer and the contractor. The plastic bags from the Natcem 35 bag are really tough and we use them for removing debris off of jobs. They are so tough they can be used over and over.
Mixing The Dryzone Damp Resistant Plaster
We mix in the giant buckets these days rather than the bath and it is done with a Refina Mega Mixer. The literature says 1 bag will do around 1m2 of plaster at around 15-20mm thickness. one bag at a time is no good to us so we decided to mix 4 at once. 500ml of water is recommended per bag so we stuck in 2l to cater for the 4 bags. This was a bit of a schoolboy error as when the 4 bags went in it came right up to the top and we had to empty some into another bucket.
The volume of the mix escalates about two thirds the way Sovereigns Renderlite or Tilcons Limelite backing plaster does.
It does mix up lovely but the mix creates a hell of a lot of dust (and we mixed outside) so make sure ppe is worn and items are well covered up if you are inside.
The Plaster and Using The Plastering
With the information, that Safeguard provides with the product it is recommended to apply a 5mm Base (scratch) coat and before that to fill any holes or large hollows. This is because when you spread the plaster at first it rolls back out of holes onto its self. The texture reminds me of Thistle Renovating plaster and like large buts of chewing gum and it has a kind of elasticity to it. if you turn it over on the hand board it slowly slumps down.
One thing I noticed was that it is gritty when taking it from the hand board and spreading on the wall, this means that the trowel does not sit completely flat or flush with the hand board surface and small amounts of plaster fall through. When I say small amounts I don’t mean drops I mean rice size particles that just drop through the gap left by the grit. It is very annoying for a plasterer who prides himself on being clean. This is the same with NatCem 35 so both products can be messy and this should be thought of before starting.
Once the first scratch coat is on the product does hang (stay wet) for quite a while before you can put on the second coat, so overall it is not a quick process. They says to damp down high suction areas but we always damp down brickwork. It could be that some areas don’t need damping down so clarification should be sought at their main office.
The second coat was great to put on and ruling off was a dream. There was no dragging and the plaster did not pull in (dry out too quick) so large or small amounts could be ruled off and the waste sticks to the straight edge just right. It rubbed up like a dream too.
Skimming It with finish Plaster
The next day we came back to skim the walls and I was really surprised that the walls had completely dried out. Sometimes you will go the next day with Renderlite and the walls still are holding moisture (are green). Sand and cement renders would need to be left a couple of days. These were dry as a bone and had dried completely naturally. The plaster was rock hard too, I would compare it to a sand and cement render for giving it a light scrape before skimming.
When we skimmed it I used thistle board finish as we did not know what they recommend, board finish would pull in quicker than multi finish I thought and I was right because once the finish was on it hung around quite a while so you have plenty of time.
Salt neutralising plasters will stop salts coming through while the moisture that is in the wall evaporates out once the damp proof course has been installed and this can take up to 12 months depending on the wall thickness and amount of moisture. What can happen though is crystals and efflorescence can form on the surface of plaster in a damp atmosphere and customers assume the salts are coming through the wall. Dryzone damp resistant plaster is the only one that guarantees this will not happen apart from natural lime plasters. The wall will dry naturally and the plaster is warmer on the surface than a sand and cement render and any metal beads will not rust.
Overall I loved the product, We survey each job and recommend different products for that specific contract depending on background and price accordingly.
We would use this for renovating old farm houses or cottages with solid stone walls or heritage listed buildings using their high lime product. The sand cement 3-1 mix is very dense and can damage the masonry substrate as well as having issues with shrinkage and cracks Dryzone Damp Resistant plaster does not and will be a big favorite on site.
With this product, Safeguard has filled a niche in the market and as with Dryzone cream, others may follow. With these products and the fast damp proofing system as well as StormDry they are leading the way yet again.
We give it a thumbs up.