Welcome to the PROBOND FAQ section, your go-to resource for quick answers to commonly asked questions. As specialists in subfloor preparation, including Primers & DPMs, Smoothing Compounds, and adhesives, with an on-site technical support service, we’re dedicated to helping you make informed decisions for your flooring projects. If our most frequently asked questions don’t answer your query, contact us for advice.
What smoothing compound is the best to be used under a wood floor?

We recommend FL330 Fine Flow Smooth Levelling Compound or FL307 Fast Setting Flexible Levelling Compound because of their higher compressive strength. 

Which underlayment can be bulked out?

All our underlayments can be bulked out with aggregate to enable them to be applied to greater thickness. Check the relevant data sheets for this information.

Do I need to remove adhesive residue before using PROBOND® smoothing compound?

Yes, you should always remove as much residue as possible, paying particular attention to any friable residue. Both FL390 and FL301 can be applied directly over old adhesive residues without priming in most situations. Surfaces should always be sound and free of any contaminants that may inhibit adhesion of the primer system, moisture control system or smoothing compound.

Which of the PROBOND® self-levelling compounds can be pumped?
Our PROBOND® FL330 Fine Flow Smooth Levelling Compound , FL305 Rapid & Flexible Renovation Levelling Compound and FL307 Fast Setting Flexible Levelling Compound can all be pumped.
Which products can be used externally? (Series 300 and 400)
Our PROBOND® FL305 Rapid & Flexible Renovation Levelling Compound is moisture tolerant and frost proof so works well in an external environment. Our PROBOND® B490 Flexi-Grip can be applied to absorbent and non-absorbent surfaces and can be used outside.
Can you apply smoothing / levelling compound over expansion joints?

No, the expansion joint should be taken through to the floor finish and a suitable expansion joint / cover fitted. 

Do you need to prime smoothing / levelling compound prior to application of adhesives?

No, most smoothing compounds are polymer modified and have a controlled level of absorbency.

Which types of subfloor pose most risk of moisture?

Old buildings pose the most risk however new buildings still remain susceptible to moisture, as the drying time of a new sand/cement screed is estimated to be 1mm per day up to a thickness of 50mm. A 150mm thick concrete subfloor can take up to a year to dry out naturally. Therefore, to ensure that a concrete subfloor is sufficiently dry to receive a floorcovering, all projects should be tested for moisture.

I’m installing floorcoverings over a newly-installed concrete screed. Will a waterproof surface membrane be required?

A recently-installed concrete screed is likely to contain a large amount of residual construction moisture, which can potentially cause complete floor failure if no waterproof surface membrane is in place to stop it rising up to the level of floorcoverings. You will need to leave at least seven days but check with the subfloor installer, as different products have varying drying times.