Advice on sander selection

30 Nov 2019
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United Kingdom
I am planing to repaint 3 window sills. Each one is 54cm x 178cm. 2 are south facing and get full sun (as and when) most of the day.
I need to sand down and am not sure what sander to get. I have had a orbital, which was great for dry walling but I don't think so in this situation. A detail sander is too small, possibly. I have no idea about belt sanders. Any advice ?
I plan to have a top coat of an oil based gloss. Mainly to stand up to the sun. Is this the best option ?
These are being repainted because of some staining and some orange peal due to my previous efforts using some water base product.

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How many layers of paint are on the sills? Are they actually proper wood or are they MDF?
If they are real wood and old (so many layers of paint) I'd burn the bulk of it off, finish with wirewool and paintstripper then light sand by hand with 120 grit and away to go

Belt sanders are great for removing lots of material very quickly but not great at getting into corners/edges (without leaving some damage). Orbitals in my experience aren't clever on painted surfaces (great on car body filler though). Multitools are good for spot detailing of high spots, blemishes etc.

Pics would be handy to see how bad the orange peel effect is, you may be just as well scraping all the loose rubbish off then hand sanding with 60 then 120 then 200 (if you want to go to those lengths)
I'd use a random orbital sander. They remove stock much faster than orbital sanders.

I'd start with 80 grit paper and then (if need be, drop down to 150-180 grit).

You can use your existing orbital sander for the internal corners.

Belt sanders remove stock even faster but in the wrong hands you risk gouging the surface.

Are these exterior concrete/stone sills? You will need to use oil based undercoat as well as gloss. Apply the paints early in the day. At this time of the year the early afternoon dew will make the gloss become dull if you apply it to late in the day. Add some terebene to the paint to help it cure faster.
Thank you for your replies. These are internal sills in ply wood (I think). I'm not sure how much paint is on here but I suspect not much but old. I don't want to burn off as the windows are UPVC. Top of the picture is the edge. The pic shows the surface which I suspect is other than orange peel but I am not up on paint problems.
Window Sill 1.JPG
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It is difficult to say why the paint has crazed like that.

If I had to guess... It may be the case that whoever first painted the sill used PVA as a primer.

I understand why you wouldn't want to use a heatgun but with a "window shield" on the gun you should be fine.


BTW I am not recommending the attachment above. Different guns have different diameters. Sometimes I use a very wide metal filling knife to protect surfaces form the heat.

Personally I would sand the area back to the wood but unless you buy a good trade quality random orbital sander, the heatgun might be faster.
I have decided to go with a random orbiter sander. I'm not keen on using the heat gun in my smallish flat. So it may take a bit longer I can live with that. I have ordered

I have in the past used Bosch and have found their kit fine.

I guess when I have got it rubbed down I should apply a couple of coats of undercoat and one of gloss.
BTW, you don't have to buy the Bosch branded abrasives. They tend to be massively over priced.

The following might be a better option

I have never used them though. I tend to buy my Festool 125mm abrasives in boxes of 50.

Given that you need to sand back to the bare wood, I'd recommend a packet of 60 grit, followed by the 120 grit and possibly the 240 grit at the end.

If the holes don't line up use a nail punch or screwdriver to punch new holes in the paper.

The dust bags on sanders tend to be a bit rubbish, with the assistance of gaffer tape, you can connect the sander to your vacuum cleaner.

Don't apply too much pressure and keep moving the sander so that you don't overheat the paint otherwise it will clog the paper.
Thanks for the pointer on sanding discs. Is there an overall issue with quality ? I have seen offers of 40 discs for £5 (in fact not much cheaper than the ones you pointed to). On using a vacumn cleaner. I have a Dyson which is not easy/effective when used with it's hose. I guess I would be better to get something like a "Henry" or similar light industrial type.
I haven't used the ones I linked to. I have however used their belt sander belts. They were fine and half the price of the Bosch branded ones I last used.

All of my sanders are made by Festool. I tend to pay a premium for their Granat sanding sheets. I find they last much longer, ie the abrasive stays sharp for longer. A while back I purchased some budget Mirka sanding sheets (approx 3 times cheaper than the Festool ones) but they went blunt after about 5 minutes. The backing paper was also much thinner. Had I been a novice there is the risk that I would have applied more pressure to the sander to try to sand the surface. Doing so would have potentially damaged the "velcro" on the pad because of the heat generated. A replacement pad on a £500 sander is about £50.

I would advise against connecting a cyclonic vacuum cleaner to any sanders. The dust is too fine and may damage it. A Henry would be ok, as would one of those Titan vacuum cleaners. A big advantage of using a vacuum with a power take off is that it turns on automatically when you turn the sander on.

I have no idea how frequently you need to connect tools to a dust extractor. The cheapest suitable vacuum at Screwfix is currently £35. It doesn't have the auto switching option though. Pay much more and you will have longer and anti-static hoses, auto aswitching, better filters, lower noise and so on but the price jumps up to in excess of £300.

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