Rocktop

[WhoMe?]

Hi

Does anyone have any advice for applying Rocktop on painted MDF? Should I lightly sand the surface before applying and then in between each coat?

Thanks

 

[opps]

Hi

Does anyone have any advice for applying Rocktop on painted MDF? Should I lightly sand the surface before applying and then in between each coat?

Thanks

I have never used it

Rocktop — Smith & Rodger - Paints & Shellacs since 1877

Rocktop is a muti-surface clearcoat that has been expertly formulated for even the most high traffic areas in the home.

www.smithandrodger.co.uk

I would however strongly recommend that you sand the surface first though. Obviously you don't want to cut through the paint and down to the MDF, so I would hand sand with 180/240 paper. Rather than aluminium oxide, I would use sterate coated silicon carbide paper, or Abranet.

Sponge Abrasive Pads 220G (Fine) | Toolstation

Double sided silicon carbide. Will adapt to most contoured surface shapes. • Ideal for denibbing and sanding • Can be used wet for dust control • Ideal for sanding intricate profiles

www.toolstation.com

Abranet® 115 mm x 2.5 m Grip

VERY FINE SANDING: Unique net sanding product for dust-free sanding. Abranet is suitable for sanding putty, primers, lacquers, composite materials and a wide range of other materials.

www.mirka.com

 

[WhoMe?]

Are they just more forgiving that regular sand paper?

 

[opps]

Are they just more forgiving that regular sand paper?

More forgiving in so far as you are less likely to accidentally cut through the existing paint and back to the bare MDF. They are, additionally less likely to clog as quickly. You do need to exercise caution when sanding edges, areas most likely to chip. The softer backed abrasives should be less likely to cut through those edges.

On reflection, given that you are using a clear coat over existing paint, you may be better off with 320 grit abrasives. I don't want you to be able see score marks in the finish. I would not recommend anything over 320g, you risk polishing the surface and impairing adhesion.

Once you apply the first coat of rockwool, if you apply the second coat within a week, you won't need to sand in between coats (from a bonding perspective). Waterbased products typically take up to 10 days to cure fully. After 10 days, yeah, slight abrasion is recommended.

One major caveat is that any fibres of clothing/etc that lands on the surface whilst the paint is still wet, will be visible forever. When I specialised in hand painting cabinets, I would only ever wear old(ish) white cotton t-shirts that had been washed multiple times.

I suggest that you ring Smith and Rodgers and ask if you can add the MDF paint to the Rockwool if you have some- I have no idea what paint you used on the MDF. I have always found their technical support to be helpful. Adding the coloured paint will (potentially) hide clothing fibres.

At a guess, 10% paint and 90% Rockwool should not compromise the integrity of the finish. Again I don't know that paint you used previously.

 

[WhoMe?]

Thanks for the very thorough answer. I shall call the manufacturer to check the paint is compatible. Rockwood tin says you can add paint but is none specific on type.