Our technical guru, Roger Moore, is back with some guidance on avoiding a sticky ending when it comes to subfloor prep.
When we’re told a floor has failed, our technical team try to find out why, and how we can help sort the problem. When we take a close look at these installations it’s a good bet that in most cases the culprit is a problem with the subfloor. You don’t need me to tell you how costly pulling up and replacing a floor you’ve fitted is, so today I’m going to run through the most common problem with subfloors; damp. We’re often told there isn’t one magic solution to a problem; well in this case there are several, so read on. If you’re specifying, rather than fitting floors, the following could help avoid problems right at the start.
Subfloor types generally fall into 3 categories; concrete, wood and specials, so the first step is always to identify what type of subfloor you’re dealing with. Today I’m going to look at concrete as this is the most common.
Concrete subfloors could be within a new-build or a refurbishment so I’ll cover both. If you’re dealing with an anhydrite, please speak with your Altro Consultant, or call the technical helpline to make sure you get the right guidance.
Regardless of the type of subfloor and how new the building is, here is the golden rule, the simple nugget that can head off a host of problems and potentially save you money and your reputation; test for damp.
If I’m preaching to the converted then great but you would be amazed at how often no reading is taken, or wires are crossed and an installer gets the green light to install the floor, yet no one has actually tested for damp. In a new-build it can take the subfloor one day per 1mm to dry and that’s that, so don’t let anyone push you into installing any sooner, unless the reading is right. As far as I’m concerned, best practice is to check for yourself.
What reading to look for
There are many measurement tools on the market with hygrometers or Protimeters being the most common. As with most things they vary greatly in price, so you can go as simple or souped-up as you like. A reliable meter certainly doesn’t have to break the bank but an investment here could save you a lot of money long term. Some meters use a traffic light green to red system which gives an indication of a problem, but a full on test will need to be done to get the relative humidity (RH) figure.
When you take a RH reading and the reading is 75% or less, crack on. If that reading is over 75%, there are a number of options available to you but adhering a floor straight onto it isn’t one of them.
When it's a refurb
If you’re dealing with a refurb rather than a new build, inspect the old floor before you remove it. If it shows signs of damp issues then pull up the floor and take a good look at the subfloor. How old is the building? Pre-1970ish, there might not be a damp proof membrane (DPM) in the floor. Anyway, your RH reading will dictate how you continue. Whatever the reading you may have to cover old adhesives so it’s important that you choose a levelling compound that’s suitable to cover them. Your chosen levelling compound supplier will have guidance on what’s best to use in each case.
So, the subfloor is damp. What are your options?
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Adhesive-free flooring
Altro adhesive-free floors can be laid up to 97% RH, and with no adhesive and no DPM required it can also save you time and money. They’re designed to lay flat and hold just as effectively as an Altro floor installed using adhesive. Altro XpressLay gives you a safety floor option, while Altro Cantata is smooth, so you have a choice depending on the area you’re installing in.
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Apply a damp-proof membrane (DPM)
If your damp subfloor is in an area where a specialist floor is needed, such as a kitchen or a wet environment, you can apply a DPM, such as Altro Proof. If the subfloor is uneven, use a moisture-tolerant levelling compound first. Once you have a coating of Altro Proof, if the floor is still bumpy don’t rub it down as you’ll take off too much of the DPM. Instead, put another layer of levelling compound on top. Make sure the adhesive you use can cope with moisture and off you go. A word to the wise: If you don’t use a moisture-tolerant levelling compound on a damp subfloor, it’s a bit like when you take a plaster off your finger and it goes wrinkly - the moisture has been drawn out of your skin. The same thing will happen to the smoothing compound and it could fail.
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Use a fibreglass underlay sheet
If you’re under pressure to install quickly and adhesive-free flooring is not an option, then you can lay a fibreglass sheet, such as Altro Everlay A or B. As Altro Everlay B is 4mm thick, it offers comfort underfoot and additional sound absorption which, for installations where staff are on their feet a lot, or the sound needs to be reduced, is ideal. If you choose this option, make sure you use our A19 adhesive as this has been designed specifically for use with Altro Everlay.
What to do if it's all gone wrong?
We’ve all seen the signs: split joints, blisters in the floor and a musty smell. In extreme cases the floor can also stain from damp being drawn up into it. Unfortunately there is no quick fix and, to quote Edwin Collins, the only solution is to rip it up and start again. If this means disconnecting equipment, moving people out and causing a business loss of earnings, plus your time to strip it all out, treat the subfloor and re-lay, as well as material costs, then it could be very expensive.
So, a damp subfloor doesn’t have to cause problems as long as you know it’s there, and finding out is dead simple.
Don’t forget we’re always here at the end of the phone if you have any questions about what I’ve covered here. Just call the technical helpline on 01 907 5821, tweet us @askAltro, or chat to us using the online chat box on our website.
If there is something you would like me to cover in a future blog piece, just comment below and I’ll see what I can do!
Until next time, Roger Out.