There May Be No Way Round Preparation
Neil Sanders on preparing non-absorbent surfaces
My previous articles in CFJ on best ways to prepare difficult substrates, included calcium sulphate screeds, subfloors suffering from laitance and in January on wooden floors. This month I cover the preparation of non-absorbent surfaces.
Surfaces that do not allow water to pass through them can be described as non-absorbent. These include painted floors, asphalt, ceramic and quarry tiles and power floated concrete. Often if they are in good condition they can be cleaned and primed to receive a smoothing underlayment or flooring adhesive. However, in many other situations, additional preparatory work must be undertaken.
• Coated surfaces: Brittle or flaking paint, or traditional oil or acrylic based emulsion, must be totally removed. The easiest method of removing old paint is contained dust-free shot or grit blasting. Some surfaces painted with epoxy or polyurethane based products can be overcoated, providing they are in good condition and well adhered to the substrate.
The surface would then normally be lightly scarified and cleaned before applying a suitable primer and underlayment system or adhesive. If there is any doubt on the coating’s integrity, it would be prudent to
• Waterproof surface membranes (WSM): Epoxy-resin systems can be overcoated with smoothing underlayments or certain adhesives. Waterproof sur face membranes should be primed with a neoprene emulsion primer and allowed to dr y before applying a smoothing underlayment. Some polymer emulsion adhesives or reactive systems can be applied directly to epoxy-resin systems.
• Asphalt: Flooring grade and BS 8204 compliant asphalt in good condition, which has not suffered rutting or softening and is free from any form of contamination, can form part of an acceptable substrate. A 3mm
application of an appropriate smoothing underlayment should be applied to the surface after it has been cleaned, dried and primed.
• Ceramic, terrazzo and quarry tiles: Sound and well bonded tiles without lipped tiles or cracks should be skimmed with a minimum of 3mm smoothing underlayment after being cleaned and primed. However, heavily glazed surfaces should be mechanically prepared to aid adhesion before priming.
Terrazzo and quarry tiles are unaffected by dampness but may be sufficiently permeable to allow the passage of moisture vapour, and are often laid in areas not incorporating a DPM. In these cases, cover the tiles with asphalt or sufficiently prepare them to receive a waterproof surface membrane. If either of those methods is not possible, lift the tiles and prepare the floor to receive a new covering.
• Power floated concrete slabs: These should be treated in the same way as traditional concrete and sand / cement screeds, ensuring any laitance or weak material is removed. In some cases it is possible to use a pressure sensitive adhesive or tackifier applied directly onto the power floated slab, providing the moisture content of the slab is below 75 % relative humidity.
• Adhesive residues: Remove any old adhesive residues using mechanical methods such as scraping, shot/grit blasting and grinding. At least 75% of the floor area should be exposed prior to the application of a smoothing underlayment.
Any remaining adhesive on wooden floors should be overpinned with flooring grade plywood and thoroughly secured at 100-150mm centres, as detailed in the British Standard Code of Practice.
Neil Sanders is technical manager at F Ball and Co
T: 01538 361633
This article has been reproduced from the Contract Flooring Journal website. You can find them at www.contractflooringjournal.co.uk.